Materials Science and Technology

Linear friction welding (LFW) is a solid state joining process in which a joint between two metals can be formed through the intimate contact of a plasticised layer at the interface of the adjoining specimens. This plasticised layer is created through a combination of frictional heating, which occurs as a result of pushing a stationary workpiece against one that is moving in a linear reciprocating manner, and applied force. The process is currently established as a niche technology for the fabrication of titanium alloy bladed disc (blisk) assemblies in aeroengines, and is being developed for nickel based superalloy assemblies. However, interest is growing in utilising the process in a wider range of applications that also employ non-aeroengine metallic materials. Therefore, it is the objective of this report to provide a broad view of the capabilities of the LFW process for joining metals. This review paper will cover relevant published work conducted to date on LFW. The basics of the process and the fundamental aspects of operating a LFW machine will first be described, followed by a description of the different materials that have been welded using the process. The review will then go on to describe the microstructural changes, including texture variations, and residual stresses that are produced as a result of the welding process.

In the present study, high strain rate deformation and flow characteristics of AA 6061 were investigated under dynamic uniaxial compression and combined compression and shear loading conditions. The uniaxial compressive behaviour was obtained at strain rates in the range of 10²–10⁴ s⁻¹ using a split Hopkinson pressure bar (SHPB); ultrahigh strain rate plate impact compression and shear experiments were conducted to investigate the material behaviour at plastic strain rates in excess of 10⁴ s⁻¹. In order to understand the effect of material microstructure on the mechanical behaviour of the AA 6061 alloy, both the T6 and overaged (OA) heat treatments were investigated. The results of the SHPB experiments indicate that the two heat treatments show positive strain rate sensitivity at strain rates up to 4660 s⁻¹. However, at strain rates in excess of 4660 s⁻¹, Al6061-T6 exhibits a somewhat negative strain rate sensitivity. Estimates for temperature rise, assuming that all the plastic work is converted to heat, indicate that the specimen temperature may be elevated into a regime where both thermal effects on the flow stress and the resulting strain rate sensitivity change the flow stress response. This suggests that one contributing reason for the observed decrease in flow stress at the highest strain rates is due to thermal softening. Moreover, at strain rates in excess of 10⁴ s⁻¹, the flow stress levels for both the Al6061-T6 and Al6061-OA heat treatments are observed to approach their saturation stress levels.

The effect of process variables on flow response and microstructure evolution during hot working of Ti-17 (Ti–5Al–2Sn–2Zr–4Mo–4Cr) alloy with lamellar microstructure was established using isothermal hot compression tests at strain rates of 0·001–10 s⁻¹, test temperature between 780 and 860°C, and height reductions of 15–75. All of the flow curves exhibited a peak stress followed by noticeable flow softening, and tended to exhibit a noticeably lower rate of flow softening at the strain of the order of 0·7. The peak flow stress decreased with increasing temperature and decreasing strain rate. Flow softening of the Ti-17 alloy was caused by kinking, break-up and globularisation of lamellas during deformation and, to a small extent, by deformation heating. At high strain rate, adiabatic shear bands and flow localisation were observed to play a role in flow softening. In α+β phase region discontinuous yielding was discovered at higher temperature (⩾820°C) and 10 s⁻¹. According to the deformation microstructure, lamellar α phase gradually kinked, broke up and globularised of lamellas resulting from the development of shear bands and the penetration of β phase during deformation in the α+β phase field. The degree of dynamic globularisation of α phase increased with increasing strains, temperature and decreasing strain rate.

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g⁻¹, and the first charge specific capacity is up to 903 mAh g⁻¹ for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.

Microstructural features and thermal insulation capability of plasma sprayed nanostructured and traditional yttria partly stabilised zirconia (YPSZ: ZrO₂–8Y₂O₃) coatings were investigated. Both nanostructured YPSZ coating and traditional YPSZ coating were mainly composed of non-transformable t-ZrO₂ phases. The detailed microstructures of the nanostructured YPSZ coating were observed using FESEM, which presented three types of microstructures: columnar grains, equiaxed grains and nanosized zirconia particles embedded in the so called matrix formed by melted powders. However, the traditional YPSZ coating only contained columnar and equiaxed grains. The average porosities of nanostructured and traditional YPSZ coatings are 12·5 and 9·7 respectively. Compared with the traditional YPSZ coating, the nanostructured coating contained finer microcracks. The nanostructured YPSZ coating has higher thermal insulation capability than the traditional YPSZ coating. For YPSZ coating of 200 μm in thickness, the temperature drop ΔT (thermal insulation capability) of the nanostructured coating at 1350°C increased by 27 compared with that of the traditional coating.

Ten tropical hardwoods are impregnated with methyl methacrylate and polymerised in-situ by use of catalysts and heat techniques. Treatability of the wood, as determined from the fractional volumetric retentions of monomers that are a fraction of voids filled by the impregnant, showed that the mean retention range from 15·03 (Acacia Mangium) to 56·59 (Cratoxylum Arborescens). The penetration of the monomer evaluated using ultrasonic waves showed that the treated wood had higher velocities which indicated significant increase in density. The present paper deals with the viscoelastic relaxation of polymerised treated wood. The efficiency of the monomer as a plasticiser is studied through the temperature dependence of the storage modulus (E′) and loss tangent (tan δ) of treated and untreated wood by dynamic mechanical thermal analysis (DMTA) over a temperature in the range from −100 to 200°C. The storage modulus E′ decreased with temperature and as the maximum mechanical damping developed, the glass transition temperature (T_g) of the plasticised wood decreased with the plasticiser content.

Creep characteristics of solid solution Al−2·9 wt-Mg alloy have been investigated under the effect of cyclic stress reduction of different amplitudes (12·47−26·18 MPa) and frequencies (0·20−0·44 Hz) at different working temperatures ranging from 533 to 593 K. It was found that increasing both amplitude and frequency of cyclic stress reduction resulted in an increase in both transient and steady state creep stages. The enhancement of creep rate was observed above either a threshold stress or a threshold frequency. The activation energy values of the mechanisms operating in both transient and steady state creep stages were found to be 130 and 171 kJ mol⁻¹ respectively.

C_f/SiC composite and Ti alloy (TC4) were successfully joined by the mixed powders of Ag, Al, Ti and short carbon fibres under vacuum condition. The Microstructure of the joints was investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The results show that the good chemical bonding and reactive composite brazing joints are obtained by reactive composite brazing with both (Ag–6Al)+Ti and (Ag–6Al)+Ti+C filler materials. The addition of short carbon fibres contributes a lot to the shear strength by alleviating the thermal stress of the joints and to the in situ synthesised TiC which surround the uniformly distributed short carbon fibres. Ti element can improve filler metal's wettability to C_f/SiC composite and restrain the oxidation of Al element. The max shear strength obtained is 90·8 MPa and the optimal parameter is brazing at 910°C within 10 min.

The effects of compatibiliser molecular weight, temperature of the first mixing zone of the extruder and nanoclay loading on the mechanical and thermal properties of polymer–clay nanocomposites (PCNs) were investigated. It was found that the molecular weight of the compatibiliser, the temperature of the first mixing zone of the extruder and the nanoclay content have significant effects on the mechanical and thermal properties of the polyethylene–clay nanocomposites. The blending of the high and low molecular weight compatibilisers allowed a more efficient interface between the nanoclay and the polymer matrix. Coupling a more efficient bonding with the high shear in the first mixing zone of the extruder at a low temperature produced an intercalated/exfoliated nanoclay filler resulting in enhanced mechanical properties of the PCNs.

The electron beam welding of SiCp/101Al composites has been carried out. The influence of welding parameters on weldability and mechanical properties of the welded joints was discussed. The welding parameters were therefore optimised under the current experimental circumstance. Results show that only weak interfacial reaction between SiC particle and liquid aluminium occurred. Minute quantity brittle Al₄C₃ compounds and single phase Si were generated in the welded joint. The interfacial reaction between SiC particles and Al matrix could be greatly suppressed by adopting appropriate technique measures such as high welding speed and low heat input. The content of Al₄C₃ can be therefore greatly decreased in the welded joint. Moreover, modification welding and electron beam scanning could further improve the appearance of weld, and the welded joint with better quality could be obtained.

Commercially pure aluminium and titanium alloy Ti–6Al–4V were welded by gas tungsten arc welding (GTAW) process using AA 4047 Al–Si filler material. The chemical composition of reaction layer at the interface of titanium alloy and weld zone was determined by electron probe microanalyser (EPMA) showing that continuous layer of intermetallic compound of TiAl base phase was formed and aluminium is partly replaced by silicon. Transmission electron microscopic examination confirmed formation of (AlSi)₃Ti intermetallic compound formed at the interface of Ti alloy and weld. In the weld zone, intermetallic phases containing Fe and Si were identified by EPMA analysis. These intermetallics were confirmed by X-ray diffraction technique. No intermetallic compound was found at the interface of weld and aluminium. Optical microscopy, scanning electron microscopy, microhardness, and tensile testing of the joints were used to characterise the resulting joints. The transverse strength of the weld joint is higher than that of the aluminium.

Effect of rare earth (RE) metals addition on the microstructure, formation of Fe–Zn intermetallics and corrosion resistance of the batch galvanising Zn–0·18Al coating were studied. Microstructure of the coating was observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. Salt spray test and surface potential measurement were employed for corrosion resistance determination. The results show that the addition of RE can improve bath liquidity, refine surface spangles, stabilise the Fe₂Al₅ inhibition layer, decrease coating thickness and enhance corrosion resistance of the coating. However, corrosion resistance of the coating did not increase continuously with increasing RE content and the optimum RE content lies between 0·045 and 0·069 in the experiment. Mechanism of RE on the corrosion resistance of the galvanised coating was briefly analysed.

A method for revealing the localised work hardened region (plastic deformation zone) in Mg–9Al–1Zn alloy (AZ91) has been developed using a new etching technique. With this technique, etching with the solution (9 g picric acid, 30 mL acetic acid, 150 mL ethyl alcohol and 20 mL H₂O) was executed on the samples after plastic deformation and then heating to 300°C for 3 h. Because of the high strain energy in the plastic deformation zone, the microstructural characteristic in the deformation zone changed substantially after the heating process, where severe precipitation of Mg₁₇Al₁₂ phase occurred in the Mg rich α phase. With the change of microstructural characteristics, the deformation region can be revealed. The plastic zone was revealed by the different degrees of etching response in the deformation and undeformed regions; the plastic zone was slightly etched, whereas the other region was deeply etched. From the different surface height level, the deformation zone was found to be observable even at low magnification.

Alumina borate whisker reinforced aluminium metal matrix composites were liquid bonded in air. The liquid filler metal of a Zn–Al eutectic alloy could get into the clearance between composites couples by the action of ultrasonic capillarity. The bond/composite interface was eroded, so that a rough interface formed and the oxide film could be removed completely under the action of ultrasonic vibration for 3 s. The shear strength of the bond increases with ultrasonic time. A removal model for the oxide film on the composites during ultrasonic aided liquid bonding was established.

The use of high strength steel grades in automotive applications has been widely recorded. This is due largely to vehicle weight reduction programmes as well as increases in vehicle crash safety legislation. This represents the steel industry's response to the challenge that vehicle components manufactured from steel could get replaced with alternative materials, such as aluminium and polymers. Consequently, new high strength steel grades have been developed to offer credible alternatives. Recently, the UK government has released a new specification, BS EN 1317-1-2-3-4: Road Restraint Systems, to which all new safety barrier designs have to comply. However, much of this development and subsequent usage has been targeted at automotive manufacturers. Road safety barrier technology has not evolved in the same way when compared to vehicle technology. Therefore, a study has been undertaken to assess the outcome of using some of these novel high strength steel grades for the manufacture of road safety barrier components. Quasi-static and dynamic tensile testing at different velocities was undertaken. Representative connection coupons were used to understand the energy absorbing properties of a dual phase steel grade when compared to the current CMn steel grade. The present study presents some initial results as to the increased performance that could be gained from utilising new high strength steel grades for the production of road safety barrier systems.

The authors present a theoretical investigation of the thermal conductivity of SiC_p based metal–matrix composites at various temperatures from a viewpoint of heat conduction mechanism across the SiC_p/matrix interface. The interfacial thermal conductance associated with the electron–phonon (e–ph) coupling and the phonon–phonon (ph–ph) coupling is characterised using a simple calculational procedure. The predictions for the composite thermal conductivity obtained by a Hasselman and Johnson model incorporated into a Majumdar's relation reveal good correspondence with the experimental results and explore that the temperature dependent thermal conductivity is essentially governed by the competitive interaction of e–ph coupling and ph–ph coupling. This work also accounts for the temperature dependent thermal conductivity of SiC_p based composites, which is sensitive to the particle size and volume fraction when these two materials properties lie within certain range.

The hot ductility of twin induced plasticity (TWIP), 0·6 wt-C steels containing 18–22 wt-Mn with N levels in the range 0·005–0·023 wt- and the Al additions either low (<0·05 wt-) or high (1·5 wt-) has been examined. Little change in ductility occurred in the temperature range 1100–650°C as the structure was always fully austenitic. Ductility was generally poor (<40), reduction of area values, the best ductility at the higher Al level being given by the steel with the lowest N and S levels. Because the steel is fully austenitic, the ductility is solely dependent on that for unrecrystallised austenite. Therefore, to avoid transverse cracking the volume of second phase particles should be kept to a minimum, i.e. the N should be low to reduce the amount of AlN that can be precipitated out and the S level should be as low as possible to limit the amount of MnS inclusions. Metallographic and TEM studies were carried out and the poor ductility was found to be due to extensive precipitation of AlN at the austenite grain boundaries. Increasing the cooling rate from the melting point to the test temperature from 60 to 180°C min⁻¹ or introducing an undercooling step both led to even worse ductility.

Melt conditioning by advanced shear technology (MCAST) is a new process for microstructural refinement of both cast and wrought magnesium alloys. Melt conditioned direct chill (MCDC) casting combines the MCAST process with conventional direct chill (DC) casting. In the present work, melt conditioning has been combined with permanent mould casting to simulate the production of DC cast AZ91D billets and slabs. The results show that the MCDC process can achieve significantly finer grain size and more uniform microstructure than conventional DC process for both billets and slabs. Grain refinement in the MCDC process is due to the fine and well dispersed oxide particles produced after processing in the MCAST unit.

The aim of the present research was to subject a well known parametric model and a neural network model to an acid test of extrapolation in order to determine which can produce improved long term creep rupture life predictions for 2·25Cr–1Mo steels. Linear, squared and cubic parametric models were used and the accuracy of the predictions assessed by calculating the mean percentage absolute error. Many different neural network geometries were developed and the accuracy of the predictions was assessed again by calculating the mean percentage absolute error. As the predictions are concerned with the long term rupture life of components, the accuracy below 60 MPa is of the greatest importance. A neural network model with a 2–5–5–1 architecture provided the lowest error for predictions below 60 MPa, compared to other neural networks and the parametric models, and is therefore the optimum model from this study for predictions of long term rupture creep life for a 2·25Cr–1Mo steel.

Pure aluminium matrix composites reinforced by ZnAl₂O₄ coated Al₁₈B₄O₃₃ whiskers were fabricated by squeeze casting. The effect of ZnAl₂O₄ coating on the Young's modulus of the composite was investigated. The results show that the Young's modulus of the composite significantly increases with increasing ZnAl₂O₄ coating content. The influence mechanisms of ZnAl₂O₄ coating on the Young's modulus of the composite were analysed. The increase in load transfer area of whisker/matrix interface and the volume fraction of effective reinforcement with increasing ZnAl₂O₄ coating content can increase the Young's modulus of the composites. The steps can provide an additional load transfer from the matrix to whiskers during the tensile deformation of the composites.

There is a novel steel invented in which the structure consists of extremely fine platelets of bainitic ferrite dispersed in a matrix of carbon enriched retained austenite. The resulting large density of interfaces makes the alloy very strong in its transformed condition. The authors report the first fatigue tests on this system, by measuring the life of parallel gauged samples tested using cyclic loading in tension, with maximum stresses in the range 1·2–1·6 GPa. A comparison of the results against published data indicates that the performance of the steel is consistent with the behaviour of other strong steels, in spite of the fact that it is produced using an air melting technique.

A two-step overaging treatment was exploited in thermomechanical processing for producing fine grained Al–Mg–Li alloy sheets. The effects of each step and temperatures of overaging on the distribution of precipitates and recrystallised grain structure were investigated. The influence of preheating treatment before rolling on precipitate coarsening or dissolution was also considered. The results showed that, in contrast to rod shaped precipitates produced by single overaging at 300°C, precipitates produced by a two-step overaging tended to have globular morphologies. The globular precipitates were not deformed during the following large rolling reductions. Overaging at 200°C for 24 h then at 300°C for 24 h resulted in a distribution of globular precipitates with sizes of 1·0–1·2 μm. Preheating at 400°C or raising the overaging temperatures of each step to 300 and 400°C led to a reduction in the precipitate size. Subsequent rolling and recrystallisation resulted in a fine grain structure with an average grain diameter of approximately 8·1 μm for 200°C/24 h+300°C/24 h and 9·2 μm for 300°C/24 h+400°C/24 h overaging treated material respectively in the surface layers of the sheet.

Infrared radiation thermography has been used in the present investigation to study the strain rate effect on deformation kinetics in high strength low alloy (HSLA) steel under monotonic loading conditions. Instantaneous surface temperatures were measured on specimens under different strain rate loading, and various temperature evolution regions were identified. Strain rate effect has been found to be more significant in the thermal response than mechanical response.

Deformation behaviour and microstructures at failure were investigated in a mill cold worked 70∶30 α-brass over the test temperature range of 298–973 K and strain rate range of 10⁻⁵–5×10⁻³ s⁻¹. Tensile properties as a function of temperature revealed three distinct regions, with their temperature sensitivity being maximum at intermediate temperatures (553–673 K) and much less towards the lower and higher temperature ranges. Two values of activation energy for high temperature deformation Q were obtained to be 117·5 kJ mol⁻¹ below 623 K and 196·4 kJ mol⁻¹ above this critical temperature. In the respective temperature range the values of stress exponent n were 5·6 and 3·8. Based on the values of Q and n, the deformation mechanism was suggested to be dislocation climb creep with a probable contribution from dislocation pipe diffusion on lowering the temperature. Both grain size and cavity size were found to increase with increasing test temperature, suggesting them to be interrelated and act as an alternative steps for accommodating grain boundary sliding. Static grain growth study, over the temperature range of 773 to 1073 K, led to activation energy for grain growth to be 71 kJ mol⁻¹, with the time exponent of 0·37.

The fracture behaviour of 8Ni 980 MPa grade high strength steel is investigated by combining experimental results of crack opening displacement (COD) tests at various temperatures with detailed microscopic observations of fracture surfaces and crack configurations in unloaded specimens. The results reveal that this high strength steel possesses high toughness with a transition temperature around −150°C. Even though at a very low temperature (−196°C), cleavage cracking dominates the fracture process and the crack does not propagate immediately through the entire ligament: a ‘pop-in’ extension is observed in macroscopic tests, and the microscopic fracture mode is quasi-cleavage. It is found that resistance to crack propagation is provided by three barriers: original austenite grain boundaries, bainite colony boundaries and interlayers between bainite laths. These barriers manifest themselves by tear ridges with dimples on the fracture surfaces. At higher temperatures, the fracture mechanism is dominated by fibrous rupture, associated with a ‘dimpled’ fracture surface and some individual quasi-cleavage facets.

Based on the results of four-point notched bend tests together with detailed microscopic observations of fracture surfaces and crack configurations below the unbroken notch roots of double notch specimens, the fracture mechanisms in notched specimens of 8Ni high strength (980 MPa) steel have been observed to be as follows. A fibrous crack initiates in the bainitic matrix at the notch root and then develops into a cleavage crack at a critical length. The cleavage crack propagates in an unstable manner and causes the final fracture of specimen. The critical event controlling the cleavage fracture is the propagation of the bainitic packet-sized crack, and the local fracture stress is measured as around 1845–2200 MPa.

The mathematic model of three-dimensional aluminium profile extrusion processes using the finite volume method was established in the present paper. Basic theories and key technologies of the Simple method using the collocated arrangement strategy based on boundary fitted non-orthogonal block structured grids were studied. The governing equations were directly discretised on boundary fitted non-orthogonal grids. The coordinate transformation between the Cartesian rectangular coordinateand the curvilinear coordinate was avoided. The negative effects of grids’ non-orthogonality, such as the dislocation between the lines connecting the centre points of adjacent elements and the centre of their interface, were compensated. The volume of fluid (VOF) scheme was used to capture the free surface of the deforming material. A program was written according to the above theories and equations. A typical three-dimensional aluminium profile extrusion process was simulated by use of the program developed in the present paper. The simulation results were also compared with that simulated by Deform-3D in the same process, material and die conditions. The feasibility of the mathematic model built in the present paper was demonstrated by the simulation results and the comparison.

A pulsed magnetic field (PMF) was introduced into the solidification of pure Mg. Fine uniform equiaxed grains are acquired in the whole ingot from the PMF treatment, in contrast with the coarse columnar grains observed in conventional casting, and the average grain size is refined to 260 μm with a 200 V PMF treatment. Pulsed magnetic field increases melt convection during solidification, and the violent agitation causes warmer liquid to fracture the tip of columnar dendrites or to break off dendrite branches to promote the formation of an equiaxed structure, with the broken pieces transported into the bulk liquid acting as nuclei. In addition, the uniform temperature field resulting from the stirring increases the likelihood of nuclei survival. The Joule heat effect also participates in the structure refinement. The pure Mg produced with a 200 V PMF treatment exhibits improved mechanical properties, such as the ultimate compressive strength (227 MPa) and fracture strain (33·2).

Magnetic carbon nanotube (CNT) composites have been successfully fabricated by employing a microwave assisted method after sensitisation and activation. The phase structures and morphologies of the composites were characterised in detail by transmission electron microscope and X-ray powder diffraction. The results show that sensitisation and activation are absolutely necessary for a dense layer of magnetic nanoparticles obtained on the surface of CNTs. Magnetic measurements using a vibrating sample magnetometer demonstrate that the prepared composites are ferromagnetic.

The present study mainly covers the effect of adding cobalt on the mechanical and structural properties of Cu–2Be alloy. The stress–strain technique has been employed to investigate the effect of aging time and testing temperature on the work hardening characteristics of Cu–2Be and Cu–2Be–0·3Co alloys aged below half its melting temperature. The obtained results have been discussed based on the structural changes resulted during the aging process.

The present paper reports the investigation of the microstructure distribution of squeeze cast AZ91D alloy. The microstructure of squeeze cast AZ91D alloy is not uniform and is composed of four zones, which are chilled layer, segregation zone, pressured crystallisation area and hot spot area respectively. Moreover, in the pressured crystallisation area, the microstructure sequence in the transverse section from the outside to the inside could be divided into four sublayers, such as fine equiaxial dendrite area, dendrite area with a high directivity, confusion dendrite area and disorder dendrite area. The volume fraction of the intermetallic compound Mg₁₇Al₁₂ also varied with the location. The volume fraction of Mg₁₇Al₁₂ in the pressured crystallisation area is the largest except in the segregated zone.

The pulsed DC tungsten inert gas (TIG) method was employed to post-spray treat an electroconductive Al₂O₃–TiB₂ coating by atmosphere plasma spraying (APS) Al₂O₃–30 wt-TiB₂ powder. The microstructure and mechanical properties of the coatings before and after treatment were comparatively investigated by scanning electron microscopy, laser scanning confocal microscopy, X-ray diffraction, microhardness tester and block on ring wear tester. It was detected that the treated coating presented a two layer structure consisting of the remelted zone and the sintered zone, which was comprised of TiB₂ and single α-Al₂O₃; surface roughness of the treated coating exhibited a remarkable decrease while microhardness and wear resistance showed a significant increase. These experimental results could be ascribed to the effect of high heat input and discharge plasma during the pulsed DC TIG treating.

The influence of shot peening on high cycle fatigue performance of notched specimen was investigated for ZK60 and ZK60-T5 magnesium alloys. The results show that the notched fatigue strengths (at 10⁷ cycles) for ZK60 and ZK60-T5 alloys increase from 150 and 155 MPa to 220 and 240 MPa at the optimum Almen intensity of 0·30 and 0·40 mmN respectively. In comparison to ZK60 alloy in extruded condition, higher notched fatigue performances of both unpeened and peened specimens were observed for ZK60-T5 alloy.

Corrosion behaviour of the banded structure known as ‘onion ring’ in the nugget of friction stir weld AA2024-T351 was investigated to find the relation to microstructure. A micro-electrochemical cell with a 50 μm diameter glass pipette tip was used for electrochemical measurements. It was found that onion rings consisted of two bands: ‘dark’ bands that contain fewer constituent particles but show extensive precipitation of S phase and ‘light’ bands that contain fewer S phase precipitates but greater numbers of constituent particles. Electrochemical results showed that the light band has more noble (less active) open circuit potential compared to the dark band. Microstructurally, this is due to the lower number of S precipitates and therefore the possibility of higher Cu solid solution within the band compared to that of the dark band.

Hydrogen can be used as a temporary element to refine microstructure and improve workability of titanium alloys. In this article, the influence of hydrogen on the microstructure evolution and tensile properties of TC21 alloy is investigated. The microstructure observation reveals that the FCC hydrides δ precipitate firstly at the grainboundaries of primary α phases in TC21 alloy with hydrogen contents above 0·319 wt-. These hydrides which block the grains deformation reduce both the strength and ductility at room temperature. With increasing hydrogen contents, the elevated temperature strength decreases first and then increases, while the ductility behaves the contrary. These are resulted from the interaction of hydrogen induced softening and hardening.

Resistance spot welding is the dominant process for joining sheet metals in automotive industry. Despite the application of three thickness resistance spot welds in this industry, present guidelines and recommendations are limited to two thickness spot welds. Study towards better understanding of weld nugget growth and mechanical properties is the first step to understanding the welding behaviour and developing proper guidelines for the three thickness resistance spot welding. In this paper, weld nugget growth, mechanical performance and failure behaviour of three thickness low carbon steel resistance spot welds are investigated. Macrostrcutural and microstructural investigations, microhardness tests and quasi-static tensile–shear tests were conducted. Mechanical performance of the joint was described in terms of peak load, energy absorption and failure mode. In order to understand the failure mechanism, micrographs of the cross-sections of the spot welded joints during and after tensile–shear are examined by optical microscopy. Unlike two thickness resistance spot welded joint, weld nugget was formed in the geometrical centre of the joint (i.e. centre of the middle sheet). Weld nugget size along sheet/sheet interface was greater than that of along geometrical centre of the joint. Increasing welding time leads to increases in peak load and energy absorption of the joint and transition of interfacial failure mode to pullout failure mode, primarily due to the enlargement of weld nugget size along sheet/sheet interface.

The effects of laser shock processing on the residual stresses of the LY2 aluminium alloy samples with elliptical spot (long axis length, 12 mm; short axis length, 3 mm) were experimentally investigated, and the effects of the overlapping rate on the residual stresses were simulated using the Abaqus software. The simulated residual stresses were basically in agreement with the measured data, and the relationship between the magnitude and uniformity of residual stress and the overlapping rate was also addressed. Results show that the largest stress magnitudes are located on the top surface of the sample, and the greatest uniformity is achieved by the overlapping of elliptical laser spots. The overlapping rate is critical for the uniformity of the residual stress across the surface. Within a certain impact number range of one to four times, increasing the shocked number can increase the magnitude of residual stress near the surface but not effectively increase the plastically affected depth.

The aim of the present study was to determine the influence of doping rare earth ion on strontium calcium aluminate (CaO–SrO–SiO₂–Al₂O₃). Therefore, the authors have manufactured luminescent material consisting of 40CaO–5SrO–5SiO₂–50Al₂O₃ doped with Dy³⁺. The compositions have been selected on the basis of chemical stability. Five pellets were prepared with different calcination temperatures and times, namely 400 and 600°C for 1 and 2 h, in order to shed light on their luminescence behaviour. X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy elaborate and characterise the formation of small particle of photoluminescent material in the phosphor matrix host material.

Aging of IMI834 welds results in toughness degradation due to interlath precipitation. It has been observed that this phenomenon is predominant if the matrix microstructure is transformed beta.

In order to obtain a fast biomimetic coating on titanium substrates, calcium enriched silica films were prepared on pure titanium substrates by sol–gel method under the following conditions: pH = 3 and the molar ratio of tetraethyl orthosilicate (TEOS)/H₂O/EtOH/Ca²⁺ = 1∶4∶11∶0·08. The titanium base calcium enriched silica film is soaked in a slightly supersaturated Ca/P solution, with the concentration of calcium ion and phosphate group being 1·5 times of that of simulated body fluid, for seven days, a uniform apatite layer is precipitated onto the surfaces of calcium enriched silica films, which is quite rapidly. The investigation adopted SEM, EDX, Fourier transform infrared spectroscope and XRD to indicate that the coating was carbonate hydroxyapatite. The results show that it is a feasible way to obtain carbonate hydroxyapatite through functionalising the pure titanium substrates by preparing calcium enriched silica films on it from a sol–gel method.

In this paper, the TiAl liquid filling process during vertical centrifugal casting into a permanent mould has been described analytically. A model has been established to simulate the forward filling and backward filling process, and two parameters were used to provide a quantitative description of the defect generation that is associated with the forward filling of the mould cavity. One of the parameters used was the forward filling cross-sectional area, and the other was the inclined angle of the free surface of forward filling flow. The cross-sectional area decreases, and the inclined angle increases when the rotational speed increases, the tendency of which becomes more obvious near the mould cavity entrance. The residual volume of the mould cavity after the forward filling is related to the volume of trapped pores. The filling process has also been investigated using numerical simulation. Based on the filling and solidification characteristic of a TiAl valve, the off-centre porosity distribution is also discussed.

The main objective of the present paper is to develop high wear resistance carbon fibre reinforced polyether ether ketone composite with addition of multiwall carbon nanotubes. These compounds were well mixed in a batch mixer, and compounded polymers were fabricated into sheets of known thickness by compression moulding. Samples were tested for wear resistance with respect to different concentration of fillers. The wear resistance properties of these samples depend on filler aspect ratio. Wear resistance of composite with 20 wt- of carbon fibre increases when multiwall carbon nanotubewas introduced. The worn surface features have been examined using scanning electron microscope. Photomicrographs of the worn surfaces revealed higher wear resistance with the addition of carbon nanotube. Also better interfacial adhesion between carbon and vinyl ester in carbon reinforced vinyl ester composite was observed.

Two-dimensional SiC fibre reinforced SiC ceramic matrix composites (SiC_f/SiC) were fabricated by vacuum infiltration and hot pressing using a 200 nm thick pyrolytic carbon coated Tyranno SA3 fabric and 50 nm sized β-SiC powder. Hot pressing was carried out at 1750°C for 3 h in an Ar atmosphere under a pressure of 20 MPa. Al₂O₃–Y₂O₃–MgO sintering additive (10 wt-) and polyvinyl butyral resin (45 wt-) with respect to the matrix SiC were found to be the optimum contents for the high density composite. Vacuum infiltration with a force gradient produced much higher amount of slurry infiltration than simple dipping. Much improved density of 3·02 g cm⁻³, compared to the previous reports, was achieved for the SiC–SiC_f containing approximately 67 vol.- of fibre. This composite showed a step increase with a stress–displacement behaviour during the three-point bending test due to the fibre reinforcement. The displacement for failure and flexural strength were 0·58 mm and 342 MPa respectively, which were much larger than those for monolithic SiC.

The polyvinyl butyral–Al(NO₃)₃ composite sols and alumina fibres were synthesised by the sol–gel process in an aqueous solution using the polyvinyl butyral (PVB) and Al(NO₃)₃.9H₂O (AN). The viscosity of PVB–AN composite sol increased with increasing AN content and aging time when it was laid at room temperature. The addition of AN leads to the formation of new weak peak and the deviation of diffraction angle to higher degrees according to the X-ray diffraction patterns (XRD). The exothermic peak of PVB disappeared and a weak endothermic peak was observed in differential scanning calorimetry curves of composite powders. The XRD pattern of fibres sintered at 1200°C showed the formation of α-alumina and the fibres showed smooth surface and uniform diameter.

Microstructure and mechanical property of CO₂ laser beam welded IN 718 superalloy were studied by electron microscopy and hardness testing. The use of a welding filler wire produced a sound fusion zone with no cracking but grain boundary microfissuring occurred in the heat affected zone (HAZ) and was observed to be significantly influenced by pre-weld heat treatment and laser welding speed. Crack-free weld was produced by a pre-weld heat treatment that minimised non-equilibirum grain boundary boron segregation and inhibited grain growth. While post-weld heat treatment (PWHT) reduced the difference between the hardness values of the base alloy, HAZ and the fusion zone, it resulted in increased HAZ cracking, which was likely aided by pre-existing cracks. The PWHT cracking was, however, avoided by subjecting pre-weld material to the heat treatment condition that produces crack-free weld during welding process.

Direct chill (DC) semicontinuous casting process has been successfully used to produce sound Mg–3·0Nd–0·4Zn–0·4Zr (NZ30K) billets. The influence of process parameters such as casting speed, casting temperature on the microstructure and macrosegregation was studied. The results show that the casting speed affects the macrosegregation greatly while it has a slight influence on the grain size of the billet; the casting temperature has a slight influence on macrosegregation of the billet while the grain size of the billet increases as the casting temperature increases. The optimal process parameters have been experimentally determined as follows: casting temperature 700°C and casting speed 90 mm min⁻¹. The ultimate tensile strength, yield strength and elongation of billets cast at the optimal casting parameters are 196 MPa, 125 MPa and 16·5 respectively.

The microstructure and mechanical properties of 30Si2CrNi4MoNb ultrahigh strength steel were investigated after austenitising over a range of temperature between 1133 and 1483 K. The experimental results show that the isotropy of impact toughness and mechanical properties were greatly improved due to the disappearance of undissolved aligned second phase when the austenitising temperature was over 1233 K. When the austenitising temperature was over 1383 K, martensite lath and packet abnormally grew up due to dissolution of spheroidal Nb rich carbonitrides; both the platelet size and morphology of martensite were changed, which has an effect on the mechanical properties of the samples. It was noticed that the finer self-tempered carbides, which strengthened martensitic matrix, appeared after austenitising temperature over 1283 K. The strength profiles show a marked plateau for the samples austenitised from 1283 to 1433 K; however, the strength was deteriorated due to coarsening of these self-tempered carbides at 1483 K. It was confirmed that calcium treatment can help improve the isotropy of mechanical properties by modifying sulphide inclusion morphology.

Nanocrystalline Nd–Fe–B magnets are the most promising permanent magnets for high value applications. Strain rate and temperature have been established as the important parameters under dynamic processing for the development of texture and optimisation of magnetic properties. Experiments have been carried out at the constant true strain rates of 0·01, 0·5 and 5·0 s^–1 at 800°C. Flow stress generated from the experiments represents the combined effect of casing and magnet. To isolate the effect of stainless steel casing, composite deformation has been studied using finite element method. In this way, flow behaviour of steel and Nd–Fe–B magnet has been evaluated.

The present paper presents the microstructural characteristics of an extruded AA6012A-T6 (AlMgSiBiSn) alloy and the microstructural changes occurring during turning operations, analysing the mechanism involved in chip breaking. An experimental investigation has been conducted to determine the effects of different cutting speed and feedrate on the machinability of the alloy. The machinability of the AA6012A-T6 alloy, where Pb is substituted by Bi and Sn, has then been compared to the standard AA6012-T6 (AlMgSiPb) and AA6082-T6 (AlSiMg) alloys. The results indicate that the extensive plastic deformation induces a preferred orientation of the grain structure and secondary phases along the shear plane, and a local increase in the alloy temperature. Low melting point compounds, such as the Sn and Bi bearing particles, transform into a soft or liquid state, changing their initial compact shape to assume a needle-like morphology. The β-Mg₂Si and α-Al(FeMn)Si particles are not influenced by the working temperature and keep their initial shape. The AA6082-T6 alloy shows a very poor machinability, with long and continuous strips, while the AA6012A-T6 alloy reveals a good chip formation with small and discontinuous C shaped chips, similar to the AA6012-T6 (AlMgSiPb) alloy. In particular, a feedrate higher than 0·2 mm rev⁻¹ provides short and suitable chips, independently of cutting speed.

Controlled amounts of cold work are shown to cause a minimum in the ductile to brittle transition temperature (DBTT) in a ferritic steel at a critical level of ∼1·5. Mechanical property assessments show that the hardness values exhibit the same trend. A theory is advanced for explanation of these effects, based on work hardening and Cottrell–Bilby locking models. Consideration is given to an alternative Ashby–Embury model, but it is concluded that the former approach is most successful in predicting the observed DBTT shift behaviour. Although independent of fracture surface type, the degree of plastic deformation shows some dependency on the grain boundary character. This leads to the conclusion that the matrix yield strength is the primary factor in determining the DBTT in these steels. Discussion focuses on methods for exploiting the effect to give higher toughness steels utilising knowledge of how to control matrix hardening and cleavage fracture strength.

The microstructure–property relationship in conventional high strength low alloy (HSLA) steel was evaluated using data obtained from transmission electron microscopy (TEM) and atom probe tomography (APT). Atom probe tomography allowed the characterisation of fine TiC particles with average radius of 3±1·2 nm that were not observed by TEM. The increase in the yield strength of steel due to the presence of fine precipitates was calculated to be 128 MPa.

In the present paper, SiO₂ glass ceramic and Ti–6Al–4V alloy were successfully brazed with Ag–21Cu–4·5Ti active braze alloy. The interfacial microstructure and evolution course of SiO₂ glass ceramic/Ti–6Al–4V joint were studied in detail. According to the experimental results, active element Ti plays a quite important role in the formation of reaction layers on the joint interface. The reaction products of the joint are TiSi₂, Ti₄O₇, TiCu, Cu₂Ti₄O and Ti₂Cu respectively. The interface evolution can be generally described by four stages, which are solution and diffusion of atoms, reaction among atoms, formation of reaction layers and precipitation of solid solution layers respectively.

In the present study, thin films prepared as a function of the Bi concentration in the BiPbSrCaCuO system were synthesised. Thin films were fabricated using radio frequency sputtering method. Crystal structure of the films fabricated was determined from X-ray diffraction measurements. The crystal orientation was analysed by X-ray pole figure and in-plane alignment. Both X-ray diffraction and pole figure analysis revealed that crystallinity in the films decreased significantly with decreasing Bi concentration in the system. A systematic decrease in the superconducting transition temperature and hole concentration per CuO plane was obtained with decreasing Bi concentration. The J_c values of the films were calculated using Bean formula. It exhibits a significant dependence on the magnetic field and temperature. It was found that J_c decreased sharply with increasing applied magnetic field. The highest J_c value was found to be 1·06×10⁶ A cm⁻² at 10 K, which corresponded to the best flux pinning among the films fabricated.

In the present study, the room temperature mechanical properties of nanocrystalline Ni and Ni–75 wt-Co alloy, prepared by pulse electrodeposition, were contrasted. Both higher strength and higher ductility were obtained for the Ni–75Co alloy with a dual phase structure and an average grain size of 7·2 nm. By means of TEM observations of grain structures before and after tensile deformation for Ni and Ni–75Co samples, a link between the ductility and the variation of stress induced grain growth during tensile deformation was established. Observations of TEM showed stress induced grain growth during tensile deformation, subjected to very high stresses and large strains, is very insignificant for the Ni–75Co alloy in sharp contrast to the significant stress induced grain growth occurring in Ni. It was proposed that suppression of stress induced grain growth during tensile deformation can delay and even prohibit formation of shear banding plastic instability and thus enhances uniform strain leading to an enhanced ductility.

Differential scanning calorimetry (DSC) coupled with microstructural analysis has been used to characterise the freezing and melting response in a typical Ni based superalloy, CMSX10K. Transition temperatures and evolution of fraction solid (or liquid) during freezing and melting are determined from enthalpy considerations. Significant differences in heat capacity (C_P) curves exist between the heating and cooling. It is shown that differences between freezing and melting kinetics occur because of undercooling, which is most significant beyond the solidus temperature up to the onset of eutectic freezing. The correlation of DSC heating and cooling curves to quantitatively characterise directional solidification has been demonstrated.

Small scale explosions, using a detonator, of 7075 aluminium alloy cylinders, 15–100 mm outside diameter, were carried out to investigate the effects of heat treatment on fragmentation. This was the finest for the strongest as received alloy and coarsest for the softest overaged alloy. This effect was similar to that seen in investigations of the fragmentation of steel. Cylinders of 50 and 100 mm in diameter did not fragment but plastically deformed with maximum deformation at the cylinder bottom. Fragmentation of 33 and 42 mm diameter cylinders produced long fragments typical of the break-up of thick walled cylinders. At smaller diameters, break-up gave fragments of several shapes, finer fragments being largely associated with the smallest diameter cylinders and the highest strength alloys. Results followed those seen in large scale studies of cylinder break-up and suggest the possibility of using small scale fragmentation experiments in the investigation of the effects of composition, heat treatment and processing on natural fragmentation.

Investment cast Co–29Cr–6Mo–0·33C alloy tensile test specimens were subjected to heat treatment at 1230°C under argon atmosphere for different times to ascertain what enhancement of tensile properties could be achieved by such processing. Improvements in tensile properties were observed in the 2 h annealed specimen. Also, tempering of this specimen at different times shows that tensile properties and hardness increase and exceed those of the ASTM specification. However, elongation decreases during tempering. The annealed specimen has better corrosion resistance in comparison with as cast specimen.

For the first time, the influence of laser power, scan speed, scan spacing and nominal laser power density on the tensile properties, dimensional accuracy, surface roughness, number of cracks and top surface concavity of samples of Hastelloy X manufactured using a laser powder bed facility, has been assessed systematically on three-dimensional samples. It has been found that the nominal laser power density is the dominant factor, but the influence of scan spacing and scan speed can sometimes be significant. Density of >99·5 can be obtained using most conditions. Cracks are observed at corners of the samples. An optimised process window can be derived from the above systematic analysis under which the component can be built smoothly, with good surface finish and dimensional accuracy, consistent mechanical properties and the properties are comparable with those of forged products.

The effect of the microstructural properties on the mechanical properties of welding thermal cycles and post-weld heat treatment of the heat affected zone (HAZ) in 2024-T3 aluminium alloy has been investigated. Gleeble HAZ simulation, differential scanning calorimetry, TEM and tensile test have been utilised to investigate the regions representative of HAZ microstructures. The decay of strength in the weld HAZ is primarily due to the precipitation and coarsening of stable S phases. The welded HAZ in the region at peak temperature of 414°C has the lowest strength after natural aged temper. Post-weld T81 artificial aging (PWAA-T81) heat treatment at 190°C for 12 h has no effect on improving the HAZ strength; the HAZ strength of 2024-T3 alloy obtained by PWAA-T81 treatment is less than that obtained by natural aging, and its lowest strength is shifted to the region of the peak temperature, which is 452°C. Scanning electron microscopy observation reveals that the fracture mode changes from transgranular to intergranular failure when the 2024 specimen is exposed to a thermal cycle up to a peak temperature of 550°C. This is caused by the liquation of grain boundary segregates or formation of a eutectic structure while the specimen is subjected to high temperature thermal cycles during welding, which results in a decrease in the strength and ductility of the grain boundary. It is also shown that the decrease in ductility in this high temperature HAZ cannot be improved using the PWAA-T81 heat treatment.

Many studies monitoring the formation of martensite during the tensile deformation of austenite report data which are, in principle, affected by both the applied stress and the resulting plastic strain. It is not clear in these circumstances whether the transformation is stress induced (i.e. the stress provides a mechanical driving force) or whether the generation of defects during deformation helps nucleate martensite in a scenario better described as strain induced transformation. The authors demonstrate in the present work that a large amount of published data relating the fraction of martensite to plastic strain can in fact be described in terms of the pure thermodynamic effect of applied stress.

The influence of R ratio in the range 0·05–0·4 on the ambient temperature fatigue crack growth behaviour of an austenitic stainless steel weld, SS 316(N), has been studied. Results indicate that the cyclic threshold stress intensity factor ΔK_th increases with decreasing R ratio. The data are compared with those for SS 316, SS 316L and SS 316L(N) base materials from the literature, and various approaches dealing with the R ratio effects are examined. Zhang's model considering the contribution of the crack tip plasticity to the fundamental fatigue crack propagation process does provide a consistent interpretation for the data.

In the present article, a modular phase transformation kinetics model has been employed to describe the static recrystallisation behaviour of a high Mn (25 wt-) twinning induced plasticity steel just after hot deformation. The modular recrystallisation model is based on site saturation with preferential distribution of nuclei, interface controlled growth and impingement of growing particles. The model prediction has been validated with the experimental recrystallisation data of twinning induced plasticity steel. The experimental data were also modelled using Johnson–Mehl–Avrami kinetics based on random distribution of nuclei, which showed worse prediction as compared to the modular transformation kinetic model, thereby indicating the possibility of preferential nucleation around the defect sites. The rate of recrystallisation estimated from the measured fraction recrystallisation decreases sharply within a small recrystallised fraction. The interface migration velocity (interface between the recrystallised grains and the deformed matrix) was estimated from the analytical model. The interface velocity decreases sharply within initial small recrystallised fraction. The calculated stored energy of deformation, from the estimated interface velocity and mobility of the interface, suggests an inhomogeneous distribution within the deformed matrix.

Interstitial free (IF) steels having excellent drawing and forming characteristics find extensive use in autobody panels. Although, resistance spot welded joints are widely used in the automobile industry, little is known about the metallurgical changes which occur during the spot welding process. The investigation of the metallurgical changes is very important for the safety strength of the welded joints. In the present research work, microstructures of the different zones of spot welded interstitial free steels have been characterised by optical, scanning electron and transmission electron microscopes. Microstructural changes at weld and heat affected zone have also been correlated with welding heat input and microhardness values.

Machined titanium components, such as medical prosthesis, require the greatest reliability, which is determined by process induced surface integrity. However, surface integrity of milled titanium components easily deteriorates due to the poor machinability of titanium alloys and cyclic chip loading during milling. Milling induced surface integrity, including anisotropic surface roughness, residual stress, surface microstructure alterations and microhardness, has received little attention. In the present study, a series of end milling experiments were conducted to comprehensively characterise surface integrity at various milling conditions of titanium alloy Ti–6Al–4V with TiAlN coated carbide cutting tools. The experiments were carried out under dry cutting conditions. For a range of cutting speeds, feeds and depths of cut, analyses of machined surface roughness, residual stress, microhardness and the microstructural observations were carried out. The present work aims to evaluate the influence of different milling conditions on workpiece surface integrity.

The microstructure evolution and precipitation kinetics of maraging steel C300 have been studied in the aging temperature range from 400 to 600°C. The relation between mechanical properties and precipitation hardening response is explained, and modelling is used to optimise the properties. Ultrafine needle shaped Ni₃Ti phase is the main strengthening precipitate in maraging C300, and it shows very high resistance to coarsening. A spherically shaped Fe₂Mo phase is formed at higher temperatures and in the overaged condition. Inter- and intralath reverted austenite nucleates at higher temperature (∼600°C). Rolling and aging treatment can produce the highest hardness by a combination of work hardening and precipitation strengthening. Microstructural evolution simulation using Monte Carlo modelling has been applied to this alloy, and the modelling has been validated by the experimental results.

Using a vacuum electromagnetic stirring system, a high quality rheological material is developed in order to fabricate the engineering components without defects like internal porosities, which are caused by the entrapment of external air into the melt and impurities arising from the penetration of surface oxides by vacuum electromagnetic stirring. For practical application in vehicle industry, forming of the knuckle component that is used in automobiles was demonstrated by both direct and indirect type rheoforging processes. Here, insufficient filling behaviour occurred during direct forging processes, whereas indirect rheoforging of material with a solid fraction of 30–40 produced a completely formed knuckle component; thus, an indirect forging process may be suitable for forming the knuckle part. Through microstructural investigations and tensile tests before and after T6 heat treatment of the material, mechanical properties were characterised. By obtaining data about the rheoforging process and material properties of the rheoforged product associated with microstructural features, feasibility for future practical application was investigated. Moreover, the die structure for direct and indirect rheological forging processes was comparatively studied.

Ultrafine grained nickel (UFG Ni) and microcrystalline nickel (MC Ni) were fabricated on two types of substrates, i.e. the amorphous (Ni–P) and polycrystalline (stainless steel) substrates by pulse electrodeposition without additives. This study demonstrates that when inhibiting the epitaxial growth by first depositing a thin amorphous layer on the polycrystalline substrates, the grain size of the subsequent Ni deposit decreases dramatically from microscale to the UFG regime, which depends on the deposition conditions. Compared with MC Ni, which has an ultimate tensile strength σ_UTS of 397 MPa and an elongation to failure ε_TEF of 11·98, UFG Ni with an average grain size of 120·72 nm exhibits an enhanced σ_UTS of 807 MPa and a comparable ε_TEF of 10·44. The electrodeposited method used in this study provides an effective and low cost way to produce UFG materials with both high strength and ductility, which can meet the demands for practical application as structural materials.

The precipitation behaviour of β and γ′ in a low thermal expansion superalloy IN783 was investigated. It was demonstrated that coarse γ′ precipitates do form during β aging at 845°C. During aging at lower temperatures, not only fine γ′ particles are formed, the coarse γ′ particles also change from spherical to cuboidal. Therefore, a bimodal distribution of γ′ is formed in the matrix after standard aging treatment. The formation of β consumes Al atoms, which constrains the formation of coarse γ′ in the zone around β during aging at 845°C. During γ′ aging, a fine γ′ precipitating zone is formed around β. Prolonging the β aging duration markedly promotes the formation of β at grain boundaries and in the matrix, significantly enlarges the fine γ′ precipitating zone and influences the precipitation of coarse γ′.

Effect of Ti addition on the morphology and size of primary M₇C₃ type carbide in hypereutectic high chromium cast iron was investigated. The results indicated that the carbide is refined gradually, and its morphology becomes more equiaxed as titanium addition increases, but rather slowly when Ti addition exceeds 0·95. The qualitative measurement result indicated that value shape factor K increases clearly first and then changes little, and the average equivalent diameter D changes against K exactly. Furthermore, by TEM analysis and Brammit's theory calculation, the results also indicated that there are orientation relationships of _TiC|| _M7C3 and [011]_TiC||[0001]_M7C3 between M₇C₃ type carbide and TiC, and the lattice misfit δ between _TiC and _M7C3 is 1·32, explaining that _TiC may provide the effective substrate plane for _M7C3 nucleation to ameliorate morphology and size of primary M₇C₃ type carbide.

This paper studied the primary Al₃(Sc, Zr) particles formed during solidification in three Al–Sc–Zr alloys with various Zr contents. It has been shown that the primary Al₃(Sc, Zr) particles formed during solidification since the Sc and Zr concentrations are above the solid solubility limit in Al matrix. Scanning electron microscopy line scanning results indicated that the distributions of Sc, Zr and Al atoms in the primary Al₃(Sc, Zr) particles differ a lot from those in the secondary Al₃(Sc, Zr) particles formed during annealing. In the primary Al₃(Sc, Zr) particles, both Sc and Zr contents are found from rim to the centre of the particles, with an increasing trend from the rim to the centre, while the Al content drops sharply on the rim of the particle and slightly from the rim to the centre.

The closed cell aluminium alloy–fly ash particle composite (Al/FA) foams containing 1·5 wt- fly ash were manufactured by molten body transitional foaming process. The quasi-static compressive properties of Al/FA have been investigated. Results show the compressive stress–strain curves of Al/FA foams exhibit three regions, i.e. the elastic region, the plastic plateau region and the densification region. A linear relationship between the densification strain and the relative density was obtained. The relation between the plastic collapse stress and the relative density can be described with Gibson and Ashby's model. The energy absorption capacities of the Al/FA foams gradually increase with increasing strain and relative density.

Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.

As an improved directional solidification (DS) method, the complex directional solidification (CDS) method is used for purifying and preparing multicrystalline silicon ingot in this experiment. The induced electromagnetic field is imposed to control refining and solidification process. An integral silicon ingot with the diameter of 130 mm, the length of 130 mm and the weight of 4 kg is successfully fabricated in a self-designed CDS furnace. Metallographic analyses reveal that the direction of the most grains is parallel to the axial of silicon ingot. Analyses proved that the distribution of impurities in the cross-section is more homogeneously, the distribution in axial is improved and the effective length of silicon ingot is increased. Theoretical calculations indicate that the effect of solidified rate on the removal of impurities is limited and the impurities can be removed effectively after more than two times directional solidification process.

The thermal expansion behaviours of aluminium composites reinforced by ABOw with and without Bi₂O₃ coating are studied. The results show that the coating could influence the thermal expansion behaviour of composite. The coefficient of thermal expansion (CTE) of the composite with Bi₂O₃ coating is higher than that of the composite without coating. In addition, the heat treatment influences the thermal expansion behaviours of composite with Bi₂O₃ coating. The CTEs of the heat treatment composites are lower compared to as cast composite. At the same time, the quenching can boost the CTE of the composite compared with the annealing.

This study details the development of microstructure of Ti14 alloy as a function of the forging temperature and forging ratio in semisolid state and influence of resulting microstructure on the mechanical properties. The results reveal that dynamic recrystallisation occurred during semisolid forging, and the grain refinement was attained. Grain size increased in the forging temperature and decreased in the forging ratio. High ultimate tensile strengths and low elongation have been achieved after semisolid forging. The strength decreased with increasing forging temperature, while the ductility increased with increasing forging ratio. The relative contributions of tensile properties were attributed to the varieties of grain size obtained by thixoforging.

The hot deformation behaviour and microstructural evolution in Ti–6Al–2Zr–1Mo–1V alloys have been studied using isothermal hot compression tests. The processing map was developed at a true strain of 0·7 in the temperature range 750–950°C and strain rate range 0·001–10 s⁻¹. The corresponding microstructures were characterised by means of a metallurgical microscope. Globularisation of lamellae occurring to a greater extent in the range 780–880°C and 0·001–0·01 s⁻¹ had a peak power dissipation efficiency of 58 at about 850°C and 0·001 s⁻¹. The specimens deformed in 750–880°C and 0·01–10 s⁻¹ showed an instability region of processing map, whereas the specimens deformed in 880–950°C and 1–10 s⁻¹ indicated three kinds of flow instabilities, i.e. macro shear cracks, prior beta boundary cracks and flow localisation bands.

This short communication extends earlier modelling of the tensile strength and failure strain of jute technical fibres. A maximum likelihood estimate (MLE) model, a linear model and a natural logarithmic interpolation model (NLIM) are compared. The NLIM model is found to give superior predictions.