Materials Science and Technology

Porous TiNb-based alloys have attracted considerable attention in the medical field of orthopedic applications because of excellent biocompatibility, porous architecture, appropriate mechanical property, etc. The literature reviews the current progress of fabrication methods, porous structure, mechanical properties, corrosion resistance, bioactive hydroxyapatite surface modification, in vitro and in vivo biocompatibility of porous TiNb-based alloy. Moreover, future research directions are pointed out to expand its possible biomedical applications.

The influence of liquid metal feeding on the flow and macrosegregation during direct chill (DC) casting of Al-4.5wt-%Cu billets is investigated. An analytical study for constricted inlets predicts that the inflow only reaches the bottom of the sump for narrow inlets, a result confirmed by steady-state axisymmetric simulations of equiaxed solidification. For wide inlets, and inlets using a combo bag, the inflow is swiftly entrained towards the chill and the final macrosegregation predictions are all similar. For narrow inlets without a combo bag, penetration of the thermal jet to the bottom of the sump locally delays solidification producing an inclination in the packed solid interface and the possible growth of columnar dendrites in this region.

The aim of the submitted work is to study the influence of applied loads (test forces) between 0.09807 and 2.9421 N on the measured value of micro-hardness of sintered Fe/3.3 wt-%Cu + C_nH_m. The Indentation Size Effect (ISE), i.e. the influence of the load on the micro-hardness is expected. The results were evaluated by Meyer's index n, t-test, and non-parametric tests. The applied load has a statistically significant influence on the type and size of the ISE. Tested sintered material shows ‘normal’ ISE with Meyer's index n = 1.7588.

Ti, Co, Cr, Fe, Ni and graphite powders were used to fabricate TiC reinforced CoCrFeNi composite by mechanical alloying and consequently hot pressing sintering at 1200°C for 1 h. Results indicated that Co, Cr, Fe and Ni powders were deformed, cold welded and crushed repeatedly during milling and an face-centred cubic-structured solid solution was obtained after milled for more than 10 h. Nano-sized TiC and micron-sized Cr₇C₃ type carbides were formed and embedded in the CoCrFeNi matrix dispersedly after sintering. The hardness and compressive fracture strength of the sintered composite reached 501 HV and 2.55 GPa, respectively, which could be ascribed to the presence of large amount of in-situ formed TiC and Cr₇C₃ type carbides in the composite.

Ti–6Al–4V plates were subjected to warm rolling at 600°C up to 85% reduction in thickness followed by annealing at 850°C for different soak periods. It was observed that the ‘β’ grains were prevalent along the grain boundaries and at the triple junctions of ‘α’ grains. The samples were found to be fully recrystallised after 30 min of annealing time. Further, globularizarion of ‘α’ grains was observed during the progress of annealing. The recrystallisation mechanism was identified to be through sub-grain formation and its growth. A dominant near basal texture, i.e. , was observed in the samples after annealing.

The microstructure and mechanical properties of explosively welded TA1/3A21 composite plate were studied. The results suggested that the bonding interface had a wavy appearance, and two types of Ti–Al solid solutions were found in the crest region. Most of the interfaces had a thin diffusion layer with a thickness of approximately 3 µm, and no brittle intermetallic compounds were formed. The interface of the explosively welded TA1 Ti/3A21 Al composite plate exhibited reliable shear and bending properties. The propagation of the facile cracks initiated at the Ti–Al solid solution/Al interface, and the Ti–Al solid solution region at the vortex could be terminated by the Ti matrix. In addition, the complex bonding interface structure inhibited the crack propagation along the interface.

Welding porosity and nitrogen content are considered significant factors affecting the mechanical properties of fusion-welding joints of high-nitrogen steel. In this study, a method of applying mechanical vibration in the welding process to reduce weld porosity and increase weld nitrogen content was investigated. The effects of mechanical vibration on porosity, tensile, and impact properties were analysed. The results indicated that the bubble floating speed in the vibrating weld pool is faster than that in the general welding mode. With the increase of mechanical vibration frequency, the porosity of the weld decreased at first and then rose. The tensile strength and impact energy increased first and then decreased, and the fracture surface indicated a ductile fracture.

This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND > TD > RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared.

The microstructure and mechanical properties of the Al–4Cu–2.7Er–0.3Zr alloy were investigated. The precipitates of the L1₂ structured phase with sizes 37 ± 12 nm were formed in lines and homogenously distributed inside the aluminium matrix after annealing at 605°C for 1 h. The as-rolled Al–4Cu–2.7Er–0.3Zr alloy developed an increased hardness after 1 h annealing at 100–550°C and 0.5–6 h annealing at 150–250°C due to precipitation of the Al₃(Er,Zr) phase. Addition of Zirconium improved the tensile properties relative to those of the Zr-free alloy by approximately 20 MPa: yield strength = 273–296 MPa and ultimate tensile strength = 296–328 MPa in the alloys annealed at 100–150°C.

GRAPHICAL ABSTRACT

The effects of Mn on the microstructure and impact-abrasion wear resistance of bainitic steel were studied. Results showed that the Mn-containing steel possessed finer microstructure and higher volume fraction of retained austenite, in comparison with the Mn-free steel. This was caused by lower transformation temperature and higher strength of undercooled austenite. The weight loss of Mn-free steel varying with the impact load was larger than that of Mn-containing steel. High strength, hardness and toughness of Mn-containing steel were conducive to improving wear resistance. More retained austenite in Mn-containing steel played an active role in work hardening and hindering crack propagation. However, the portion of retained austenite that induced martensitic transformation was the same with increasing impact-wear load.

A novel one-pass integrated severe plastic deformation method, entitled extrusion compression angular pressing forward extrusion (ECAP-FE), was designed and used for fabricating a fine-grained as-cast AZ31 Mg alloy. Subsequently, mechanical (room temperature compression, tensile and microhardness) and microstructural properties of the processed sample were investigated in detail. In addition, a finite element simulation of the proposed method was carried out for evaluating the equivalent plastic strain and strain rate distribution. The results showed that the ECAP-FE method is a powerful method for processing the ultrafine-grained as-cast AZ31 Mg alloy in a single pass to achieve a uniform and fine microstructure with enhanced mechanical properties. Therefore, it appears that the proposed method has a great potential to a wide range of industrial applications.

Recent studies indicated that precipitation-hardened high-entropy alloys (HEAs) possess outstanding properties. It is difficult to obtain substantial precipitated particles for HEAs at the as-cast condition. In this paper, cast precipitation-hardened high-entropy superalloys (HESAs) Ni_48−x Co₁₈Cr_10.5Fe_9.3Al_9.7Ti_4.5Mo _x (at.-%, x = 1, 2, 3) were designed and prepared. All HESAs possess a high-entropy matrix and a fine γ′ particles structure. HESAs have higher ultimate tensile strength and elongation at room temperature than conventional Ni-based superalloys and close yield strength. All HESAs possess high compressive strength at elevated temperature. At 850 °C, the strengths of all alloys are higher than 800 MPa. Solid solution strengthening and precipitation strengthening were discussed. Precipitation strengthening has the greatest contribution to yield strength.

As-cast transformation-induced plasticity (TRIP) steels with two different aluminium contents (2.80 and 6.75 wt-%) were subjected to investigate the effect of aluminium content on the tensile strength and hot ductility. As the Al content increases from 2.80 to 6.75 wt-%, the third brittle zone of the steel is shifted from 950–750°C to 800–750°C. The 6.75 wt-% Al-TRIP steel is a typical δ-TRIP steel that contains 44.5 wt-% δ-ferrite compared with no δ-ferrite in the 2.80 wt-% Al-TRIP steel. The solidification behaviour of these two types of TRIP steel was compared by calculating equilibrium phase diagrams. The 6.75 wt-% Al-TRIP steel was found to have better ductility than the 2.80 wt-% Al-TRIP steel below 1100°C.

In this work, dedicated isothermal transformation studies were performed in a Fe–C–Mn–Nb alloy to obtain two types of precipitate morphology embedded in a similar ferritic matrix. Nano-hardness of individual ferrite grain was measured by using an in situ nano-mechanical tester. The peak of nano-hardness distribution from interphase and dispersed precipitate strengthened ferrite corresponds to the nano-hardness range of 2.6–2.8 and 2.5–2.6 GPa, respectively. A wider spread of nano-hardness from interphase precipitate strengthened ferrite was observed and rationalised by considering the variation in inter-particle spacing on slip planes. The ‘pop-ins’ on the load-depth curve was not able to be correlated with the morphology of a precipitate.

We propose an effective heat treatment involving a combination of intercritical hardening and tempering to obtain high strength–high ductility in hot-rolled 0.2C–1.5Al–(6–8.5)Mn–Fe transformation-induced plasticity (TRIP) steels. An excellent combination of high ultimate tensile strength of 1045–1380 MPa and total elongation of 34–39% was obtained when the steels were subjected to intercritical hardening at 630–650 °C and tempered at 200 °C. Intercritical hardening impacted the co-existence of austenite, ferrite and martensite, such that the deformation behaviour varied with the Mn content. The excellent properties of the steels were attributed to cumulative contribution of enhanced TRIP effect of austenite and ferrite and martensite constituents. The discontinuous TRIP effect during tensile deformation involves stress relaxation and led to consequent enhancement of ductility.

Sucrose, as a precursor of carbon, and titanium powders were used to prepare TiC powders by a spray-drying/precursor-pyrolysis method. Using the powders, TiC/Ti composite coatings were deposited by reactive plasma spraying. The results show that submicron-sized TiC is formed. The TiC phases have three kinds of crystal morphology: spherical TiC with a diameter of about 600 nm, dendrite TiC with a primary dendrite spacing of about 450 nm and a secondary arm spacing of about 150 nm, and cellular-dendrite TiC with a width of about 120 nm and a length of about 600 nm. The TiC/Ti coatings exhibit high microhardness and excellent wear resistance, which is about 2–3 times and about 200 times higher than that of TC4 alloys, respectively.