Tribology - Materials,Surfaces & Interfaces

This paper presents the investigation of the surface roughness on the material dislocation using bonded interface technique. The influence of the surface roughness on three different materials was focused on this study. By using the bonded interface technique, the half-specimens of stainless steel, aluminium and brass were bonded and microindentations were conducted on the bonded interface surfaces with roughnesses ranged from 0.05 to 0.37 µm. The results revealed that the increase of surface roughness induced an exponential decrease in material dislocation in vertical direction beneath the permanent indent. Using Nix-Gao model, rougher surface produced higher load independent hardness which the materials experience the hardening effect. From the observation on the plastic deformation zone, the shear bands of harder material stainless showed limited material dislocation compared to softer material aluminium and brass.

The tribological characteristics of coconut oil added with ceria-zirconia hybrid (Ce-Zr) nanoparticle additives are investigated using a sophisticated pin-on-disk tribometer. A chemical processing technique namely, precipitation method (PM) is used for the synthesis of Ce-Zr nanoparticles. High-end characterization practices using microscopy and spectroscopy analyses were utilized to determine their morphology, composition, and structure. A model was developed through the Response Surface Methodology (RSM) technique, in which the Box Behnken Design (BBD) was chosen to develop the experimental design. The extent of influence held by the various factors, viz. speed, load, temperature, and nanoparticle concentration (wt.%) were evaluated using distinct methods such as analysis of variance (ANOVA), regression analysis and normal probability distribution. The thermo-physical properties such as kinematic viscosity, flash, and fire point of the lubricant were also subject to examination for any possible improvement. The optimum concentration of Ce-Zr nanoparticles for maximum performance of the formulated fluid was determined to be 0.62 wt.%.

In this work, erosion tests conducted to evaluate the resistance of two materials, Metal Babbitt Grade 7 and AISI T1 against SiC particles. The erosion rates of these two metals compared with those obtained using AISI D2 steel in a previous work with similar testing conditions. Metal Babbitt and AISI T1 steel selected due to their high ductility and strength, respectively. A test rig similar to that shown in ASTM G76-95 standard used to perform the tests. Silicon carbide particles had a particle size between 350–450 µm. Tests carried out using different impact angles, 30°, 45°, 60° and 90° with a particle velocity of 24 ± 2 m/s and the abrasive flow rate was 0.7 ± 0.5 g/min. SEM photographs used to identify the wear mechanisms on the Babbitt and T1 steel and also obtained cross-section images of the wear scars on metal Babbitt to measure their depth.

Development of the space engines with liquid propellants necessitates the use of bearings of high quality. During recent years, a new family of high strength corrosion resistant steels, with partial replacement of carbon by nitrogen, known as high nitrogen steels were developed having higher impact strength and fracture toughness coupled with high hardness for antifriction bearing of cryopumps in rocket. In this research work, wear characteristics of cryogenically treated high nitrogen martensitic stainless steels were investigated by Pin-on-disc wear testing machine. After conventional hardening treatment, specimens were subjected to cryogenic treatment at −196°C with cryosoaking period varying from 8 to 32 h in the interval of 8 h followed by soft tempering. These specimens were analysed for hardness, wear resistance, subsurface and worn surface features by SEM. It is established that there is a profound influence of nucleation and growth of precipitates on the wear behaviour and the underlying wear mechanisms.

The present research work examines the impact of temperature on the dry sliding wear behaviour of AA7075 aluminium strengthened zirconium diboride (ZrB₂) particulate composite (0, 3, 6, 9 and 12 wt.%). The dry sliding wear behaviour of the AMCs was inspected utilizing a pin-on-disc machine at differing temperatures (40, 60, 120, 180 and 240°C). The wear resistance of AMCs improved with the increased substance of ZrB₂ particulates at all test temperatures. The worn surface of the AMC pins was described utilizing FESEM. It was found from the SEM micrographs of worn surface, that at different temperatures, adhesion and metal flow were the prime wear process of the AA7075 composites, while for in situ formed AMCs, metal stream and oxidation were the factors affecting the wear process. The worn surface of the AMCs showed that there was a modification in wear component from abrasive wear to metal flow.

The present comparison is mainly based on the type of restrictor employed in the conical journal bearing with hole-entry in hydrostatic mode. It suggests efficient restrictor to be used in the subjected conical journal bearing. To find the characteristics, Reynolds's equation is applied to the fluid present in the space between conical journal and bearing, the flow equations for various restrictors have been presented using FEM. Different parametric characteristics have been obtained for the range of eccentricity ratio ( ) = 0.1–0.7. The outcome of the comparative characteristics depict the significant variations in the restrictor-based conical hole-entry journal bearing performances in hydrostatic mode which may be useful for the bearing designer to precisely design the conical hole-entry journal bearing. Comparatively, the constant flow valve fitted hydrostatic conical journal bearing with hole-entry may be recommended based on the present study.