Gaurav Gautam

Dry sliding wear behavior of Al-SiO2 composites

Abstract Al-base composites with different amount of silica (5, 10, 15 and 20 wt.%) were developed using powder metallurgy route and compacts were sintered at 550 °C for 2 h. XRD analysis of all compositions was conducted for phases and amount of the second phase present. Morphology of the composites shows quite uniform distribution of the SiO2 particles but at higher percentage of SiO2 particles the clustering starts. Mechanical properties such as uniaxial compressive strength (UCS) and hardness were evaluated and it is seen that among all compositions, composite with 10 wt.% SiO2 has maximum UCS and hardness. Wear behavior of all composites was studied with sliding distance, applied loads, sliding velocity and composition. All composites show a linear increase in cumulative wear with distance and load. Wear rate with load increases continuously for all compositions, however, composite with 10 wt.% SiO2 revealed minimum wear rate with distance, sliding velocity and loads. Wear rate with sliding velocity increases sharply after attaining minima at 3 m/s sliding velocity. SEM analysis of wear tracks is in agreement with wear results. Al-10 wt.%SiO2 also shows minimum wear coefficient values for all loads, however, wear coefficient decreases with load for all compositions.

Strengthening mechanisms of (Al3Zrmp + ZrB2np)/AA5052 hybrid composites

To establish the correlation between grain size, dislocations, dispersed particles (size and vol.%) along with their solid solution strengthening effects in alloy and combined effect of all on the strengthening of advanced composite materials (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been selected for the investigation. (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been synthesized by the direct melt reaction of AA5052 alloy and inorganic salts (K2ZrF6 and KBF4). These composites have been characterised by X-ray diffractometer, optical microscopy, scanning-electron microscopy with energy-dispersive spectroscopy, transmission-electron microscopy, tensile and hardness test. Results indicate the successful formation of second phase reinforcement particles namely Al3Zr and ZrB2 in the AA5052 alloy matrix. Al3Zr particles exhibit rectangular and polyhedron morphology within an average of micron size while ZrB2 show hexagonal and rectangular within an average of nano size. Grain refinement of Al-rich phase observed in the composites, increases with increasing vol.% of reinforcement particles. TEM observation shows the presence of dislocations in the composite matrix which help to improve the strength parameters. Tensile results show the improvement in strength parameters which improve with the increasing amount of particles whereas percentage elongation also improves up to certain vol.% of particles and beyond that decrease. However, bulk hardness shows an increasing trend continuously with vol.% of particles. The strengthening mechanisms, namely dislocation, Orowan, grain-refined and solid solution are quantified for the hybrid (Al3Zrmp + ZrB2np)/AA5052 composites and the total of above are in agreement with experimental results. Solid-solution and Orowan are the predominant strengthening mechanisms in the composites.

Synthesis and tribological properties of AA5052-base insitu composites

Abstract It is important to optimize the properties of a material for a particular application, hence, to find the suitable material for tribological applications, the wear and friction behaviour of AA5052 in situ composites with different kind of reinforcements have been investigated. For present study, three in situ formed composites have been produced with different reinforcements namely Al3Zr, ZrB2 and combination of both (Al3Zr + ZrB2) by direct melt reaction (DMR) technique. The as-cast composites and base alloy have been characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy, tensile testing, hardness and dry sliding wear and friction tests. XRD results indicate the successful formation of second phase reinforcement particles in all composites. Wear test results indicate that the cumulative volume loss increases with an increase in sliding distance while coefficient of friction shows a fluctuating tendency, whereas with increasing applied load, wear rate shows an increasing trend while coefficient of friction shows decreasing trend. The variation of wear rate with composites indicates that the composite with multiple reinforcement (Al3Zr + ZrB2) has lowest wear rate among all as-cast composites and base alloy, while coefficient of friction is higher. The responsible mechanisms concerned with wear and friction results have been discussed in detail with the help of the observation on worn surface analysis by scanning electron microscope (SEM) and 3D-profilometer. All tribological results have been correlated with the microstructural properties, strength parameters and bulk hardness of the composites.

Effect of Primary Silicon Refinement on Mechanical and Wear Properties of a Hypereutectic Al-Si Alloy

This study explores the effect of primary silicon refinement of hypereutectic Al-Si alloy on the mechanical and wear properties. Refinement has been carried out by purging N2 into hypereutectic Al-Si alloy melt for different period of time. Hypereutectic Al-Si alloy with 16.2 wt.% of Si was taken for the study and purged by N2 gas for different time. Hypereutectic alloy under different conditions was characterised for various properties. X-ray diffractometer (XRD) analysis doesn’t show formation of any nitride but optical microscopy (OM) and scanning-electron microscopy (SEM) results show modified/refined morphology of silicon. Mechanical and dry sliding wear properties were evaluated at ambient temperature and results reveal improvement in these properties. Worn surfaces were also studied under SEM and 3D-profilometer for surface analysis. Results indicate that at low load/sliding velocity, wear is oxidative/mild in nature, whereas, oxidative-metallic/severe wear is observed at high load/sliding velocity.