Study of Dry Sliding Wear Behavior of Hot-Rolled and Mushy-State Rolled Al-4.5Cu-5TiB 2 In-Situ Composite with Analysis
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and RAHUL MITRA are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India. Contact e-mails: [email protected], [email protected] Manuscript submitted January 10, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
INTRODUCTION
THE lightweight Al alloys have the potential for widespread use as structural components in the automobile and aerospace sectors due to their high specific strength and ductility,[1,2] but their main drawback is poor sliding wear resistance in service. Therefore, the continuous demand for lightweight wear-resistant automobile components, particularly brake discs, and cams mounted on a camshaft in engine blocks has led to the
development of Al alloy matrix composites reinforced with hard ceramic particles.[3,4] Extensive research has been carried out on the evaluation of wear behavior of discontinuously reinforced Al alloy (DRA) matrix composites as a function of size, shape, distribution, and volume fraction of reinforcement particles, as well as test parameters like applied load, track diameter, track length, and sliding velocity.[5–11] It is well reported in the literature that the wear resistance of the Al alloy matrix composites (AMCs) is improved proportionately with the increasing volume fraction of reinforcement particles up to approximately 20 pct,[12] except for a few specific cases, where the wear rates of reinforced composite samples and unreinforced alloy samples under smaller normal load or specific sliding velocity are comparable.[5,13] In many of the earlier studies, the AMC with in-situ formed TiB2 particles has been reported to have superior wear resistance due to its thermodynamic stability, as well as its excellent physical and chemical compatibility with the Al alloy by forming a strong interfacial bond.[2,14,15] The addition of TiB2 (‡ 5 wt pct) as discontinuous reinforcement to the Al alloys has been reported to significantly improve the wear resistance.[16,17] Not only the volume fraction, but also the fineness and homogeneous distribution of second-phase particles, influences the wear behavior of AMCs.[18–20] Hence, the secondary thermo-mechanical treatment is considered significant for processing of AMCs. Mushy-state rolling, hot rolling, and mushystate rolling with prior hot rolling have been implemented to refine the cast microstructure of the Al4.5Cu-5TiB2 in-situ composite.[21,22] Herbert et al.[22] have reported the wear resistance of the mushy-state rolled Al-4.5Cu-5TiB2 in-situ composite to be superior compared to that of the sample in the as-cast condition due to the chemical homogenization and redistribution of fine second-phase precipitates and particles during mushy-state rolling. Greater homogeneity of both chemical composition and reinforcement particle distribution in the microstructures of the pre-hot-rolled mushy-state rolled composite (subjected to multiple passes) have further shown improved wear resistance, particularly on the rolling surface compared
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