Dry sliding wear behavior of A356-15 Pct SiC p composites under controlled atmospheric conditions
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I. INTRODUCTION
THE dry sliding wear behavior of aluminium matrix composites (AMCs) has been studied over the past 2 decades and the findings show that in most cases the wear resistance of the AMCs is better than their unreinforced monolithic counterpart.[1–4] A comprehensive review of the current and potential application for the cast AMCs in the automotive industry has been provided by Rohatgi.[5] In general, the mechanical mixed layer (MML) formation on the composite pin surface and the consequent increased wear resistance compared to that of the monolithic counterpart is widely accepted. In this regard, Deuis et al. have recently reviewed the present understanding of the wear mechanism of AMCs.[6] It has been shown that the materials possessing high wear resistance under dry sliding conditions are associated with the stable tribolayer on the wearing surface and the formation of equiaxed wear debris.[6] The formation and removal of the tribolayer or the MML during wear depends on various factors such as sliding velocity, applied load, and nature of the atmospheric condition. Substantial work has been carried out to study the effect of load and sliding velocity on wear behavior of AMC systems. Detailed reports on the influence of the mechanical mixed layer on wear behavior are limited. Venkataraman and Sundararajan[7] have done detailed investigations on pure AMCs and have shown a correlation between the thickness of the MML and wear rate. However, reports on the nature of the layers formed at different atmospheric condition, their stability, and their influence on wear behavior are not available. In order to elucidate the role of the MML on the wear R.A. SARAVANAN, formerly Senior Researcher with the Korea Institute of Machinery and Materials, is Senior Researcher with Advanced Materials Research Center, Nanyang Technological University, Singapore. JUNGMOO LEE, Senior Researcher, and SUK-BONG KANG, Principal Researcher, are with the Korea Institute of Machinery and Materials, Changwon, 641-010, Korea. Manuscript submitted September 3, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
resistance of the AMCs, the dry sliding wear experiments were carried out in controlled argon and oxygen atmospheres. A study on wear rate, friction coefficient, debris morphology, worn surface, and subsurface under these inert and highly oxidative atmospheres is expected to provide a complete understanding of the MML formation and its role on the wear resistance property. II. EXPERIMENTAL PROCEDURES An A356 alloy reinforced with 15 vol pct SiC particle (Duralcan (San Diego, CA)) was used in the present investigation. The average size of the SiC particles was about 13 mm. Wear testing was carried out using a unidirectional pin-on-disc machine (Plint and Partners Ltd.). Cylindrical samples with 8-mm diameter and 15-mm height were machined from as-received ingots and the same were used for wear testing. The counterpart material was hardened cold work tool steel disc made of AISI D2 (595 VHN). Three pins of the same test material were
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