Tribological behavior and surface analysis of tribodeformed AI Alloy-50 Pet graphite particle composites
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I.
INTRODUCTION
A L U M I N U M alloy-graphite particle composite materials have been developed for self-lubricating tribological applications, u-41 The sliding behavior of A1 alloy-graphite particle composites under both dry [5-7,9] and lubricated ts,l~ conditions has been extensively tested. Very limited research, however, has been conducted to understand the tribochemical interactions between graphite particles, atmosphere, and substrate, as well as the formation of lubricating film during sliding wear. The interactions between the simultaneous processes of formation of tribochemical films and their removal through wear processes are far from understood, especially for the case of composites. Our previous w o r k I6'7] identified that a thin lubricant film of carbon was formed during sliding wear of an A1 alloy-10 pct graphite particle composite under dry sliding conditions; this film was composed of a mixture of carbon species, including a certain amount of graphitic carbon which was smeared on the worn surface. In the present study, composite samples containing close to 50 vol pct graphite particles were produced by a lowpressure infiltration technique. The thickness of the lubricating film formed during sliding wear under different sliding parameters was measured by means of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). In addition, the wear debris was analyzed to try to understand the chemistry of the mixtures of carbon species formed in the lubricating film and interactions between the simultaneous processes of film formation and its removal by the wear process. The resuits of this study are expected to contribute to a broader understanding of the tribological behavior of metal matrix composites, which is greatly influenced by these reactions at the surfaces. P.K. ROHATGI and T.L. BARR, Professors, and Y. LIU, Graduate Student, are with the Materials Department, College of Engineering and Applied Science, University of Wisconsin-Milwaukee, Milwaukee, WI 53201. Manuscript submitted June 11, 1990. METALLURGICAL TRANSACTIONS A
II.
EXPERIMENTAL PROCEDURE
The matrix alloy selected was a commercially cast A1 2014 and flake-type graphite in the size range of 180 to 8 5 0 / x m was used as the dispersoid. The composite with 50 pct graphite particles was produced by the lowpressure infiltration technique described in detail elsewhere, u2] Briefly, a 15-cm-long preform was made in a quartz tube with a diameter of 3.8 cm and a length of 26.6 cm by tamping the graphite powder into the quartz tube. The 2014 aluminum alloy was then heated to a temperature of 800 ~ The N2 was used as a source to apply pressure on the resulting melts in the range of 110 psi. Before the infiltration of the liquid, the preform was preheated in the melt for 2 minutes. The holding time for the pressure was 8 rain, and the final temperature of the liquid aluminum alloy was 770 ~ This method was successful for making aluminum matrix composites containing high volume percentages of graphite particles. The meas
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