Effect of temperature on the tribological characteristics of A356/15 wt.% SiCp functionally graded composites in unidirectional contact

Abstract

In this paper, preparation of A356-15 wt.% SiC particle reinforced functionally graded metal matrix composite[FGMMC] was done using a vertical centrifugal casting machine and elevated temperature (350 °C) tribological characteristics were reported in unidirectional sliding contact. The operating parameters of tribo pair tested were fixed with a load in the range of 15 N to 45 N under a constant sliding speed of 1 m/s slid through 350 m. The gradient distribution of FGMMC disc was evaluated using optical microscopy. Hardness values were obtained from the Brinell hardness tester and found to be well correlated with the obtained microstructures. Two types of wear and friction test pins were prepared from the disc for the elevated temperature tribo testing, one obtained from the FGM's outer zone, when the particle concentration is at its highest, and another taken from the inner zone, where the matrix concentration is at its highest. According to the wear results, both test pins exhibit an increase in wear rate as the load increases. Furthermore, for all loads, it is found that the test pin from the matrix rich portion has a higher wear rate than the test pin from the particle rich portion. At high temperatures, higher coefficients of friction are seen in the pins of the matrix rich portion, while lower coefficients of friction are observed in the test pins of the particle rich portion. The SEM images reveal that for test pins obtained from matrix rich portions, adhesion and metal flow are the main wear mechanisms, and for test pins taken from particle rich portions, abrasion, delamination and severe plastic deformation. It was observed that the pin tested in the matrix-rich region generates plate-like debris, whereas the pin tested in the particle-rich portion generates powdery-type debris.