Friction and wear of ion-beam-modified ceramics for use in high temperature adiabatic engines

An experimental program has been conducted to investigate the friction and wear behavior of ceramic materials being considered for use in high temperature adiabatic engines. Pin-on-disk-type tests were conducted in a simulated diesel environment at 8000C using ceramic-ceramic couples made up of SiC, TiC and TiC-Ni-Mo pins tested against Si3N4 and partially stabilized ZrO2 disk surfaces modified by ion beam mixing with cobalt, chromium, nickel or Ti-Ni. The coefficients of friction for each couple were determined from these tests, and the amount of wear was measured by profilometry of the wear surfaces. Scanning electron microscopy, Auger electron spectroscopy and energy-dispersive spectroscopy were used to characterize the wear surfaces. The results of these tests show that most non-ion-mixed ceramic-ceramic couples have relatively high wear rates and coefficients of friction above about 0.25. Ion beam mixing of disk material surfaces with Ti-Ni produced coefficients of friction as low as 0.06, values close to that for liquid-lubricated metal couples run at much lower temperatures. Surface modification with cobalt or nickel produced some promising results, while chromium did not improve the wear characteristics of the disk materials. Auger analysis suggests that the formation of lubricious oxide layers is responsible for the superior friction and wear behaviour of the Ti-Ni-ion-implanted disks. (orig.)