Effects of ZrO2 crystal structure on the tribological properties of copper metal matrix composites

Abstract

ZrO 2 , a promising abrasive to improve tribological properties, is introduced into copper metal matrix composites (Cu-MMCs). Micro-tribological behaviors of ZrO 2 in two crystal forms and their effects on the tribological properties of Cu-MMCs were investigated. The results showed that the fragile monoclinic ZrO 2 (m-ZrO 2 ), exhibiting a high coefficient of friction (COF) and strong bonding with the matrix, evidently enhanced the COF of Cu-MMCs at low and medium braking energy densities (BEDs). Even though the harder cubic ZrO 2 (c-ZrO 2 ) displayed a relatively low COF and weak bonding with the matrix, it produced significant improvements in wear resistance and COF of Cu-MMCs at high BED. With an increase in BED, the wear mechanisms of Cu-MMCs with m/c-ZrO 2 transformed from plough to delamination. • Tribological properties of m/c-ZrO 2 were detected via micro-macro friction tests. • m-ZrO 2 has a lower hardness, rougher surface and higher COD in micro-friction tests. • m-ZrO 2 forming a tighter bonding with Cu improved COF of Cu-MMCs at low-medium BED. • c-ZrO 2 produced improvements in wear resistance and COF of Cu-MMCs at high BED. • Wear mechanisms of Cu-MMCs transit from plough to delamination with BED increasing.