Scratch, Fretting, and Sliding Wear of a ZrB2–hardened Zr3Al2 Intermetallic–ceramic Composite

Abstract

The unlubricated wear behaviour of a very recently developed ZrB2–hardened Zr3Al2 intermetallic–ceramic composite was investigated for the first time. In particular, tribological tests of scratch, fretting, and sliding were performed with no external lubrication under varied loads against diamond counterparts to thus account for different types and conditions of frictional contacts, and the worn surfaces were characterised in detail to identify the corresponding wear modes and mechanisms. It was found that under scratch wear the Zr3Al2–ZrB2 composite undergoes a ductile-to-brittle transition with increasing applied load, with an increasing plastic damage from low loads and eventually also with macro-chipping at intermediate loads and massive meso-/macro-chipping at high loads. It was also found that the Zr3Al2–ZrB2 composite is resistant to both fretting wear and sliding wear, exhibiting low specific wear rates. Thus, under fretting wear it underwent mild damage first by fretting fatigue in the form of slight surface abrasion and then by fretting oxidation with formation of a self-lubricating oxide tribolayer. The severities of the fretting fatigue and fretting oxidation increased with increasing applied load, with the former dominating over the latter for low and intermediate loads and the opposite being the case for high loads. Similarly, under sliding wear it also underwent only mild damage, now first by mechanical sliding wear and then by oxidative sliding wear, both of increasing severity with increasing applied load, but with the abrasion dominating over the oxidation. Given the promising wear behaviour observed in this first tribological study against diamond, it is proposed that these Zr3Al2–ZrB2 composites merit further investigation under an ample set of possible engineeringly-relevant wear conditions.