Tribological behavior of (Cu42Zr42Al8Ag8)99.5Si0.5 bulk metallic glass

In this investigation, the tribological performance of (Cu42Zr42Al8Ag8)99.5Si0.5 bulk metallic glass (BMG) was evaluated and compared with that of hardened S45C medium carbon steel. Three of classes of specimen were used in wear tests; they were as-cast BMG, annealed BMG and hardened S45C. Wear tests were conducted using a cylinder-on-plate Cameron-Plint TE77 reciprocating friction machine. The worn surfaces of wear specimens are observed by scanning electron microscopy (SEM), and the chemical compositions of localized regions are characterized by energy dispersive spectroscopy (EDS).The results indicate that the dominant wear mechanisms of the as-cast BMG and annealed BMG are delamination under dry sliding conditions. In contrast, the dominant wear mechanism of hardened S45C is adhesive wear. Under water-lubricated conditions, most of the worn scars are formed by abrasive wear. Although the hardness of as-cast BMG equals that of hardened S45C, the wear performance of as-cast BMG is poorer than that of hardened S45C. However, the annealed BMG exhibited the best wear performance, because of hardening by nanocrystal precipitation. This precipitation hardening effect reduces the depth of penetration by wear particles during sliding. Oil-lubricated conditions were established using three oils, and paraffin mineral (MN) base oil was found to yield the greatest wear volume for as-cast BMG. The wear loss of the as-cast BMG test in paraffin MN base oil was the highest among all of the specimens, perhaps because of tribochemical reaction wear. However, the annealed BMG exhibited excellent wear performance in paraffin MN base oil.

► As-cast BMG, annealed BMG and hardened S45C were wear specimens.
► BMG specimens were delamination. Hardened S45C were adhesion under dry sliding tests.
► All specimens were abrasive and adhesive wear under water-lubricating conditions.
► As-cast BMG exhibited massive wear loss under paraffin MN base oil condition.