Room and high temperature dry sliding wear behavior of Boron modified as-cast Ti-6Al-4V alloys against hardened steel

Trace additions of elemental Boron to Ti-6A-4V melt has a marked influence on the as-cast microstructure and mechanical properties. In this study, dry sliding wear behavior of as-cast Ti-6Al-4V alloys containing 0%, 0.3% and 0.55% B was investigated in the temperature range of 300-573 K against the hardened steel as the counterface material. The results indicate that wear rate decreases initially with small additions of B and then increases again with subsequent additions. It is found that decrease in grain and lath sizes decreases the wear rate while the increase in volume fraction of TiB increases it. At low temperatures and low volume fractions of TiB, the wear mechanism is primary adhesive or abrasive in nature while at high temperature the mechanism changes to abrasive or delamination wear. A close examination of sub-surface microstructures of the worn surfaces reveals an intensive shearing of the laths at room temperature, while a noticeable shearing is not observed at high temperatures. The topographical analysis of the worn surfaces using SEM and AFM reveal severe plowing of the material, particularly at high TiB content. Debonding of the TiB particles and their participation in the wear appears to be the possible reasons for the high wear rate observed in a Ti-6Al-4V alloy containing 0.55% B.