Role of sliding velocity and temperature on the tribological behavior of boron modified as cast Ti6AI4V alloys

Abstract

Trace additions of boron addition into the Ti6Al4V melt reduce the grain size substantially and eliminate the most expensive step in the thermomechanical processing of Ti6Al4V. This has significant effects on the mechanical properties of the alloy like tensile strength, ultimate tensile strength, notch sensitivity, fatigue, fracture toughness, and creep performance. Titanium alloy components are subjected to severe contact loading conditions during their service. Thus, the tribological study of these alloys becomes extremely necessary. Wear experiments were done on the Pin-on-disk tribometer at varying speeds and temperatures. On carrying out wear experiments, a non-linear variation of wear rate was observed with increasing temperature while linear behavior was observed with sliding speed. Mixed behavior was obtained in the samples as several factors play a role in the wear. At 1 m/s the performance of 0.3B alloy was optimum, while at 2 m/s it was 0.55B. Both alloys at 4 m/s at elevated temperature of 573K showed worse behavior than base Ti6Al4V itself. This can be attributed to the presence of hard TiB phase in the boron modified alloys as well as to the oxides formed at 1 and 4 m/s. Presence of tribo-oxides put a marked effect on the behavior at low and high speeds. To characterize the wear tracks we used SEM, XRD, Optical profilometry and Optical microscopy. Distinct deformation features are observed in SEM analysis. High abrasive wear and delamination is obtained for boron modified alloys at high temperatures and speeds while adhesive features along with abrasive wear is obtained in Ti6Al4V alloy.