Tribological behavior of boron modified as cast Ti-6Al-4V alloys

Abstract

Trace additions of Boron to the Ti-6Al-4V melt leads to a substantial reduction in grain size by an order of magnitude, which in turn, minimizes or completely eliminates β/α+β working steps. This has a mixed effect on mechanical properties such as strength, fracture toughness, notch sensitivity, fatigue and creep performance. During the service, the components made of these alloys meet foreign objects and harder surface experiencing contact loading conditions. Hence it is important to understand the tribological behavior of these materials at both at room and elevated temperatures. Wear experiments were performed on Ti-6Al-4Vsamples having a different weight percentage of B (0, 0.3 and 0.55%), using Pin-on-disc tribometer at varying loads and temperature (from room temperature upto573K) combinations. On carrying out wear experiments with the hard surface a nonlinear variation in the wear rate with respect to test temperature for all compositions of B modifies Ti-6Al-4V was observed. Ti64 having 0.3 wt.% B showed better wear properties especially at high temperature (573K) and higher loads as compared to 0.55 and 0.0 wt.% B. Wearexperiment results shows severe wear at high temperature and for high B content (0.55B). To characterize wear tracks Scanning electron microscopy (SEM), profilometry, X-Ray diffraction (XRD) and subsurface optical microscopy is used. Characterization results clearly show prominent delamination wear at high temperature especially for 0.55B and for low temperature and low B content more adhesive wear is reported.