High temperature friction and wear behavior of cold-sprayed Ti6Al4V and Ti6Al4V-TiC composite coatings

Abstract

The poor wear resistance of titanium and its alloys often results in galling and high wear rates. One method to improve their wear resistance is by hard secondary phase reinforcement to create a metal matrix composite, which can be utilized in the bulk or as a coating. In the present study, Ti6Al4V coatings and Ti6Al4V-TiC metal matrix composite coatings were deposited on mild steel substrates using cold spray process and their dry sliding wear behavior was studied over a static temperature range of 25–575 °C. Tests were performed using a unidirectional ball-on-disc tribometer with WC-Co sphere as the counterface at a load of 2.5 N and sliding velocity of 2.1 cm s−1. Wear rate and coefficient of friction (CoF) decreased with an increase in temperature and composite coatings exhibited higher wear resistance at all temperatures. Below 200 °C, abrasive wear characterized by ploughing by wear debris resulted in high wear of Ti6Al4V coatings, whereas formation of tribolayers led to lower wear of composite coatings. At elevated temperatures (> 200 °C), oxide glaze layers formed on both coatings were composed of WO3, TiO2 and CoWO4. Electron channel contrast imaging of the wear track cross-sections showed no splat debonding, less extent of recrystallization and larger grain sizes (at 575 °C) in composite coatings compared to Ti6Al4V.