Ceramic Conversion Treatment of Titanium Aluminide for Improved Tribological Properties

Gamma-based titanium aluminides have great potential in the automotive industries (e.g. valves in a car engine), but tribological property could be one of the crucial factors in determining the life and performance of a titanium aluminide part. A surface modification technique, namely ceramic conversion (CC) treatment has been developed to improve the tribological properties of a y-based titanium aluminide (Ti-48AI-2Nb-2Cr-B), and the surface properties were fully characterised. The results indicate that ceramic conversion treatment can produce an oxide layer consisting of a top TiO2 surface followed by a mixture of TiO2 and A12O3. Such hardened layer has significantly improved the load-bearing capacity and wear resistance of the intermetallics, as evidenced by an increase of scuffing load up to 4 times and a wear rate reduction of two orders of magnitude. The coefficient of friction has also been reduced from 0.5-0.7 for the untreated to an average of 0.22 for the CC-treated alloy under dry sliding contact conditions.