Unlubricated sliding of a titanium aluminide alloy against M2 tool steel

This study is an extension of continuing research on the wear behaviour of γ-TiAl base alloys, which has demonstrated how a surface reaction layer, made of native oxides, can dramatically improve the dry sliding wear resistance of the Ti-48Al-2Cr-2Nb-1B (at.-%) alloy. The results presented provide a further insight on the wear behaviour of the coated alloy under different loading conditions. Moreover, specific attention has been paid to the study of the tribological coupling and of the wear mechanisms affecting an M2 steel couterface disc. The steel counterface is abrasively worn by the oxide asperities present on the alloy surface. Wear debris remains trapped between the sliding surfaces and gets oxidised. Therefore, wear debris may contribute to further accelerate the wear rate before leaving the system or being compacted on the wear tracks to form protective glazes. Once the main wear mechanism was clearly identified, some tests were conducted on alloy specimens which had their surface oxide mechanically smoothed. This operation proved to be very successful indeed. In fact as a result, not only did the γ-TiAl alloy have a zero wear rate, but also a significant reduction of the abrasive contribution to the wear rate of the steel counterface was detected. Both these improvements were observed even at the highest load employed in the investigation (500 N).