Pack carburisation of commercially pure titanium with limited oxygen diffusion for improved tribological properties

• A new pack carburising surface treatment method has been developed.
• The method involves both carbon diffusion and oxygen diffusion.
• A carbide layer is formed on top of an oxygen diffusion zone.
• The treatment significantly improved the tribological properties and the load bearing capacity.

In the present work a new pack carburising surface treatment method has been developed, whereby oxygen diffusion and carburisation of commercially pure titanium was undertaken. Pack carburisation was carried out with a limited amount of oxygen, at a temperature of 925 °C for 20 h. The carburising process resulted in a multilayer structure comprising a titanium carbide (TiC) network layer atop of a relatively thick α-titanium oxygen diffusion zone (α-Ti(O)). Initial tribological tests demonstrated that the new surface treatment can significantly enhance the tribological properties of titanium, in terms of much reduced friction, improved wear resistance and enhanced load bearing capacity. The TiC surface structure offers enhanced hardness (2100 HV) and low friction coefficient (μ ≈ 0.2) when in dry sliding contact with an alumina (Al2O3) ball, while the thick oxygen diffusion zone offers much enhanced load bearing capacity. When compared with untreated Ti, thermally oxidised titanium (TO-Ti) and hardened AISI 440C stainless steel, the carburised titanium allowed for a greatly improved friction and wear response.