AbstractA critical evaluation of the effect of ion implantation on wear, fatigue, and fretting fatigue of Ti-6AI-4V is presented for optimising the parameters towards a specific type of property improvement. The analysis presented is based on the extensive results available on the effect of N + or C + implantation on the wear behaviour of Ti-6AI-4 V. In order to obtain the maximum benefit from either of these species the implant conditions and post-implant processing must be such as to ensure second phase precipitation. However, this is not the case for fatigue which is predominantly in the elastic region where solid solution hardening appears to be a sufficient mechanism for increasing the fatigue strength via ion implantation. Improving the fretting fatigue strength via ion implantation is more likely to result from implanting with ions to reduce wear rather than fatigue. Because the mechanisms in unidirectional sliding wear and fretting wear are essentially the same in Ti-6AI-4 V, it appears that ions which improve unidirectional wear resistance should also improve fretting wear. However, variations may arise from the differences between the behaviour of surface oxide layers in unidirectional wear and fretting wear, respectively.