Effect of grain size on the micro-tribological behavior of pure titanium processed by high-pressure torsion

The micro-wear behavior of commercial pure Ti was investigated before and after processing by high-pressure torsion (HPT) to provide comparisons over a range of grain sizes. The HPT-processed Ti had an average grain size of ∼130 nm while the as-received and HPT plus annealed samples had grain sizes of ∼8.6 μm and ∼607 nm, respectively. The results show all Ti samples have a similar dynamic coefficient of friction but different wear mechanisms. Wear of the coarse grained (CG) Ti showed extensive plastic deformation and wedge formation which produced large wear debris whereas wear of the ultra-fine grained (UFG) Ti was dominated by abrasive wear mechanisms and produced small wear debris. In addition, the UFG Ti showed a more homogenous wear grooving and a lower wear rate than CG Ti which suggests that UFG Ti is more suitable for wear applications.