Multi-pass friction hardening treatment of Ti6Al4V alloy toward improved tribological properties

Multi-pass surface friction hardening was employed to modify the microstructure and enhance the tribology characteristics of the Ti6Al4V alloy. The process was performed by reciprocated sliding a flat-head WC-Co cylindrical pin tool on the alloy surface under different applied loads of 350, 700, 1050, and 1400 N. The sliding was conducted at different speeds of 45, 90, 180, 360, 720, and 900 mm min−1 for 30, 60, 90, 120, and 150 passes, respectively. Based on the hardness test and microstructural characterization results, the applied load of 1050 N, the sliding speed of 900 mm min−1, and the pass number of 60 (900-60 sample) were chosen as the optimum economic process parameters for the subsequent experiments. Performing surface friction hardening under the optimized conditions increased the surface hardness of the annealed sample from 350 HV1 to 564 HV1 showing an increase of about 60 %. Surface friction hardening was also found to substantially improve the tribology characteristics of the Ti6Al4V alloy. According to the obtained results, under the applied loads of 1 and 6 N, the wear rate and the average friction coefficient of the 900-60 sample were lower than those of the annealed one by 58 and 83 %, and 33 and 50 %, respectively.