Modified wear behavior of selective laser melted Ti6Al4V alloy by direct current assisted ultrasonic surface rolling process

Ti6Al4V alloy samples prepared by selective laser melting were treated by three different post-treatments: namely heat-treatment, ultrasonic surface rolling process (USRP) and direct current assisted ultrasonic surface rolling process (DC-USRP). Wear behaviors were evaluated using a block-on-disc rig under lubrication conditions. Results showed that the DC-USRP treated sample exhibited the lowest wear rate of 1 x 10(-6) mm(3) N-1 m(-1), compared to that of the as-built (4 x 10(-5) mm(3) N-1 m(-1)), heat-treated (2 x 10(-5) mm(3) N-1 m(-1)) and USRP-treated samples (5 x 10(-6) mm(3) N-1 m(-1)). Consistent with changes in the wear rate, the friction coefficient was also gradually reduced. The as-built and heat-treated samples showed severe abrasive wear and delamination, while the USRP and DC-USRP treated samples displayed only mild abrasive wear. The improved wear resistance of the USRP and DC-USRP treated samples was attributed to the modified lubrication mechanism, increased hardness and compressive residual stress. Moreover, the wear resistance of the DC-USRP treated samples decreased with the increasing depth from the surface due to the effect of gradient work hardening.