Electrical discharge shape memory alloying of Ti-6Al-4V: Mechanisms and mechanical properties

Abstract

Electric discharge alloying presents an alternate coating process for improving mechanical properties through physical and metallurgical modification. Ti-6Al-4 V is a titanium alloy used in aerospace industry and biomechanical applications but has limitations in terms of wear resistance. Alloying with nickel could provide improvements in terms of wear and other tribological properties. Nickel as an alloying element provides pseudo-elastic behaviour (such as two-way shape memory effect) by changing α-Ti to β-Ti. After coating process, surface hardness of the samples increased up to 684 HV0.5 while in the cross-section, it ranged up to 580 HV0.5. Due to porosity, areas with hardness below the base material hardness value of 260 HV0.5 were measured as well. At the lowest load, coefficient of friction had a value of 1.1 while at higher loads it decreased down to 0.8 compared with alloyed layer with average values of 0.3 to 0.7. Wear resistance properties of titanium were improved as well. Specific wear rate under 40 N was 1.0 × 10−5 N/mm2 showing higher wear resistance with minimal ploughing.