Microstructure and Mechanical Properties of Ti-6Al-4V by High-temperature Ultrasonic Nanocrystalline Surface Modification

Titanium alloys, in particular Ti-6Al-4V alloy, have been used for a wide and diversified range of engineering applications such as, aerospace, aircraft, automotive, oil and gas extraction, nuclear, chemical and other major industries due to their superior combination of strength and fracture toughness, high strength and low weight ratio, low density, good fatigue strength, excellent corrosion resistance, etc. This paper presents a feasibility study of a heat treatment by halogen lamp and its combination with an ultrasonic nanocrystalline surface modification (UNSM) technique. A heat treatment of Ti-6Al-4V alloy with and without UNSM treatment was performed at high temperatures of 600, 800 and 1000 ⁰C. The influence of UNSM treatment on microstructure, hardness, compressive residual stress and tribological properties of Ti-6Al-4V alloy were investigated. The hardness and compressive residual stress measurements results revealed that the hardness and compressive residual stress were increased with increasing the temperature, but they were further increased by the application of UNSM technique. It was also found that the wear resistance was increased in the same temperature order where the highest temperature of 1000 ⁰C exhibited the best wear resistance. However, even though the hardness was increased and compressive residual stress was induced after heat treatment at a temperature of 600 ⁰C, but no significant difference in wear resistance was found between the untreated and heat treated specimens. The wear mechanisms of each temperature were also discussed based on the obtained SEM images of wear tracks in terms of surface hardness, surface roughness and compressive residual stress. The development of combined heat treatment and UNSM technique was successfully demonstrated the feasibility of an increase in hardness and wear resistance of Ti-6Al-4V alloy.