Abstract
Titanium alloys are extremely reactive in the molten state, therefore near-net shape and complex shape components cannot be produced by many techniques used for steel, aluminum and other less reactive metals. The vacuum plasma spray (VPS) process is a well-known method for coating and forming reactive metals and alloys such as titanium alloys. In this study the internal microstructure of individual splats, porosity, and mechanical properties of Ti-6Al-4V deposited by vacuum plasma spray forming (VPSF) were studied using SEM, XRD, mercury porosimetry, image analysis and mechanical testing. Results described in a companion paper show that while tensile and yield strength rise with increasing initial powders size, elongation still remains as low as 1%. The as-sprayed structure consists of α’ martensite with a small amount of residual β between the martensite colonies as well as pores between the splats. The fracture surface within the splats is indicative of ductile failure. The low cohesion between the splats results in damage accumulation at the boundaries and failure at small elongations. Post deposition heat treatments were conducted to improve the coating structure and were successful in improving the ductility to levels approaching that of traditionally processed material.
