Influence of Air Cooling and Aging on Microstructure and Wear Properties of 3D-Printed and Conventionally Produced Medical-Grade Ti6Al4V ELI Alloy

The emergence of additive manufacturing (AM) in recent years has become one of the most demanded manufacturing technologies in the biomedical and aerospace industries due to its ease of fabrication of components with complex geometry. Ti6Al4V parts manufactured by AM process however require a post-processing to optimize their mechanical properties for engineering applications. The cooling rates after the heat treatment play a significant role in tailoring the final microstructure and properties of medical-grade Ti6Al4V ELI alloys. This study therefore aims to investigate the changes in microstructure and consequently mechanical and wear properties of both AM-fabricated (3D-printed) and conventionally produced Ti6Al4V ELI alloy by the effect of post-heat treatment, air-cooling and aging (200 °C, 500 °C and 800 °C) processes. Typically, the formation of lath colonies and precipitated needle-like lath structures after solutionization (@ 1080 °C) and air cooling above the β-transus yielded a retained cubic β-phase regardless of the manufacturing process. Different spatial distributions of the alpha (α) lath and basket-weave structures as well as coarsened AlTi₃ intermetallic (V-shaped) structures evolve, which later reduced in area fraction in 3D printing. Also, increasing the aging temperatures after slow (air) cooling gradually enhances α-β-phase transformation rates regardless of the manufacturing process because of diffusional redistribution of alloying elements. In addition, the evolution of V-shaped structures improves the hardness (up to 29 pct) and wear performance of 3D-printed materials (up to 126 pct) relative to the conventionally produced materials, regardless of the β content.