Comparison of the microstructural, mechanical and wear properties of plasma oxidized Cp-Ti prepared by laser powder bed fusion additive manufacturing and forging processes

Abstract

Selective laser melting (SLM) or laser powder bed fusion (L-PBF), which is one of the additive manufacturing methods, has gained much more importance in recent years. Commercially pure titanium (Cp-Ti) is commonly used for biomedical applications in this process but it exhibits poor wear and friction properties during its use. Therefore, this study aims to improve the mechanical and tribological properties of Cp-Ti produced by L-PBF and forging using plasma oxidation treatment in a glow discharge environment. For this purpose, Cp-Ti samples were plasma oxidized at 650 °C and 750 °C for 1 h and 4 h and their structural and mechanical properties were characterized by XRD, SEM, 3D profilometer and micro-hardness tester. Wear tests were carried out under dry and simulated body fluid (SBF) conditions by a pin-on-disk tribometer. Cp-Ti samples by forging exhibited α-hexagonal close-packed (hcp) crystal structure, whereas Cp-Ti samples by L-PBF showed acicular martensitic α'. The phase analyses and cross-sectional investigations revealed that a TiO2 layer formed on the surface of samples after plasma oxidation and their thickness was same for both Cp-Ti samples produced by L-PBF and forging. However, Cp-Ti by L-PBF showed higher diffusion zone depth and hardness than that of Cp-Ti by forging. It was deduced from analyses that finer grains occurred in L-PBF process and these grains led to increase diffusion zone depth by providing alternative diffusion paths for oxygen. Also, L-PBF showed better wear resistance than that of plasma oxidized Cp-Ti samples by forging in both dry and SBF conditions due to its superior hardness, high diffusion zone depth and acicular martensitic α' microstructure.