Preparation of High-Strength Pure Titanium by Powder Metallurgy: One-Step Pressing Versus Multi-Step Pressing Technique

Abstract

Pure titanium fabricated by powder metallurgy generally encounters problems including low relative density and low strength, which limits its application performance. This work proposed a multi-step pressing (MSP) technique for developing high-strength pure titanium. The MSP processes of spherical Ti powders of 15–53 μm, 53–105 μm, and 75–180 μm were systematically investigated through multi-particle finite element method (MPFEM) compared with conventional one-step pressing (OSP) technique. The relative density, phase constitution, microstructure, and compressive mechanical properties of the sintered bulk pure titanium were characterized. Simulation results demonstrate that the MSP technique significantly increases the relative density of green compacts by 3.2%, 3.3%, and 5.2%, respectively, compared with OSP technique. Experimental results indicate the relative density of the sintered specimens prepared by MSP spherical powders increases by 5.4%, 4.5%, and 4.5%, respectively, compared to OSP, and the yield strength improves by 16%, 13%, and 18%. For the sintered specimens prepared by MSP irregular powder of 15–53 μm, the relative density increases by 6.0% and the yield strength increases by 15%. The enhancement of relative density and yield strength is mainly because the MSP technique mitigates stress concentration between powder particles. Compared to spherical powder, irregular powder exhibits stronger mechanical interlocking owing to the greater propensity for displacement and deformation, which facilitates mutual wedging and interlocking, resulting in superior strength performance.