Formation of High-Performance Titanium Alloy with Harmonic Structure by Means of Powder Metallurgy

Abstract

Titanium alloy (Ti-6Al-4V) with bimodal “harmonic structure”, which consists of the coarse-grained structure surrounded by the network structure with fine grains, was fabricated by mechanical milling (MM) and spark plasma sintering (SPS) to achieve high strength and good plasticity. The microstructure of the MM-processed powder and the sintered compacts were characterized using a micro-Vickers hardness tester, scanning electron microscope and an electron backscatter diffraction technique. Harmonic structure was formed in the sintered Ti-6Al-4V compacts prepared from the MM-processed powders with fine grains at its surface. The Ti-6Al-4V alloy with harmonic structure exhibited high tensile strength and good plasticity. The effects of the harmonic structure on the 4-point bending fatigue properties of Ti-6Al-4V alloy were investigated. The compacts with harmonic structure exhibited higher fatigue strength compared to the conventional coarse-grained material prepared from as-received initial powders. This was because the Ti-6Al-4V alloy with harmonic structure had higher tensile strength and hardness. Moreover, fatigue fracture mechanism of the Ti-6Al-4V alloy with harmonic structure was discussed based on the fractography and crystallography. As results of observing and analyzing the fracture surfaces, the Ti-6Al-4V alloy with harmonic structure failed from the coarse grain in the harmonic structure.