Effects of different treatment processes on microstructure and tensile fracture behaviour of selected laser melting TC17 titanium alloy

Abstract

It is essential to study the tensile fracture mechanism of additively manufactured materials and develop the effective process treatment techniques to improve their fracture resistance. In this paper, the effects of different treatment processes on the microstructure and tensile fracture properties of TC17 titanium alloy melted by laser selective zone melting were investigated. The static tensile fracture morphological characteristics were observed by combining SEM and EDS. The metallographic microstructure after chemical corrosion was observed optically. And the tensile fracture morphology of the three states of TC17 titanium alloy samples at room temperature conditions was investigated. The results show that the metallographic matrix microstructure of TC17 titanium alloy after HT, HIP and HIP-HT treatments was a bimodal structure with α+β phases, i.e., β phase was in the form of a net basket, and α phase was in the form of a coarse bar. The grain sizes of the samples treated by different processes were different, but the difference in grain size of the HT-treated tissues was small, and the difference in grain size of the HIP-HT-treated tissues was large. And the coarse α-phase segregation could be seen at the edge of the samples. The 3D-printed materials had complex changes in anisotropic properties affected by the printing structure and tissue. The printed tissues were brittle and had high internal stresses. These problems were partly improved at high temperatures, but they still existed. The HIP-HT-treated materials had a large α+β-phase bimodal structure. The HT-treated material had coarse grains and precipitation phases, poor room temperature plasticity, and improved high temperature plasticity. After HT treatment, the original printing microstructure changed, the strength and plasticity were significantly improved, but the macroscopic printing structure still had a slight influence on the fracture morphology. When HIP treatment temperature was higher, the influence of macroscopic printing structure basically disappeared, but the grain and microstructure grew up, and the strength and plasticity were slightly lower than that of the HT treatment. HIP process basically eliminated the unfused defects of the three-dimensional morphology, and the local weak bonding zone formed.