Research on the microstructure and mechanical properties of doubled annealed laser melting deposition TC11 titanium alloy

Abstract

TC11 titanium alloy has the advantages of light weight and high strength, and it has great potential to replace high-strength steel as the material of aerospace main bearing to achieve lightweight application. In this study, TC11 titanium alloy was prepared by laser melting deposition, and the deposited TC11 titanium alloy was subjected to double annealing heat treatment, so as to study the effects of different annealing temperatures and time on the microstructure and mechanical properties. The results indicated that the microstructure of TC11 titanium alloy grew alternately by the turns of columnar crystal / equiaxed crystal along the deposition direction. The deposited microstructure was mainly composed of the Widmanstatten structure and mesh basketweave structure. After double annealing, the α phase was coarsened and the aspect ratio decreased, and the continuous grain boundary α phase appeared discontinuous; however, when the annealing temperature was 1025 °C, the intragranular microstructure changed into a fine basketweave structure, and the continuous α phase was reformed at the grain boundary. With the extension of high time, the coarsening phenomenon of the αs phase was obvious. The microhardness increased firstly and then decreased with the annealing temperature, and reached the maximum at 995 °C. After double annealing, the impact toughness of TC11 titanium alloy was significantly improved, which was better than the forging standard. The strength and plasticity of TC11 titanium alloy were also significantly improved, meeting the forging standard, but when the annealing time was extended to 2 h, the strength was significantly reduced. The strength anisotropy of TC11 titanium alloy was less than 3% during the annealing in the two-phase region; the anisotropic plasticity increased firstly and then decreased with the increase of annealing temperature; with the extension of annealing time, both the anisotropy of strength and plasticity showed an increasing trend.