New insight into the effect of heat input on microstructure and mechanical property of wire arc additive manufactured Ti64 alloy

다국어 초록 (Multilingual Abstract)

Wire arc additive manufacturing (WAAM) is a process that combines an electric arc as a heat source and a wire as feedstock to build a component layer by layer. In arc welding, heat input is an important characteristic because it influences the cooling rate, which could affect the mechanical properties and microstructure of the deposition part. We investigated the effect of heat input on the microstructure and mechanical property of the additive layer manufactured for Ti64 alloys. High-heat input (H; 1 kJ/mm) produced a columnar grain exhibiting a large anisotropic property of tensile strength. Low-heat input (L; 0.5 kJ/mm) transformed the columnar grains to the equiaxed ones, and its reason was associated with the solidification cooling rates accelerated. However, the H specimens exhibited a larger tensile strength and hardness than the L specimens, which can be explained by volume fraction of the hardened phase (α’ martensite and secondary α). The microstructure in H and L specimens were further identified by SEM-EDX and TEM. The thermal history in the WAAM deposits was also simulated using finite element method. At the certain temperature gradient, the faster cooling rates produced the more fraction of the equiaxed grains. Furthermore, the H specimens exhibited more thermal cycles calculated to verify the condition that can produce more α’ martensite and secondary α. Therefore, the L specimen changed the grain structure to equiaxed one and reduced the anisotropy of tensile strength significantly.