Effect of gradient decrease heat-input combined with inter-layer cooling on microstructure and mechanical properties of WAAM-Ti-6Al-2Zr-1Mo-1V alloy

In conventional Wire Arc Additive Manufacturing (WAAM), coarse epitaxial growth columnar prior-β grains always lead to a strong texture and poor mechanical properties. To solve this problem, a new deposition strategy combining gradient decrease heat-input and inter-layer cooling was proposed in this study. This deposition strategy significantly increased the cooling rate and reduced the inter-layer temperature, which interrupted the epitaxial growth of columnar grains and formed a fine columnar-equiaxed mixed grain morphology. Due to the decrease of thermal cycles, the layer band structure tended to be evenly distributed and a small amount of martensite α' remained at the bottom of layer band structure. In addition, the generation of α colony and the transformation of β phases were also inhibited by the high cooling rate. In the meantime, finer basketweave structure composed of the short rod-like α laths was formed in the mixed grains. Compared with the traditional deposition strategy, this method can obtain a WAAM-Ti-6Al-2Zr-1Mo-1V alloy with microhardness of 376.23HV0.2, ultimate tensile strength of 1014.8MPa and elongation of 4.97%.