Multi-phases transformation mechanism of Ti6Al4V/Inconel 718 composite by laser additive manufacturing

Abstract To reveal the internal phase transition mechanism of Ti6Al4V/Inconel 718 composite materials, the composites with different Ti content were prepared by laser additive manufacturing. With the increase of Ti element content, the phase transition can be divided into three stages: the typical γ + laves structure stage, the brittle phase (Fe2Ti) mass generation stage and the TiNi phase generation stage. The microstructure has a transformation of columnar dendrites → columnar dendrites + equiaxed dendrites → equiaxed dendrites + eutectic structure. The γ → Fe2Ti → TiNi transformation of the main phase is due to the transformation of the main reaction from L → L + γ to L → Fe2Ti + γ and then to L → L + TiNi. The transformation of the reaction is due to the change of Ti element content and the change of element and temperature distribution in the molten pool by laser action. In the third stage, the brittle phase Fe2Ti is greatly reduced, and TiNi and FeNiTi2 are formed. The generation of FeNiTi2 is due to the replacement of Ni atoms in TiNi by Fe atoms. In addition, nanoscale Ti2Ni particles were newly discovered, which were formed by peritectic reaction between TiNi and independent small liquid phase region under laser remelting.