Microstructure evolution behavior of gradient composition alloy between TC25G and TiAl4822 prepared by laser rapid melting

The development of advanced aero-engines with high thrust-to-weight ratios in the future has an urgent need for new high-performance lightweight high-temperature compressor blisks. Laser additive manufacturing TC25G-TiAl4822 gradient structure material is an important material system for the blisk of the lightweight high-temperature compressor. The composition selection and solidification structure research of gradient transition layer alloy have a key influence on guiding the structural performance design of related components. To understand the solidification structure evolution behavior of （1-x）TC25G-xTiAl4822 transition layer alloy with the change of TiAl4822 pre-alloyed powder content in powder raw materials， two kinds of single raw material （TC25G or TiAl4822） alloy ingots and alloy ingots with nine kinds of mixed raw materials are prepared by laser melting technology. Material characterization equipment and hardness measurement devices such as optical microscope， scanning electron microscope， XRD， and TEM are used for the study. The research results show that with the increase of the content of TiAl4822 alloy powder in the raw material， the characteristics of solidified grains change to dendrite → equiaxed → dendrite. The microstructure of the alloy at room temperature changes as follows： αp+αs+β+α2→αp+ αs+α2+β/B2 → α+α2+β/B2 → α2+B2 → α2+γ+B2 → α2+γ. Due to the change of the phase content of different alloy compositions， the Vickers hardness of the matrix first increases and then decreases， the overall hardness value changes in the range of about 450-620HV when the powder proportion is 50%-70%. If the intermediate composition alloy is directly used as the transition layer， the hardness will suddenly change. Therefore， the selection of the transition layer alloy composition should consider the range close to pure TC25G or TiAl4822.The above results provide the basis for the composition selection of bimetallic transition layer alloys to avoid the intermediate proportion of powder content range.