Microstructure evolution of TC25G/Ti₂AlNb structural gradient material fabricated by laser directed energy deposition

Laser directed energy deposition (LDED) is one of the most effective ways to manufacture structural gradient materials. The microstructure changes in transition zone (TZ) and heat-affected zone (HAZ) are often considered to be very important which could affect the mechanical property of the component. In this study, a titanium based gradient material, which is potentially used in high pressure compressor was fabricated by deposition of Ti₂AlNb alloy on a forged TC25G alloy substrate. The thickness of the transition zone is around 2000 μm, and the phase transformation from TC25G alloy to Ti₂AlNb alloy is followed as: α + β (TC25G alloy) → α + β (Heat affected zone) → α + α₂ + B2/β + O (Transition zone) → α₂ + B2/β + O (Ti₂AlNb alloy). There is no any sudden change of microhardness in the gradient material with the lowest microhardness is found in Ti₂AlNb alloy.