Suppression of cracking and microstructure-property investigation of TiAl4822 alloy by laser directed energy deposition with integral high-temperature assistance

The TiAl4822 (Ti-48Al-2Cr-2Nb) alloy, renowned for its exceptional high-temperature mechanical properties and low density, stands out as a highly promising candidate for critical aerospace components. However, its high chemical reactivity and inherent room-temperature brittleness pose significant challenges to the conventional manufacturing of large and complex geometries. Laser directed energy deposition (LDED), characterized by its high fabrication efficiency and remarkable process flexibility, has emerged as a crucial approach for preparing TiAl4822 alloy components. Nevertheless, the rapid melting-solidification cycle during LDED induces a substantial temperature gradient and residual stress, which results in component cracking. Currently, there is no well-established method to completely prevent crack formation. In this study, a dense and crack-free thin-walled TiAl4822 alloy component with dimensions of 30 mm×25 mm×6 mm is successfully fabricated using the whole high-temperature-assisted LDED technique. An investigation is conducted on their macro-morphology, microstructure, porosity, and microhardness. The results reveal that the thin-walled TiAl4822 alloy specimen prepared by LDED at room temperature is prone to brittle fracture primarily through cleavage, and its microstructure mainly comprises fine equiaxed grains. After implementing whole high-temperature assistance at an integral temperature of 800 ℃, the grains in the deposited layer transform from bottom to top into inclined columnar grains. The porosity is significantly reduced from 0.05% to 0.008%, accompanied by a more uniform pore-size distribution, and no macroscopic cracks are observed on the surface. Concurrently, the microhardness decreases from 390.46HV0.2 to 354.94HV0.2, which can be attributed to grain coarsening, a decrease in grain-boundary density, and precipitate evolution under high-temperature conditions. Overall, the integral high-temperature-assisted LDED effectively inhibits crack initiation and the formation of large pores while homogenizing the microstructure, providing a novel pathway for high-density, high-performance TiAl4822 preparing.