Effect of core–shell structure formed by Y₂O₃-doping on cracking inhibition in SLMed Y₂O₃/Mar-M247 alloy

To reduce cracking in Mar-M247 superalloy of Selective Laser Melting (SLM) manufacturing, this research explores the impact of the core–shell structure formed by adding different contents (0.5 and 1.0 wt%) of Y₂O₃ nanoparticles on the microstructure, crack behavior, and mechanical properties. Y₂O₃-doping facilitates the transition from columnar to equiaxed grains in the SLM process. The reaction of Y₂O₃ nanoparticles with oxide-forming elements in Mar-M247 alloy promotes the formation of Y₂Hf₂O₇, which could act as the nucleation sites for MC carbides, forming a core–shell structure with Y₂Hf₂O₇ as the core and MC carbides as the shell. The dispersed core–shell nanoparticles lead to the distribution of carbides both inside cells and at the cell boundaries, contribute to the reduction of dislocations pinned by MC carbides near the core–shell structure, and reduce the formation of dislocation walls, which helps to inhibit cracking. Moreover, both the γ′ phase and the core–shell structures can impede dislocation motion, alleviating local stress concentration at cell boundaries. The effect of Y₂O₃ nanoparticles on the metallurgical behavior of the molten pool and precipitation characteristics during the SLM process is analyzed to reveal the mechanism of the interactions between precipitates and dislocations as well as the crack inhibition.