Selective Laser Melting of Carbon-Free Mar-M509 Co-Based Superalloy: Microstructure,Micro-Cracks,and Mechanical Anisotropy

In this work, the microstructural evolution, micro-crack formation, and mechanical anisotropy of the selective laser melted (SLM) carbon-free Mar-M509 Co-based superalloy were systematically studied under different linear energy densities (LED). Observation shows that the SLM Mar-M509 superalloy possesses a fully dense structure, whereas some micro-cracks exist along the building direction. The electron backscatter diffraction results reveal that dominant columnar grains tend to elongate along the building direction parallel to the XZ plane. Meanwhile, both a < 001 > near fiber texture and a {100} < 001 > near sheet texture are observed in different specimens. For the specimen with fiber texture, a high misorientation angle exists among different columnar grains, which aggravated the generation of micro-cracks under thermal stress. Higher LED results in higher micro-crack density in the SLM specimen due to higher thermal stress. Mar-M509 specimen fabricated under lower LED exhibits higher tensile strength due to more significant grain refinement. More prominent anisotropy of tensile performance was found in the high LED specimen, which can be attributed to the higher density of micro-cracks and crystallographic texture. Furthermore, the SLM Mar-M509 superalloy exhibits better mechanical properties than the traditional cast technique. In summary, this work can contribute to the development and the future application of SLM-fabricated Co-based superalloy.