Effect of Post Treatment Process on Microstructure and Low Cycle Fatigue Properties of Selective Laser Melting Formed Hastelloy-X Alloy

Hastelloy-X alloy was fabricated by selective laser melting (SLM) process, and the effects of different post treatment processes (solution treatment of 1 175℃×2 h, hot isostatic pressing of 1 175℃/150 MPa×1 h or 1 175℃/150 MPa×2 h) on the microstructure and low cycle fatigue properties of the alloy were studied. The results show that the SLM formed alloy had a typical molten pool boundary morphology and a columnar crystal structure composed of fine dendrites, and there were metallurgical defects such as microcracks, pores and holes. Solution treatment eliminated the boundary of the alloy molten pool, and the grains transformed from columnar to equiaxed. Hot isostatic pressing could further close the cracks and pores in the alloy, and small discontinuous M₆C carbides precipitated along the grain boundaries. Compared with solution treated alloy, hot isostatic pressed alloy had better low cycle fatigue properties, and the low cycle fatigue life of the alloy obtained under 2 h hot isostatic pressing time was slightly higher. Fatigue cracks propagated in a transgranular manner for solution treated alloy, while propagated in a mixed transgranular+intergranular mode for hot isostatic pressed alloy.