Microstructure and high temperature creep properties of Inconel 625 alloy by selective laser melting

Microstructure and high temperature creep properties of laser welded joints of Inconel 625 alloy fabricated by selective laser melting (SLM) method were investigated using optical microscope, scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometer. The results show that the quality of laser welded joints of Inconel 625 alloy by SLM is superior, and no obvious manufacturing defects are found. The microstructure of the laser welded Inconel 625 alloy by SLM specimen is mainly composed of the austenitic in the base metal and columnar dendrites in the fusion zone. High temperature creep test results show that the creep time of the alloy drops sharply with the increase of the applied stress level. The higher stress level (200 MPa) has a great influence on the creep property of the alloy at the same temperature, which will lead to the creep deformation directly entering the third stage of creep - acceleration stage, and cause the sample to fracture earlier. The mechanism of creep failure was discussed by analyses of the fracture surface. It is found that the fracture of all specimens occurred in the base metal or near the heat-affected zone. A large number of secondary cracks were observed in the base metal, while no obvious cracks were found in the fusion zone. Also, the fracture morphology is characterized by a rock candy pattern, indicating the intergranular fracture mode. The deformation displacement induced by the grain boundary slipping at elevated temperature is the principal mechanism of the cavity nucleation.