Micro-Crack Formation and Controlling of Inconel625 Parts Fabricated by Selective Laser Melting

Micro-crack is one of the most serious defects in selective laser melting (SLM), which impair the mechanical properties of the fabricated parts. In this study, Inconel625 superalloy specimens were fabricated by SLM process with progressive alternative scan strategy. The morphology of the cracks, elements distribution were detected by optical microscope (OM), scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). The results showed that a large numbers of micro-cracks occurred at room temperature, with the average length of approximately 100 µm. It was found that crack formation was attribute to the local segregation of Nb and Mo element in the process of rapid solidification, resulting in the generation of low melting temperature eutectic solidification (γ+Laves). Micro-cracks grows along the interface of (γ+Laves) under the thermal stress. Base-plate preheating shows an efficient method to reduce the scales and number of cracks. The residual stress was reduced by more than 50% when preheating at 300℃.Mechanical Engineerin