Predicting solidification cracking in directed energy deposition of Hastelloy X alloys based on thermal-mechanical model

Directed energy deposition (DED) has received extensive attention in recent years owing to its advantages of near-net forming and high design freedom. However, the thermal stress induced by rapid heating and cooling during fabrication of DEDed Hastelloy X (HX) alloys usually results in solidification cracking. To suppress or even eliminate solidification cracking by optimizing processing parameters, it is necessary to establish a correlation between stress in the last stage of solidification and solidification cracking sensitivity (SCS) of DEDed HX alloys. In this study, we first confirmed the critical role of stress in solidification cracking by comparing the simulation results calculated by a thermal-mechanical model with an experimental crack distribution and then proposed a stress-related index for describing the SCS. By calculating the index in different deposited regions and with different processing parameters, we successfully predicted the crack-prone regions at the part scale and the relationship between processing parameters and SCS. The results show that there are almost no cracks in the edge region of the DEDed HX alloy sample, while cracks are mainly generated in the region within a quarter of the width from the edge of the DEDed HX alloy sample. Moreover, solidification cracking can be effectively suppressed under a high heat input. All these simulated results are in good agreement with the experimental results. These findings are of significance to understand the solidification cracking mechanism in DED, which can be used to guide the fabrication of DED crack-free HX alloys.