Effect of plastic strain on the solidification cracking of Hastelloy-X in the selective laser melting process

Abstract

There is a growing demand to produce parts from Hastelloy-X materials, which exhibit a high unit cost per weight, by the selective laser melting (SLM) process. However, when the Hastelloy-X material was employed, solidification crack occurred during the SLM process. This cracking can be reduced or eliminated by optimizing the process parameters, such as the laser power and scan speed, although the optimization is time- and cost-intensive. In this study, we evaluated the possibility of exploring the change in the plastic strain, obtained by thermal elastoplastic analysis, during the solidification process, as an indicator of the occurrence of solidification cracking. The experimental observations of solidification cracking in the single-track formation tests for various laser conditions, and the degree of change in the plastic strain during the solidification process obtained by the thermal elastoplastic analysis, were compared. The single-track formation part was the foundational part of the parts made by SLM process. There was a clear correlation between the maximum change in the plastic strain in the melted area and the existence of solidification cracking. The maximum change in the plastic strain was less than 0.0041 when no crack was found, whereas it was in the range larger than 0.0048 when the cracks were observed. These results indicated the possibility of assessing the occurrence of solidification cracking, in terms of the maximum change in the plastic strain in the melted area.