Hot cracking during the fabrication of Inconel 625/stainless steel 308 L functionally graded material by dual-wire arc additive manufacturing

In the present work, dual-wire arc additive manufacturing was used to fabricate the functionally graded material (FGM) with a smooth composition transition from 100 wt% Inconel 625 (IN625) to 100 wt% stainless steel 308 L, whose composition transition was along the torch-travelling direction. With such a composition transition, po-sition with the weakest mechanical properties could be clearly and easily located in the composition gradient path, allowing the issue to be fully exposed. During the fabrication, cracks were found near the position with IN625 of 20 wt%. By analyzing the fracture morphology and crack location, they were judged as liquation cracks, which belong to hot cracks. The segregation and aggregation of carbides at the grain boundary formed the low -melting-temperature eutectic phase, which is liquefied into the liquid film by the heating of subsequent layers and is then pulled apart by residual stress. According to the experimental results and the calculations of phase diagrams, the cracks always appeared near the position with IN625 of 20 wt%, where the FGM has the highest crack sensitivity. Therefore, it was determined as the weakest position of the FGM and its weakening mechanism could be clarified easier owing to the composition transition, which provides a high possibility to get better mechanical properties if a more targeted optimization method is applied. Process parameter optimization re-duces the heat input per unit height to thin dendrites and to alleviate cracking, but there is still a cracking tendency in the weak composition range. The composition gradient path optimization, by removal of the cor-responding composition range, can solve the cracking issue more thoroughly, and the tensile strength and elongation increased by 39.5 % and 221.7 %, respectively, which greatly improved the mechanical properties of the FGM.

Automated summary

This study utilized dual-wire arc additive manufacturing to fabricate a functionally graded material with a smooth composition transition. By analyzing the fracture morphology and crack location, it was determined that the weakest position of the material was near the composition of 20 wt% IN625. By optimizing the process parameters and the composition gradient path, the mechanical properties of the material were greatly improved.