Study on cracking mechanism of Inconel 625 alloy surfacing metal

In this paper, the large thickness surfacing test was carried out by GTAW process, the welding hot crack of Inconel 625 alloy was studied, and the cracking mechanism of ERNiCrMo-3 welding wire surfacing metal was explained. It was indicated that the fabricated Inconel 625 sample consists of cellular dendritic which grew epitaxially from the substrate. Laves(Ni,Fe,Cr)₂(Nb,Ti,Mo) phase, MC-type carbide and acicular δ(Ni₃Nb) phases were also observed in the microstructure of as-welded sample. There are local crystal cracks in the microstructure of large thickness surfacing metal. The cracks are located between primary dendrites along the direction of columnar crystals. There is a large amount of δ(Ni₃Nb) phases, near the cracks and on the fracture surfaces. δ phases is related to the formation of cracks. There are two solidification modes for 625 alloy surfacing: (1) and (2). At the end of crystallization, mode (2) with L → γ + δ eutectic reaction has greater sensitivity to thermal cracking, resulting in cracking of Alloy 625.