Investigation on the solidification segregation behavior of GTAW nickel alloy deposited metal

The solidification segregation behavior of deposited metal with nickel alloy wires by GTAW was investigated by Optical Microscope (OM), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and Electron probe X-ray microanalyser (EPMA), etc. Results indicated that microstructure was composed of γ phase, MC carbides, Laves phases in the deposited metal. The metallurgical structure was columnar crystals with segregation zone of 5~10 μm in width. The segregation coefficients of primary elements were calculated with EPMA results according to Scheil formula, k_Nb=0.23, k_Mo=0.68, k_Ni=1.07, k_Cr=1.05, k_Fe=1.23. During solidification, Nb and Mo tended to segregate in the liquid phase, while Fe prefers to distribute into solid phase, Ni and Cr did not show significant distributions differences between liquids and solids. The reaction sequence of deposited metal with experimental nickel alloy wires during solidification was L→L+γ→L+γ+MC→L+γ+MC+Laves→γ+MC+Laves.