Study of Welding Metallurgy, Alloying Element Redistribution, and Alloy Solidification in Hastelloy B-2 Superalloy Under Pulsating Current Waveform Gas Tungsten Arc Welding

In this study, fusion welding of a Ni-Mo base superalloy (Hastelloy B-2) is examined to study and disclose the chemistry–processing–microstructure links. Moreover, welding metallurgy, alloying element redistribution, and alloy solidification are studied in depth under pulsating current waveform-induced heat generation and successive solidification. Characterizing effects of current intensity and frequency on microstructure evolution and alloying element redistribution at different weld zones is the main goal of the current work. The pulsed current gas tungsten arc welding (PC-GTAW or PCGTAW) process and ERNiCrMo-2 filler metal are used for the preparation of welded samples. Microstructure, chemistry, and precipitate formation in the samples are analyzed by optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that a decrease in the maximum current intensity leads to a severe decrease in the dendrite size of the weld metal, while the grain size of the heat-affected zone does not experience a significant increase. Moreover, a significant decrease in the number of molybdenum carbides at interdendritic regions of the weld metal is observed. Meanwhile, the weld pool size and thus weld metal dimensions increase by an increase in the pulse frequency. It also extends the overlap of the successive pulses, which results in more heat input into the molten pool at a shorter time and thus increasing weld size. The microstructural studies indicate an increase in the dendrite size and grain size of the HAZ with pulse frequency increasing. Meanwhile, microstructure evolution, alloying element redistribution, and alloy solidification are studied in depth to understand the welding metallurgy of the alloy.