Microstructural studies of Stellite 6 hardfacing deposited on nickel-based superalloys subjected to long-time aging

Stellite 6 hardfacing is deposited on Haynes 282 and Inconel 740H via plasma transferred arc (PTA) welding. The fabricated hardfacing specimens are subjected to different post-welding heat treatments, and then aged at 760, 815 and 871 °C for a time length ranging from 1000 to 30,000 h. The microstructures of the hardfacings before and after long-time aging are investigated with SEM/EDS/XRD. It is shown that the PTA welding process causes the hardfacing microstructure deviating from Stellite 6 alloy due to dilution. With participation of other elements from the substrate material, the compositions of both solid solution and carbide/intermetallic of the Stellite 6 hardfacing are modified. In the meanwhile, Ti–rich or Ti/Nb-rich new phases are generated. Long-time aging has an impact on the microstructures of the hardfacings, but at 760 °C, especially for an exposure time less than 20,000 h, the microstructures of the hardfacings do not show obvious change. However, when the hardfacing specimens are aged at 815 and 871 °C even for an exposure time of 1000 h only, Al-rich precipitates can occur, and the amount of the precipitates increase with aging time. These brittle precipitates generally have a detrimental effect on the performance of the hardfacings because they can deteriorate the ductility of the hardfacings. With the presence of Al-rich precipitates the hardness of the hardfacings decreases.