Microstructure evolution in boronized inconel 718 superalloy

This study was focused on the pack-boronizing of Inconel 718 alloy to understand the microstructure evolution at 950 and 1050°C. Cross-section of the specimens boronized at 950°C showed the formation of silicide top layer and boride layer beneath to it. The separate layer of silicide was not observed for the specimens boronized at 1050°C. Ni-, Cr-and Fe-borides were observed in the boride layer. Unlike 950°C, borides of various shapes, like the square, pentagonal and hexagonal, were observed in boride layer at 1050°C. Boride layer showed very good adhesion to the substrate. Maximum hardness of the boride layer was about 1600–2000 HV, which was about 4–6 times the hardness of the core. On the basis of obtained results, mechanisms of the microstructure development in the boride layer were proposed.