EFFECTS OF B ON THE MICROSTRUCTURE AND HYDROGEN RESISTANCE PERFORMANCE OF Fe–Ni BASE ALLOY

Effects of B on the microstructure and hydrogen resistance performance in an Fe–Ni base alloy were investigated by means of optical microscopy, scanning electron microscopy, thermal hydrogen charging experiments and tensile tests. The results show that abundant η(Ni3Ti) phases precipitate at grain boundaries (GBs) in the alloy without boron (FN) after aging treatment, while only a few carbides precipitate at GBs in the alloy with boron (FNB). Tensile tests indicate that the FNB exhibites not only higher ductility but also lower hydrogen–induced ductility loss than those for FN alloy. Fracture observations show that the brittle intergranular fracture is the main feature of peak aging and over aging FN alloy and quite a few secondary cracks can be observed on fracture surface of the hydrogen charged samples due to the precipitation of η phase at GBs. However, the intragranular fracture is dominant feature for the FNB alloy whether hydrogen charging or not.