Synergistic effect of hydrogen and impurity segregations on the grain boundary embrittlement in Nb

Niobium and its alloys are the candidate materials for fusion reactors and can be used at high-temperatures. This paper was intended to study embrittlement of niobium by high-concentrations of hydrogen and impurity segregation at grain boundaries. Specimens of commercial Nb were subjected to heat treatment at 1100°C and 500°C and subsequently charged with deuterium in an electrolytic cell. The charged specimens were placed into the high-vacuum chamber of a special self-made Auger electron spectrometer. They were then fractured under high-vacuum conditions and the chemistry of grain boundaries was analysed. Carbon and oxygen were found as the main impurities on the grain boundaries and effective energies for hydrogen–impurity-grain boundary interaction have been estimated. It was found that there is a noticeable reduction of fracture strength corresponding to the grain boundary oxygen and carbon segregation levels.