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 embrittl ement of niobium by high-concentrations of hydrogen and impurity segregatio n at grain boundaries. Specimens of commercial Nb were subjected to heat tr eatment at 1100 degreesC and 500 degreesC and subsequently charged with deu terium in an electrolytic cell. The charged specimens were placed into the high-vacuum chamber of a special self-made Auger electron spectrometer. The y were then fractured under high-vacuum conditions and the chemistry of gra in boundaries was analysed. Carbon and oxygen were found as the main impuri ties on the grain boundaries and effective energies for hydrogen-impurity-g rain boundary interaction have been estimated. It was found that there is a noticeable reduction of fracture strength corresponding to the grain bound ary oxygen and carbon segregation levels. (C) 2000 Elsevier Science B.V. Al l rights reserved.