FRACTURE IN NI3AL - ENVIRONMENTAL AND DOPANT EFFECTS

Environmental and dopant effects are by far the most significant of th e extrinsic factors that influence intergranular fracture in Ni3Al. En vironmental embrittlement is a result principally of the atomic hydrog en generated in the reaction with water vapor in ordinary ambient air. Dry hydrogen gas, in contrast, is relatively benign, presumably becau se it does not dissociate readily into atomic H on the Ni3Al surfaces. The effect of boron doping is primarily to suppress moisture-induced embrittlement, and secondarily to improve grain-boundary cohesion. In gaseous hydrogen atmospheres, boron has a third (unexpected) embrittli ng effect, which produces brittle intergranular fracture in otherwise ductile Ni3Al, presumably by enhancing the dissociation of H-2 on the grain boundaries. These and other extrinsic factors that affect the du ctility and fracture behavior of Ni3Al are reviewed.