Influence of precipitate size and crystallographic orientation on strength of a single crystal Ni-base superalloy

摘要

The influence ofγ' precipitate size and crystallographic orientation on the high-temperature mechanical properties of single-crystal nickel-base superalloys was investigated. Three kinds of initial microstructures were produced by different aging heat treatments. Tensile tests at 900℃ were performed to examined the influence of initialγ' size on tensile properties. The specimen having smallerγ' precipitates showed higher strength. Creep tests at 900℃ were performed under stresses whereγ'precipitates directionally coarsen to form theγ-γ' lamellae in the early stage of creep deformation. The specimen with [113] orientation exhibited the longest rupture life as a result of a balance between the rupture strain and creep resistance. Thecuboidalγ' precipitates directionally coarsened into the lamellarγ-γ' structure (rafted structure) in the [001] orientation, and creep resistance was low. A clear influence of heat treatment was observed in the [011] and [111] orientations. It wasfound that the formation of interfacial dislocations assisted the development of rafted structures, and that the creep resistance of the specimen that has the smallest precipitate size was the highest because dislocation motion was significantlysuppressed due to the small mean surface-to-surface spacing (l{sub}s) between precipitates.