Creep softening and strengthening mechanisms due to y' raft development in SMP14 single cristal nickel base superalloy at 1000°C

The high temperature mechanical behaviour of nickel base superalloys depends mainly on the reinforcing gamma' precipitate volume fraction and on its morphology that evolves significantly during deformation particularly at high temperature. In single crystal nickel base superalloys characterised by negative misfit between gamma' and the gamma phases, the original cuboidal gamma' microstructure develops into a lamellar gamma/gamma' pattern perpendicular to the loading axis, when the alloys axe crept at high temperature under tensile load along a (001) crystallographic direction. The typical creep curves of nickel base superalloys are characterised by three or four different creep stages. Such stages can be rationalised in terms of evolution of the reinforcing gamma' phase morphology during creep. The aim of this paper is to investigate the effects of gamma' morphology evolution on the long tertiary creep behaviour of the nickel base superalloy SMP 14 at 1000degreesC.