Small-angle neutron scattering investigation of gamma ' precipitate morphology evolution in creep-exposed single-crystal Ni-base superalloy CMSX-4

In order to assess the material degradation of exposed gas turbine high temperature components, the creep degraded CMSX-4 single-crystal nickel-base superalloy with two axial orientations [001] and [111] was investigated. Constant load creep tests were conducted in the stress/temperature ranges of 250-780 MPa/750-950 °C resulting in rupture time variation from 50 to 4000 h. A combination of scanning electron microscopy and a non-destructive small-angle neutron scattering method (SANS) was used to investigate the directional coarsening (rafting) of the ?' precipitates in relation to the stress and temperature applied as well as to the initial crystallographic orientation of the specimens. The SANS results are discussed in terms of the correlation with the raft development, the axial orientation of specimen, the creep parameters and the mechanical properties.