Microstructure of creep-exposed single crystal nickel base superalloy CSMX4

Main changes which appear in microstructure of Ni base superalloys during creep exposure is the directional coarsening (rafting) of originally cubic γ' precipitates embedded in γ matrix. The progress in γ' degradation can be assessed with help of the analysis of geometrical parameters of the γ' microstructure. Determination of the morphological changes of γ' in creep-exposed single-crystal Ni-base superalloy CMSX4 using SANS was carried out. A new sample design (conic specimen) was tested in order to get continually changing stress levels in one sample and corresponding variety of micro structural change. Evolution of rafts with stress magnitude is clearly observable from the parameters obtained using SANS (the mean thickness of the γ channel in different crystallographic directions of the single-crystal, the evolution of the γ' precipitate size and distance, the evolution of the specific interface). The use of conic specimen and spatial scan facilitate determination of microstructure evolution in dependence on the exposure parameters.