Notch effects on creep behaviour of CMSX-4 superalloy single crystals

Smooth and notched specimens of CMSX-4 superalloy single crystals of orientations 〈001〉, 〈011〉 and 〈111〉 were creep tested at 850°C. For the same net-section stress, the notched specimens exhibited a longer lifetime than the smooth specimens. Stress–strain analysis of notched specimens was carried out by an elastic–plastic finite elements procedure; the creep data for smooth specimens were used as input data. An excellent correlation was found between the lifetime of the notched specimens and the average value of the calculated steady-state creep strain rate. For all orientations the life curves of this type were found to be identical to the life curves for smooth specimens expressed in terms of lifetime versus steady-state creep rate. Thus a modified Monkman–Grant relationship is valid both for smooth and notched specimens.