An investigation on the creep and fracture behavior of cast nickel-base superalloy IN738LC

Abstract

The creep-rupture properties of cast nickel-base superalloy IN738LC were studied over the temperature range 750 to 950 °C. Our results show that primary and steady-state creep should not be regarded as distinct stages and that they have basically the same deformation mechanism. The dependence of the steady-state creep rate,es, on stress,δ, and on temperature,T, for this superalloy can be described ases = Aδ nexp(−Qc/RT).n = 8.3 - 9.8 andQc = 570 - 730 kJ mol−1 at high stress levels, whereasn = 4.1 - 4.9 andQc = 370 - 420 kJ mol−1 at low stress levels. The observations of dislocation structures during steady-state creep confirm that the creep mechanism is different in the high and low stress regimes. The observations of the microstructure show that the initial acceleration in creep rate during the tertiary stage is connected with changes in the size and distribution ofγ′ particles during creep. Rupture occurs by the propagation of oxidized intergranular cracks which initiate at the specimen surface, and the rate of crack propagation is controlled by the deformation behavior of the superalloy.