Strain-rate insensitive yield strength and deformation mechanisms of Ni-base superalloy CM247LC at 600 °C

The compression deformation behavior and deformation mechanisms of [001]-oriented single crystal CM247LC are investigated at 600 degrees C and at the strain rate of 5 x 10(-6) to 5 x 10(-3) s(-1). We found that although the Protevin-Le Chatelier effect appears during plastic deformation under the investigated strain rates, its yield strength is strain-rate insensitive. Transmission electron microscopy observations on the slightly deformed specimens reveal that in contrast to previous findings, shearing of gamma' precipitates is accomplished by pairs of a/2 < 110 > dislocations as well as partial dislocations, which result in the formation of superlattice stacking faults and extended stacking faults, in the experimental alloy at the early stage of plastic deformation at all the strain rates. Meanwhile, it is also found that the frequency of occurrence of the two shear processes is not influenced by the strain rate. Based on these observations, the formation of stacking faults and the relationship between operative deformation mechanisms and the yield strength of the experimental alloy are discussed.