CREEP OF CMSX-4 SUPERALLOY SINGLE CRYSTALS: EFFECTS OF MISORIENTATION AND TEMPERATURE

摘要

In order to better understand the creep performance of CMSX-4 superalloy single crystals, creep strain testing has been carried out on various specimens systematically misaligned by up to 20°from 〈 001〉. At 750℃, significant primary creep is observed, the extent of which depends strongly upon small misorien- tations away from the 〈 001〉/〈011〉symmetry boundary. ln this regime there is evidence of secondary creep which is associated with primary creep strain sufficient for two or more further {111}〈112〉systems to become active. At 950℃, tertiary creep is prevalent, there being little primary creep exhibited under the stress levels tested. Measurements of the shape change and the lattice rotation, as deduced from analysis of electron backscatter patterns in the scanning electron microscope (SEM), confirms that the macroscopic shape deformation is due to {111}(112) at 750℃ but that this changes to {111}〈110〉at 950℃. This con- clusion is supported further by observations made using transmission electron microscopy (TEM). The extent of creep as a function of misorientation away from 〈001〉has been rationalised with a numerical model which takes account of the underlying deformation mechanisms. In the case of primary creep, the model accounts for the initial orientation of the tensile axis, the lattice rotation, the hardening on the pri- mary slip system, the extent of primary creep, the onset of secondary creep and the evolution of the macro- scopic creep strain. There appears to be evidence to suggest that the maximum creep rate in the primary regime can be correla