Creep of single-crystals of nickel-base γ-alloy at temperatures between 1150 °C and 1288 °C

A gamma-analogue of the superalloy CMSX-4 that does not contain the strengthening gamma '-phase and only consists of the gamma-solid solution of nickel has been designed, solidified as single-crystals of different orientations, and tested under creep conditions in the temperature range between 1150 and 1288 degrees C. The tests have revealed a very high creep anisotropy of this alloy, as was previously found for CMSX-4 at supersolvus temperature of 1288 degrees C. This creep anisotropy could be explained by the dominance of (011){111} octahedral slip. Furthermore, the analysis of the creep data has yielded a high value of the creep activation energy, Q(c)approximate to 442 kJ/mol, which correlates with the high activation energy of Re diffusion in Ni. This supports the hypothesis that dislocation motion in the gamma-matrix of Re-containing superalloys is controlled by the diffusion of the Re atoms segregating at the dislocation core. The Norton stress exponent n is close to 5, which is a typical value for pure metals and their alloys. The absence of gamma '-reprecipitation after high-temperature creep tests facilitates microstructural investigations. It has been shown by EBSD that creep deformation results in an increasing misorientation of the existing low angle boundaries. In addition, according to TEM, new low angle boundaries appear due to reactions of the a/2 (011) mobile dislocations and knitting of new networks.

Automated summary

A gamma-analogue of the superalloy CMSX-4, without the strengthening gamma '-phase, showed high creep anisotropy and activation energy, indicating that dislocation motion may be controlled by the diffusion of Re atoms. The absence of gamma '-reprecipitation after high-temperature creep tests facilitates microstructural investigations.