The high-temperature decrease of the yield strength of the gamma'-strengthened superalloys NIMONIC PE16 and NIMONIC 105

摘要

Above T_(max) approx=1050K, the yield strength sigma_t of the commercial gamma'-strengthened nickel-base superalloys NIMONIC PE16, NIMONIC 105 and of many similar superalloys decreases drastically. In order to elucidate the physical reasons for this softening effect, sigma_t has been measured as a function of the deformation temperature and of the plastic strain rate. Moreover, the configurations of dislocations in deformed specimens have been studied by transmission electron microscopy (TEM). The results are as follows: in NIMONIC 105, the relevant dislocation processes change at T_(max): below T_(max) pairs of dislocations with Burgers vectors of the type 1/2<110> shear the strengthening gamma'-precipitates athermally whereas above T_(max) single 1/2 <110>-dislocations overcome them thermally activated. The effects of changes of the gamma'-precipitate dispersion with temperature are negligible. In NIMONIC PE16, however, both mechanisms-changes of the gamma'-dispersion and thermally activated dislocation processes-strongly affect sigma_t above T_(max).