Effect of Fine Precipitation on Creep Strength of B2-NiAI(Hf) and L1_2-Ni_3(Al,Ti) Mermetallics

摘要

The creep rates of polycrystalline B2-ordered NiAl-Hf and L1_2-ordered Ni_3(Al.Ti) intermetallics decrease appreciably by the fine precipitation of the Ni_2AlHf phase and disordered coherent phase. In case of B2-ordered NiAl containing L2_1-Ni_2AlHf precipitates, transmission electron microscope observations of the interaction between dislocations and spherical precipitates revealed that the dislocations tend to be strongly attracted to the particle interfaces during the creep deformation. Oh the other hand, in case of L1_2-ordered Ni_3Al, the significance of the threshold stress is discussed based upon the transmission electron microscope observations of the interaction between dislocations and precipitates. The superdislocations produced during deformation tend to be strongly attracted and dissociated as they meet the coherent disordered precipitates because the anti-phase boundary energy in the disordered phase is zero. An extra force required to pull the dislocations out of the disordered particles during the creep deformation establishes the threshold stress which is beneficial in improving the creep strength under lower stresses.