Deformation microstructures in Ni3(Al, Hf)

The dislocation structures resulting from compression tests on Ni3 (Al, Hf) single crystals are studied as a function of the deformation temperature between 77 and 900 K. Mechanical parameters are also reported, such as the 0.2% offset stress, the work-hardening coefficient, the microscopic activation volume and the dislocation exhaustion rate. The two latter parameters are measured using repeated load relaxation experiments. It is shown that the microstructural features are qualitatively similar to those reported for other Ni3Al compounds: Kear Wilsdorf locks are observed in the temperature domain which corresponds to the strength anomaly, the peak temperature seems to be associated with the occurrence of cube slip. Therefore, the spectacular strengthening due to Hf additions is discussed in terms of other parameters of the dislocation structure such as the complex stacking fault energy.