Plastic flow of Ni3(Si,Ti) Single crystals

Activation Volumes in the Yield Strength Anomaly Domain of Ni3(Al,Ta)

Ni3(Al,Ta) single crystals have been deformed in compression in the temperature range of the flow stress anomaly (293–780K). The strain-rate sensitivity (SRS) of the flow stress has been characterised by using a technique of repeated stress relaxations that allows for the measurement of the true (or effective) activation volume (Veff). When measured at the conventional critical resolved shear stress (CRSS), Veff exhibits as a function of temperature a sharp discontinuity close to 470K. When the temperature is held constant (420K), the discontinuity of Veff occurs along the stress-strain curve at approximately 3% strain; the stress for both discontinuities is approximately the same. These results suggest a change in the rate controlling mechanism that is dependent on stress as much or more than temperature.

Mechanical Properties of Binary Ni3Al Single Crystals

The mechanical properties of binary Ni76.6Al23.4 single crystalline specimens have been studied in compression test over a wide range of temperature (293–1100K). The resolved proof stress (τ0.2%) and the corresponding work-hardening rate (θ0.2%) have been measured as a function of temperature. In addition, a technique of repeated stress relaxations has been used to investigate the related microscopic activation volume (V0.2%) and to characterize the variation in the density of mobile dislocations that occurs during such transient tests. It is observed that not only τ0.2% exhibits an anomalous behavior with temperature but also θ0.2%, while the stress dependence of V0.2% may be considered as normal, i.e. V0.2% is a monotonie decreasing function of stress.