Temperature Dependence of Dislocation Mobility in Ni3Al

Abstract

AbstractThe stress and temperature dependence of the dislocation velocity v(σ, T) has been studied experimentally in Ni3AI single crystals. The mobility of individual dislocations was measured by the stress pulse-etching technique at temperatures between 77 and 873 K at the resolved shear stresses between 25 and 150 MPa over a range of dislocation velocities from 3×l0−7 to 3×10−5 m/s. Fresh dislocations were introduced and revealed by a selective etchant on {001} surfaces of electropolished specimens annealed at 1473 K for 120 hours in argon. The specimens were deformed in three point bending around <110> bending axis at a constant temperature. The dislocation arrays moved in two acting <110> {111} primary glide systems. The motion occurred over a range of applied stresses close to the macroscopical yield stresses y The dislocation velocity decreased as temperature increased, in perfect analogy to the experimental data on y obtained before 1 on the same Ni3Al.. No detectable violation of the Schmid law was observed. The stress dependence of the dislocation velocity was rather steep resulting in a relatively large activation area of A=100-200b2. Such an activation area is greater than that one could expect in a kink-mode crystal with predominant Peierls mechanism for dislocation motion, although it is considerably less than A measured in other materials controlled by local obstacles.