The average velocities of dislocations moving on octahedral and cube planes in Ni3Al single crystals were measured as a function of the resolved shear stress in the temperature range from 293 to 1133K by the etch-pit technique. The resolved shear stress dependence of the velocities could be expressed by an equation of the form v = v0(τ/τ0)m in all cases. Some of the parameters associated with the dislocation mobility were deduced from the experimental data. For the octahedral slip, the exponent m lies between 20 and 31 and the activation area A* = (81-99)b2. For cube slip, m = 12 to 16 and A* = (56-84)b2. Three temperature domains were defined where different glide systems operate. In the first domain the dislocation could move only on the octahedral plane, in the second domain it could move on both octahedral and cube planes, and in the third domain it could move only on the cube plane. It was found that the velocity of dislocations moving on the octahedral plane exhibits anomalous behaviour, consisting of a positive temperature dependence of the RSS as required for a constant dislocation velocity and a tension-compression velocity asymmetry. No obvious anomalous velocity behaviour for the cube glide system was observed. All of the results suggested that positive temperature dependence of the critical resolved shear stress and the tension-compression flow asymmetry in Ll2 Ni3Al could be directly related to the behaviour of individual dislocation velocities.

Dislocation Velocities in Ni3Al Single Crystals. Jiang, C.B., Patu, S. , Lei, Q.Z., Shi, C.X.: Philosophical Magazine Letters, 1998, 78[1], 1-8