The deformation of single crystals of the NiNi3Al system

The deformation behaviour of single crystals of the system NiNi3Al containing volume fractions between 0.09 and 0.54 of the compound Ni3Al has been studied using compression testing. The detailed interaction of dislocations and the second-phase particles of Ni3Al have been studied using X-ray methods and transmission electron microscopy. The results indicate that the mode of deformation is markedly dependent on both the size and volume fraction of the ordered particles. For small particles less than 500 Å in radius deformation occurs by shearing of the particles for all the volume fractions studied. However, in crystals containing high volume fractions of precipitates, inhomogenous yielding occurs either by kink band formation or by discontinuous yielding. In a Ni-17% Al alloy containing large particles 1 μ in diameter, the particles are initially undeformed and the accumulation of dislocations at the matri-particle interface results in a rapid rate of work hardening. After further plastic strain the particles are forced to shear and the rate of work hardening exhibits a concomittant decrease.