X-Ray Study of Deformed and Transformed Co–Ni Single Crystals

Abstract

Plastic deformation and the fcc⇄hcp martensitic transformation have been studied in a cobalt-30.5% nickel alloy. Small spheres were examined using a single-crystal x-ray diffraction technique with monochromated CuKβ radiation. In both the fcc and hcp structures the probability of intrinsic and growth stacking faults, the strains, and the particle size introduced by plastic deformation and/or transformation were evaluated using Fourier analysis and shifting of intensity profiles. It was found that: (1) In both the hcp and fcc phases, growth faults were present in larger numbers than intrinsic faults; (2) strains in the hcp phase were usually higher than those in the fcc phase, and the hcp→fcc transformation generally reduced the amount of strain; and (3) the particle size decreased with transformation and was affected by transformation on other variants. The faults resulting from single slip were only present on the slip planes whereas the hcp→fcc transformation introduced faults on more than one variant of close-packed plane. There was also some evidence of the formation of extrinsic faults. These data are evaluated in the light of the existing transformation theories.