A TEM INVESTIGATION OF THE DEFORMATION MICROSTRUCTURE OF COZR AND CO40NI10ZR50 ORDERED ALLOYS

The results of a transmission electron microscope investigation of the effect of temperature on the deformation microstructure of CoZr and Co40Ni10Zr50 are presented. Similar to a number of intermetallic alloys, these ordered compounds (B2 ordered structure) exhibit a how stress peak which takes its origin in the properties of dislocation cores. In both alloys, strain is essentially achieved by slip on [001] {110} systems. Above the peak temperature, the slip direction is unchanged; cube slip has been noticed to contribute to the total plastic strain but in minor proportions. Superdislocations with [111] Burgers vectors have been identified only in Co40Ni10Zr50 where they occur in small densities. Both alloys contain a distribution of a second phase with an orthorhombic (B33) structure whose composition is identical to that of the matrix. These particles are shown to stem from a martensitic transformation which is induced by the applied stress over the domain of temperature investigated. It is proposed that this transformation contributes to the unusually good ductility of these alloys.