Order-Disorder Transitions in Ternary Alloys A Study on the Microstructure of L10and L12Alloys

Abstract

ABSTRACTThe order-strengthening mechanism in the ternary alloy, Cu-Ni-Zn, is investigated by comparing stress-strain curves and electron micrographs of corresponding dislocation structure in disordered, partly ordered and ordered samples. Around the composition Cu2NiZn two different types of ordering are found experimentally: L10and L12. The degree of ordering is determined by measuring the equilibrium distance between superlattice dislocations and by single crystal neutron diffraction. The long-range zinc order parameter thus obtained appeared to be in agreement with calculations using the cluster variation method (CVM) in the tetrahedron approximation. Electron microscopic observations show that even in the disordered phase, when short range order exists, superlattice dislocations are created by Frank-Read sources, rather than the generation of single dislocations.