The role of dislocations in the precipitation of M23C6 in Co-Cr-C alloys

Abstract

An investigation is reported of the mechanisms of M23C6 precipitation from supersaturated fcc solid solution in two Co-Cr-C alloys of compositions (wt %): Co-25.3 Cr-0.26 C and Co-32.9 Cr-0.18 C. Electron microscope investigations were made with particular reference to the role of dislocations in the nucleation and growth of carbide particles formed on ageing in the range 650 to 800° C. Carbide precipitation occurred initially as a fine homogeneously distributed dispersion of matrix-nucleated particles. Extrinsic stacking faults were nucleated at some of the matrix particles. Stacking faults grew and repeated carbide precipitation occurred on the bounding Frank partials. The fault density increased with ageing time, and various stacking fault interactions were observed. Carbide precipitation occurred also on undissociated dislocations and on Shockley partials.