The martensitic transformation at the surface of cobalt



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Low energy electron diffraction (LEED) has been used to study the martensitic transformation which takes place in cobalt. The transformation consists of a structural lattice change from hexagonal-close-packed (HCP) structure in the low temperature phase to a face-centered-cubic (FCC) structure in the high temperature phase. The mechanisum responsible for the transformation has not been fully understood to date. Various mechanisums have been proposed. The two mechanisms which have emerged as the most popular are surface soft phonon modes and frozen in place surface embryos. It is hoped that the information presented here will aid in determining the correct mechanisum. The temperature of the transition of cobalt in the bulk has been widely reported: the information presented here involves the measurement of the transition on the surface of a cobalt single crystal. Considerable hysteresis was found; the transition temperature was found to be 457° C t 3° C when heated and 402° C I 3° C when cooled.