X-Ray Investigation of a Co−0.25 wt% C Alloy: Stacking Disorder in the Martensite Phase and Reverse H.C.P. to F.C.C. Martensitic Transformation

Abstract

Cobalt samples with a nominal content of 0.25 wt% C (1.22 at% C) have been studied by X-ray diffraction at room temprature and after cooling to −196°C. From the lattice constants an actual value of 0.18 wt% C (0.88 at% C) can be calculated, the rest of carbon being exsolved. In this alloy the f.c.c. → h.c.p. transition is observed. Absolute values of intensities were measured and related to stacking disorder. The disorder is analysed in terms of a correlated distribution of stacking faults by a Monte Carlo simulation technique. Diffuse intensity was also recorded during the reverse h.c.p. to f.c.c. martensitic transformation up to 700°C. The results indicate that f.c.c. phase appears by regular growth of a small number of embryos within the product phase.