X-ray investigation of a Co-0.25 wt% C alloy: Stacking disorder in the martensite phase and reverse HCP to FCC martensitic transformation
Physica Status Solidi a-Applied Research 154(2): 517-530
Cobalt samples with a nominal content of 0.25 wt% C (1.22 at% C) have been studied by X-ray diffraction at room temperature and after cooling to -196 degrees 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 degrees C. The results indicate that f.c.c. phase appears by regular growth of a small number of embryos within the product phase.