Stacking faults and phase transformations study in ball milled Co100−xCrx (x = 0, 20, 50) alloys

The structural evolution and the phase transformations occurred during milling process of Co100−xCrx (x = 0, 20, 50) alloys are investigated by X-ray diffraction. Microstructural parameters such as the crystallites size, the microstrains, the stacking faults, the dislocation density and the phase fraction were determined from the Rietveld refinement of the X-ray diffraction patterns. The results show the formation of nanostructured alloys which depend on the initial composition of the mixture. In addition, X-ray diffraction indicates that the ball milling induces the fcc to hcp phase transformation in the first stage of milling and the reverse hcp to fcc phase transformation at the end of milling. On the basis of Warrenʹs model, these allotropic transformations were explained by the presence of dislocations and the accumulation of stacking faults in the hcp and the fcc structures.