On the fcc→D019 transformation in Co–W alloys Original Research Article

The continuous precipitation of D019 Co3W from a highly supersaturated Co-rich fcc matrix has been investigated. A detailed analysis of planar defects generated in the precipitates has been carried out using conventional and high-resolution transmission electron microscopy. The spatial arrangement of stacking faults and antiphase boundaries revealed the actual defect formation mechanisms and disclosed important aspects of the phase transformation at an atomic level. The results point to a displacive/diffusional Widmanstätten type of transformation, which is not simply based on a common ledge growth and, furthermore, follows the path: fcc→hcp→D019. The α′+Co7W6→Co3W peritectoid transformation has also been studied.