Mechanism of the Y-2(Fe, V)(17) -> Y-3(Fe, V)(29) phase transformation

The mechanism of the Y-2(Fe, V)(17) --> Y-3(Fe, V)(29) solid-state transfor mation was studied. The transformation was shown to proceed by the formatio n and growth of Y-3(Fe, V)(29) nuclei throughout the volume of matrix grain s. The crystal lattices of the nuclei and matrix are coherent and orientati onally related. The existence of coherent stresses controls the emergence o f regions that are intermediate in content and crystal structure between Y- 2(Fe, V)(17) (ThzZn(17) type) and Y-3(Fe, V)(29). These regions are likely to be localized along the interfaces between the nuclei and matrix. The vol ume that is occupied by these regions and the stability of this transition structure in R-Fe-M alloys with different R and M are essentially dependent on the magnitude of coherent stresses.