Coherent phase equilibrium in the NiV system

The influence of coherency strains on phase equilibrium has been examined experimentally in NiV alloys using in-situ high-temperature X-ray diffraction. The composition changes due to coherency strains have been sampled through shifts in the peak positions. The misfit versus temperature and the elastic constants of the α and β phases were investigated in order to compare experimental results with existing theories. Long-range order vs. temperature was also measured to examine its contribution to the misfit. The influence of coherency is small, but the basic tenets of the theories are supported: (1) the lever rule does not hold in the presence of coherency strains; (2) the composition is different for coherent and incoherent phases. The incoherent phase boundaries were also calculated from the data.