Internal stresses in the α -α′ phase transition of coherent metal-hydrogen systems

In anα-α′ phase transition of the type discussed by Wagner and Horner, the smoothly varying hydrogen distribution generates coherency stresses in the metal crystal. The system is in a metastable state, which is expected to have a long lifetime if the internal stresses are smaller than some critical stress for destroying coherency. A comparison of the calculated internal shear stress with the experimental value of the critical shear stress for the onset of plastic deformation in a Nb crystal suggests that there may well be an appreciable region in which a coherent transition is experimentally observable.