Shock-Induced Martensite Reversal in Fe/30%Ni

摘要

It is pointed out that variations of shear stress in a solid undergoing transition may have an important effect on the conditions under which transitions occur. Such variations are not calculable from present knowledge, and for practical reasons description of the state of shear during the transition must be made part of the constitutive relations. The difficulty of defining a Gibbs energy in a solid is pointed out and the thermodynamic problems are indicated in some details. Experiments are described which promise to reveal the state of shear in the alpha-gamma transition in Fe/30%Ni at high temperatures using shock wave methods. Attempts to carry out these experiments are described, and numerical calculations of phase transitions with and without shear stress show that characteristic shock wave structures do indeed result from various shear conditions during transformation. Transformation experiments at various initial temperatures suggest that there may be a third phase--perhaps epsilon--which is reached in shock experiments for modest driving pressures and for initial temperatures less than 200 C. A description of the metallographic state after shock transition is given. There is minimal evidence that the shear stresses were sharply reduced for initial temperatures of 400 C. (Author)