Decomposition Pressure Hysteresis in the Zirconium-Hafnium-Hydrogen System

Abstract

A RECENT investigation¹ of the Zr–Hf–H equilibrium system at pressures less than one atmosphere of hydrogen gas revealed the presence of hysteresis. Although this was not unexpected², it was somewhat disconcerting and demanded further elucidation. Results presented here will show that: (1) decomposition pressure hysteresis must be considered when dealing with equilibrium between gases and multi-component alloy systems; (2) hysteresis always involved a region of more than one phase and was most prominent at lower temperatures where diffusion was slowest; (3) no evidence for an interfering surface film was found; (4) internal factors such as stress and large surface area accompanying a martensitic reaction are prominent in the hysteresis reactions of the Zr–Hf–H system.