Lengthening kinetics of $$(01\bar 10)$$ γ-TiH precipitates in α-Ti in the temperature range of 25 °c to 80 °c

Abstract

Formation of y hydrides in α titanium involves a hcp → fct lattice transformation with hydrogen as an interstitial diffusing species. Since the crystallography of this reaction resembles that of a martensitic transformation and the hydrides form at temperatures where both titanium and hydrogen atoms may have negligible mobility, many investigators have concluded that γ hydrides form by a martensitic mechanism. In this study, the lengthening kinetics of \((01\bar 10)\) γ hydrides were determined using conventional transmission electron microscopy (TEM). The length of the hydrides was measured as a function of time, temperature, and hydrogen concentration in samples isothermally aged in the range of 25 °C to 80 °C. These measurements were compared with the Zener-Hillert model of volume-diffusion-controlled precipitate growth. The experimental results indicate that y hydride growth is diffusionally controlled at 25 °C and possibly interfacially controlled at aging temperatures of 50 °C and higher. These and other aspects of the transformation are discussed.