Effect of temperature on hydrogen absorption characteristic and microstructural evolution of TC21 alloy

摘要

TC21 alloy was hydrogenated at different temperatures, and its hydrogen absorption characteristic, hydrogen content, hydrogen absorption kinetics, microstructural evolution and mechanism of hydride formation were investigated. Results show that under the same initial hydrogen pressure, hydrogen absorption rate of TC21 alloy is very slow and hydrogen content of the alloy is close to zero when hydrogenation temperature is lower than 500 degrees C. The initial hydrogen absorption rate achieves the maximum value at 600 degrees C. Hydrogen content increases first, then increases up to a maximum at 600 degrees C and decreases last with the increase of temperature. Hydrogen absorption reactions reach equilibrium faster when temperature increases. Hydrogen absorption reaction occurred during hydrogen absorption process of TC21 alloy is a complicated process which contains different stages according to hydrogen absorption kinetics. Hydrogenation temperature has a significant effect on microstructural evolution of TC21 alloy. With the addition of 0.68 wt.% H in the alloy, beta transus temperature drops below 750 degrees C but still higher than 650 degrees C. HCP alpha(2) phase and FCC delta hydride appear in the specimens hydrogenated at 550 degrees C and 650 degrees C according to XRD and TEM analyses. The morphologies of d hydrides in the alloy hydrogenated at different temperatures are not identical, acicular d hydrides exist in the alloy hydrogenated at 550 degrees C, while large amount of lamellar d hydrides exist in the alloy hydrogenated at 650 degrees C. Furthermore, the formation mechanism of d hydride is discussed, results reveal that d hydrides precipitate directly in b phase at high temperature, and the most appropriate temperature for the precipitation of d hydrides in b phase is 600 degrees C . (C) 2015 Elsevier B.V. All rights reserved.