Precipitation and dissolution peaks of hydride in Zr-2.5Nb during quasistatic thermal cycles

Two internal friction peaks and corresponding discontinuity ('knee') points of elastic modulus have been observed in hydride-forming metals upon heati ng and cooling, respectively. In the present work, measurements of Young's modulus as functions of temperature and hold time during a quasistatic ther mal cycle were made in Zr-2.5Nb samples containing hydrogen using a composi te oscillator technique. The increment of modulus during an isothermal hold is proportional to the decrease in hydrogen concentration in solid solutio n of the Zr alloy. As a result, elastic modulus measurements provide a mean s to determine the amount of transformed hydride during the transition. It is confirmed experimentally that the two peaks reflect the variation of the hydride transformation rate during heating or cooling. It is demonstrated by the present work that the maximum-slope point of each peak, on the high temperature side, is coincident with the knee point on the curve of modulus Versus temperature and this point provides the most reliable and physicall y sensible indicator of the end of hydride dissolution during heating, or t he beginning of hydride precipitation during fooling. (C) 2000 Published by Elsevier Science S.A.