Differential scanning calorimetry (DSC) has been used to study the phase changes in samples of as-received Zr-2.5Nb pressure tube material by continuous heating and cooling. Two different heating rates (5 and 20°C/min) were used to heat the sample up to 1050°C. After a short time hold at 1050°C, all the samples were continuously cooled to 300°C at a rate of 20°C/min. On continuous heating, the DSC signals obtained showed two endothermic transitions. The lowtemperature transition, occurring between about 500 and 650°C, is attributed to a thermal decomposition of metastable niobium-stabilized β-phase. The higher-temperature transition, occurring between 600 and 950°C, is due to phase transformations of hcp α-Zr to bcc β-Zr, as previously confirmed in a companion study on the same pressure-tube material that was examined in-situ by neutron diffraction. The neutron diffraction results provided a positive identification of the two phases and also a quantification of the β-phase present in the sample at different heating temperatures, and thus provided a guide to extract the volume fraction of β-phase from the DSC signals obtained in this study. The DSC signals revealed only one exothermic transition which is correlated to the reverse transformation of β-Zr to α-Zr, as previously identified in the companion neutron diffraction study of the same pressure tube material.

Continuous heating, Cooling, DSC, Neutron diffraction, Phase changes, Zr-2.5Nb
Materials Science Forum
Department of Mechanical and Aerospace Engineering

Fong, R.W.L. (R. W L), Saari, H, Miller, R, Teutsch, J. (J.), & Vogel, S.C. (S. C.). (2012). A differential scanning calorimetry (DSC) study of phase changes in an as-received Zr-2.5Nb pressure tube material during continuous heating and cooling. In Materials Science Forum. doi:10.4028/www.scientific.net/MSF.706-709.853