A Differential Scanning Calorimetry (DSC) Study of Phase Changes in an As-Received Zr-2.5Nb Pressure Tube Material during Continuous Heating and Cooling
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 low-temperature transition, occurring between about 500 and 650°C, is attributed to a thermal decomposition of metastable niobium-stabilized β-phase. The highertemperature 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.
T. Chandra, M. Ionescu and D. Mantovani
R.W.L. Fong et al., "A Differential Scanning Calorimetry (DSC) Study of Phase Changes in an As-Received Zr-2.5Nb Pressure Tube Material during Continuous Heating and Cooling", Materials Science Forum, Vols. 706-709, pp. 853-858, 2012