Oxidation kinetics and oxygen diffusion in Low-Tin Zircaloy-4 up to 1523K
Résumé
This paper deals with the study of oxidation kinetics and the identification of oxygen diffusion coefficients of low-tin Zy-4 alloy at intermediate (973Ket8804;Tet8804;1123K ) and high temperatures (Tet8805;1373K). Two different cases were considered dissolution of a pre-existing oxide layer in the temperature range 973Ket8804;Tet8804;1123K and oxidation Tet8805;1373K . The results are the following ones in the temperature range 973-1073K, the O diffusion coefficient in alphaZr phase can be expressed as Det945;=1.483exp(-202.81kJ-RT) cm2-s. In the temperature range 1373-1523K, the O diffusion coefficient in alphaZr, betaZr and ZrO2, were determined using an inverse identification method from experimental high temperature oxidation data (i.e., ZrO2, and alpha(O) layer thickness measurements), they can be expressed as followsDet945; = 1.5430exp(-201.55kJ-RT) cm2-s, Det946; = 0.0068exp(-102.62kJ-RT) cm2-s and = 0.1158exp(-143.64kJ-RT) cm2-s.In order to check these calculated diffusion coefficients, oxygen concentration profiles were determined by Electron Probe MicroAnalysis (EPMA) in pre-oxidized low-tin Zy4 alloys annealed under vacuum at three different temperatures 973, 1073 and 1123K for different times. At last, in the framework of this study, it appeared also necessary to reassess the Zr-O binary phase diagram in order to take into account the existence of a composition range in the two zirconia phases, alpha-ZrO2 and beta-ZrO2.