Microstructual and Micro-Chemical Analysis of Zr Cladding Alloys on Corrosion and Creep Properties

Abstract

This paper conducts in-depth research on zirconium alloys by combining results of out-of-pile corrosion and creep performance with microstructual and micro-chemical analysis using state-of-the-art (S)TEM, EDX and EBSD. The mechanism of different heat treatment processes on the macroscopic properties of zirconium alloys is explained from the microscopic level. By comparing various Zr-Sn-Nb alloys with different intermediate temperatures, it is discovered that creep resistance becomes better and the corrosion resistance becomes worse. It is found that average grain size increases gradually with increasing intermediate temperature, creep deformation is related with grain boundary slip, so the smaller grain size, the faster creep rate. In alloys with Nb content less than its solid solution limit in zirconium, when increasing the intermediate annealing temperature, there are fewer Nb-rich Zr-Fe-Cr-Nb second phase particles (SPPs) but more Cr-rich Zr-Fe-Cr-Nb SPPs, so the amount of Nb in solid solution in the matrix increases, which lead to better creep resistance due to solid solution strengthening and lower diffusion coefficient, however, with higher Nb solid solution content, there is more tetragonal to monoclinic oxide phase transition, which causes more cracking in the oxide and increases the corrosion rate.