Characterization of surface coarse-grained structure and improved corrosion resistance for Zr-4 alloy at high temperature

A surface coarse-grained structure (SCGS) layer is introduced in Zr-4 alloy after surface mechanical rolling treatment and then vacuum annealed at 800 degrees C. The microstructures and textures of SCGS is characterized by Electron Backscattered Diffraction, and grains orientation are analyzed in detail by Inverse Pole Figure and Pole Figure. The corrosion tests of the Zr-4 alloy with SCGS layer and as-received were carried out at 360 degrees C/18.7 MPa in water and in steam at 700-800 degrees C, respectively. The coarse grain in SCGS layer is 10 times larger than that of as-received samples and has <1010> preferred orientation in cross section of cylindrical samples. The weight gain of the SCGS specimens is lower than that of the as-received specimens at high temperatures. As for corrosion in steam at 700 degrees C for 1 hour, the weight gain of SCGS sample is 40% less than that of the as-received sample. The high temperature oxidation process is dominated by the diffusion of O2-along the grain boundaries. The grain boundary density of the SCGS layer is six times less than that of the as-received specimens, which reduces the grain boundary diffusion channels for oxygen ion, and improves corrosion resistance of Zr-4 alloy at high temperature.