Research Of Precipitates Of N18 And Its Component-modified Alloys By Quantitative Metallography

Due to excellent its anti-corrosion capacity and mechanical ability, zirconium alloy is widely used in the nuclear industry. Moreover, the precipitates of zirconium alloy, such as the size, distribution, and kind of that, have a profound influence on both anti-corrosion and mechanical ability. The kind, size, distribution of the precipitates in zirconium alloy are not completely understood and controlled, especially the quantitative research of precipitates following the manufacturing processes, and it is arguable that the relationship between precipitates and anti-corrosion capacity exists by many scholars. So, in this paper, precipitates are quantitatively investigated by Scanning Electron Microscope (SEM) following the manufacturing processes, especially on the parameter of size, distribution and volume fraction. Based on this research, it is found the two key factors—which affect the precipitates during the manufacturing processes are the hot-rolling temperature and annealing temperature, respectively, supporting the improvement of the process for controlling the precipitates better.the research of following the manufacturing processes shows that (1)the shape of precipitates in N18 zirconium alloy is sphere or nearly sphere, and those particles during the rolling processes are not destructible; In the N18 samples obtained from hot-rolling process to final-annealing process, the size and volume fraction of precipitates do not vary largely, but the distribution of the particles in the annealed samples is more homogeneous than the distribution of the particles in the rolled samples; the statistical results by means of quantitative metallography show that the average size of the particles in N18 zirconium alloy from different processes sample is no more than 100nm and the volume fraction is about 2.00% and the particles mainly concentrated on the range from 10 nm to 100nm.(2) during the annealing and re-crystallization processes (including hot-rolled and annealed, cold-rolled and annealed, final-rolled and annealed), grains are pinned by the precipitates, which is so-called zener pinning effect and the grain size is roughly corresponding with the zener grain size which is calculated by the average size and the volume fraction of the precipitates; Furthermore, due to the interaction between grain boundary and particles in the alloy, the distribution of the particles is also affected by the grain as the grains grow and the grain boundaries migrate during the re-crystallization processes; Consequently, the particles is more evenly distributed after the annealing processes.(3) In terms of the statistical results from the quantitative metallography, both precipitates of N5 and N6 alloys, the former alloy which is added more Sn element and the latter alloy which is added more Cu element, is smaller than N18 alloy except the sample from the final-annealed process but the volume fraction does not vary largely; The reason why precipitates in both N5 and N6 alloys are smaller might be related with the adding element Cu and Sn, so further research is need.(4) It is found that precipitates in the final-annealed samples in both N5 and N6 alloys have abnormal growth, the repeated experiment is unstable because the size and the distribution of the particles totally changed. That phenomenon might be due to the heterogeneity of the rolling plates and other factor might be the control of the annealing temperature or the holding time. (5) Based on the equation of the accumulated annealing parameter, accumulated time and temperature might profoundly influence the particles in zirconium alloy, so the experiments of changing annealing and hot-rolling temperature are designed. The results show that the particles grow as the temperature goes up, especially above 600℃. But under 600℃, the size of particles keeps almost the same.