Research On Surface Microstructure And Texture Of Zr702 By High Current Pulsed Electron Beam And Pulsed Laser

Multiple characterization and analysis techniques including electron backscatter diffraction (EBSD), electron channeling contrast (ECC), X-ray diffraction (XRD) and microhardness test were jointly employed to investigate a commercially pure zirconium (Zr702) alloy. Systematic work was conducted on microstructural evolution, orientational characteristics and microhardness variation during ??? transformation with different cooling methods (WC, AC and FC), analysis of the variant selection and its effect on the texture during the phase transition. High current pulsed electron beam (HCPEB) and pulsed laser were employed to conduct the surface modification treatment on Zr702 alloy, the effect of pulse number and laser power on their microstructures and textures. The main conclusions can be obtained from the present study are as follows:(1) Zr702 alloy specimens cooled by water, air and furnace from ?-phase present Basket-weave Widmanstatten, Parallel-plate Widmanstatten and Lenticular structures, respectively. Among them, detailed characterization work of WC specimen by EBSD, which demonstrated that the {10(?)1} twin relationship (57.05°/< 11(?)0>) between a plates should be correctly identified as the second Burgers misorientations (60°/< 11(?)0>), and the shared plane with such a Burgers misorientation is determined to be {10(?)1.06} for the firs time. The results of FC specimen showed that strong variant selection occurred in ?? a transformation process, produced a strong "texture memory" phenomenon, completely inherited the initial bimodal basal texture characteristics with a slightly enhanced maximum density; the twin-like lamellae found in FC specimen were confirmed to be {10(?)2} < (?)011> and {11(?)1} <(?)26> tensile twins; AC and WC specimens had no significant variant selection. The width of a plate gradually decreases with increasing cooling rate and the linear relationship between their logarithm was determined.(2) Surface microstructure results shows that martensitic transformation occurred and produced fully a martensite on the surface of Zr702 alloy, and typical craters is also induced due to the rapid melting and cooling processes after HCPEB irradiation. XRD analysis shows that the width of the diffraction peaks increases obviously with increasing pulse number, in which the diffraction peak intensity of {0002},{11(?)0} and {10(?)0} were changed significantly, and the preferred orientation is changed from a typical bimodal basal texture to {11(?)0} uniaxial texture. Surface microhardness of Zr702 alloy after the HCPEB treatment are also remarkably improved, and gradually increased with increasing pulse numbers.(3) 400,200,100,50 and 25W five different laser powers were employed to conduct the surface modification treatment on Zr702 alloy, the texture becomes more scattered after laser treatment. Results show that in the 400W specimen, laser-modified zone can be divided into three parts:melting zone (MZ), solid state phase transformation zone (SSPTZ), and recrystallized zone (RXZ), linear distributions of SPPs inside bulk grains in the RXZ suggest the occurrence of recrystallization from earlier formed plate structures. For 200, 100 and 50W specimens, laser-modified zone can be divided into MZ and SSPTZ two parts. And 25W specimen, because the power is small enough, there is no melting but only solid phase transformation occurred on the surface of Zr702 alloy, modified zone only includes SSPTZ. The SSPTZ could be distinguished as SSPTZ-1 or SSPTZ-2 for cooling from ? or ?+? domains accordingly. For those untransformed a grains in the SSPTZ-2, they slightly subdivided by many subgrains, which should result from extensive dislocation slip induced by martensitic transformation stresses and their recovery. An aggregate of three a plates with the "indentation mark" morphology is frequently observed for the martensitic plate structures in the 50 and 25W specimen and boundaries between them are determined to be the second Burgers boundary with the misorientation of 60°/< 11(?)0> The microhardness of the modified zones significantly increased after the laser treatment, and the average hardness within the MZ greater than the SSPTZ. The depth and width of the modified zones decreases with decreasing laser power, approximately linear relationship.