Microstructure Evolution of Dilute Mo-Re Alloy Tubes under Biaxial Stress

Dilute Mo-Re alloy is one of the candidate materials for reactor core cladding, so its high-temperature stability performance, which maintains structural stability under high-temperature biaxial stress, is the most important performance indicator. In order to obtain the deformation mechanism of dilute Mo-Re alloy tube under high-temperature biaxial stress and provide theoretical basis for further improving its high-temperature stability, the microstructure evolution process of dilute Mo-Re alloy tubes under biaxial stress (circumferential stress of 36 MPa and 60 MPa, respectively) at 1 350 K was studied. The raw material rod of the dilute Mo-Re alloy was prepared by powder metallurgy method, and the alloy tube was machined along the axial direction of the raw material rod. This experiment achieves high-temperature biaxial stress on the dilute Mo-Re alloy tubes by sealing inert gas within them and storing them in a vacuum high-temperature furnace at a certain temperature for a long time. Under the action of high-temperature biaxial stress, the dilute Mo-Re alloy tubes underwent significant circumferential deformation after a certain period of time. EBSD, TEM, XRD and EDS were used to compare and analyze the samples of dilute Mo-Re alloy tubes before and after biaxial stress experiments. The characteristic changes such as particle size, crystal orientation, cell parameters and dislocations were obtained, and the deformation mechanisms and microstructure evolution process were speculated. The research results indicate that the microstructure of the annealed original sample is columnar grains with <101> directionality along the axial direction. During the process of 8% circumferential deformation at 1 350 K, the sample with circumferential stress of 36 MPa undergoes recrystallization and grain growth, and loses the <101> directionality. Most grains have a large number of dislocation cells inside, while a small portion of the grains aggregate rhenium rich and molybdenum poor materials, and with fewer dislocations. During the deformation process, the lattice parameter increases and some Mo crystal structure is destroyed. The deformation mechanism is mainly characterized by dislocation sliding and grain boundary sliding. During the process of 19% circumferential deformation at 1 350 K, many columnar grains of the sample with circumferential stress of 60 MPa undergo severe deformation along the circumferential stress direction, and many Mo crystal structure is destroyed. Partial columnar grains recrystallize into small grains, and the lattice orientation also undergoes a transition from <101> to <001>. During the deformation process, the lattice parameter increases more. In addition to internal deformation of the crystal, the deformation mechanism also includes grain boundary sliding.