Microstructure And Texture Evolution Of Zr-4 Alloy In Deformation And Subsequent Annealing

Due to its excellent corrosion resistance,low thermal neutron absorption cross section and moderate mechanical properties,zirconium alloys are widely used in the nuclear industry.Zr-4 alloy is a typical commercial zirconium alloy,which is mainly used for fabricating cladding tubes and positioning spacers in nuclear reactor fuel assemblies.In this paper,the evolution tendency and mechanism of microstructure and texture of Zr-4 alloy in two deformation processes(rolling,in-plane unidirectional compression)and subsequent annealing are studied,which provides a certain theoretical guidance for the further improvement of the forming performance of Zr-4 alloyIn this paper,the hot rolled annealed Zr-4 plates were used as the experimental materials,and electron backscatter diffraction(EBSD)was used as the main research method.Firstly,the initial Zr-4 alloy plate rolling deformation and follow-up at room temperature and liquid nitrogen temperature were analyzed.The evolution of the microstructure during the annealing process.Then,for the rolling and annealed Zr-4 alloy sheet,the evolution tendency and mechanism of microstructure and texture in the process of compressive deformation in the rolling direction and subsequent annealing were studied.The main conclusions are as follows:At the temperature of liquid nitrogen,when the rolling deformation reaches 40%,there is no obvious twin layer in the initial Zr-4 alloy sheet.This may be due to the smaller initial grain size demands the higher stress to activate twinning.Compared with rolling at room temperature,the phenomenon of inhomogeneous deformation in liquid nitrogen rolling is more significant.This may be because the critical shear stress(CRSS)value of the sliding system increases significantly with the decrease of the deformation temperature,thereby enhancing the dependence of grain deformation on initial orientation;Under the same rolling strain,liquid nitrogen rolling enhanced the growth of recrystallized grains compared with room temperature rolling,which may be attributed to the inhomogeneous deformation induced by low temperature rolling,which gives the size advantage of the nucleation and the local orientation difference.In the process of RD compression deformation of liquid nitrogen rolled and annealed Zr-4 plates,the area fraction and number of tensile twins increase with the increase of deformation.In the annealing process after compression deformation,the pre-manufactured twin boundaries may undergo thermal activation and migration,and the thermal migration in the twin boundaries mainly causes the twins to grow.At the same time,the twin-induced texture components are strengthened.The thermal activation of pre-manufactured twin boundaries is related to the magnitude of the deformation.The lower the amount of deformation,the higher the temperature required for twin boundary migration,and no migration occurs even near the phase transition temperature.At larger deformations,the lower the migration temperature,This may be due to the large deformation caused by the loss of coherency of the twin boundaries(increasing the mobility of the twin boundaries),and at the same time increasing the strain energy on both sides of the twin boundaries(increasing the driving force of twin boundaries migration).