Effect Of Texture And Temperature On The Biaxial Deformation Mechanisms Of Zirconium Alloy

Zirconium alloys are widely used in the nuclear industry due to their excellent comprehensive properties,mainly as materials for cladding tubes in nuclear reactors and other structural materials in reactors.Zirconium alloys with HCP structure have obvious anisotropy,and the complex deformation mechanisms are affected by many factors.Zirconium alloys are usually in a high temperature and complex stress state during using and forming,exhibiting completely different deformation behavior and performance characteristics from uniaxial stress at room temperature.This paper takes commercial pure zirconium as the research object,and studies the effects of texture and temperature on the deformation coordination mechanisms under biaxial stress,which provides theoretical guidance for the performance improvement and safe application of zirconium alloys.This paper studies the effect of texture on the biaxial deformation mechanisms and forming properties of zirconium alloys at room temperature.Through in-plane compression and annealing,the strong basal texture of the original sheet is weakened,and a weakened texture with two parts of c//ND and c//RD texture is obtained.The results of uniaxial and biaxial tensile experiments and Schmidt factor analysis of two textured zirconium alloys show that they activate different deformation mechanisms.The basal-textured zirconium alloy activates prismatic slip during uniaxial tensile test,while the prismatic slip is suppressed during biaxial stretching,and the pyramidal slip is activated.The weakened textured zirconium alloy deforms coordinately by prismatic slip and tension twin in the uniaxial tensile experiment in the RD direction,and by the prismatic slip in the uniaxial tensile experiment in the TD direction.Under equal biaxial stress,weakened textured zirconium alloy mainly uses the grains of the c//RD part to activate prismatic slip and tension twin to coordinate the deformation in the thickness direction.However,the stress in the TD direction inhibited the activation of some twin variants.The results of Erichsen test show that the deformation in ND direction of the basal texture is not easy to coordinate under biaxial stress,so the grain boundary slides,and then small cracks are generated.The weakened texture is easy to coordinate the deformation in the thickness direction under biaxial stress,and its stretch formability is better.Its Erichsen value is increased by 48% compared with the basal texture.This paper also studied the effect of temperature on the biaxial deformation mechanisms of zirconium alloys.The results of uniaxial and biaxial tensile experiments and microscopic analysis of zirconium alloys at high temperatures of 200℃ and 400℃show that the high temperature of 200℃ has a limited effect on the activation of tension twin,while the number of tension twins decreases and the slip activation increases at400℃.The deformation coordination between adjacent grains has an important impact on the mechanical behavior and deformation mechanisms.When the weakened texture is stretched in the TD direction,the deformation of different grains is not easy to coordinate and the grain boundary resistance is high,which improves the strength and activates tension twins with negative Schmidt factor.Further microscopic analysis showed that the basal-textured zirconium alloy activated a large number of {10-11}compression twins under biaxial tensile stress at a high temperature of 400℃.This is due to the increased activation of basal slip at high temperatures,which promotes the activation of compression twins.High Schmidt factor and the stress concentration caused by the uncoordinated deformation under biaxial stress also promotes the activation of compression twins.The activation of the secondary tension twins in the{10-11} compression twins is affected by the Schmidt factor and the deformation coordination coefficient m,where m is the deformation coordination coefficient between the primary compression twins in the parent grains and the secondary tension twins in the primary compression twins.