Experimental Study On Fabrication Of High Strength And Toughness Zr Strips By Liquid Nitrogen Low Temperature Rolling

Metal Zr has six sides close packed structure,because of its many special properties,it has been widely used in many industrial fields.In this paper,metal Zr was taken as the object of study,and the large deformation experiment of liquid nitrogen rolling at low temperature was carried out.The microstructure evolution law of high strength and toughness was studied after the severe plastic deformation combined with annealing control.Firstly,the rolling platform with liquid nitrogen low temperature cooling environment has been improved,and the severe plastic deformation of high purity Zr metal has been finished.Through the low temperature environment,the work hardening ability of the material can be enhanced,and the dynamic response of the dislocation can be effectively suppressed,so as to obtain the sample with high density dislocation,which provides favorable conditions for subsequent annealing treatment.In the process of rolling,the intermediate samples with different accumulative deformation were intercepted,and the effect of accumulative deformation on the properties and microstructure was investigated.The results show that the greater the cumulative deformation degree is,the more obvious the effect and advantage of liquid nitrogen at low temperature.The larger the dislocation density,the more refined grain size will be.At the same time,in the liquid nitrogen cold rolling test,a number of different rolling speeds were adopted.The influence of the strain rate of liquid nitrogen low temperature cold rolling on the properties of the sample was investigated.It is found that with the increase of rolling strain rate,the deformation degree of grain is more severe,and the grain refinement degree is increasing.the dislocation density inside the sample can increase and the low temperature cold rolling can also be increased,which can provide more room for the control of the sample to obtain multi-scale structure.Finally,all of the preparation of liquid nitrogen rolling severe plastic deformation of metal Zr samples were treated with 450?,475?,500?,525? annealing treatment,in order to obtain high strength and toughness.The results show that with the increase ofannealing temperature,the strength decreased after annealing,plastic increased toughness is increased at first and then reduced.Observation of annealed samples of TEM microstructure photos,found that annealing the dislocation density of the samples decreased rolling,dislocation annihilation,grain growth,grain distortion degree decreases,showing a nanometer crystal ultrafine grained coarse crystal transition trend.It can be inferred that at a certain annealing temperature can achieve the internal micro crystal,ultra-fine grain,coarse crystal ideal coexistence of multi-scale microstructure,so as to obtain the best toughness,reflected in the strength and plasticity of the characteristics of synchronous improvement.