Investigation Of Diffusion Behavior And Mechanical Properties Of Zr-Cu And Zr-Nb System

Zirconium alloys are widely used for nuclear fuel cladding of nuclear reactors because of their excellent nuclear properties,mechanical properties and corrosion resistance.The microstructure and mechanical properties of Zr-based alloy are very important to the safety of nuclear reactor.Therefore,it is necessary to study the microstructure and mechanical properties of Zr-based alloys.Two systems,Zr-Cu and Zr-Nb,were chosen as the target in the present thesis,aiming at refining the diffusion kinetics and thermodynamic parameters of Zr-Nb and Zr-Cu systems,the main research contents are as follows:(1)Six compounds(Cu9Zr2,Cu51Zr14,Cu8Zr3,Cu10Zr7,CuZr and CuZr2) have been experimentally observed in all diffusion couples in the temperature range of 770 ? to 840 ?.The growth mechanism of each phase is not the bulk diffusion at the initial stage.With the increase of annealing time and the growth of diffusion layer,the mechanism of each phase changes to bulk diffusion.In other words,the growth of intermetallic compounds increases linearly with the annealing time.(2)In this paper,the interdiffusion coefficient and diffusion activation energy of Zr-Cu intermetallic compounds at the range of 770-840 ? were calculated.The diffusion coefficients and diffusion activation energies:of the six compounds follow the orders as:DCu51Zr14>DCu9Zr2>DCu8Zr3>DCuZr>DCuZr2,QCu51Zr14>QCu8Zr3>QCu9Zr2>QCUZr>QCuzr2?(3)The nano hardness(11.61GPa)and the elastic modulus(146.96GPa)of Cu51Zr14 is slightly larger than the nano hardness(10.09GPa)and the elastic modulus(143.04GPa)of Cu9Zr2,but they are greater than those of the pure Zr and Cu.(4)Zr/Nb diffusion couple is used to investigate the interdiffusion of Zr-Nb system.The occurrence of the Kirkendall interface closing to the side of Nb clearly suggests higher mobility of the Nb.The diffusion profiles of the Zr-Nb system is a typical solid solution diffusion profiles,and the interdiffusion coefficients of Zr-Nb system are found to decrease with increase of Nb concentration.(5)Zr/Zr-5Nb diffusion couple is used to investigate the impurity diffusion of Zr-Nb system.There is no Kirkendall hole and Kirkendall interface in all the samples.The impurity diffusion coefficient of the Zr-Nb system increases with the increase of temperature.The diffusion activation energy and the pre-exponential factor are 108.21 kJ/mol and 0.95 × 10-9 m2/s,respectively.