Yuanzineng kexue jishu (Mar 2023)
Study on Flow Behavior and Constitutive Model of Zr-Sn-Nb-Fe Alloy in Two-phase Region
Abstract
Zr-Sn-Nb-Fe series alloys have gradually replaced Zr-4 alloys as the material of choice for nuclear fuel element cladding tubes due to their excellent corrosion resistance, and the fabrication of new zirconium alloy cladding tubes is a research hotspot for scholars at home and abroad. In order to provide support for the selection of process parameters and numerical simulations of the Zr-Sn-Nb-Fe alloy, the thermal deformation behavior of the Zr-Sn-Nb-Fe alloy was investigated in this paper by using unidirectional compression tests at temperatures of 650-800 ℃, strain rates of 0.01-1 s-1, and a maximum deformation of 70%. A strain-compensated Arrhenius intrinsic model for the Zr-Sn-Nb-Fe alloy was established. The results show that the flow stress of Zr-Sn-Nb-Fe alloy decreases with the increasing temperature and strain rate. The rheological profile of this alloy can be divided into 3 stages. In the process-hardening stage, the dislocation proliferation leads to rapid increase in dislocation density and rheological stress. In the dynamic recrystallization stage, when the dislocation density increases to the critical density for dynamic recrystallization to occur, the softening effect of dynamic recrystallization causes the rheological stress to begin to decrease. In the steady-state rheological stage, the rheological stress gradually stabilizes when the work hardening and dynamic softening reach equilibrium. the true stress of Zr-Sn-Nb-Fe alloy decreases with the increase of deformation temperature and the decrease of strain rate. During high-temperature deformation, due to the short heating time, only a portion of the original α-grain phase becomes β-phase, and then undergoes martensitic phase transformation during the quenching process and reverts to a neatly arranged lamellar α-organism. There is also β-transformation in the 800 ℃ heat deformation sample, but no β-transformation at 650 ℃. When the temperature is low (650 ℃), the recrystallization driving force is small, the phase transformation is low, and the β- and α-transformation grains cannot be produced during the heat deformation process, and only the initial lamellar α-transformation tissue is present in the water quenched tissue. At high temperature (800 ℃), the recrystallization driving force is large, the phase transformation degree is large, and β-grains and α-recrystallized grains can be produced, so the organization after water quenching has initial lamellar α-deformation organization, β-transformation organization and α-recrystallized grains. the heat deformation activation energy of Zr-Sn-Nb-Fe alloy is not less than 288.62 kJ/mol. The intrinsic relationship model of the Zr-Sn-Nb-Fe alloy was established by the strain-compensated Arrhenius equation based on the stress and strain data. To validate the model, a rheological curve (725 ℃, 0.05 s-1) not involved in the construction of the intrinsic model was selected in the process parameters range (650-800 ℃, 0.01-1 s-1). The verification results show that the predicted values of rheological stress at this process parameter agree well with the experimental values. To further evaluate the accuracy of the present constitutive model, the correlation coefficient and the average relative error absolute value of the predicted stress and the experimental value were calculated. The average absolute relative error between the predicted values of flow stress and experimental values is 4.77%, and the correlation coefficient is 0.988 3. The above results indicate that the present constitutive model has a high prediction accuracy.
