Finite Element Simulation And Experiment Of High Pressure Torsion For Zirconium Alloys

High pressure torsion(HPT)is a typical severe plastic deformation process.The material grain size can be effectively refined by this process so as to improve the physical chemical and mechanical properties of materials to a large extent,improving the ability of plastic deformation of materials,and it is especially suitable for plastic processing of the difficult-to-deformation materials.HPT technology has become a hot research topic in material preparation and performance optimization of the field.The zirconium alloy specimen is treated adopting the combined process of heat treatment of phase transition with electric field-high pressure torsion-heat treatment of recrystallization with electric field in this paper.The change law of the equivalent strain in the process of HPT is researched using the finite element simulation,and the microstructure of the material after processing and heat treatment is analyzed at last.In this paper,the Deform simulation software is applied to simulate process of the high pressure torsion under different pressures(3GPa,4GPa and 5GPa)and different torsional cycles(2π rad and 4π rad)and the change law of the equivalent strain in the process of high pressure torsion is obtained.By comparing the equivalent strain distribution of samples under different process parameters,the influence rule of loading pressure,relative torsion angle and friction factor on high pressure torsion process is obtained.Deform simulation software is also used to simulate the high pressure torsion process of specimens with different height to diameter ratio.By comparing the distribution law of the equivalent strain of the specimens with different height to diameter ratios,the influence height to diameter ratios on the high pressure torsion process is analyzed.The original samples of zirconium alloy are first treated by heat treatment of phase transition with electric field under 700℃ for 5min,so as to obtain the beta phase with strong plastic deformation capacity,and then the heat treated samples are processed by high pressure torsion under 5GPa pressures and 4π rad cycles.At last,the deformed samples are treated by heat treatment of recrystallization with electric field under different temperatures(500℃、600℃、650℃、680℃ and 700℃)and different holding time(0.5 min、1 min、2 min、5 min、15 min and 25 min).Microscopic observation as well as XRD diffraction analysis is carried and the effect of different heat treatment processes on the microstructure and phase composition of zirconium alloy samples is obtained.The microstructure and texture of the samples after heat treatment are analyzed by TEM and EBSD.And the effects of different heat treatment temperatures and holding time on microstructure,texture and recrystallization behavior of the samples are determined.