Martensitic Transformation And Shape Memory Effect Of Electron Irradiated TiNi Alloy

TiNi shape memory alloys have been widely used in spacecraft,and their components are often in the space environment.Under the space environment,TiNi alloys are radiated by charged particles,causing performance degradation,affecting spacecraft performance,which may even cause mission failure.Therefore,in order to explore the changes in the microstructure and properties of TiNi alloys under electron irradiation conditions,this experiment used CASINO software to initially simulate the energy distribution of electrons in TiNi alloys,and used XRD analysis,DSC testing,TEM analysis and mechanical properties testing to analyze the microstructure,martensitic transformation behavior,shape memory effect and mechanical properties of TiNi alloy after electron irradiation.The results show that the phase composition and the microstructure of TiNi alloys irradiated by 1.2 MeV energy electrons have no change compared with the unirradiated TiNi alloys,and both the parent phase and the martensitic phase coexist,and the martensite substructures are {11(?)} type I twins.The electron irradiation has a significant effect on the martensite transformation behavior of TiNi alloys.The unirradiated TiNi alloy are a one-step martensitic inverse transformation,and the TiNi alloys undergoes a three-step martensite reverse transformation after electron irradiation.The stop temperature of the martensite transformation decreased by 8 ?,and the peak temperature of the martensite reversed phase transition decreased by 4.7 ?.According to the electron energy distribution simulated by CASINO software,five different thickness samples were selected to investigate the effects of different energy electron irradiation on the martensitic transformation of TiNi alloys.The results show that the number of reverse phase transitions of TiNi alloys depends on the energy of electron irradiation.The trend of increasing first and then decreasing is shown,and the maximum five-step martensitic reverse transformation occurs at 0.36 mm.The phase transition temperature decreases first and then increases with increasing electron irradiation energy,and The lowest value of the phase transition temperature is obtained at 0.36 mm.The electron-irradiated TiNi alloys exhibit good phase transition stability.During the first 15 thermal cycles,the phase transition temperature of the electron-irradiated TiNi alloy decreases monotonously with the increase in the number of thermal cycles,but in the subsequent thermal cycling process,the phase transition temperature remains basically unchanged.However,the unirradiated TiNi alloys' phase transition temperature decreases monotonously with the increase of the number of thermal cycles during 20 thermal cycles,which indicates that the unirradiated TiNi alloys' phase transition stability is poor.The electron-irradiated TiNi alloys were annealed at different temperatures.When the annealing temperature was 250?,the TiNi alloys returned to their unirradiated state.The electron-irradiated TiNi alloys were annealed at different holding times,150? heat for 20 min and 200? heat for 20 min,which return to the unirradiated original state.After electron irradiation,the yield strength of TiNi alloy decreased,the elongation increased by 10.8%,and the shape memory effect was slightly lower than that of unirradiated TiNi alloy.After irradiation,the elastic modulus and microhardness of TiNi alloy are related to the irradiation energy.Both the elastic modulus and the microhardness increase first and then decrease with the increase of irradiation energy.At the incident depth of 0.36 mm,25% remains,the maximum elastic modulus and microhardness were obtained.