Study On Cyclic Deformation Behavior Of NiTi Shape Memory Alloy In Wide Temperature Range

As a representative of new smart materials with sensing and actuation capabilities,NiTi shape memory alloys are widely used in many fields due to their unique superelasticity,shape memory effect,and biocompatibility.In the actual service process,the superelastic NiTi shape memory alloys will inevitably be subjected to the thermalmechanical coupling cyclic load,which has a significant impact on the reliability and service life of the component.Therefore,the cyclic deformation behavior of the superelastic NiTi alloys was investigated.Research has an urgent engineering need.In the past 30 years,domestic and foreign scholars have carried out certain experimental and theoretical studies on the cyclic deformation behavior of superelastic NiTi alloys at room temperature and human body temperature.There are still relatively few studies on the effect,which hinders the application of this material in a wide temperature range.Therefore,it is necessary to carry out systematic macroscopic and microscopic experimental studies on the cyclic deformation behavior of NiTi alloys in a wide temperature range（313K-393K）,so as to reveal the macrophysical properties and microscopic mechanisms of NiTi alloys cyclic deformation behaviors.The following research work was done:（1）Uniaxial tensile,cyclic deformation and multi-stage loading experiments with different strain peaks were carried out on NiTi alloys under a wide temperature range,and the stress-strain,transformation stress,residual strain and dissipation during the experiment were analyzed.Energy evolution curves,the effects of temperature and strain peak on the cyclic deformation behavior of NiTi alloys are discussed,and the cyclic deformation characteristics related to temperature-strain peaks of NiTi alloys are summarized.（2）In view of the strain rate under wide temperature range,the influence of cyclic deformation behavior of NiTi alloy,carried out cyclic deformation experiment of different strain rate,and the stress and strain,phase transformation stress,residual strain,dissipation energy and surface temperature in the process of circulation evolution is analyzed,discussed and summarized the related to temperature and strain rate deformation behavior of NiTi alloys cycle.（3）On the basis of macroscopic experiments,electron microscope observations were carried out on the samples of NiTi alloys after uniaxial cyclic deformation experiments under different working conditions,and microscopic experimental methods such as scanning electron microscope（SEM）and transmission electron microscope（TEM）were used.The microscopic appearances such as residual martensite,dislocation configuration,and deformation band generation in the material were observed,and the evolution of the cyclic deformation behavior on the microstructure under different macroscopic experimental conditions was analyzed,and the microstructure mechanism of cyclic deformation behavior of NiTi alloy under wide temperature condition was proposed.