| TiNi alloy is widely used in aerospace and civil industry because of its shape memory effect and good mechanical properties.Ultra-high pressure will influence the formation of new materials phase,and the different ultra-high pressure aging process has an important influence on the microstructure and mechanical properties of Ti Ni alloy.Effects of ultra-high pressure and different aging process on microstructure,morphology,martensitic transformation and mechanical properties of Ti-51(at%)Ni alloy was researched by X ray diffraction technique,transmission electron microscope,differential scanning calorimetry,tensile test and hardness test system.Under the condition of ultrahigh pressure aging,the test results showed that the size of alloy grain increased gradually with the temperature rose or time increased,and the shape of precipitated phase grew from granular to elliptical,elliptical,flaky,and finally grows into coarse flakes.As the pressure increases,the size of precipitated phase decreased.Ultrahigh pressure resulted the formation of high density dislocations in the grains,and the distribution of precipitate phases was not obviously different between grain boundaries and grain interiors;With the increase of aging temperature,the alloy phase transition changed from two steps to one step;With the increase of aging time,the phase transition of alloy is gradually changed from two steps to three steps;With the increase of pressure,the phase transformation of alloy changes from one step to the two step,and further to the three step;The tensile strength at maximum temperature of600 ? is 960 MPa,the elongation reaches the maximum of 19.5% at 500 ?,the maximum hardness is 382.4HV at 500 ?,the tensile strength reaches the maximum of1150 MPa at 2h,The elongation reached a maximum of 18% at 2h,the hardness reached a maximum of 433.9HV at 5h;the tensile strength reached a maximum of960 MPa at 5.5GPa,the maximum elongation of 1GPa was 22%,the hardness reached the maximum at 3GPa For 404.7HV.The test results showed that the high pressure leaded the diffusion coefficient decreased,under the ultra-high pressure process,the size of precipitates of Ti3Ni4 was smaller than the size of precipitation which under the normal pressure,and the size of Ti3Ni4 precipitates was decreased with the increase of pressure;ultra-high pressure leaded to high dislocation density which would provide the impetus for the nucleation of precipitates,and make there was no difference of precipitates between grains inside and grain boundary of Ti3Ni4;and the relationship between matrix and precipitates was coherent or semi coherent which would make local stress not uniform and result the R phase transition;Precipitates of Ti3Ni4 leaded to uneven distribution of internalcomponents which changed the martensitic transformation temperature and resulted a three-step phase change;Ultra-high pressure aging processes of TiNi alloy leaded the formation of precipitates and the high density of dislocation which could improve the mechanical properties and obtain the good superelasticity.By researched on the influence of different ultra-high pressure process aging on the microstructure,martensitic transformation and mechanical properties of TiNi alloy,determined the root cause of different influence of ultra-high pressure aging and atmospheric pressure aging aging on the Ti3Ni4 was that the high pressure caused the coefficient decreased and produced high dislocation density,which resulted the difference distribution and difference size of precipitation of Ti3Ni4 phase and further affected the transformation and mechanical properties of martensitic transformation. |
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