Martensite Phase Transformation And Strain Recovery Characteristic Of TiNi Based Alloy Under Hypervelocity Impact

TiNi based alloys are widely used in spacecraft.They are exposed to the space environment and often suffered the threat of space debris.High-velocity impact of space debris is one of the main factors of the spacecraft and component failure.In this work,simulation the space debris,TiNi based alloys are high-velocity impacted by gunpowder,at the microstructures and strain recovery characteristics of TiNi based alloys were investigated by adopting the combination of simulation and experiment methods,The deformation mechanisms were expounded and analyzed.They would provide theoretical guidance and experimental basis for reliability evaluation of the space application of TiNi based alloy and its components.ANSYS/LS-DYNA software was used to simulate high-velocity impact process;the stress field distribution and the relationship between strain rate and time in the process of high-velocity impact were ascertained.For Ti₅₀Ni₅₀ alloy,the stress value at grain boundary was no different than that in the interior of grains.For aged Ti₄₉Ni₅₁ alloy,the stress mainly concentrated in the grain boundary,meanwhile,the stress value in Ti₃Ni₄ precipitation particles and matrix was obviously smaller than that in grain boundary.For Ti₄₄Ni₄₇Nb₉ alloy,the stress mainly concentrated in phase interface between ?-Nb particles and matrix.The strain rates of three alloys showed the fluctuant decline as the impact time increased.Tests indicated that,Ti₅₀Ni₅₀ alloy was impacted,a large number of macroscopic cracks appeared at the bottom and sidewall of the crater.Martensitic and reverse phase transformation temperature lowered long different zones.Martensite and inverse phase temperature increased with the distance increase from the bottom of crater along impact direction.In the distance of 5 mm from the bottom of crater,martensite and inverse phase temperature was similar with not impact.In the impact affected zone,the martensitic variants lost self-accommodated morphology,the plates seriously fragmented,and the high density dislocations appeared.The strain rate was 4.32×10⁴ s^-1 under the high-velocity impact by simulation,the deformation mechanism of Ti₅₀Ni₅₀ alloy changed to the slip and proliferation of dislocation from twin orientation again of static deformation.In the impact affected zone,the microhardness enhanced and the shape recovery ratio reduced.With the increase in distance from the crate,the microhardness reduced and the shape recovery ratio enhanced gradually,which was connected with high density dislocations introduced in alloy by high-velocity impact.To indicate different shapes second phase significantly affect the impact area,the second phase Ti₃Ni₄ particles with elliptic sphere,lens flake,thick sheet were separated out by aging process.Martensitic and reverse phase transformation temperature of impacted Ti₄₉Ni₅₁ alloys lowered long different zones,phase peaks disappeared at the bottom of crater?0¹ mm?,with the increase in distance from the crate,phase peaks were gradually obvious.In the distance of 2 mm from the bottom of crater,martensitic and reverse phase transformation temperature of impacted Ti₄₉Ni₅₁ alloys with elliptic sphere,lens flak Ti₃Ni₄ particles were similar with not impact.As the distance was 4 mm from the bottom of crater,phase transformation temperature of impacted Ti₄₉Ni₅₁ alloys with thick sheet Ti₃Ni₄ particles are similar with not impact.A lot of martensitic plates produced in the grain boundary and extended to the interior of grains for three alloys.The dislocation density of Ti₄₉Ni₅₁ alloys with elliptic sphere Ti₃Ni₄ particles was not increased obvious,the dislocation density of Ti₄₉Ni₅₁ alloys with lens flake,thick sheet Ti₃Ni₄ particles increased obviously.The deformation mechanism of aged Ti₄₉Ni₅₁ alloys were stress-induced martensite?elliptic sphere?,stress-induced martensite and the slip and proliferation of dislocation?lens flake and thick sheet?,which were attributed to the extent of strengthen matrix of Ti₃Ni₄ particles.The microhardness and shape recovery ratio increased significantly,with the increase in distance from the crate,the microhardness reduced gradually,and the shape recovery ratio increased at first and decreased subsequently.Tests indicated that,deformational behavior of Ti₄₄Ni₄₇Nb₉ alloy was different from that of Ti₅₀Ni₅₀ alloy,martensitic phase transformation peaks disappeared around the bottom of crater,martensitic and reverse phase transformation temperature lowered long crater lateral edges,martensitic phase transformation peaks disappeared at the the bottom of crater?0¹ mm?along the impact direction,with the increase in distance from the crate,phase peaks were gradually obvious,the phase temperature increased.As the distance was 5 mm from the bottom of crater,phase transformation temperature was similar with not impact.The area near crater emerged localized characteristics,a large number of amorphous emerged on the bottom of crater,martensite nanocrystalline and amorphous were coexistence.At long distance from the bottom of crater,the stress induced martensitic phase transformation appeared in the alloy,and nucleated at the interface between matrix and ?-Nb particles,and grew into matrix.With the increase in distance from the crate,the organization was similar to not impact.Localized formation mechanism was that stress mainly concentrated in the phase interface.The deformation mechanism of Ti₄₄Ni₄₇Nb₉ alloy was the combination of stress-induced martensite and the slip and proliferation of dislocation.The microhardness and shape recovery ratio increased significantly,with the increase in distance from the crate,the microhardness reduced gradually,and the shape recovery ratio increased at first and decreased subsequently.