Influence Of Compressive And Tensile Loads On Recovery Strain Of Ni-Ti Shape Memory Alloy

Compressive and tensile deformations are main deformation ways of shape memory treatment of NiTi memory alloy actuators.Now, study on effect of alloy component, processing and so on, on phase transformation and microstructure, and deformation behavior and restoration strain under tensile load have largely been conducted.And study on compressive deformation behavior of NiTi alloy has not been reported systematically. It has importantly academic and practical significance to investigate compressive deformation behavior and two-way shape memory effect of NiTi alloy to exploit new driving actuators and reuse couplings.The paper systematically investigated the restoration strain of Ti-49.7at%Ni and Ti-49.8at%Ni alloys at different compressive pre-strains, and the restoration strain of shape memory alloy tube actuator, and effect of tensile pre-strain temperatures and pre-strains on the restoration strain of Ti-50.8at%Ni alloy wire by differential scanning calorimetry (DSC), programmable precise resistance tester and tension tester.The results show that with the increase of compressive pre-strain, As and thermal hysteresis of Ti-49.7at%Ni and Ti-49.8at%Ni alloys increase and Ms drops a little; The restoration strain and reverse martensite transformation temperature As drop with the increase of compressive amount in Ti-49.8at%Ni, the restoration strain is 3.29% and As is 134℃at 8% pre-strain; With the increase of compressive pre-strain, the restoration strain increases first and then lowers in Ti-49.7at%Ni alloy, and reverse martensite transformation temperature As drops, the restoration strain is 3.2% and As is 144℃at 8% pre-strain; Ti-49.8at%Ni shape memory alloy tube actuators used in notched bolts whose fracture forces are 1.5 and 2.0 T are heated to restore freely after being compressively deformed.their restoration strains are 3.0%, displacement along axis direction of tube are 1 mm, which can realize heating departure of notched bolts;Tensile restoration strain is greater than compressive restoration strain in Ti-49.7at%Ni and Ti-50.0at%Ni alloys;The one-way shape memory strains of Ti-50.8at%Ni alloy wire are about 6% at-30℃～-70℃and 10% tensile pre-strain, and 8%-16% pre-strain at-60℃.And the two-way shape memory strain increases gradually first, reaches the maximum at 14%, then lowers with the increase of tensile pre-strain at -60℃.