Study On Microstructure, Deformation Characteristics And Torsion Memory Behavior Of TiNi Based Memory Alloy

TiNi shape memory alloy is a new functional materials which developed in the 1960 s.Due to its unique shape memory effect and excellent mechanical properties,it has attracted worldwide attention,it has been in a number of areas plays a irreplaceable role. In this paper, the research on different heat treatment system of TiNi based shape memory alloy phase transformation behavior, microstructure, deformation characteristics and torsion behavior and memory, for TiNi based shape memory alloy helical springs, Torsion Actuator developed to provide reference data.The phase transformation behavior of TiNi based memory alloy was studied by differential scanning calorimetry. The results showed that: heat treatment temperature level of Ti-49.8at.%Ni alloy transformation temperature, thermal hysteresis and phase transition types are not significantly affected, while the Ti-50.85 at.%Ni alloy phase transition temperature, and thermal hysteresis in greater impact; the third element Nb added significantly changing the phase transition temperature, so as to increase the thermal hysteresis.Microstructure of TiNi based memory alloy was studied by optical microscope. The results showed that the microstructure of Ti alloy mainly contains martensite, Ti4Ni2 O and very small amount of B2 phase, while the microstructure of Ni alloy mainly contains B2 phase, Ti4Ni2 O phase, granular Ti3Ni4 phase and a small amount of martensite.The deformation characteristics of TiNi based memory alloy are studied by universal tensile testing machine and torsion testing machine. The results showed that Ti-50.85 at.%Ni alloy the tensile properties of 500℃ /30min/AC treated best. And super elasticity in 400℃/30min/AC when dealing with the best under the different temperature torsion Ti-49.8at.%Ni alloy, appear different shear stress-shear strain relationship, and with the heat treatment temperature increased, τb and γ increased.Torsion and torsion- free and constrained recovery behavior reversed the memory of TiNi based memory alloy on torsional specimen. Research shows that: with a heattreatment system, torsional different deformation of Ti-49.8at.%Ni alloy specimens, with increase of deformation, constrained heating after the maximum recovery shear stress tends to rise in a straight line; reverse the same amount of deformation and different heat treatment temperature specimen with heat treatment temperature increasing, the alloy’s maximum recovery shear stress decreases, γr and η first and then decreases, torsion recovery temperature A’s gradually increased.