The Study On The Application Of Ti₅₀Ni₅₀ Shape Memory Alloy Wire In Drive Element

Transformation characters and shape memory effect (SME) of aged TiNi shape memory alloy (SMA) wire have been systematically investigated by means of thermo-mechanical training,thermal cycling,differential scanning calorimetry (DSC) sa well as scanning electron microscopy (SEM). Ageing time-temperature-transformation table was established after studied the characteristics of DSC curves in aged Ti₅₀ Ni₅₀ SMA wire. Stress-strain curve of Ti₅₀ Ni₅₀ helical spring aging at 450℃and 500℃an hour were ploted so these can provide reference imformation for Ti₅₀ Ni₅₀ SMA wire used in design of drive element.The experimental results show that martensite transformation temperature (M_s, M_f) increases with the increase of the aging temperature when the aging temperature is between 500℃and 600℃; R(the start temperature of R transformation) decreases slowly with the increase of aging temperature; R_f (the finish temperature of R transformation) firstly increase when the aging temperature is between 300℃and 400℃, when upon 400℃, R_f decreases. The thermal hysteresisΔT_m (A_s-M_s) doesn't change dramaticly when the aging temperature between 300℃and 450℃, when upon 500℃, it decreases rapidly because of the disappearance of R phrase. The transformation temperature of Ti₅₀ Ni₅₀ SMA wire increases with the increase aging time, but the influence is not dramtic as aging temperature does.The influences of aging heat treatment and thermomechanical training on shape memory (η_s·η_t) effect of Ti₅₀ Ni₅₀ shape memory alloy: the one-way recovery rateη_s firstly contains stability with the increase of the aging temperature when the aging temperature is between 300℃and 500℃, when upon 500℃,η_s decreases rapidly.The 550℃and 600℃have lowered the 56．7% and 68．3% of original value respectively. There is an increase of the two-way recovery rateη_t to a steady value between 400℃and 600℃. Theη_s decreases slowly with the increase of the training cycle numbers.After training 75 cycle,η_s is only 60% of original value.While theη_t increases rapidly with the increase of the training cycle numbers, and reaches top value after training 75 cycle, which has increased 200%. When the aging temperature is higher than 500℃, theη_t isn't influenced by thermomechanical training cycle numbers. Thermal cycling has obvious effect on the two-waye shape memory effect (TWSME) in the aged Ti₅₀ Ni₅₀ SMA. Theη_t firstly decrease rapidly in the first several cycles, and then keeps constant after 100 thermal cycles. The order ofη_t in different aging temperature from higher to lower is 450℃, 400℃, 500℃and 550℃.The helical spring has been designed by using the stress-strain (Ï„-γ) curve of Ti₅₀ Ni₅₀ helical spring aging at 450℃and 500℃an hour.