Abstract
Ni-Ti is known as one of the most excellent shape memory alloys because it has large recovery strain and recovery stress. However, shape memory effect (SME) is much affected by its composition, heat treatment and strain at heat treatment.
Five compositions of Ni-Ti alloys [50.0-52.0 (at%Ni)] were chosen and treated at various temperatures [573-873(K)] and for various times [15min-4hr]. Then the measurements of shape change, transformation temperature and tensile mechanical properties were carried out.
Moreover, the all-round shape memory effect (ARSM) of Ni-rich specimen [51.0 at%Ni] was examined after thermal cycle, strain cycle and exposure to high temperature.
The results obtained are summarized as follows:
(1) Ti-50.0 at%Ni alloy could induce good SME.
(2) Pseudo-elasticity (PE) was much affected by the composition of alloy and heat treatment.
(3) Compositions in a range from 51.0 at%Ni to 51.5 at%Ni and heat treatment at a range from 673K to 723K were most effective in increasing reversible shape memory effect (RSM). While PE declined with increasing strain, strain below 1% was effective in enhancing ARSM. Moreover, heat treatment below 623K for a short time made RSM opposite.
(4) Thermal cycle was effective in enhancing ARSM because it increased shape change and hysteresis. Exposure above 473K induced abnormal ARSM.
