Thin Film Shape Memory Alloys PDF Download

The production of thin film TiPdNi shape memory alloys (SMA) using ion beam assisted deposition (IBAD) is being studied as a way to increase the actuation frequencies and transformation temperatures of thin film SMA for micro-actuator applications. The capability to transmit extremely high forces along with a large stroke, large strain memory, and high corrosion resistance makes shape memory alloys prime candidates for use in micro-actuator applications. However, low actuation frequency (~1Hz at macro-scale), and low transition temperature (below 100°C) makes commercially available NiTi incompatible with applications in extreme environments. The transformation temperature and actuation frequency of shape memory alloys can be improved through the production of thin film TiPdNi. Through the substitution of Pd for Ni in equiatomic NiTi, the transformation temperature can be varied from approximately room temperature to 527°C. The composition that has received the most attention is Ti50Pd30Ni20 because of its transformation temperature of over 200°C. However, the shape memory effect of Ti50Pd30Ni20 is adversely affected by the low critical stress needed for slip at high temperatures, which results in unrecoverable strain. Age hardening or thermo-mechanical treatments such as cold rolling have been found to improve the critical stress for slip in bulk form SMA due to an increased density of dislocations. Precipitation hardening, as well as, ion bombardment, is expected to increase the high temperature properties in IBAD deposited Ti50Pd30Ni20 film SMA. Additionally, ion bombardment during deposition can be used to improve film properties such as morphology, density, stress level, crystallinity, as well as, limit defects. Due to the refined grain size, increased density, and reduced defects, IBAD is able to produce films of 1 micron or less, which will greatly reduces the SMA actuation time due to the increased surface area --to -- volume ratio. In t.