Functionalities of Ni–Ti Shape Memory Alloys and Their Efficiency as Event Actuators of Microelectromechanical Systems

Abstract

The functionalities of Ni–Ti alloys subjected to different deformation treatments are studied. A critical stress corresponding to the onset of degradation of the functional properties were determined; it was found that this stress is about twice as low as the yield stress. The efficiency coefficients of virtual thermodynamic machines with a working body made of the investigated materials were calculated and compared with the efficiency of a Carnot engine based on the same materials; the ideality factor has been calculated under the condition of actuating at stresses no higher than critical ones. It has been established that, at the single actuation, the highest ideality factor (9.7%) is characteristic of a material consisting of bars 20 to 5 mm in diameter obtained by warm forging at 350°C. It has been determined that, at discontinuous operation under stresses lower than the critical ones by a factor of 1.2, the ideality factor is 7.4–7.7% for alloys subjected to hot forging or equal channel angular pressing combined with warm forging.