Shape memory microactuation design by substrate's reinforcement layers

The use of a reinforcing non-transforming layer, deposited on one or on the other side of the substrate of shape memory-based microactuators, as an additional way to control the thermoelastic stress in the active material film is analyzed. A model developed in this view shows that, depending on the position of the reinforcing layer, a substantial change may result in the deflection vs. temperature relationship. Experimental data for cantilevers consisting of NiTi films deposited on Si substrates show a positive effect (an enhancement of the actuation) of a Ni reinforcing layer deposited on the opposite side of the substrate, compared to a reference NiTi bimorph actuator with the film of the same composition deposited on a non-reinforced Si substrate. On the contrary, when deposited as intermediate layer between the substrate and the NiTi shape memory alloy film, the same Ni layer only causes a limitation of the actuation potential. A model embedding the thermal evolution of the martensite volume fraction was proposed to describe or to predict the actuation (deflection) of such cantilevers. (C) 2016 Elsevier Ltd. All rights reserved.