This paper presents an overview of the principles governing the formation of shape memory alloys (SMA) martensite in thin films SMA/Si composites and some examples. The transformation in these composites is constrained by the compatibility conditions at the martensite/austenite interface and as the martensite. Due to the difference of the thermal expansivities of the bimorph layers and due to the martensitic transformation in the active layer, internal stresses arise upon changing the temperature. These internal stresses together with the dual constraint determine the martensitic microstructure and, with it, the actuation characteristics of the bimorph. For tetragonal martensites bi- and uniaxial tensile and compressive stresses lead to larger or smaller hystereses. Details depend on the sign of the eigenstrain, c/a-1, and the texture of the film.

Date Published: 19 June 2000
PDF: 6 pages
Proc. SPIE 3984, Smart Structures and Materials 2000: Mathematics and Control in Smart Structures, (19 June 2000); doi: 10.1117/12.388789

Published in SPIE Proceedings Vol. 3984:
Smart Structures and Materials 2000: Mathematics and Control in Smart Structures
Vasundara V. Varadan, Editor(s)