Anisotropy in microdevices produced by micromachining of cold-rolled NiTi sheets

The process of fabrication and characterisation of three types of NiTi microdevice are described: a double-beam cantilever of constant beam width and two designs of cantilever of stress-optimised width profile, with thicknesses ranging from 17 to 95 μm produced by cold rolling. The technology of electrolytic photoetching was used as a versatile tool for micromachining. The transformation behavior of the specimens was investigated by differential scanning calorimetry and electrical resistance measurements. Anisotropies caused by rolling-induced textures have been investigated by beam-bending experiments. Strong anisotropies were found in results on thickness-dependent Young’s modulus in the parent phase as well as in the beam-bending characteristics in the rhombohedral and martensitic phase. For beam directions transverse to the rolling direction, beam-bending experiments revealed a thickness dependence of hysteresis associated with the martensitic transformation, which was not observed in the rolling direction. Cantilevers with stress-optimised width profile display favorable beam-bending characteristics compared with cantilevers of constant beam width due to an optimum use of the shape memory effect.