30 March 2010 Processing and characterization of composite shape memory alloy (SMA) thin film structures for microactuators
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The high work to volume ratio and the stress recovery of Shape Memory Alloy (SMA) thin films with temperature makes them an ideal choice for microactuators. However, these materials have not gained widespread acceptance due to issues associated with phase transformation. Primary concerns are rapid change in stress at the transformation temperature giving the actuator a step function like response and a significant shift in transformation temperatures due to a wide hysteresis. In the present research, TiNiCu (53.59at%Ti, 39.05at%Ni), TiNi (50.32at%Ti) and TiNiHf (39.56at%Ti, 48.63at%Ni) composite SMA thin films that display close to linear stress temperature behavior (slope: 2-7 MPa/°C) with high stress recovery (300-550MPa), wide transformation range (60-130°C) and low hysteresis (10-30°C) were fabricated. Properties were achieved through the deposition of SMA thin films with varying composition in a layered (composite) format on Si wafers. The TiNi+TiNiCu composite exhibited a two-step transformation (slopes of 2.5 and 3.9 MPa/°C) without a significant impact on stress recovery. Displaying identical recovery stresses, the TiNiHf film possessed a 65°C transformation range and the TiNiHf+TiNi composite exhibited a wider range of 120°C. A strong correlation between deposition conditions, annealing parameters and transformation characteristics was observed for all the SMA films.
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Shiva K. Mandepudi, Harold D. Ackler, "Processing and characterization of composite shape memory alloy (SMA) thin film structures for microactuators", Proc. SPIE 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010, 76440N (30 March 2010); doi: 10.1117/12.848773; https://doi.org/10.1117/12.848773

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