Differential scanning calorimetry of superelastic Nitinol for tunable cymbal transducers

Recent research has shown that estimations of the transformation temperatures of superelastic Nitinol using differential scanning calorimetry can be inaccurate, in part, due to the residual stress in the material. Superelastic Nitinol is selected as the end-cap material in a tunable cymbal transducer. The differential scanning calorimetry accuracy is initially probed by comparing transformation temperature measurements of cold-worked superelastic Nitinol with the same material after an annealing heat treatment, administered to relieve stresses from fabrication. The accuracy is further investigated through a study of the vibration response of the cymbal transducer, using electrical impedance measurements and laser Doppler vibrometry to demonstrate that the change in resonant frequencies can be correlated with the transformation temperatures of the Nitinol measured using differential scanning calorimetry. The results demonstrate that differential scanning calorimetry must be used with caution for superelastic Nitinol, and that an annealing heat treatment can allow subsequent use of differential scanning calorimetry to provide accurate transformation temperature data.