Thermal expansion in various phases of Nitinol using TMA

Phase transformation in the near-equiatomic, cold-worked Nitinol, exhibiting shape memory effect, has been investigated through the study of thermal expansion by employing thermomechanical analyser (TMA). The characteristic transformation temperatures determined by this method are compared with those obtained through DSC thermograms. The reliability and sensitivity of the thermal expansion probe have been discussed. The variation of thermal expansion coefficient with temperature in different heat treated samples has been studied in the range 30-120 degrees C. Thermal expansion coefficient is found to be - ve during M<->A transformation and + ve in R<->A transformations. Thermal expansion coefficient in martensitic region in the presence and absence of R-phase has been determined. (C) 1999 Elsevier Science B.V. All rights reserved.