Effect of Deformation and Thermal Treatment of NiTi Alloy on Transition Sequence

Abstract

Transformation sequences in a NiTi shape memory alloy after deformation and subsequent annealing were studied using various methods. Low temperature annealing of the deformed alloy caused that the R-phase preceeded the martensitic transformation. The R-phase formation during both cooling and heating depends strongly on the deformation degree and temperature of annealing. On DTA curves an additional peak in the martensitic transformation range was observed for specimens annealed at 500 and 550°C. It is suggested that this peak was caused by presence of dislocation cell structure and subgrains whose boundaries interact with growing martensite plate.