Control of R-Phase Transformation in a Ti-50.8at.%Ni Shape Memory Alloy

A Ti-50.8at.%Ni alloy was heat treated at different conditions. The evolution of transformation behavior with respect to the ageing time was investigated using a differential scanning calorimeter (DSC). The thermal-induced martensite transformation is successfully suppressed in the sample aged for 4 hours or longer, leaving only R-phase transformation detected in the temperature range from -150°C to 150°C. The Rs temperature rapidly increases from 6°C to 27°C with the increase of aging time from 4 hour to 24 hours, and further increases to 33°C with increase of ageing time to 210 hours. The latent heat associated with B2→R transformation in the sample aged for 4 hours is 4.3J/g. The latent heat varies from 5.4J/g to 5.7J/g with increase of ageing time from 8 hours to 210 hours, while the Rs temperature increases from 17°C to 33°C with increase of ageing time from 8 hours to 210 hours. Results about the influence of this ageing treatment on the work output and two way shape memory effect associated with the R-phase transformation will be discussed.