Influence of incorporated nanoparticles on superelastic behavior of shape memory alloys

The internal elastic strain resulting from an ensemble of nanoparticles in the crystal lattice of a shape memory alloy (SMA) is introduced as a key parameter into a quantitative theory of superelastic behaviour of SMA-nanoparticle composites. Experimental stress-strain loops obtained for a Co-Ni-Ga-nanoparticle system are analysed and a good agreement between the experimental and theoretical results is demonstrated. It is shown that even small (approximate to 10(-3)) internal strains can lead to profound differences in stress-strain response between SMA-nanoparticle composites and "particle-free" SMA. The internal strains can enlarge the attainable value of superelastic strain, will strengthen the crystal lattice of the SMA and can give rise to high-temperature superelasticity of SMA-nanoparticle composites. The theory predicts that the larger the volume change is during the MT, the more pronounced is the influence of the nanoparticles on the superelastic behaviour of SMA.