a b s t r a c tFeMnAlNi shape memory alloys were recently discovered to have a small temperature dependence of the superelastic critical stress in a large superelastic temperature window from À196°C to 240°C. In this work, we investigated the effect of B2 nanoprecipitates on the superelastic characteristics of [1 0 0] oriented Fe 43.5 Mn 34 Al 15 Ni 7.5 single crystals under compression, and found that the size, volume fraction and composition of precipitates strongly influence the transformation temperature, superelastic strain, critical stress for stress-induced martensitic transformation and stress hysteresis of the single crystals. The single crystals aged at 200°C for 3 h show 7.2% superelastic strain with the precipitate size of about 6-10 nm. Longer aging times or higher aging temperature reduces superelastic recovery due to the coarsening of the precipitates.

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The effects of crystal orientation on the tensile superelastic response of the Fe 43.5 Mn 34 Al 15 Ni 7.5 single crystalline shape memory alloy, oriented along the <100> and <123> directions were investigated. The single crystals aged at 200°C for 3 hours demonstrated superelastic strains of 3.6% along the <100> orientation and 7.8% along the <123> orientation. Although the theoretical transformation strain in the <100> orientation is higher than that in the <123> orientation, the <123> oriented single crystals demonstrate better superelastic recovery in tension due to higher number of active martensite variants, which promotes better accommodation of internal strains and help minimize defect formation during transformation.

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