Combined effects of work hardening and precipitation strengthening on the cyclic stability of TiNiPdCu-based high-temperature shape memory alloys

The combined effects of work hardening and precipitation strengthening were employed to improve the cyclic stability of TiNiPdCu-based high-temperature shape memory alloys. Annealing after cold deformation resulted in the formation of nano-scale TiPdCu and Ti2Pd precipitates, stable at high temperatures in Ti50Ni25−xPd25Cux alloys. The nano-scale precipitates were also observed to retard recovery/recrystallization processes at higher temperatures. It was found that the combined effects of work hardening and precipitation strengthening remarkably enhanced the high-temperature stability of the Ti50Ni20Pd25Cu5 alloy and increased its maximum working temperature range while keeping the transformation temperatures and recovery strains at sufficiently high levels. Precipitation strengthening helped to greatly improve the high-temperature cyclic stability of the alloy. Creep tests at 673 K under 500 MPa confirmed that the better high-temperature cyclic stability of the precipitate-containing alloy was mainly due to its higher creep resistance.