Research on multi-mechanism collaborative optimization of mechanical and functional properties of NiTiNb shape memory alloys

In order to investigate the microstructure influence mechanism of NiTiNb shape memory alloys on the mechanical property and functional stability, various amounts of rolling deformation (30 %, 65 %, and 80 %) was designed to obtain different microstructures characterized by grain sizes, dislocation density, precipitates distribution, and deformation texture types, respectively. Multiple microscopic mechanisms, especially the synergistic relationships that improve the mechanical and functional properties of NiTiNb alloys, were explored via XRD, SEM, EBSD, TEM, STEM and DSC. The results indicate that compared to the as-cast state, the phase transformation temperature hysteresis, mechanical property, and shape memory effect of the hot-rolled NiTiNb alloy are markedly improved with an increase at least 20 %, after a severe rolling deformation of 80 %. The increase of the wide thermal hysteresis of the NiTiNb alloy is primarily attributed to the elastic strain relaxation of the martensite interface, which is influenced by the β-Nb phase. This relaxation reduces the driving force of the martensite reverse transformation and enhances the martensite stability. The favorable mechanical property is due to the obvious grain refinement and the substantial increase in dislocation density that introduced by rolling deformation. Additionally, the rolling deformation facilitates the precipitation of the β-Nb phases and promotes the fragmentation and spheroidization of the NiTi (Nb) eutectic structure. The notable enhancement of the shape memory effect is derived from the microstructure refinement and β-Nb spheroidization, as well as the density reduction of the deformation texture orientation and the evolution of the 〈111〉 texture. The above research shows that the excellent performances of NiTiNb alloys arise from the synergistic effects of multiple mechanisms. All the findings will offer a scientific foundation for the development of NiTiNb shape memory alloys, which exhibit outstanding comprehensive properties in aerospace fields.