The Structure Evolution, Phase Transformation And Shape Memory Behavior Of Shape Memory Alloy With Low Nb Content

At present, the ternary alloy of Ni47Ti44Nb9 is adopted as the typical shape memory alloy with wide hysteresis home and abroad both for basic application and engineering study. However, high cost blocks its extensive application. Since shape memory effect and wide hystersis of the Ni47Ti44Nb9 is derived from the base phase of Ni-Ti in the alloy, the study takes the components of the base phase as reference and discusses lowered cost shape memory alloy with wide hysteresis resulted by lowering Nb content (4.5%).The influence of Ni/Ti ratio variation on the structure evolution and phase transformation characteristics, dynamic behavior as well as the effects of transformation on the hysteresis and strain recovery rate of NiTiNb alloy with low Nb (4.5%) was studied systematically through TEM, X-rd, DSC, resistant-temperature measurement apparatus and tensile test under different temperature. The paper investigated the mechanism of the wide hysteresis in NiTiNb alloy either.It is found this alloy is consist of NiTi base phase, β -Nb phase and oxide phase. β -Nb phase will decrease with the increase of Ni/Ti ratio and β -Nb phase quantity is much lower than that in Ni47Ti44Nb9. The phase transformation process of the alloy with low Nb content is B2(?)B19 . The temperature of phase transformation of the alloy will decrease with the increase the Ni/Ti ratio.Through comparing the recovery rate of transformation, it can be found that contributing to the irreversibility of the plastic transformation of β -Nb phase, the recovery rate of NiTiNb with β -Nb phase couldn't reach100% with 4% strain was taken. While, Ni49.6Ti45.9Nb4.5 could recover completely less than 8%. Moreover, when the applied strain was less than 16%. Ni49.6Ti45.9Nb4.5 possessed better shape memory effect thanWith certain pre-deformation, NiTiNb with low Nb (4.5%) content possess wide transformation hysteresis. Whereas deformation can achieve similar effect in improving the stability of the reversible martensitic transformation in Ni49.6Ti45.9Nb4.5 and Ni47Ti44Nb9, β -Nb phase is supposed have little contribution in wide hysteresis effect of NiTiNb. That Nb dissolves solidly in NiTi base, which changes the dynamic characteristics of martensite, can be used to reason the wide hysteresis of NiTiNb.