NiTiNb shape memory alloys have attracted much attention in pipe coupling or sealing system because of their large transformation hysteresis upon a proper pre-deformation. In order to clarify the effects of adding Nb ...NiTiNb shape memory alloys have attracted much attention in pipe coupling or sealing system because of their large transformation hysteresis upon a proper pre-deformation. In order to clarify the effects of adding Nb on the mechanical properties as well as the transformation behavior of NiTiNb shape memory alloys, Ni47Ti44Nb9 and Ni49.8Ti45.2Nb5 alloys with different microstructures but with similar martensitic transformation start temperature, are prepared. Comparative studies on the microstructures, mechanical proPerties and transformation characteristics are conducted by means of scanning electron microscopy （SEM）, phase transformation measurements and mechanical property tests. It is found that Nia7Ti44Nb9 and Ni49.8Ti45.2Nb5 alloys possess similar transformation hysteresis in the as-annealed state. However, the presence of Nb and its status exerts important effects on the mechanical properties, especially the yield strength and the yield behavior of the alloys. Ni49.8Ti45.2Nb5 alloy exhibits remarkable increase in the yield strength than the Ni47Ti44Nb9 alloy. The transformation hysteresis of both alloys under pre-deformation is characterized and the relative mechanism is discussed.展开更多
Two near single-phase NiTiNb alloys--NisoTi4sNb2 and Ni49.5Ti46.5Nb4-are prepared and studied by means of scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, differential scanning calorimetry...Two near single-phase NiTiNb alloys--NisoTi4sNb2 and Ni49.5Ti46.5Nb4-are prepared and studied by means of scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, differential scanning calorimetry （DSC） and tensile tests in order to unearth the effects of Nb-atom solid solution in NiTi phase on the yield strength induced by self-accommodation of martensite variants. The results show that the yield strength of near single-phase NiTiNb alloys varies inversely with the amount of Nb-atoms solid-dissolved in NiTi phase. From the results out of the prior and current studies, it can be surmised that the effects of Nb content on the yield strength of NiTiNb alloys in martensite state depend on the coaction. Nb solid solution weakening mechanism and β-Nb phase composite strengthening mechanism. This inference might be a satisfactory explanation to the fact that the yield strength of （NiTi）50-0.5xNbx alloys in martensite state begins with decline and then rises when the Nb content increases.展开更多
The transformation hysteresis and stability of strain martensite in Ni_(47)Ti_(44)Nb_ alloy have been studied by means of tensile tests at various temperatures and electrical resistance measurements as well as TEM obs...The transformation hysteresis and stability of strain martensite in Ni_(47)Ti_(44)Nb_ alloy have been studied by means of tensile tests at various temperatures and electrical resistance measurements as well as TEM observations.It was shown that there is a characteristic deformation temperature and a strain range,in which the critical yield stress for stress-in- duced transformation acquires optimum matching with the yield strength of the β-Nb parti- cles.In this case,deformatian can effectively increase the transformation hysteresis,while the strain recovery ratio remains usefully high.The martensite with irreguldar fine.twin substructure and martensite containing some dislocations as well as martensite intersected by the β-Nb particles possess high stability.展开更多
采用Nd:YAG脉冲激光器实现了200μm厚热轧态Ni Ti Nb形状记忆合金的激光焊接,研究激光平均功率、激光脉宽和激光频率等主要工艺参数对焊接接头形貌的影响,分析了焊缝热影响区显微组织、力学性能的变化规律。结果表明:激光平均功率、激...采用Nd:YAG脉冲激光器实现了200μm厚热轧态Ni Ti Nb形状记忆合金的激光焊接,研究激光平均功率、激光脉宽和激光频率等主要工艺参数对焊接接头形貌的影响,分析了焊缝热影响区显微组织、力学性能的变化规律。结果表明:激光平均功率、激光脉宽和激光频率需要良好匹配才能获得较好性能的焊接接头。当激光平均功率为16.8 W、激光脉宽为4.5 ms、激光频率为4.5 Hz时,焊缝的抗拉强度最高,达到母材的95%。随着激光平均功率、激光脉宽的增加,焊缝热影响区的宽度先增加后减小。激光频率增加后,热影响区晶粒变粗。当频率为27Hz时,在靠近热影响区的焊缝出现了一个粗大树枝晶区域。母材断口的韧窝大而深,为典型的韧性断裂。焊缝断口的韧窝小而浅,呈鱼卵形。热影响区的显微硬度高于母材的,低于焊缝中心区域的。展开更多
基金Foundation items： National Natural Science Foundation of China （50971009） National High-Tech Research and Development Program of China （2006 AA03Z102） Aeronautical Science Foundation of China （2009ZF51059）
文摘NiTiNb shape memory alloys have attracted much attention in pipe coupling or sealing system because of their large transformation hysteresis upon a proper pre-deformation. In order to clarify the effects of adding Nb on the mechanical properties as well as the transformation behavior of NiTiNb shape memory alloys, Ni47Ti44Nb9 and Ni49.8Ti45.2Nb5 alloys with different microstructures but with similar martensitic transformation start temperature, are prepared. Comparative studies on the microstructures, mechanical proPerties and transformation characteristics are conducted by means of scanning electron microscopy （SEM）, phase transformation measurements and mechanical property tests. It is found that Nia7Ti44Nb9 and Ni49.8Ti45.2Nb5 alloys possess similar transformation hysteresis in the as-annealed state. However, the presence of Nb and its status exerts important effects on the mechanical properties, especially the yield strength and the yield behavior of the alloys. Ni49.8Ti45.2Nb5 alloy exhibits remarkable increase in the yield strength than the Ni47Ti44Nb9 alloy. The transformation hysteresis of both alloys under pre-deformation is characterized and the relative mechanism is discussed.
基金National Natural Science Foundation of China （50971009） Science Fund for Creative Research Groups （50921003） Aviation Science Foundation of China （2009ZF51059）
文摘Two near single-phase NiTiNb alloys--NisoTi4sNb2 and Ni49.5Ti46.5Nb4-are prepared and studied by means of scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, differential scanning calorimetry （DSC） and tensile tests in order to unearth the effects of Nb-atom solid solution in NiTi phase on the yield strength induced by self-accommodation of martensite variants. The results show that the yield strength of near single-phase NiTiNb alloys varies inversely with the amount of Nb-atoms solid-dissolved in NiTi phase. From the results out of the prior and current studies, it can be surmised that the effects of Nb content on the yield strength of NiTiNb alloys in martensite state depend on the coaction. Nb solid solution weakening mechanism and β-Nb phase composite strengthening mechanism. This inference might be a satisfactory explanation to the fact that the yield strength of （NiTi）50-0.5xNbx alloys in martensite state begins with decline and then rises when the Nb content increases.
文摘The transformation hysteresis and stability of strain martensite in Ni_(47)Ti_(44)Nb_ alloy have been studied by means of tensile tests at various temperatures and electrical resistance measurements as well as TEM observations.It was shown that there is a characteristic deformation temperature and a strain range,in which the critical yield stress for stress-in- duced transformation acquires optimum matching with the yield strength of the β-Nb parti- cles.In this case,deformatian can effectively increase the transformation hysteresis,while the strain recovery ratio remains usefully high.The martensite with irreguldar fine.twin substructure and martensite containing some dislocations as well as martensite intersected by the β-Nb particles possess high stability.
