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采用真空感应法制备高铌含量Ni47Ti44Nb9形状记忆合金,结合差示扫描量热法、金相显微镜、扫描电镜,探索了热处理制度对马氏体相变温度的影响。结果表明,Ni47Ti44Nb9合金在300℃以前或400℃以后处理,相变温度As、Af、Ms、Mf变化很小,而在300～400℃处理,相变温度As、Af、Ms、Mf呈近似线性上升,即300～400℃是Ni47Ti44Nb9合金相变温度调节工艺敏感温度区间。相变焓的变化与马氏体转变开始温度Ms呈相反趋势,即Ms随热处理温度的升高而递增,相变焓则呈递减趋势。组织分析表明,在300～400℃进行处理,由于发生了动态再结晶,所以马氏体相变及其逆相变温度发生明显变化。因而,300～400℃的特征相变处理温度区间对Ni47Ti44Nb9合金的加工、热处理具有重要的意义。
Ni47Ti44Nb9 shape memory alloy with high niobium content was prepared by vacuum induction method. The effects of heat treatment on martensitic transformation temperature were explored by differential scanning calorimetry, optical microscope and scanning electron microscope. The results show that Ni47Ti44Nb9 alloy treated before 300 ℃ or after 400 ℃, the transformation temperature As, Af, Ms, Mf little change, while at 300 ~ 400 ℃, the phase transition temperature As, Af, Ms, Mf was approximately linear Rise, that is 300 ~ 400 ℃ is Ni47Ti44Nb9 alloy phase transition temperature adjustment process sensitive temperature range. The change of phase transition enthalpy is opposite to that of martensite transformation onset temperature Ms, ie Ms increases gradually with the increase of heat treatment temperature, while the enthalpy of phase transformation shows a decreasing trend. Tissue analysis shows that the martensite transformation and its reverse transformation temperature change significantly due to the dynamic recrystallization at 300-400 ℃. Therefore, the characteristic phase transition temperature range of 300-400 ℃ is of great significance to the processing and heat treatment of Ni47Ti44Nb9 alloy.