Microstructure and martensitic transformation characteristics of CoNiGa high temperature shape memory alloys
Microstructure and martensitic transformation characteristics of CoNiGa high temperature shape memory alloys
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DOI：
10.1016/j.actamat.2010.10.050
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发表时间：
2011-02
期刊：
影响因子：
9.4
通讯作者：
E. Doğan;I. Karaman;Y. Chumlyakov;Zhiping Luo
中科院分区：
文献类型：
--
作者：
E. Doğan;I. Karaman;Y. Chumlyakov;Zhiping Luo
研究了 Co46Ni27Ga27 和 Co44Ni26Ga30 高温形状记忆合金在铸态和热轧条件下的显微组织演变和马氏体转变特征随热处理的变化。选择热处理来引入单相、两相和三相结构，其中沉淀相不会发生马氏体转变。揭示了这些沉淀物以及相关的成分变化对热循环过程中转变温度、热滞后和微观结构演变的影响。研究发现，如果Ga含量恒定，马氏体起始温度与基体的价电子浓度(e/a)线性相关。对于给定的e/a，Ga含量越高，转变温度就越高。 γ'析出物的存在和γ相的体积分数对相变热滞后有很大影响。确定了具有窄滞后（<40°C）的最循环稳定的组合物。在这些组合物中，发现了可能由点缺陷介导的室温老化现象，该现象恢复了热循环时的转变温度变化。他们还在恒应力热循环实验中证明了可逆马氏体转变。然而，应设计它们的晶体结构以增加相变应变，并应减少延性 γ 相含量以提高循环可逆性。
Microstructural evolution and martensitic transformation characteristics of Co46Ni27Ga27and Co44Ni26Ga30high temperature shape memory alloys were investigated in as-cast and hot-rolled conditions as a function of heat treatment. Heat treatments were selected to introduce single-, two-, and three-phase structures, where the precipitate phases do not martensitically transform. The effects of these precipitates, and associated compositional changes, on transformation temperatures, thermal hysteresis, and microstructural evolution during thermal cycling, were revealed. It was found that martensite start temperature linearly depends on the valence electron concentration (e/a) of the matrix, if the Ga content is constant. For a given e/a, the higher the Ga content is, the higher the transformation temperatures become. The presence of γ′ precipitates and the volume fraction of γ phase were shown to have strong influence on transformation thermal hysteresis. The most cyclically stable compositions with narrow hysteresis (<40°C) were identified. In these compositions, a room-temperature aging phenomenon, possibly mediated by point defects, was discovered, which recovers the transformation temperature changes upon thermal cycling. They also demonstrate reversible martensitic transformation in constant-stress thermal cycling experiments. However, their crystallographic texture should be engineered to increase the transformation strain, and ductile γ-phase content should be reduced to improve cyclic reversibility.