基于多重集束拉拔的镍钛形状记忆合金制备方法与机理

Ni-Ti shape memory alloy is considered to be the most superiority and potential intelligent structure material due to its shape memory effect, super elastic effect, and large recovery stress and strain combined strong shock resistance ability. Based on the requirement of intelligent structural material for morphing aircraft, a novel method of combined clustered drawing with the thermo-mechanical treatment was used for in-situ synthesis of high quality and fine grained Ni-Ti shape memory alloy. By using this method, negative effects of the impurity elements such as oxygen, nitrogen, carbon could be avoided; shape memory performance and mechanical properties of Ni-Ti alloy could be guaranteed. Meanwhile, the growth of grain formed through in-situ synthesis could be regulated and controlled by the dense microscopic interface caused by severe plastic deformation, thus, the grain could be refined, and the recovery stress and phase transition temperature could be increased. According to the theoretical and experimental research, the fine grain Ni-Ti shape memory alloy would be fabricated by in-situ synthesis through the control and optimization of clustered drawing and the thermo-mechanical treatment. The microstructure evolution law and the in situ synthesis mechanism would be explored, and the shape memory effect of Ni-Ti alloy would be evaluated. In order to predict, design and control performance of Ni-Ti alloy, the stress-strain-temperature relation during heat engine cycle would be studied. All these would set up a theoretical and technology foundation for its application in morphing aircraft.

镍钛形状记忆合金以其独特的形状记忆效应、超弹性效应、大的恢复应力和恢复应变以及抗冲击能力强等突出优点，被认为是最具优势和潜力的智能结构材料。针对变体飞行器对智能结构材料的需求，本项目提出集束拉拔和热机械处理技术相结合原位制备高品质细晶镍钛形状记忆合金，避免氧、氮、碳杂质元素的影响，保证镍钛合金的形状记忆性能和力学性能,同时依靠剧烈塑性变形产生的密集微观界面网络调控原位合成的晶粒生长，实现晶粒细化，提高镍钛合金的恢复应力和相变温度。本项目基于理论和试验研究，通过对集束拉拔和热处理制度的控制与优化，原位合成细晶镍钛形状记忆合金，探明其微观结构的演变规律以及原位合成机理，并评价镍钛合金的形状记忆效应，且通过对原位合成的镍钛合金热-机循环过程中的应力-应变-温度关系的研究，达到预测、设计和控制镍钛形状记忆合金性能的目的，为其在变体飞行器中的应用和发展奠定理论和技术基础。

针对变体飞行器对智能结构材料的需求，本项目提出了集束拉拔和热机械处理技术相结合原位制备高品质细晶镍钛形状记忆合金，避免氧、氮、碳杂质元素的影响，保证镍钛合金的形状记忆性能和力学性能,同时依靠剧烈塑性变形产生的密集微观界面网络调控原位合成的晶粒生长，实现晶粒细化，提高镍钛合金的回复应变。本项目基于理论和试验研究，通过对集束拉拔和热处理制度的控制与优化，在1000℃下保温4h原位合成了镍钛合金，其平均晶粒尺寸达到了0.93μm；通过扫描电镜(SEM)，能谱仪(EDS)、电子背散射衍射(EBSD)和X射线衍射(XRD)等微观分析手段探明了其微观结构的演变规律以及原位合成机理；对镍钛合金的形状记忆效应进行了评价，结果表明较传统材料提高了16.7%；对制备的镍钛合金开展了热-机循环过程中的应力-应变-温度关系的研究，达到了预测、设计和控制镍钛形状记忆合金性能的目的，为其在变体飞行器中的应用和发展奠定了理论和技术基础。