NiTiNb形状记忆合金相变应力松弛机制与规律研究

It is not clear why the recovery stress in wide-hysteresis NiTiNb alloys exhibited a wide plateau existed during the process of heating and directly begun to drop upon cooling, instead of the increase due to thermal expansion. It is also not clear about the effects of changes in phase constitution and defects amount on the stress-induced martensitic transformation. In this research, we will investigate: effects of different volume fractions of phases and different amounts of defects on mechanical behavior of the NiTiNb alloys and their influencing mechanism as well as their relationship with stress-induced martensitic transformation; the thermodynamics and kinetics of martensitic phase with temperature and time and their relationship with recovery stress relaxation; the relaxation behavior and mechanism of the tightening stress of NiTiNb couplings in the system of coupling/connected pipe during the process of thermal cycling. This research will not only help us know and grasp the characteristics and mechanism of the recovery stress relaxation in the NiTiNb alloys, but also help us know the relationship between the stress-induced martensitic transformation in the NiTiNb and NiTi-based alloys with different microstructures more comprehensively. Based on this research, we will find the methods controlling stress relaxation. In addition. It will directly guide the design and preparation of fasters made from NiTiNb shape memory alloys and other ones.

为认识NiTiNb形状记忆合金相变应力松弛的规律和机制，针对目前的研究不能解释其加热过程中的回复应力存在一个宽的平台温度区间，冷却时随温度下降并没有由于热胀冷缩而增加的反常现象，相组成和缺陷数量的改变对应力诱发马氏体转变的影响规律和机制不清楚的问题，本项目拟研究不同的相组成和缺陷数量对合金力学行为的影响规律和机制，及其与应力作用下马氏体转变的关系；约束力条件下母相和残余马氏体相随时间和温度的演变热力学和动力学机理，及其与回复应力松弛的关系；以NiTiNb管接头/被连接管作为一个整体，研究紧固力冷热循环过程中的松弛行为和松弛机制。上述研究不仅能让我们认识和掌握NiTiNb合金回复应力松弛的规律和机制，而且能让我们更全面地认识NiTiNb和NiTi基合金应力诱发马氏体转变与微观组织形态的关系，找到控制应力松弛的途径和方法；同时研究结果能直接指导NiTiNb和其它形状记忆合金连接件的设计和制备。

宽滞后的NiTiNb形状记忆合金在机械连接密封上已获得了具体的应用，但目前的研究未解释加热过程中的回复应力存在一个宽的平台温度区间，冷却时没有由于热收缩而增加。针对上述问题，本项目系统研究了加热回复温度对NiTiNb合金加热及冷却过程中回复应力的影响规律；不同温度条件下，热循环对回复应力的影响规律；约束加热及冷却过程中回复应力的演变规律及对应的相组成变化；不同缺陷组态和相组成条件下，NiTiNb合金力学行为、记忆行为以及加热过程中所能达到的最高回复应力；以NiTiNb管接头/被连接管作为一个整体，通过有限元数值模拟仿真方法研究了NiTiNb合金管接头系统在装配过程中的力学行为以及装配完成后的应力松弛行为。取得了如下重要结果和关键数据： 1）明确了马氏体逆转变的不完全是NiTiNb合金冷却时回复应力不因热收缩而上升的原因；2）相较于增加NiTiNb合金的可回复变形量，提高母相基体的屈服强度对增加热产生的最大回复应力的更有效；3）不同加热温度对完全约束下冷热循环过程中合金回复应力的稳定性没有影响；4）提出了可室温储存的超低温服役NiTiNb合金的设计原则，并初步开发出了可在-150度超低温使用的Ni48Ti43Nb9合金；5）建立了NiTiNb管接头/被连接管系统的蠕变/松弛有限元模型，实现了将抱紧后的结构在指定温度下进行长时间的蠕变/松弛行为模拟。上述研究结果不仅有助于认识和掌握NiTiNb形状记忆合金相变应力松弛的规律和机制，而且研究结果能直接指导NiTiNb和其它形状记忆合金连接件的设计和制备。开发出的Ni48Ti43Nb9合金有望在超低温服役的新型战略武器及航空航天装置中获得应用。

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