NiTiHf-Nb共晶合金延性及高温形状记忆性能协同调控微观机理研究

The NiTiHf alloys have important application potential in national defense technology and aerospace industry. However, both the ductility and high-temperature shape memory property were insufficient in the NiTiHf alloys, which have significantly restricted the development of NiTiHf alloys. To improve the ductility and high-temperature shape memory property simultaneously, we proposed an idea of introduce the concept of eutectic alloy into NiTiHf high-temperature shape memory alloys. More specifically, the ductility and high-temperature shape memory property will be simultaneously enhanced due to the soft phase and the interfacial strengthening of the lamellar eutectic structure. We succeeded in fabricating the NiTiHf-Nb eutectic high-temperature shape memory alloy with good ductility and high-temperature memory property by realizing nearly the above proposition. Based on that, we will further investigate: (1) effects of Ni/(Ti+Hf) ratio and Nb content on the morphology and distribution of eutectic structure in NiTiHf-Nb alloys; (2) effects of morphology and distribution of eutectic structure on the mechanical property and high-temperature shape memory property of NiTiHf-Nb alloys; (3) effects of thermo-mechanical treatment on the eutectic morphology and high-temperature shape memory property in NiTiHf-Nb eutectic alloys. The above research will not only lay foundation for the composition design and preparation technology of NiTiHf-Nb eutectic alloy to achieve excellent ductility and high-temperature shape memory property, but also develop a guideline for the simultaneous enhancement in the ductility and high-temperature shape memory property for other high-temperature shape memory alloys.

NiTiHf高温形状记忆合金在国防科技及航天航空领域具有重要应用潜力，但延性及高温记忆性能不足严重制约了其实际应用。针对如何同时提高NiTiHf合金延性和高温记忆性能的问题，本项目将共晶合金的理念引入NiTiHf合金中，提出基于共晶组织内软相提高延性及片层状共晶相界面强化基体提高记忆性能的构想，并通过初步制备NiTiHf-Nb共晶高温记忆合金验证了该构想的可行性。在此基础上，本项目拟研究不同Ni/(Ti+Hf)比值和Nb含量的匹配关系对NiTiHf-Nb合金共晶组织形态与分布的影响规律；研究共晶组织形态与分布对NiTiHf-Nb合金力学性能及高温记忆性能的影响机制；研究热机械处理对NiTiHf-Nb共晶合金共晶组织界面形态及记忆性能的影响机制。上述研究将为获得兼具优良延性及高温记忆性能的NiTiHf-Nb共晶合金成分设计及制备技术提供理论基础，而且为其它脆性高温记忆合金的研究提供新思路。

NiTiHf高温形状记忆合金在国防科技及航天航空领域具有重要应用潜力，但延性及高温记忆性能不足严重制约了其实际应用。针对如何同时提高NiTiHf合金延性和高温记忆性能的问题，本项目将共晶合金的理念引入NiTiHf合金中，提出了基于共晶组织内软相提高延性及片层状共晶相界面强化基体提高记忆性能的构想，并制备了NiTiHf-Nb共晶高温记忆合金验证该构想的可行性。在此基础上，本项目系统研究了不同Ni/(Ti+Hf)比值和Nb含量的匹配关系对NiTiHf-Nb合金共晶组织形态与分布的影响规律；研究了共晶组织形态与分布对NiTiHf-Nb合金力学性能及高温记忆性能的影响机制；研究了热机械处理对NiTiHf-Nb共晶合金共晶组织界面形态及记忆性能的影响机制。上述研究获得了如下结果：当Nb含量为15at.%时将获得共晶NiTiHf-Nb高温记忆合金，而Ni/(Ti+Hf)比值将进一步调控马氏体相变温度；在富Ni型NiTiHf-Nb合金中通过共晶反应引入的共格β-Nb相可有效促进应力诱发马氏体相变的产生，半共格β-Nb相有助于抑制裂纹在基体中的扩展，上述作用有助于提高合金的高温形状记忆效应以及加工性能；通过热机械处理进一步细化共晶组织形态，提高形状记忆性能，并且其形状记忆性能随着热机械处理次数的增加而逐渐增加。综上，本项目的研究结果为获得兼具优良延性及高温记忆性能的NiTiHf-Nb共晶合金成分设计及制备技术提供理论基础，而且为其它脆性高温记忆合金的研究提供新思路。