激光选区熔化NiTiHf高温形状记忆合金的基础研究

NiTiHf high temperature shape memory alloys, which could provide both sensing and actuation capabilities in the same components, are attracting increasing interest in the fields such as aero-engine and nuclear reactor, which require self-actuation components at high temperatures. However, it is quite challenging to fabricate complex NiTiHf alloy structures with multi-functionality via conventional approaches. In order to overcome the limitation of conventional fabrication methods, the fundamental research on selective laser melting of NiTiHf ternary alloys will be conducted in this work. The characteristics of metallurgical defects and the evolution of microstructure during laser rapid melting/solidification will be investigated first. Afterwards, the response of martensitic phase transformation behavior, mechanical and functional properties of NiTiHf alloys with respect to the microstructure will be studied. As a result, the interrelationship between selective laser melting process, microstructure and the functional properties of NiTiHf alloys could be established. Consequently, it is able to fabricate NiTiHf alloys with comparable mechanical and functional properties as those fabricated by conventional methods, and to develop an approach to tailor the phase transformation temperatures of NiTiHf alloys by modifying the selective laser melting process parameters. Through this project, we will be able to fabricated complex NiTiHf structures by selective laser melting. Meanwhile, the multi-functional and programmable NiTiHf smart structure could be fabricated through tailoring the phase transformation temperature at different positions. The results of this work has great significance on promoting the application of NiTiHf high temperature shape memory alloys, especially in the field of aerospace and military industry.

NiTiHf高温形状记忆合金是一种集传感与驱动为一体的智能材料，在航空发动机、核反应堆等高温场合具有良好的应用前景。然而，采用传统方法制备的NiTiHf合金构件通常结构简单、功能单一，严重限制了NiTiHf合金的推广应用。针对上述问题，本课题拟开展激光选区熔化NiTiHf合金控形控性的基础研究。通过研究激光快速熔化/凝固条件下NiTiHf合金冶金缺陷特征及组织演化规律，揭示NiTiHf合金马氏体相变行为、力学性能及功能特性对快速熔化/凝固组织的响应特征，建立“激光选区熔化—显微组织—功能特性”之间的关系，制备具有良好力学性能的NiTiHf合金，同时实现对NiTiHf合金相变温度的有效调控。本项目的完成可解决NiTiHf合金加工难题，同时制备具有多动作、可编程变形特征的NiTiHf合金智能构件，对NiTiHf高温形状记忆合金的推广应用，以及我国航空航天、军事工业等领域的发展具有重要推动意义。

激光增材制造是解决传统NiTiHf高温形状记忆合金构件结构简单、功能单一等瓶颈难题的理想方法。本项目针对激光选区熔化NiTiHf合金控形控性关键问题开展攻关，研究了工艺参数对NiTiHf合金冶金缺陷、显微组织、马氏体相变行为以及力学性能的影响规律及机理，建立了“成分—工艺—组织—性能”之间的关系。研究了NiTiHf合金相变行为随激光功率、扫描速度等的演化规律，通过大范围改变激光选区熔化工艺参数实现了对NiTiHf合金相变温度的有效调控。研究了层间开裂、裂纹以及气孔等缺陷随激光选区熔化工艺参数的演化规律，发现仅通过工艺参数优化难以消除热裂纹等缺陷。利用机械混合方法添加Nb元素，通过增材制造原位冶金，极大改善了NiTiHf合金的工艺适应性，获得了致密的NiTiHf合金，提升了其力学性能，并结合后续热处理获得了延伸率>4%的NiTiHf合金。研究结果为制备复杂NiTiHf合金智能构件提供了基础，能够促进高温形状记忆合金构件在航空航天等领域的应用。研究结果也可为增材制造原位冶金解决其他合金体系热裂问题提供新思路。

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