多孔Ni-Ti-Nb合金中相变应变有序度调控的阻尼行为及其微观机制研究

The outstanding damping capacity of porous Ni-Ti-Nb shape memory alloys dominated by their transformation behavior enable them to be promising candidates of intelligent damping materials of low density and high strength. As a significant feature of the phase transformation behavior, strain ordering plays an important role in tailoring the damping behavior of these alloys. However, the micro-mechanism and intrinsic essence of this phenomenon have not been clarified yet. This project will perform quantitative two dimensional microstructure characterization, three dimensional reconstruction and in-situ TEM study on the porous Ni-Ti-Nb alloys. Also, quantitative thermal and dynamic mechanical analyses will be combined. In this way, the typical structure characteristics of the porous Ni-Ti-Nb alloys will be revealed, which include the site-occupation of solid-soluted Nb and distribution of secondary particles, determined by the porosity and nominal composition of the alloys. The effect of the above atomic-micron scaled structure characteristics on the phase transformation strain ordering will be clarified. The micro-macro scaled dynamic evolution of phase transformation strain ordering and its influence on the damping behavior of the alloys under different thermo-mechanical loadings will be investigated. The micro-mechanism of the short-long range strain-ordered transformation evolution and the essential mechanism of the damping behavior tailored by this transformation strain order variation will be understood. It is expected that the above studies will promote the development of the theory of phase transformation and internal friction behavior in porous alloys, provide theoretical background for the modulation of the damping capacity of porous Ni-Ti-Nb alloys via controlling the fabrication process and phase transformation, and offer a theoretical guide for the design and property evaluation of porous Ni-Ti-Nb alloys towards a wide application in the future.

多孔Ni-Ti-Nb合金因其相变行为主导的高阻尼能力成为极具应用潜力的轻质高强智能阻尼材料。作为相变行为的重要特征，应变有序度对合金阻尼行为有关键调控作用，但尚不清楚微观机制和内在本质。本项目拟采用二维定量显微表征、三维重建和原位电子显微术等表征手段，结合定量热分析和动态力学分析结果，再现多孔Ni-Ti-Nb合金中由孔隙构造和成分因素主导的Nb元素固溶和原子占位及第二相析出等结构全貌，阐明以上原子-微米尺度结构对相变应变有序度的影响机制，探明不同热-力加载条件下多孔Ni-Ti-Nb合金相变应变有序度演化的宏微观动态演化过程及其对合金宏观阻尼行为的影响规律，掌握短程-长程应变有序相变演化的微观机制及其在合金阻尼行为调控中的本质机理，丰富和发展含孔隙记忆合金的相变及内耗理论，实现通过控制多孔Ni-Ti-Nb合金制备方式和相转变来调节合金阻尼能力，为其广泛应用提供材料设计和性能优化方面的理论。

多孔Ni-Ti-Nb形状记忆合金因其相变行为主导的高阻尼能力成为极具应用潜力的轻质高强智能阻尼材料。但目前尚不清楚马氏体相变行为对合金阻尼行为关键调控作用的微观机制和内在本质。本项目利用优化的梯度烧结法和造孔剂法，成功创制了成分和孔隙构造可控且具有高阻尼特性的轻质高强多孔Ni-Ti-Nb形状记忆合金，系统深入地研究了多孔Ni-Ti-Nb形状记忆合金由名义成分与烧结工艺决定的合金相组成、第二相分布和孔隙构造等关键微观结构特征对合金相变行为及其调控的阻尼性能的影响规律，掌握了通过对多孔Ni-Ti-Nb合金的成分和孔隙构造设计实现对其相变行为进行调控的规律，实现了多孔Ni-Ti-Nb形状记忆合金结构成分可控制备以及合金性能优化的目标，为多孔Ni-Ti-Nb合金材料的制备工艺优化提供了理论指导，为具有可控阻尼性能的含孔隙Ni-Ti基合金材料的设计提供了理论依据。此外，通过对合金NiTi基体中刚性和柔性析出相在合金阻尼性能中的贡献进行系统对比研究，并结合相场模拟和三维微观结构定量分析，获取第二相在合金NiTi基体中生长行为的关键定量参数，研究不同类型析出相对合金马氏体相变行为的影响，探明了合金热处理工艺对相变行为及其主导的阻尼性能的影响规律，对进一步理解Ni-Ti基形状记忆合金中的扩散相变和第二相生长行为提供了有力的理论支撑，丰富和发展了含孔隙的Ni-Ti基形状记忆合金的相变和内耗理论。在此基础上，通过对Ni-Ti基形状记忆合金基于马氏体相变失稳的功能疲劳行为的研究，掌握了合金的功能疲劳行为以评价其长期使用时的功能稳定性，阐明了合金功能疲劳的微观机制，为Ni-Ti基形状记忆合金提供切实可靠的功能疲劳行为理论依据和评估机制，并对拓展其在长周期服役领域的应用具有重要意义。