调控金属液态结构优化非晶合金的结构不均匀性及力学性能的研究

Due to their unique disordered atomic structures different with metallic crystalline alloys, bulk metallic glasses show many desirable properties. However, the application of bulk metallic glasses as engineering materials is severely restricted due to their room-temperature brittleness, which can be effectively improved by introducing microstructural inhomogeneities into the glassy matrix. In this project, both the structural and dynamical heterogeneities of Zr-based and CuZr-based superheated melts and undercooled liquids were investigated using the synchrotron X-ray diffractometer, the magnetic levitator, the high-temperature X-ray diffractometer, the high-temperature viscometer, and the dynamic mechanical analyzer. Based on the measured structural and dynamical information, the first principles molecular dynamics simulation was conducted to clarify microstructural evolutions of metallic liquids with decreasing temperature. Furthermore, when metallic liquids were stabilized to different liquid states, bulk metallic glasses will be fabricated using a clap-type rapid solidification device equipped in a magnetic levitation machine. Then the structures of the as-cast metallic glasses quenched from different liquid states were investigated using the synchrotron X-ray diffractometer, the high-resolution electron microscope, and the first principles molecular dynamics simulation in order to reveal their different heterogeneous structural features and then bring to light the genetic regularity between liquid and amorphous structures. Moreover, the mechanical properties of bulk metallic glasses quenched from different liquid states were measured in order to elucidate the correlation between deformation mechanism and heterogeneous amorphous structures. The present studies will improve our understanding about the formation of microstructural inhomogeneities in bulk metallic glasses, and provide guidance for the optimization of mechanical performation of bulk metallic glasses.

金属非晶合金因其异于晶态材料的无序结构呈现出许多优异的性能，但其室温脆性严重限制了其工程应用，通过在非晶合金中引入结构不均匀性可有效改善其力学性能。本项目拟以锆基和铜锆基非晶合金为研究对象，采用磁悬浮技术、同步辐射X射线衍射仪、高温X射线衍射仪、高温熔体粘度计和动态机械分析仪采集液态金属在过热和过冷状态下的结构和动力学不均匀性信息，结合第一性原理分子动力学模拟，解析不同温度下液态结构的演变规律；通过磁悬浮熔炼和拍掌式快速凝固一体设备制备保留了不同液态结构信息的非晶合金，结合高分辨电镜、同步辐射技术和分子动力学模拟手段揭示不同液态结构条件下制备出的非晶合金的结构不均匀性特征，阐明液态合金与非晶合金之间的结构遗传性规律；测量具有不同团簇结构的非晶合金的力学性能，探寻非晶结构不均匀性与塑性变形之间的内在联系，揭示其潜在的物理机制，为有效调控非晶合金中的结构不均匀性及其力学性能奠定理论基础。

金属非晶合金由于其优异的力学性能和物理化学性能而受到人们广泛关注，但其室温脆性等缺点极大的限制了非晶合金作为结构材料的广泛应用。 因此，有效提高金属非晶合金的室温塑性成为非晶研究领域中的热点之一。 本项目从调控金属液态结构优化非晶合金的结构不均匀性作为出发点，采用实验和模拟相结合的方法，研究了不同脆性的金属液体的结构特征和动力学特征的演变规律，进而通过控制降温和升温过程来调控其结构不均匀性，实现非晶合金的塑韧化，多角度阐明其室温变形机制。 第一，通过对弱脆性和强脆性的金属液体的深入研究，阐明其在凝固过程中的结构演变的异同及其液-液相变规律，揭示了拓扑短程有序结构和化学短程有序结构的重要作用。 第二，研究了不同合金成分的液态结构和非晶结构的演化过程，探究了非晶在结构弛豫和回春过程中结构不均匀性的变化规律，阐明了金属液体与非晶合金结构之间的内在联系。 第三，通过多重方法来调控非晶合金中不同尺度的结构不均匀性和动力学不均匀性，实现非晶合金室温塑性提高的目的。 第四，研究了不同非晶合金体系甚者复合材料体系在变形过程中不同结构不均匀性对剪切带萌生扩展的影响规律。 本项目的研究工作为深入理解金属液体与非晶合金之间的结构遗传性规律提供了有效支持，为开发新型高强高韧非晶合金材料提供了一种新的思路。