【作者】 孙康；

【导师】 王刚；

【作者基本信息】 上海大学 ， 材料科学与工程， 2021， 博士

【摘要】 非晶合金,又被称为“金属玻璃”,是液态金属以极快的速度被冷却时,结晶被抑制,通过玻璃转变过程获得的固体材料。在微观结构上,非晶合金无晶体材料中的晶界、位错等缺陷,原子排列表现为长程无序而短程有序。其微观结构的有序化程度通常借用“自由体积”的概念得以描述或者利用分子动力学模拟的方式得以表现。非晶合金的性能在很大程度上会受到自由体积含量与分布的影响。由此可见,寻找有效调控非晶合金内部微观结构的方法将对改善与提高其宏观性能具有重要的意义。本文通过不同的处理手段对锆基非晶合金的微观结构进行调控,并对不同状态的非晶合金样品进行宏观性能测试,借助球差校正透射电镜与高能同步辐射技术手段表征不同环境条件对非晶合金原子结构及演化过程造成的影响,以此建立结构与性能的联系。本论文的研究结果旨在为认识、理解及调控非晶合金微观结构提供更多的理论依据,主要内容如下:利用液氮作为制冷剂,对Zr₅₅Cu₃₀Ni₅Al₁₀非晶合金进行超低温深冷处理。通过对铸态锆基非晶合金样品实施不同时长的浸泡,实现从材料表面深入其内部的整体改性。借助X射线衍射技术及高分辨透射电镜系统地研究非晶合金原子结构受深冷时长的影响。通过室温力学性能测试,分析锆基非晶合金宏观力学性能与深冷处理时间之间的关联。利用高能同步辐射技术手段,认识与理解锆基非晶合金内部原子结构在液氮温区下的结构演化过程,以此建立锆基非晶合金微观结构与宏观性能之间的关联。利用快速退火设备对Zr₆₁Cu₂₅Al₁₂Ti₂非晶合金实施不同温度条件的热处理,获得了不同能量状态的锆基非晶合金样品。利用热力学手段分析合金内部自由体积含量受纯热作用的影响。对比室温条件下不同能量状态样品的力学性能,分析结构的变化对宏观性能带来的影响。利用球差校正透射电镜配合自相关函数分析方法,定性与定量地研究退火温度与非晶合金纳米尺度有序结构的关联。利用高能同步辐射X射线光源,分析快速退火温度的变化对非晶合金内部短程有序结构与中程有序结构的影响,探讨原子尺度上有序度的变化。由于非晶合金是液态金属通过急冷方式凝固得到的,其结构特征与合金熔体具有一定的相似性。通过对Zr₆₁Cu₂₅Al₁₂Ti₂及Zr₄₆Cu₄₆Al₈两种不同成分的锆基非晶合金体系进行原位电磁悬浮实验,获得了锆基非晶合金体系在过热态及过冷态的结构信息,揭示了过热度与过冷度之间存在的关联。通过分析合金熔体结构随温度变化的过程,认识了合金熔体的固有结构及性质。通过对合金熔体过热态和过冷态的原子结构演化分析,发现了类二十面体团簇作为非晶合金的基本单元结构,也存在于其熔体结构中。本章内容对理解合金熔体结构、认识与研究非晶合金的结构起源具有深远的意义。借助新设备新技术手段:电磁悬浮熔炼设备,获得了不同深过冷程度的Zr₆₁Cu₂₅Al₁₂Ti₂非晶合金样品。通过对不同深过冷程度的锆基非晶合金样品结构及热力学表征,揭示了锆基非晶合金的微观结构与深过冷程度的内在联系。利用硬度测试分析方法,从宏观角度表征深过冷程度对锆基非晶合金性能的影响。借助高速摄影机捕捉锆基非晶合金的深过冷快速凝固过程。利用同步辐射衍射技术获取锆基非晶合金原子结构随深过冷程度的演化规律。更多还原

【Abstract】 When a metallic liquid is cooled sufficiently fast,its crystallization can be avoided,i.e.,a supercooled liquid transforms into a solid via the glass transition.Such a solid is termed as amorphous alloy,which is also known as metallic glass（MG）.It shows long-range disordering and short-range ordering in the microstructure without any crystal-like defects,e.g.,grain boundaries and dislocations.The degree of structural ordering proceeded during cooling is often described in terms of free volume,and occasionally characterized by molecular dynamics simulations.The mechanical performance of MGs is strongly affected by the variations of the local structure,i.e.,the amount and the distribution of free volume.In this case,it is vital to develop methods that are capable of modifying the local structure in order to improve the macroscopic deformation behavior of MGs.In this work,we tried various processing methods to tailor the microstructure of MGs and applied macroscopic measurements for alloys after different treatments.The characterization of internal structures and the evolution of atomic structures were achieved by means of high-resolution transmission electron microscope and high energy X-ray synchrotron radiation in order to establish the relationship between the microstructure and macroscopic properties.The results of this thesis aim to provide more theoretical evidences for deeply understanding the nature of MGs.The research contents are shown as follows:The liquid nitrogen is induced as a refrigerant for the cryogenic treatment.Zr₅₅Cu₃₀Ni₅Al₁₀MGs are subjected for immersing with different durations in order to achieve an overall modification of materials from outside to inside.The influence on the microstructure of MGs under different cryogenic conditions is systematically studied with the aid of X-ray diffraction technology and high-resolution transmission electron microscopy（HRTEM）.The alteration of mechanical properties after distinct immersion times is analyzed via room temperature compression tests.The structural evolution at low temperatures is studied by means of high-energy X-ray synchrotron radiation technology so as to establish the relationship between the microstructure and macroscopic properties of MGs.Zr₆₁Cu₂₅Al₁₂Ti₂ MG is selected for the flash-annealing treatment under various conditions in order to obtain samples with different energy states.The influence from pure heating on the internal structure of MGs is analyzed by thermodynamic measurements.The mechanical differences of MGs flash-annealed at distinct temperatures are also displayed and discussed.The alteration of microstructures on nano-scale is characterized by a spherical aberration corrected coefficient（Cs）-corrected HRTEM combining the autocorrelation function（ACF）analysis.The variation of microstructures on atomic scale including the short-range ordering（SRO）and the medium-range ordering（MRO）induced by flash-annealing is studied by high-energy X-ray synchrotron radiation.Since MGs are also known as liquid metals,their structural characteristics are similar to those of the liquid.The structural information of two amorphous systems,i.e.,Zr₆₁Cu₂₅Al₁₂Ti₂and Zr₄₆Cu₄₆Al₈,during overheating and undercooling is obtained by conducting in-situ electromagnetic levitation（EML）experiments.The relationship between overheating and undercooling is discussed.In addition,the inherent structure and property of metallic melts are initially understood.By means of in-situ diffraction results,the icosahedral-like cluster,which is the basic unit in MGs,is found to be existed in its metallic melt as well.The content of this chapter plays a significant role for understanding the liquid structure,also the origin of the structure of MGs.With the help of the new equipment and the new technology:EML,Zr₆₁Cu₂₅Al₁₂Ti₂ MGs with different degrees of the undercooling are obtained.By means of structural and thermodynamic characterizations,the intrinsic relationship between the microstructure and degrees of the undercooling is revealed.The influence of the deep undercooling on the mechanical property of MGs is characterized from a macroscopic perspective.The solidification process of MGs is captured by a high-speed camera.The evolution of atomic structures with different undercooling degrees is analyzed by high-energy X-ray synchrotron radiation.更多还原