摘要：研究报道，金属玻璃的表面具有与内部截然不同的原子排列方式和驰豫模式，从而在结晶过程中会体现截然不同的动力学。玻璃转变温度以上，表面和内部的原子动力学相当，而玻璃转变温度以下，由于表面原子的超快动力学，会形成类超点阵结构，其形成机制尚缺少有力的实验证明。最近研究发现，Pd41.25Ni41.25P17.5金属玻璃在玻璃转变温度以上一定温度区间的结晶的产物也为类超点阵结构，其生长机制为二维形核生长模式。本论文的目的在于揭示Pd41.25Ni41.25P17.5金属玻璃在玻璃转变温度上下表面和内部结晶动力学的差异，为探明表面类超点阵结构的形成机制提供实验参考。

  本论文首先通过氧化硼熔融包覆法制备得到Pd41.25Ni41.25P17.5金属玻璃，随后将块状金属玻璃样品原位冷却至玻璃转变点以上和以下不同温度处进行等温退火，使样品表面和内部结晶化。利用扫描电子显微镜(Scanning Electron Microscopy, SEM)、能量色散谱(Energy dispersion spectroscopy，EDS)以及X射线衍射(X-ray Diffraction，XRD)检测样品表面和内部结晶产物的形貌核结构，以揭示表面和内部结晶动力学的差异。结果表明，在玻璃转变温度以上不同温度处退火，玻璃内部的晶化动力学比表面快，表面为由外向内的单向形核长大机制，而内部结晶机制为，Tc温度(340°C)以下，表现为缓慢生长的共晶形核长大机制，Tc温度以上(350°C)结晶产物为类超点阵纳米析出物，接近Tx(380°C)结晶产物为类超点阵纳米析出物和共晶形核长大相结合的模式。在玻璃转变温度以下(295°C)长时间(100小时)保温，玻璃内部几乎没有结晶析出物，而表面体现为较快的结晶动力学，模式仍然为由外向内的形核长大机制。

关键词: 钯镍磷金属玻璃；超晶格；表面结晶；内部结晶

毕业设计说明书外文摘要

Title Electron Microscopy Study of the Surface Crystallization in Palladium-based Bulk Metallic Glasses                                                      

Abstract：It is reported that the surface part of metallic glasses (MGs) has different atomic arrangements and relaxation behaviors when compared to the inside part of the MGs. So the crystallization on the surface would reflect unique dynamics. There are differences of atomic dynamics on the surface or inside the MGs at a temperature above and below glass transition. Reference studies show that, due to the ultra-fast kinetics of surface atoms, the surface will form a superlattice-like structure under thermal annealing at a temperature below the glass transition temperature. There is no strong experimental evidence to explain the formation mechanism of superlattice-like crystals .Recent studies have found that Pd41.25Ni41.25P17.5MGs may crystallize to be superlattice-like when annealing the samples at a temperature just below the crystallization temperature, The mechanism has been proposed to be a two-dimensional nucleation growth mode. The purpose of this paper is to reveal the difference of surface and internal crystallization kinetics of Pd41.25Ni41.25P17.5 MGs below and above glass transition temperature, and to provide experimental reference for the formation mechanism of superlattice-like structure.

In this paper, Pd41.25Ni41.25P17.5 metal glass was prepared by fluxing techniques, which use boron oxide as the fluxing agent. Then, the bulk metallic glass samples were in-situ cooled to target temperatures for isothermal annealing. So differences for the surface and internal crystallization could be revealed. X-ray Diffraction (XRD) was used to detect the atomic structure of the samples. The morphology of the crystalline products developed during the thermal annealing has been observed by Scanning Electron Microscopy (SEM). Energy Dispersive Spectroscopy (EDS) was employed to check the composition variations for the surface part and the internal part of the sample. The results show that the crystallization kinetics of the inner part of the MGs become faster and faster with increasing the annealing temperature above the glass transition temperature. The surface of the glass is a one-way nucleation mechanism in the outward direction, and at temperature of Tc (340℃).the internal crystallization mechanism is the slow growth of the eutectic nucleation growth mechanism.Above temperature Tc (350℃) crystallization is the superlattice precipitation. Close to Tx (380℃). crystallization is the mixture of the super-lattice precipitation and the eutectic nucleation. Isothermal annealing under temperature of the glass transition(295℃) for a long time (100 hours), there is almost no crystalline precipitate inside the glass, and the surface of the glass is characterized by faster crystallization kinetics, and the mode is still nucleation mechanism from the outward.