【作者】 田学雷；

【导师】 陈熙琛；

【作者基本信息】 山东工业大学 ， 材料加工工程， 1999， 博士

【摘要】 以X-射线衍射技术为主要手段,以DSC 和电镜为辅助手段,对有关金属的液态和固态结构的相关性进行了研究。为使液态X-射线衍射仪适合于本研究工作,作者对其进行了一些改进。以有限固溶共晶系为基础建立的“液态微观多相结构模型”的思想也适用于固态无限互溶固溶体系合金。但是,由于两种体系中同类与异类原子间键合力的差别,在固态无限互溶固溶体系中,液态由两种原子随机置换的多种微原子团所构成,微原子团之间的数量关系呈以合金成分为中心的统计分布,边界值则由该合金成分相对应的固、液相最大溶解度来决定。在固液两相区间,多种微原子团将向两极（所处温度线与固、液相线的相交点）成分分化,形成由两种成分原子团组成的局面,它们之间的数量比符合杠杆定律,由固相线决定的微原子团将向晶体相转移使晶体生长,而由液相线决定的微原子团则存在于液相中。这一适合于固态无限互溶固溶体系的“液态微观多相结构模型”的提出和建立的意义是:a) 它可以解释为什么在液态急冷、深过冷时可以达到无偏析凝固,为制备无偏析凝固新工艺奠定理论基础;b) 它揭示了平衡状态图与液、固相结构之间的定量关系;c) 它深化了对有限固溶共晶系“液态微观多相结构模型”固溶体段的认识。通过对Cu₇₀Ni₃₀合金在两相区过冷状态下的液态X-射线结构分析和理论计算,首次初步证实了“液态微观多相结构”模型适合于固态无限固溶体系这一思想的正确性,但由于实验的难度未能用多种合金进行考核,这是我们今后要进一步做的工作。对Cu₇₀Ni₃₀合金的液态、过冷液态和固态进行的结构分析结果,证实了该合金在液态时具有其固态时的面心立方的近程序结构。发现在液相线以上的1250～1400℃温度范围内,其微原子团的相关半径和原子团中的原子数目没有明显的变化,约为1.125nm 和457 个;而过冷液态的Cu₇₀Ni₃₀合金原子团的相关尺寸和原子数目有明显的增加,约为1.3nm 和704 个。这说明此合金液态中原子团的fcc 近程序结构,在冷却过程中达到过冷时,通过原子团尺寸的增大,使fcc 近程序结构保持并发展成为固态的fcc 固溶体。对Al₆₅Cu₂₀Fe₁₅合金的液态X-射线结构的分析结果表明,其液态结构由二十面体近序结构的原子团组成,证明了Frank F. C.的“在液态中有大量二十面体团簇存在”论断的正确性。并发现二十面体准晶Al₆₅Cu₂₀Fe₁₅ 合金在加热过程的液体中,存在着微观不均匀区域,这个区域中的液态结构是:具有二十面体准晶相近程序的原子团+更多还原

【Abstract】 In this paper, the correlation between structures of liquid and solid in some metals has been studied with an elevated temperature X-ray diffraction as a main means, DSC and electron microscopy as assistant means. In order to adapt the X-ray diffraction equipment for the research work, some improvements have been done. The “liquid micro-multi-phase structure mold”based on an eutectic alloy system in which the solid solubility is limited. The idea of this model is also suit to the unlimited intersolubility solid solution system. Because there is a difference of the bond forces between congeneric atoms and heterogeneous atoms in the two system alloys, the liquid of unlimited intersolubility solid solution system consists of multi-phase clusters in which different atoms are randomly displaced each other. The clusters with different ingredient are statistically distributed about the alloy ingredient. And the boundaries of the distrbution are the maximum solubility of solid and liquid of this alloy ingredient. In the region between liquidus and solidus, multi-phase clusters polarize to two points, which are the intersection points of temperature line and liquidus, solidus. In this case, the liquid is made of two type clusters that their ingredient change along the liquidus and solidus, and the ratio of the two type clusters coincides with level rule. The clusters which ingredient change along solidus will move to crystal phase to make it grow, and the clusters their ingredient change along liquidus will still stay in liquid. It is of significance to develop the “liquid micro-multi-phase structure model”to suit to the liquid alloys which are unlimited solubility solid solution system. First, to explain why there is no segregation in rapid and undercooled solidification, it is the theory fundament for the new technology to prepare material without segregation. Second, to indicate the quantitative relationship between phase diagram and structure of liquid and solid. Third, to improve the understanding on the usage of “liquid micro-multi-phase structure mold”to solid solution region of the eutectic alloy system. It is the first time and elementary to prove it is right that the “liquid micro-multi-phase structure model”is suit to unlimited solubility solid solution system by the structure analysis of liquid metal X-ray diffraction and theory calculation on Cu70Ni30 alloy liquid and undercooled liquid between its liquidus and solidus. Because the difficulty of the experiment, the proving work is not done for other unlimited solubility solid solution alloys and this is future work for us. By analyzing the structures of liquid, undercooled liquid and solid of Cu₇₀Ni₃₀ alloy, it is indicated that this alloy melt is of a short order structure of fcc which is its solid structure. And it is discovered that the cluster correlation radius and atom number of cluster in the alloy melt do not significantly change in the temperature range from 1250 to 1400℃, they are 1.125 nm and 457. But they significantly increase in the undercooled liquid （1200℃）, they are 1.3 nm and 704. This shows that the fcc short order structure of liquid cluster is retained to the solid by cluster size increasing and nucleation in undercooled. Analyzing on the structure of Al65Cu20Fe15 alloy melt illustrates that its melt is consist of clusters with icosahedral short order structure, then the correctness is proved for “There exist a lot of icosahedral clusters in liquid”, the judgment of Frank. The micro-inhomogeneous structure region is discovered in the melt of icosahedral quasicrystal Al65Cu20Fe15 alloy during heating process. In this region the structure is icosahedral short order cluster and undisintegration icosahedral quasicrystal phase, the temperature range of this region is from 1056 to 1250℃. In the liquid above 1400℃, the structure is homogeneous, it is only consisted of icosahedral short order clusters. Then there exist a correlation between liquid structure and solid structure of icosahedral quasicrystal Al65Cu20Fe15 alloy. The correlation radius and atom number of clusters in liquid of Al65Cu20Fe15 alloy at 1150℃are about 1.2 nm and 400, and its coordination number is 10.3. After analyzing the structures of liquid, supercooled liquid and solid of amorphous Zr41Ti14Ni10Cu12.5Be22.5 alloy, it is discovered that the amorphous structure at solid is directly kept from its liquid structure, but the degree of order at solid is higher than that at liquid. And the amorphous structure in supercooled liquid region is still the same structure as in liquid and solid, but it is of a tendency to crystallizing. When the amorphous alloy is crystallizing, it will crystallize to CuZr2, Be2Zr and an unknown phase. The melting temperature range of intermetallic compounds made from amorphous alloy component elements is 650 to 728℃, it is far lower than melting point temperatures of their pure elements. Using the technology of computer numerical calculation of temperature distribution, the amorphous cooling process can be simulated. According to the simulation cooling rate, it can be predicated wether the amorphous can be formed in the alloy.更多还原