【作者】 蒋淑英；

【导师】 李世春；

【作者基本信息】 中国石油大学 ， 材料学， 2010， 博士

【摘要】 二元金属液/固界面异类原子的扩散溶解现象在材料工程上有极其广泛的应用。将二元金属液/固体系置于一定温度并且保温一定时间,则在液/固界面将发生异类原子的扩散与溶解,大多数二元金属体系会形成金属间化合物新相区—扩散溶解层。扩散溶解层的组织和性能对最终产品的质量起着至关重要的影响。因此,研究界面区金属间化合物新相的形成机理,并对扩散溶解层的组织加以预测和控制具有非常重要的理论和现实意义。但到目前为止,对二元金属液/固界面异类原子的扩散溶解问题还没有形成规律性的认识,在理论上尚不成熟,更不能广泛的用来指导工业生产。本文选择应用极为广泛的Al-Fe、Al-Ni、Al-Ti二元系为实验对象,根据热处理实验结果,分析了Al/Fe、Al/Ni、Al/Ti液/固界面扩散溶解层的形成机理、生长机制及组织结构演变,建立了扩散溶解层的生长动力学方程。此外,采用余瑞璜的固体与分子经验电子理论计算了Al-Fe、Al-Ni、Al-Ti二元系金属间化合物的价电子结构、键能、结合能和生成热,提出了界面新生相析出顺序的EET模型最小生成热判据,从价电子理论角度分析了Al/Fe、Al/Ni、Al/Ti液/固界面新生相的形成及生长,利用EET模型最小生成热判据对Al/Fe、Al/Ni、Al/Ti界面新生相的析出顺序进行了预测,预测结果和实验结果吻合。在分析Al/Fe、Al/Ni、Al/Ti液/固扩散偶实验结果的基础上,得出在A/B二元金属液/固界面,金属间化合物初生相析出的动力学条件是B原子向液相A中溶解直至界面处的液相达到饱和,热力学条件是EET模型生成热为负并且在同一体系的所有金属间化合物中其EET模型生成热最小。如果初生相与液相在相图上不存在两相共存区,初生相将形成连续单相层,反之,将形成初生相与液相的混合组织区。在动力学条件满足的情况下,在新的界面还将按照EET模型最小生成热判据顺序析出新的化合物相。晶体的本征性能与其价电子结构密切相关,提出了表征晶体强度、硬度、塑性和稳定性的价电子结构因子,并给出了四个价电子结构因子的数学表达式。晶体的强度取决于晶体中的共价电子密度,共价电子密度越大,强度越高;硬度取决于原子平均键合能,原子平均键合能越大,硬度越高;塑性与晶格电子密度、共价键结构对称性和强度对称性有关,晶格电子密度越大,共价键结构对称性和强度对称越高,塑性越好;稳定性则由原子平均成键能力决定,原子平均成键能力越强,稳定性越好。根据提出的表征晶体性能的价电子结构因子的数学表达式,计算了Al-Fe、Al-Ni、Al-Ti二元系金属间化合物的价电子结构强度因子、硬度因子、塑性因子以及稳定性因子,并以此为依据分析了同体系金属间化合物的相对性能,分析结果与实验结果吻合。知道了A/B二元金属液/固界面新生相的形成条件、析出顺序及相关性能,就可以根据材料使用工况的要求,通过控制液相A和固相B的相对量、热处理温度和保温时间得到所需要的组织结构。因此,对生产工艺的制定和产品性能的预测具有重要的理论指导意义。更多还原

【Abstract】 Diffusion and solution phenomena of heterogeneous atoms in binary metallic liquid/solid interface have a very wide range of applications in materials engineering. The diffusion and reaction of heterogeneous atoms in liquid/solid interface under certain temperature for certain time will form a new intermetallic phase region—diffusion -solution zone. The structures and properties of the diffusion-solution zone play an important influence on the final product quality, therefore, the study of the formation mechanism of the new intermetallic phases in interface, and prediction and control of the structure of the diffusion-solution zone have very important theoretical and practical significance. Yet so far, there aren’t unified awareness and mature theory about the diffusion and solution of heterogeneous atoms in binary metallic liquid/solid interface which can be widely used to guide production.Al-Fe, Al-Ni and Al-Ti binary systems which have wide applications in materials engineering were selected as the experimental subjects. The formation and growth mechanism and the structure evolution of the diffusion-solution zones in Al/Fe, Al/Ni, and Al/Ti liquid/solid interfaces were analyzed and their growth kinetics equations were set up according to the heat treatment experimental results. Moreover, the valence electron structure, bond energies, cohesive energies and formation heats of intermetallic compounds in Al-Fe, Al-Ni, and Al-Ti binary systems were calculated based on the empirical electron theory of solids and molecules, the minimum formation heat criterion based on EET was given to predict the formation order of new phases in interface. The formation and growth of new phases in Al/Fe, Al/Ni, and Al/Ti liquid/solid interface were studied from the perspective of the valence electron theory, the new phases formation sequence in Al/Fe, Al/Ni, and Al/Ti liquid/solid interfaces was predicted using the minimal formation heat criterion based on EET model, and the predicted results agree well with the experimental results.In a binary metallic liquid/solid interface A/B, the formation kinetics condition of intermetallic primary phase is that B atoms dissolve in the liquid phase A until the liquid in interface saturated, and its thermodynamic condition is that its EET formation heat is negative and minimum in all compounds in this system. If the primary phase and liquid A do not have coexistence region in the phase diagram, the primary phase will grow to form a continuous single-phase layer, otherwise, to form the hybrid area of the primary phase and A. If the dynamic conditions are met, new compounds will also be formed in the new interface in accordance with the formation heat criterion based on EET model.The intrinsic properties of crystals are closely related to their valence electron structure. The valence electron structure factors characterizing the strength, hardness, plasticity and stability of crystal were defined and their Mathematical expressions were given. Strength of crystal is proportional to its covalent electron density; hardness is proportional to its average atomic bonding energy; plastic depends on its lattice election density and covalent bond structure and intensity symmetry, the greater the lattice election density and covalent bond structure and intensity symmetry, the better plasticity; Stability is proportional to its atomic average bond capacity. The intensity factors, hardness factors, plastic factors and stability factors of intermetallic compounds in Al-Fe, Al-Ni and Al-Ti binary systems were calculated, and their relative performances were analysed. The analysed results agree well with the experimental results.If the formation conditions, precipitating sequence and related properties of new phases in the A/B binary metal liquid/solid interface are known, the properties of the interface can be controlled by the amount of A and B, heat treatment temperature and holding time. Therefore, it has very important theoretical guidance significance to develop the production process and predict the product performance.更多还原