Study On Diffusion-solution Zones In Al/Fe, Al/Ni And Al/Ti Liquid/solid Interfaces

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.