Phase-field Study Of Interfacial Periodic Layered Structure In Diffusion Couples

The interface of the materials plays an important role in material design and performance control.The interface microstructure determines the local or overall properties of the material.So far,it is still a very effective method to study the interface composition and microstructure of the two alloys by experimental mesurements of diffusion-couple.Recently,the periodic layered structure formed near the interface of diffusion couples is widely reported in materials such as metals,semiconductors,and ceramics.In view of the fact that this interfacial structure has a great influence on the properties of the material,conducting a research of evolutionary laws of periodic layered structure at interface in diffusion couples is of great significance for optimizing the interface microstructure and performance of materials.In this dissertation,the phase field methods are used to simulate the evolution of periodic layered structure at the interface of diffusion couples in binary and ternary spinodal decomposition alloys and the ternary multiphase alloys.The influence of factors such as initial composition,elastic anisotropy,atomic mobility,and initial concentration difference on the periodic layered structure at the interface of the diffusion couples are studied.The main conclusions are as follows:(1)The phase field method was used to simulate the evolution of the interfacial microstructure of the binary spinodal-decomposition alloy under the conditions of different initial concentration fluctuations induced by temperature and different elastic anisotropies.The effects of initial concentration fluctuations and elastic anisotropies on periodic layered structure at the interface of the diffusion couples were investigated.The results show that the initial concentration fluctuations caused by the temperature has an important influence on the periodic layered structure of the binary spinodal-decomposition alloy.The small concentration fluctuation at lower temperature could cause the formation of multiple layers of lamellar structure near interface.When the elastic anisotropy of the alloy is large,the number of layers of the periodic layered structure near the interface and the distribution of the internal structure away from the interface are affected by the elastic strain field.The elastic anisotropy leading to the preferable growth direction paralleled to the diffusion interface,more periodic layered structure may form near the interface.In addition,when the volume fractions of the two decomposed phases differ greatly,it is not conducive to the formation of periodic layered structure.(2)The phase field method was used to simulate the evolution of the periodic layered structure at the interface in diffusion couples of the ternary spinodal-decomposition alloy.The effects of initial concentration fluctuations induced by temperature,the concentration difference between the initial alloys of diffusion couples and the atomic mobility of the solute elements were studied.The results show that the number of layers for periodic layered structure at the interface in diffusion couples of the ternary spinodal decomposition increase with the decrease of initial concentration fluctuations.The concentration difference between the initial alloys of diffusion couples and the atomic mobility of the solute elements have slight effect on the number of layers for periodic layered structure,but have a great influence on the formation time and roughening process of the periodic layered structure.The greater the atomic mobility,the faster the periodic layered structure will form and disappear.(3)The multiphase-field model was used to simulate the evolution of periodic layered structure at the interface in diffusion couples of the ternary multiphase alloy.The sequence of the precipitation of the binary and ternary intermetallic phase at the interface in the ternary multiphase alloy system was analyzed.The influence of the nucleation position of the interphase on the periodic layered structure was studied.The results show that the sequence of the precipitation of the intermetallic compound phase at the interface of the original diffusion couple is related to the diffusion rate of the solute element.The higher the diffusion rate,the greater the interfacial migration rate of the new precipitated phase is.The different diffusion rate of the solute elements could lead to the formation of the periodic layered structure whether nucleation in the phase region or at the interface.The formation mechanism of periodic layered structure of the diffusion couple is consistent with the experimental results.The formation of this kind of structure is due to diffusion reaction and different elements’ diffusion rate.