Molecular Dynamics Study Of Crack Propagation At The Interface Between Al And α-Al₂O₃

The ceramic/metal interfaces widely exist in ceramic/metal composites, and have been used in variety of applications in chemical industry and electrical industry, such as thermal-barrier coating, military armor, catalytic converters, field-effect transistor, anticorrosive coating. The physics, chemistry, and materials science of metal/ceramic interfaces are active areas of research with important ramifications for structural composites, electroceramic devices, and environmental coatings. Therefore, to investigate the micro-structure and stress strength of the ceramic/metal interfaces and their mechanical behaviors and failure processes not only have great importance on the composites applications and understanding of their destructions, but also have profound significance to other field concerned with composites.The molecular dynamics simulation of the Al/α-Al2O3 interfacial crack model has been carried out to investigate the pattern in which the crack propagates at room temperature by the open source software LAMMPS. The main content is as follows:1. By consulting the relevant literature, the master orientation and the atomic configuration at the Al/α-Al2O3 interface are obtained, and the atomic model of the interface is constructed.2. Elastic constants, surface energy, and interfacial energy are several fundamental physical quantities which characterize the properties of materials and their interfaces. These quantities should be represented accurately by the correct potential function. Hence we make evaluations on several potential functions, and select precise ones. Based on the consideration of atomic bonding, with the results about the atomic interactions at the interface derived from experiments and theories, then the expressions of potential function are determined. With the first-principle results on interfacial energy to be the reference value, the parameters and thus the potential itself are obtained by function-fitting. Finally, the relevant potential functions have been validated from structural stability to configuration of interface atoms.3. The Al/a-Al2O3 interfacial crack model has been simulated by molecular dynamics method under 300K with mode I loading. The results show that the dislocations are emitted from crack tip and form a loop when the strain is 5.52%and 6.36%, respectively. The angle between three main planes of the loop and the crack plane is about 71°. As the strain increases, dislocations glide towards the Aluminum field, and accumulate at the otherα-Al2O3/AI interface which is free of crack, when they reach there. With the keep-increasing density of dislocations, the Aluminum is strengthened continuously. When the moving obstacle of the dislocations is larger than that of the crack, the deformation energy could not be absorbed by producing dislocations any more, and then the crack starts its propagation. It would be proposed that the whole material would become invalid due to ductile fracture of Aluminum, as the strain increasing continues.