Multiscale Simulation of Metal/Ceramic Interface Fracture

Interface failure in metal/ceramic composites plays an important role in modern materials technology, as evident by their use in a variety of applications. High-strength materials, such as metal-matrix composites consist of internal interfaces between ceramic (e.g. SiC or Al2O3) particles or filaments within a metallic host. In microelectronics packaging, interfaces between metallic (Cu and/or Al) interconnects and SiO2, carbide/nitride (TiCN) or oxide (Al2O3) ceramics are commonplace, and impact the performance and longevity of solid state devices. Despite their widespread use, a basic understanding of these interfaces has been elusive. For example, given a particular metal/ceramic interface, it is not yet possible to accurately predict such fundamental properties as its fracture energy. In most of the cases, improvements in interface properties proceed via a costly and time consuming trial-and-error process in which numerous materials are evaluated until suitable performance is obtained. Computational methods provide a wide range of possibilities to study the fracture behaviour of such metal/ceramic interfaces. In the first part of the presented work, the deformation behaviour of niobium single crystals has been simulated using crystal plasticity theory. An automatic identification procedure has been proposed to identify the crystal plasticity parameters for each family of slip systems and simulation results of the mechanical behaviour of single crystal niobium are compared with the experiment. Good agreement between the experimental and simulation results was found. The second part presents effects of the different niobium single crystalline material orientations on crack initiation energies of the bicrystal niobium/sapphire four-point-bending-test specimens for a stationary crack tip. The trends of crack initiation energies are found to be similar to those observed during experiments. In the third part, crack propagation analyses of niobium/alumina bicrystal interface fracture have been performed using a cohesive modelling approach for three different orientations of single crystalline niobium. Parametric studies have been performed to study the effect of different cohesive law parameters, such as work of adhesion and cohesive strength, where work of adhesion is the area under the cohesive law curve while cohesive strength is the peak stress value of the cohesive law. The results show that cohesive strength has a stronger effect on the macroscopic fracture energy as compared to work of adhesion. Cohesive model parameters are identified for different combinations of cohesive strength and work of adhesion by applying a scale bridging procedure. In the last part, a correlation among the macroscopic fracture energy, cohesive strength, work of adhesion and yield stress of niobium single crystalline material will be derived.