ABSTRACT
High silicon alloyed ductile cast iron (Si-DCI) can show unpredictable brittle fracture which currently prevents a widespread application of this material. The brittleness is associated with local superstructure formation due to silicon segregation which influences the deformation mechanisms of the matrix phase. In order to understand the effect of silicon segregation on the mechanical properties of Si-DCI under monotonous loading, three alloys with different cooling conditions were examined and micromechanical simulations were carried out by using the phenomenological crystal plasticity model. Here, the segregation profiles were determined through multi phase field simulations. The influence of segregation on the mechanical properties was only evident from the model but not from the experimental results. The simulated results show that the toughness of Si-DCI decreases with stronger silicon segregation when ductile damage is considered.
ABSTRACT
Reactive Air Brazing (RAB) enables the joining of vacuum-sensitive oxide ceramics, such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), to metals in a one-step process. However, damage may form in ceramic or joint during RAB. In this work, experimental microstructure characterization, measurement, and prediction of local material properties using finite element analysis were combined to enlighten these damage mechanisms, which are currently not well understood. Micromechanical simulations were performed using representative volume elements. Cooling simulations indicate that small-sized CuO precipitations are most likely to cause crack initiation in BSCF during cooling. The ball-on-three-balls experiment with porous BSCF samples was analyzed numerically to determine the values of temperature-dependent BSCF fracture stresses. The inversely calibrated fracture stresses in the bulk BSCF phase are underestimated, and true values should be quite high, according to an extreme value analysis of pore diameters.
