LAUSR

Abstract Micro scale fracture strength of grains and grain boundaries in polycrystalline La-doped β-Si3N4 ceramics were investigated and compared with theoretically predicted values. The fracture behaviour of SiO2-La2O3 intergranular glassy phase (IGP) between β-Si3N4 grains was modelled by ab initio simulations. Microcantilevers were FIB-milled both from polycrystalline regions and single grains of β-Si3N4 and were tested in bending using a nanoindenter. The fracture strength of β-Si3N4 grains which fractured at fixing was 10.6 ± 0.8 GPa while the strength of the beams that failed at defects was 5.9 ± 2.3 GPa. Polycrystalline β-Si3N4 samples showed intergranular fracture with decreasing strength values in the range of 2.9 ± 0.4 – 2.1 ± 0.5 GPa. The comparison of single grain results with theoretical values in the literature revealed a correlation between theoretical and experimental results, which was used to convert our ab initio simulations from subnano to micro size samples. The converted strength for IGP showed quantitative agreement with micro-bending experiments.