Layered composites with self-diagnostic ability

Design of layered materials depends on the residual stresses introduced into the composite as a consequence of different thermal expansion coefficients, Young's moduli, Poisson's ratios and shrinkage behavior of ceramic layers. Layers must be sequenced in such a way that gradually increasing residual stresses are distributed across the whole sample. Model experiments and simple equations explained the increased strength of the three-layer composite (1042 MPa) compared to the relating monoliths with the strength of 987 and 779 MPa, respectively. Based on above knowledge, a layered composite with repeating layer units consisting of Si3N4 with different microstructure and sialon–TiN laminates was designed. 3-point bending strength of this composite is higher than 1.1 GPa and fracture toughness is close to 10 MPa m1/2. Measurement of the electrical resistance of the conductive sialon–TiN layer enables to predict the formation of the cracks in the measured layer. This phenomenon can be utilized for self-diagnostic ability of samples.