Influence of type of inclusions on stress state, strength and reliability of partuculate composites with alumina matrix
Zbigniew Pędzich, Grzegorz Grabowski
Quarterly No. 2, 2009 pages 149-153
DOI:
keywords: composites, alumina, zirconia, tungsten carbide, residual stress, reliability
abstract The paper describes differences in selected mechanical properties of particulate composites with alumina matrix with different type of inclusions. Materials containing 10 vol. % of zirconia or tungsten carbide were investigated. Microstructures of both composites were compared. I was stated that morphologies of zirconia and tungsten carbide inclusions were not the same. They differ in created aggregates and the size of single inclusion grains. For both types of composite residual stress state caused by thermal expansion coefficients mismatch of constituent phases was calculated. By the finite elements method distribution of the main stresses and the von Misses stresses were calculated. In Al2O3/ZrO2 composite the matrix is under compressive stresses and in Al2O3/WC composite the matrix is under tensile stresses. Values of these stresses locally reached even over 1.5 GPa. It was confirmed by microstructural observation that essential differences in the stress state in both compared materials influenced decisively the way of cracking in the composite. In Al2O3/WC composite cracks went along the interphase boundary, while in Al2O3/ZrO2 composite crack went through alumina phase. It influenced essentially measured mechanical properties (bending strength) and reliability. In the paper the bending strength and the Weibull modulus as a reliability measure of composites, were determined. Obtained results were compared to pure alumina properties. It was confirmed that incorporation of compressive stresses into the matrix is the strengthening factor for the material. In Al2O3/ZrO2 composite case, it was stated the spectacular bending strength increased from 600 to 1200 MPa. It was also stated that the increase of the Weibuill modulus value observed for composites was an effect of decrease of critical flaw size by the decreasing of the grains size in sinters.