Microhardness studies on functionally graded polymer composites

Functionally graded polymer composites based on an epoxy resin matrix and SiC filler particles were prepared. By controlling the preparation conditions during centrifugation, a high gradient in the particle distribution (from 0 to 45 vol.%) could be achieved. The gradient of the mechanical properties along the centrifugal force axis was mapped by means of microhardness measurements. A continuous increase of the hardness from 210 up to 640 MPa over the length of the samples was observed. An almost linear dependence of the Vickers hardness on the SiC volume content in the broad range from 7 to 45% was found. An attempt was made to explain the deviation of this relationship from the usual microhardness additivity law (rule of mixtures). It was shown that the elastic modulus derived from the universal hardness measurements can be successfully used for studying the trend of the elastic properties in functionally graded materials.