STRUCTURE AND PROPERTIES OF FUNCTIONALLY GRADIENT ALUMINUM-ALLOY-2124 SIC COMPOSITES

Functionally gradient materials exhibit a progressive change in composition, structure, and properties as a function of position within the material. Functionally gradient materials and conventional metal matrix composites have been manufactured from gas atomised aluminium alloy 2124 powders (matrix) and particulate silicon carbide (reinforcement) by mechanical mixing followed by hot pressing at 500 degrees C at a pressure of 1.5 GN m(-2). In this work the structure and mechanical properties of model functionally gradient materials consisting of two discrete layers are compared with those of composites of homogeneous composition. A careful microstructural investigation has revealed a uniform distribution of the reinforcing SiC and defect free interfaces between adjacent layers of the functionally gradient materials. The strengths of the functionally gradient materials and composites have been determined via three point bend tests and the fracture toughness properties assessed using single edge notch bend type specimens. In the tests the crack in the functionally gradient materials was propagated from a high SiC region into a low SiC region (generally more ductile) and retardation of the crack growth investigated. For most compositions the mechanical performance of the functionally gradient materials was superior to that of the conventional composite having a SiC content corresponding to the high SiC region.