Fracture properties of Fe-40 at.% Al matrix composites reinforced with ceramic particles and fibers

The fracture mechanism of Fe-40 at.% Al matrix composites reinforced with ceramic particles and continuous fibers was investigated to clarify the primary factor governing their mechanical properties. Composites with carbide, boride and oxide reinforcements can be successfully fabricated by reactive hot-pressing. The fracture toughness of the composites with several types of fine particles decreases with an increase of yield strength due to the suppression of ability of plastic deformation. The environmental effect, which is the hydrogen embrittlement originated from moisture in air, further influences their fracture toughness. The environmental embrittlement of the composites can be reduced by micro-alloying with B and the addition of boride particles. On the other hand, the bearing of load by the fibers during the multiple-fracture behavior can significantly contribute to the improvement of fracture strength for the composites reinforced with Al2O3 continuous fibers. The composites completely fracture by the crack propagation from cracks in the fractured fibers. The fracture resistance of the matrix against the crack propagation also depends on the environmental effect. Therefore the optimization of the matrix properties by alloying techniques is an indispensable problem for the composite design of Fe-40 at.% Al alloys. (C) 1998 Elsevier Science S.A. All rights reserved.