Work of fracture in aluminum metal-matrix composites

Abstract

The effect of isothermal exposure and thermal cycling on the toughness of B/Al (1100), B/Al (6061), and A1₂O₃/A1 composites has been investigated. In B/Al (1100), isothermal exposure at 773 K for 45 × 10⁴ s (125 hours) reduced toughness, measured by the work of fracture, from 76 kJm^-2 to 10 kJm^-2, and a similar reduction occurred after equivalent thermal cycling. The corresponding reduction in toughness after isothermal exposure in B/Al (6061) was from 44.5 kJm^-2 to 8 kJm^-2; however, the effect of thermal cycling was less detrimental. In the FP-A1₂O³/A1 composite, the work of fracture was insensitive to both forms of thermal treatment. Changes in the toughness of the B/Al composites have been correlated with and analyzed in terms of modifications to matrix, fiber, and interface properties, in particular, matrix softening, interface reaction products, and fiber notch sensitivity.