FRACTURE-TOUGHNESS OF DISCONTINUOUSLY REINFORCED AL-4CU-1.5MG/TIB2 COMPOSITES

The effect of particle size, particle volume fraction, and matrix microstructure on the fracture initiation toughness of a discontinuously reinforced aluminum composite was examined. The. composites were Al-4 wt pet Cu-1.5 wt pet Mg reinforced with O to 15 vol pet of TiB2, having an average particle diameter of 1.3 or 0.3 mu m produced in situ by the XD process. The room-temperature plane-strain toughness measured using compact tension specimens ranged from 19 to 25 MPa root m. Toughness was adversely affected by increases in TiB2 volume fraction. The fracture toughness of all composites was affected by changes in the matrix microstructure produced by aging. The response of the composites to artificial aging deviates from that of the matrix. Fractography revealed that these composites failed in a ductile manner, with voids initiating at the reinforcing TiB2 particles. The experimentally measured plane-strain toughness properties of Al-4Cu-1.5Mg composites with well-dispersed, 1.3-mu m TiB2 reinforcements agree with the Rice and Johnson model.