アルミナ連続繊維強化アルミニウム合金基複合材料の引張特性に及ぼす粒子分散の効果

抄録

Aluminum alloy matrix hybrid composites reinforced with particle-attached continuous alumina fibers were fabricated by squeeze casting, and the effects of the particle-dispersion on their strength in the temperature range 293 to 623 K were investigated by microscopy and fractography. It was found that the particle-dispersion among the fibers minimizes the preform contraction and fiber-to-fiber contact due to melt infiltration during the squeeze casting, resulting in a homogeneous distribution of the fibers in the composite. The tensile strength, 0.2% proof stress and elastic modulus of the composites in the longitudinal direction increased due to the particle-dispersion over the whole temperature range measured. The fracture surface of the particle-free composite was flat and close-packed fibers were frequently observed, indicating that stress concentrated in the neighboring fiber, then the cracks initiated at the points of fiber contact, followed by progressive fracture of the touching fibers. In contrast, the surface of the hybrid composite was irregular and close-packed fibers were rarely observed, showing that the matrix around a fiber relieved the stress concentration and the strengthening by the fibers was satisfactory. The transverse tensile strength and proof stress of the particle-free composite were lower than that of the unreinforced alloy. Many fibers and grooves remaining in the matrix were observed on its fracture surface. This is considered to be due to the initiation of the cracks at the points of fiber contact and their propagation mainly along the fiber-matrix interface. In contrast, the strength of the hybrid composite was close to that of the unreinforced alloy. The matrix was dominant on its fracture surface. This is attributed to the strong fiber-matrix interface and the propagation of cracks mainly throughout the matrix.