Effect of homogeneity of particle distribution on tensile crack propagation in mushy state rolled in situ Al-4.5Cu-5TiB2 particulate composite

The effect of mushy state rolling with 20 vol% liquid at 626 °C for 5% thickness reduction per pass on homogeneity of TiB2 and CuAl2 particle distribution in the in situ Al-4.5Cu-5TiB2 composite has been examined. These particles, appearing as segregated at grain boundaries in the as-cast composite, are redistributed on mushy state rolling. The homogeneity of particle distribution has been quantitatively evaluated by developing a computer program for multi-scalar analysis of area-fractions in scanning electron microscope (SEM) images to estimate homogeneous length scales. The optimum homogeneity is found in the composite subjected to two mushy state roll passes. The matrix microhardness increases with decrease in the homogeneous length scale. In situ tensile straining experiments inside SEM have shown linkage of particle-matrix interfacial microcracks at particle-clusters as fracture mechanism in as-cast or 4-pass mushy state rolled composites. In contrast, crack propagation through matrix is favored in the 2-pass mushy state rolled composite.