Fractographic Features in Eutectic Composites

An extensive literature has emerged on the flow and fracture behavior of aligned eutectic composites. However, there have been few attempts to systematically record and compare fractographic features in eutectics as a function of microstructural variables (for example, interfiber spacing) or test conditions (for example, temperature, load application). This paper constitutes a compilation and evaluation of fractographic features from specimens loaded parallel to the eutectic growth direction, obtained by scanning and transmission electron microscopy from the following fibrous alloys: Al-Al₃Ni, Ni,Cr-TaC, and Co,Cr,Ni-TaC; and lamellar alloys: Ag₃Mg-AgMg, Mg₁₇Al₁₂-Mg, and Al-Ag₂Al. Tensile, creep, and fatigue loading at a variety of test temperatures are included for several of these alloys. It will be shown that fatigue fracture morphology is particularly sensitive to microstructural variables. For example, a shift from striation-free Stage I cracking to profusely-striated Stage II cracking in Ag₃Mg-AgMg is obtained by post-solidification heat treatment.