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A comparative study has been carried out on tensile properties and failure mechanisms of Al-4?5 wt-%Cu alloy and in situ Al-4?5Cu-5TiB 2 composite in as cast or mushy state rolled conditions. For the alloy, mushy state rolling at temperature for 30 vol.-% nominal liquid content to 2?5% thickness reduction leads to marginally higher strength but poorer ductility, while both these properties worsen significantly on 5% reduction because of grain growth and intergranular solute segregation. Contrarily, mechanical properties of the composite are significantly improved on mushy state rolling at temperatures for 10-30 vol.-% liquid to 2?5-5% reduction. Improvement in mechanical properties of the composite on mushy state rolling is attributed to evolution of globular and finer grains. Examination of fracture surfaces by scanning electron microscope has shown evidence of ductile failure in as cast alloy and in cast or mushy state rolled composite, but that of brittle failure in mushy state rolled alloy.

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The initiation of small cracks has been studied on dumble-shaped plate type specimens of an interstitial free (IF) steel at the load ratio of Rϭ0 under varied cyclic stress amplitudes between 0.6 and 1.0 of yield stress. Nucleation of cracks were observed at ferrite-ferrite grain boundary (FFGB) as well as inside ferrite grain body (FGB), but the former location was found to be the preferred one. The average length of FFGB cracks is found larger than that of the FGB cracks for identical cyclic loading conditions. The formation of slip bands inside the grain body, slip band impingement at grain boundary and elastic-plastic incompatibility synergistically influence the event of crack initiation in the investigated steel. In addition, nucleation of voids inside slip bands was found to be a new phenomenon associated with the above possibilities to affect the nucleation of cracks in the investigated steel.KEY WORDS: fatigue; crack initiation; small crack; interstitial free steel.