An evaluation of cavity development in the tensile testing of ultrafine-grained iron processed by ECAP

Iron of commercial purity was subjected to Equal-Channel Angular Pressing (ECAP) to reduce the grain size from an annealed value of similar to200 mum to a final value of similar to0.2-0.4 mum. Following ECAP, tensile samples were cut from the as-pressed billets with their tensile axes lying along the pressing direction. These samples were pulled to failure at elevated temperatures using an initial strain rate of 1 x 10(-3) s(-1). After fracture, selected samples were sectioned, polished and examined carefully in an optical microscope equipped with a video camera and a facility for recording quantitative information on the size and shape of any internal cavities. This paper describes the results obtained in this investigation including the average shapes of the cavities and their orientations with respect to the tensile axis.