Hot-press consolidation and tensile strength characterization of mechanically alloyed nanostructured Fe-Al and Fe-C powder.

Abstract

Previous studies of nanostructured materials have typically concentrated on characterization of microscopic properties, principally because of the inability to produce samples of sufficient size to determine macroscopic properties. In this study consolidation of mechanically alloyed Fe-Al and Fe-C powders was accomplished by hot-pressing. Microstructure characterizations of both the attritor processed powder and the consolidated material were determined using X-ray diffraction and SEM. Consolidated samples were of sufficient size (25 mm in diameter and 5–7mm thick) to determine macroscopic properties most notably: tensile strengths. Tensile strength increased with increasing density reaching a optimal strength of 700 to 900 MPa as the compacts reached full density. The maximum nanostructure tensile strength is consistent with tensile properties of HSLA steels. Compact characteristics (density, hardness, tensile strength) were determined as a function of hot-pressing conditions (processing temperature, time, pressure). During consolidation FeC samples developed second phase spinel and carbide precipitates. During consolidation FeAl samples developed a duplex submicron- and nanograin bcc-Fe microstructures and nanograins of (Fe,Al) 3O 4. The grains of the consolidated samples were free of grain disorder, e.g., dislocations, twins, etc., With few exceptions, density and grain size increased with increasing hot-press processing time, temperature, and/or pressure.