Fabrication of high-strength magnetocaloric Fe2AlB2 MAB phase ceramics via combustion synthesis and hot pressing

Abstract

The work focuses on the study of the structure, phase composition, mechanical, electrical, and thermophysical properties, as well as the heat resistance and magnetocaloric effect of Fe2AlB2 MAB phase obtained by combining the self-propagating high-temperature synthesis and hot pressing. An investigation of the phase composition and structure of a consolidated sample disclosed that the main component of the ceramic is plate-like Fe2AlB2 grains with a thickness of 170–200 nm and a length of 2–5 μm. The resulting single-phase hot-pressed ceramics exhibited hardness values up to 12.8 GPa, fracture toughness up to 5.2 MPa∙m1/2, bending strength up to 429 MPa, and a thermal conductivity coefficient up to 7.47 W/(m∙K). A differential scanning calorimetry analysis revealed that at a temperature of 1284 °C the complete decomposition of Fe2AlB2 occurred. The magnetocaloric effect measured by the direct method was 0.92 K at a Curie temperature of 291 K. The heat resistance of Fe2AlB2 was studied at 1000 °C. It has been established that the oxidation process is governed by a linear law, whereby a multilayer structure of a heterogeneous oxide film is formed on the surface of the sample. The surface layer of the oxide film consisted of hematite α-Fe2O3, while the inner layer comprised boron-containing oxides in the form of iron warwickite Fe2BO4 and a porous layer of aluminum borate Al4B2O9, formed as needle/wire-shaped crystals. The formation of a FeB-based sublayer at the interface with the substrate has been established. The calculated oxidation rate after 30 h of testing was 5.55∙10−4 mg/(cm2∙s).