High-pressure phase transformations, microstructure, and magnetic properties of the hypereutectic alloy 10Ni-90Al

Abstract

Phase transformations of the hypereutectic alloy 10Ni-90Al have been studied by differential barothermal analysis at temperatures of up to 900°C and pressures of up to ≅100 MPa. We have determined the pressure coefficients of the liquidus and solidus temperatures and the temperatures of solid-state dissolution and precipitation of the intermetallic phase Al₃Ni. At high pressures, the solid-state decomposition of the supersaturated solid solution of nickel in aluminum occurs at 622°C and yields an (Al) + Al₃Ni mixture. We assume that, during cooling of the alloy at high pressure, intermetallic particles form in three steps. Barothermal analysis data have been compared to the canonical t-x phase diagram of the Al-Ni system. As a result of melting and crystallization at high pressure, the microcrystalline structure of the as-prepared alloy transforms to a macrocrystalline, dendritic structure and the micropore concentration increases. X-ray diffraction data indicate an increase in the unit-cell volumes of the Al and Al₃Ni in the alloy crystallized at 100MPa. We have studied the magnetic properties of the alloy after barothermal analysis.