Effect of melting pressure and superheating on chemical composition and contamination of yttria coated ceramic crucible induction melted titanium alloys

摘要

When melting reactive alloys, chemical compositionand alloy homogeneity strongly depend on processingconditions, especially if melting is performed in ceramiccrucibles. In this case, the nature of crucible materials, themelting stock composition and the melting parameters(atmosphere, pressure, superheating time and temperature)are critical processing variables. In this work, a Ti–48Al alloywas induction melted in a ZrO2 SiO2-based crucible withY2O3 inner layer using different superheating temperatures(1600 and 1650 C) and times (0, 60 and 90 s) and poured intoa graphitemould. The influence of different temperature/timecombinations in the alloy composition, Al loss by evaporationand metal/crucible interaction was studied for differentmelting pressures. Al loss was found to increase significantlyfor melting pressures below 10-2 mbar and increases withincreasing superheating time and temperature. The experimentalresults concerning to Al loss are in agreement withtheoretical (and experimentally validated) models availablefor induction skullmelting of TiAl.Metal/crucible interactiondirectly increased with melting pressure, superheating timeand temperature, leading to alloy contamination withYand O.For the experimental set-up used in this work, optimal temperature/superheating time/pressure combinations that lead toacceptable alloy composition have been identified.