Vacuum induction melting and solidification of TiAl-based alloy in graphite crucibles

Abstract

The effect of vacuum induction melting and solidification in graphite crucibles on chemical composition, microstructure and mechanical properties of Ti-46.6Al-5Nb-0.2B-0.2C (at.%) alloy was studied. The induction melting and solidification under a vacuum pressure of 1 × 104 Pa (low vacuum) has no significant effect on the content of the alloying elements such as Ti, Al, Nb and B but leads to an increase of carbon content to 0.49 at.%. A vacuum pressure of 6.8 Pa (medium vacuum) leads to an increase of C content to 0.68 at.% and decrease of Al content to 45.5 at.% due to its evaporation loss on the expense of increasing Ti and Nb. The medium vacuum results in lower cooling rates, coarser columnar grain structure and finer interlamellar spacing compared to those of the samples prepared under the low vacuum. The Vickers microhardness and hardness of the samples prepared under the medium vacuum is higher than that of the samples prepared under the low vacuum. The melting and solidification under the medium vacuum leads to an increase of compression yield and peak flow stresses at temperatures of 850 and 900 °C compared to those of the as-solidified samples prepared under the low vacuum.