A thermodynamic approach has been used to progress in the understanding of the chemical
processes taking place in the casting furnaces. The ceramic mould materials used for
the casting of superalloys vaporize at high temperature under vacuum and the vapors
condense then in the colder zones of the furnace. In addition, the graphite of the
furnace resistor perturbs the vaporization regime of the moulds and is at the origin
of other vaporization and condensation processes. The deposition regime of impurities
leading to inclusions formation during the casting of the metal is modified. The
thermodynamic analysis is confirmed by observations made on the superalloy casting
furnaces. The deposits observed and characterized correspond to those predicted by
the thermodynamic analysis, but the mass losses of the moulds producing these
deposits are 60 times smaller than predicted.