Dear Sara,

the formation of oxides clearly depends on the vacuum pressure as well as on the composition of the residual gas and the temperature. Usually, the is a thermodynamic equilibrium between the different involved phases depending on temperature and pressure. Check the literature for more details, there are theoretical calculations on this topic, and there is software available for this purpose. Also the solubility of oxygen in the different phases plays a role, as well as the enthalpy of formation… see e.g.

Article Influence of atmosphere during vacuum heat treatment of stai...

https://doi.org/10.1016/j.jmatprotec.2018.08.038

or

Article A surface analytical approach to the high temperature chlori...

https://doi.org/10.1016/S0010-938X(96)00112-6

and related works. Hope this helped, Dirk

Dear Sara,

as Dirk said above, the formation of certain oxides in a vacuum when heated depends on the temperature and on the partial pressure of oxygen in the vacuum furnace. When the vacuum is very high, thin transparent films of aluminum oxide form on the surface of your Inconel. It is also possible to stain the transparent film of aluminum oxide in a blue color from the admixture of titanium oxide. If the vacuum in the furnace is poor, then, just as when heating in air, green chromium oxide is formed.

Thank you Sara Aghaie for the interesting question. Vadim Verlotski well addressed the explanation for what oxides that can be formed after we put a clean piece of Inconel 738 into the vacuum furnace . I just want to add that practically this oxidation problem becomes the reason why one would nickel plating the Inconel 738 surface prior to vacuum brazing process as this action will shield the surface of the alloy against any oxygen from being able to reach any of the titanium or aluminum atoms in the Inconel 738 to form oxides.

Hope you success and progress

Best regards

Thank you all for your great guidance Mohammed Hussein j. H. Al'Atia

Dirk Luetzenkirchen-Hecht Vadim Verlotski