Feature Article Continued from pg 41
During the thermodynamic calculation, the program considers an ideal contact between the melt and the oxide ceramic, which ensures even the same temperature of the ceramic at the interphase interface between the melt and the refractory. The model resolves the thermodynamic feature of the mentioned interactions, i.e. it addresses the driving force of these reactions and thus does not deal with their kinetics. The program is created in the Czech language and its English version is in progress. The description as above states the basic principles of
thermodynamic calculations used in the compiled program. Use of the program makes it possible to model which elements in the given alloy can react with the selected oxide phase that is formed by the melting crucible in the furnace or that forms the wall of the foundry mould. It is possible to reduce or even completely eliminate their interactions within the concentration range of the given element in the alloy. It is also possible to change the type of oxide ceramics as needed according to the established interactions. Carbon has a crucial impact for metallurgy. It is an element that under the standard conditions, i.e. gas pressure of
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Metsch offers a complete line of pre-formed consumable ceramic products for use directly on investment casting molds to provide high temperature mechanically strong support of the wax assembly and shell throughout the casting process. The Metsch product line includes Pour Cups, Mold Support Rods and Vent Plugs.
101325 Pa above the melt, does not have a sufficiently high affinity to oxygen for reduction of the assumed oxides. In case of nickel alloys, vacuum metallurgy is used as a rule. Under these conditions (deep vacuum), carbon already has a high affinity to oxygen and can react with oxide ceramics to form carbon monoxide and dissolve metal from oxide ceramics into the melt. Some authors assume formation of oxide particles of films and bifilms during vacuum casting of nickel alloys [2,3]. Their formation is always linked to the melting conditions, especially to the value of gas pressure above the melt and temperature of the given alloy. Some authors, on the other hand, consider occurrence of these particles and films improbable under optimal vacuum melting conditions [4,5]. The program enables to model conditions of the vacuum melting (pressure of gases above the melt and temperature of the melt) so that reduction of possible oxide phases by carbon may take place. This avoids formation of oxide phases during melting and subsequent casting. This also clarifies the reason why, for example, even the alloys for single crystal casting also contain carbon, which plays an important metallurgical function here, i.e. eliminates formation of oxides of the elements with a high deoxidation capacity [6]. The created program gives the opportunity to understand better the issue of interactions between the molten metals and oxide ceramics. In some cases, this even allows to optimize composition of the melt or to choose a more suitable type of the oxide ceramics for producers of nickel alloy castings and ingots. The aim of the authors is to extend interactions of oxide ceramics by iron alloys as well. Further expansion of the model, be it by new oxide materials or alloys, is often related to the lack of suitable and complete thermodynamic data.
Literature [1] BŮŽEK, Z. Hutnické aktuality, 20, 1-2, 1979 [2] RASHID, A.K.M.B., CAMPBELL, J. Oxide defects in a
vacuum investment-Cast Ni based turbine blade. Metallurgical Transactions A, Volume 35A, 2004, pp. 2063-2071. [3] CAMPBELL, J. TIRYAKIOGLU, M. Bifilm defects in
Ni-based alloy Castings. Metallurgical Transactions B, Volume 43B, 2012, pp. 902-914.
[4] KAPLAN, M.A, GUARRIELLO, R.K., FUCHS, G.E.
Investigation of oxide bifilms in investment cast superalloy IN100. Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys. pp. 313-322. [5] KAPLAN, M.A, FUCHS, G.E. Investigation of
oxide bifilms in investment cast superalloy IN100: Part II Characterization. Metallurgical Transactions A, Volume 47A, 2016, pp. 2362-2375.
[6] MIHALISIN, J.R., CORRIGAN, J., LAUNSBACH,
Metsch Refractories Inc., 12413 Ohio River Blvd, Chester, WV 26034 USA +1 (304) 387–1067
info@metschinc.com
www.metschinc.com
M., LEONARD, E., BAKER, R., GRIFFIN, B. Some effects of carbon in the production of single crystal superalloy castings. Superalloy 2004. pp. 795-800.
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