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Effect of carbon on structural changes in Ni3Al phase

Janas A., Olejnik E.

Archives of Foundry Engineering

2011

Vol. 11, iss. 4

65-68

The paper presents diffraction and microscopic researches of a carbon influence on structural changes in Ni3Al phase. Ni3Al phase was acquired thanks to vacuum casting technology with a use of Exo-Melt process. A casting process was conducted in the atmosphere of argon. Two basic alloys were made with maintaining the nominal nuclear share equivalent to stoichiometry of Ni3Al phase. Next, carbon was instilled into the liquid alloy in the rate of 0,2% and 1,25% respectively for the first and for the second alloy. Final casts were cut into pieces and the samples were prepared in order to undertake and microscopic researches. Their phase composition was analyzed as well as their structural changes occurring within Ni3Al phase. Some changes along the lattice constants of Ni3Al phase were noticed, and they were 0,3580 nm and 0,3589 nm respectively for 0,2% C and 1,25% C. In the alloy consisting of 2,25% C a graphite (001) atomic plane was noticed. Its existence is connected with transgression in solubility limit of carbon in Ni3Al phase. This result was also confirmed by researches with SEM imaging, in which we observed numerous of separation of graphite of lamellar and nodular shape.

Synthesis and evaluation of the structure of Ni3Al/C alloy

Kmita A., Janas A., Hutera B.

Metallurgy and Foundry Engineering

2009

Vol. 35, no. 2

147-154

The article specifies a method used for the manufacture of a new Ni-Al-C alloy with the description of alloy microstructure. When proper conditions are maintained, the said alloy after solidification forms a natural "in situ" Ni3Al/C composite. Particular attention was paid to the process of synthesis of Ni3Al phase by the technique of cost-effective melting and to the process of the formation of different graphite forms after the solidification in ceramic mould of casting characterised by different wall cross-sections, and hence by different heat transfer rates. Metallographic examinations were carried out by the commonly used techniques and by scanning electron microscopy. The use of the latter enabled the determination of the chemical composition of phases formed during casting process. The aim of the present studies was to evaluate the microstructure of this unique alloy. The phase morphologies were examined and their chemical composition was determined. These fundamental studies should enable the determination of conditions under which the graphite eutectic is formed in Ni-Al alloy and, as a consequence, the synthesis of Ni3Al/C composite.

W prezentowanym artykule przedstawiono metodę otrzymywania nowego stopu Ni-Al-C oraz opisano jego mikrostrukturę. Przy zachowaniu odpowiednich warunków stop ten, po procesie krystalizacji, tworzy naturalny kompozyt ,,in situ" Ni3Al/C. Zwrócono szczególną uwagę na proces syntezy fazy Ni3Al metodą OPW (oszczędnościowego procesu wytopu) i tworzenia się różnych form grafitu po procesie krystalizacji w formie ceramicznej, przy różnych grubościach odlewu, co za tym idzie, przy różnych prędkościach odprowadzenia ciepła. Do badań metaloznawczych wykorzystano tradycyjne metody metalograficzne oraz badania z wykorzystaniem mikroskopu skaningowego. Zastosowanie tego ostatniego umożliwiło określenie składu chemicznego faz, wytworzonych w procesie odlewniczym. Celem podjętych badań było dokonanie oceny mikrostruktury tego nietypowego stopu. Zbadano morfologię występujących faz i określono ich skład chemiczny. Te badania o charakterze podstawowym, pozwolą określić warunki powstawania eutektyki grafitowej w stopie Ni-Al, co w konsekwencji umożliwi syntezę kompozytu Ni3Al/C.