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Direct Determination Of γ′ / γ′+γ / γ Phase Boundaries in Ni-Al-Cr System Based on Enthalpy of Formation Results Obtained by Calorimetric Solution Method

Maciąg T., Rzyman K., Węcki B.

Archives of Metallurgy and Materials

2015

Vol. 60, iss. 3A

1657--1662

he work is a continuation of the research carried out on a high-temperature calorimeter solution type on alloys from Ni-Al-Cr system. Thanks to the construction innovation introduced by authors the device allows the determination of the formation enthalpy of alloys at ambient and elevated temperatures. Experiments described in this article were carried out at three temperatures: 873K, 996K and 1150K on the alloys of the chemical compositions from the Ni75Al25 ÷ Ni87Cr13 section of the Ni-Al-Cr system. On the basis of changes in the enthalpy of formation with increasing chromium content of the alloys, points corresponding to places of phase boundaries γ′ / γ′+γ / γ in Ni-Al-Cr system were determined. A similar relationship was observed in previous studies of alloys from Ni75Al25÷Ni75Cr25 section. For precise determination of these characteristic points a statistical model was applied.

Praca jest kontynuacją badań prowadzonych na skonstruowanym przez autorów wysokotemperaturowym kalorymetrze typu rozpuszczania. Urządzenie pozwala na określanie entalpii tworzenia stopów w podwyższonej temperaturze. Opisywane badania przeprowadzono w trzech temperaturach: 873K, 996K i 1150K na stopach o składach chemicznych znajdujących się na linii Ni75Al25÷Ni87Cr13 układu Ni-Al-Cr. Na podstawie zmian wartości entalpii tworzenia wraz ze wzrostem zawartości chromu w stopach stwierdzono istnienie punktów odpowiadających miejscom występowania granic międzyfazowych γ′ / γ′+γ / γ w układzie Ni-Al-Cr. Podobną zależność zaobserwowano w poprzednich badaniach dotyczących obszaru Ni75Al25÷Ni75Cr25. Aby precyzyjnie wyznaczyć te charakterystyczne punkty opracowano i zastosowano model statystyczny.

Calorimetric studies of the enthalpies of formation of alloys from Ni75Al25-Ni75Cr25 and Ni75Al25-Ni85Cr15 sections at 873 K

Maciąg T., Rzyman K.

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 55, nr 2

275--279

Purpose: The main purpose of the study was to determine value of formation enthalpy ΔfH of Ni3Al-based alloys with chromium additions at temperature 873 K. Experiment was carried in order to determine the course of phase boundaries γ’ / γ’+ γ / γ for Ni-Al-Cr system. Design/methodology/approach: Experiment was performed with use of high temperature solution calorimeter. This “in situ” method allows to determine formation enthalpy in a wide range of temperature thanks to intermediate multi socket container which was applied in the device. It is fundamental because keeping the structure of examined alloys during quenching is extremely difficult, often impossible in this type of alloys. Findings: Distinct breaks in the course of enthalpy of formation ΔfH as a function of chromium concentration were discovered, that are assigned to courses of γ’ / γ’+ γ / phase boundaries. Research limitations/implications: Experiment will be proceeded at higher temperatures and completed with resistometric measurements. All results will be used in CAPLHAD procedure in order to optimize course of phase boundaries. Originality/value: The results are valuable thermodynamic data and method proposed can become a new way of direct determination of phase boundaries in metallic systems.