E système Mo-Ni-Re est un sous-système majeur des superalliages à base de Ni conçus pour une utilisation dans les applications à haute température. Compte tenu des contradictions entre les informations publiées antérieurement, cette étude a été consacrée à la détermination expérimentale complète des équilibres entre phases dans le système Mo-Ni-Re, à la caractérisation structurale des phases intermétalliques et à la modélisation thermodynamique du système à l'aide de la méthode CALPHAD. L'étude expérimentale des équilibres entre phases a été effectuée en utilisant des alliages à l'équilibre, et les diagrammes de phases du système Ni-Re et Mo-Ni-Re (à 1200°C et à 1600°C) ont été proposées. En comparaison avec les études précédentes, le diagramme de phases Ni-Re déterminé au cours de ce travail a montré des différences significatives en termes de domaines d'homogénéité, des domaines de cristallisation et de température de réaction péritectique. La coupe isotherme à 1200°C du système Mo-Ni-Re proposée lors de cette étude a montré l'extension importante de la phase σ du système binaire Mo-Re et de la phase δ du système Mo-Ni dans le diagramme ternaire. En outre, la présence de deux phases ternaires jusque-là inconnues a également été observée. La coupe isotherme du système Mo-Ni-Re à 1600°C a également montré une grande extension de la phase σ dans le diagramme ternaire tandis que l'extension de la phase χ du système Mo-Re dans les deux coupes isothermes est limitée à un étroit domaine de composition. Les phases ternaires observées dans la coupe isotherme à 1200°C ne sont pas présentes dans la coupe isotherme à 1600°C. D'autre part, les études partielles des domaines de composition des phases dans les systèmes binaires Mo-Ni et Mo-Re ainsi que la détermination de la projection du liquidus du système Mo-Ni-Re ont également été effectuées. La projection du liquidus du système Mo-Ni-Re proposée lors de la présente étude a également montré des champs de cristallisation primaire de la phase σ de système Mo-Re et la solution solide de Re dans la région ternaire qui sont largement étendus. Puisque la coupe isotherme du système Mo-Ni-Re a montré un domaine d'homogénéité de la phase σ très étendu, la caractérisation structurale de la phase σ du système ternaire Mo-Ni-Re a été effectuée en mettant l'accent sur la détermination de l'occupation des sites en fonction de la composition par affinement de Rietveld combiné des données de diffraction des rayons X et des neutrons. Les résultats expérimentaux recueillis au cours de cette étude ainsi que les informations disponibles dans la littérature ont été utilisés comme données d'entrée pour la modélisation thermodynamique du système Mo-Ni-Re. La description thermodynamique du système Mo-Re a été prise de la littérature tandis que les optimisations thermodynamiques des systèmes Mo-Ni, Ni-Re et Mo-Ni-Re ont été effectuées au cours de ce travail avec la méthode CALHAD.Mots-clés: Mo-Ni, Mo-Re, Ni-Re, Mo-Ni-Re; diagramme de phases; coupe isotherme; caractérisation structurale; modélisation thermodynamique; méthode CALPHAD / The Mo-Ni-Re system is one of the important subsystems of the Ni based superalloys engineered for use in high temperature applications. Considering the contradictions among previously reported information, the present study was devoted to the complete experimental determination of the phase equilibria in the Mo-Ni-Re system, structural characterization of its intermetallic phases and thermodynamic modeling of the system with the help of the CALPHAD method. The experimental investigation of phase equilibria was carried out with the help of equilibrated alloys and phase diagrams of the Ni-Re and Mo-Ni-Re system (at 1200°C and 1600°C) were proposed. In comparison with previous investigations, the Ni-Re phase diagram determined during the present study showed significant difference in terms of homogeneity domains, freezing ranges and peritectic reaction temperature. The 1200°C isothermal section of the Mo-Ni-Re system proposed during the present study showed large extension of the Mo-Re σ phase and Mo-Ni δ phase in the ternary region. In addition, presence of two previously unknown ternary phases was also observed. The isothermal section of the Mo-Ni-Re system at 1600°C also showed large extension of σ phase in the ternary region whereas extension of the Mo-Re χ phase in both isothermal sections was restricted to narrow composition range. The presence of the ternary phases observed in the 1200°C isothermal was not evidenced in 1600°C isothermal section. On the other hand, partial investigations of phase boundaries in the Mo-Ni and Mo-Re binary systems and determination of liquidus projection of the Mo-Ni-Re system was also carried out. The liquidus projection of the Mo-Ni-Re system proposed during present study also showed largely extended primary crystallization fields of the Mo-Re σ phase and Re solid solution in the ternary region. Since isothermal sections of the Mo-Ni-Re system showed largely extended homogeneity domain of σ, structural characterization of the Mo-Ni-Re σ with particular emphasis on determination of site occupancy trends as a function of composition was carried out by combined Rietveld refinement of the X-ray and neutron diffraction data. The experimental results gathered during the present study along with the information available in the literature were used as input for thermodynamic modeling of the Mo-Ni-Re system. The thermodynamic description of the Mo-Re system was taken from literature whereas thermodynamic modeling of the Mo-Ni, Ni-Re and Mo-Ni-Re system was carried out during the present study with the help of the CALHAD method.Keywords: Mo-Ni; Mo-Re; Ni-Re; Mo-Ni-Re; phase diagram; isothermal section; structural characterization; thermodynamic modeling; CALPHAD method

The Mo-Ni-Re system is one of the important subsystems of the Ni based superalloys engineered for use in high temperature applications. Considering the contradictions among previously reported information, the present study was devoted to the complete experimental determination of the phase equilibria in the Mo-Ni-Re system, structural characterization of its intermetallic phases and thermodynamic modeling of the system with the help of the CALPHAD method. The experimental investigation of phase equilibria was carried out with the help of equilibrated alloys and phase diagrams of the Ni-Re and Mo-Ni-Re system (at 1200°C and 1600°C) were proposed. In comparison with previous investigations, the Ni-Re phase diagram determined during the present study showed significant difference in terms of homogeneity domains, freezing ranges and peritectic reaction temperature. The 1200°C isothermal section of the Mo-Ni-Re system proposed during the present study showed large extension of the Mo-Re σ phase and Mo-Ni δ phase in the ternary region. In addition, presence of two previously unknown ternary phases was also observed. The isothermal section of the Mo-Ni-Re system at 1600°C also showed large extension of σ phase in the ternary region whereas extension of the Mo-Re χ phase in both isothermal sections was restricted to narrow composition range. The presence of the ternary phases observed in the 1200°C isothermal was not evidenced in 1600°C isothermal section. On the other hand, partial investigations of phase boundaries in the Mo-Ni and Mo-Re binary systems and determination of liquidus projection of the Mo-Ni-Re system was also carried out. The liquidus projection of the Mo-Ni-Re system proposed during present study also showed largely extended primary crystallization fields of the Mo-Re σ phase and Re solid solution in the ternary region. Since isothermal sections of the Mo-Ni-Re system showed largely extended homogeneity domain of σ, structural characterization of the Mo-Ni-Re σ with particular emphasis on determination of site occupancy trends as a function of composition was carried out by combined Rietveld refinement of the X-ray and neutron diffraction data. The experimental results gathered during the present study along with the information available in the literature were used as input for thermodynamic modeling of the Mo-Ni-Re system. The thermodynamic description of the Mo-Re system was taken from literature whereas thermodynamic modeling of the Mo-Ni, Ni-Re and Mo-Ni-Re system was carried out during the present study with the help of the CALHAD method.Keywords: Mo-Ni; Mo-Re; Ni-Re; Mo-Ni-Re; phase diagram; isothermal section; structural characterization; thermodynamic modeling; CALPHAD method