Costa, A. M.S.Lopes, E. S.N.Contieri, R. J.Caram, R.Baldan, R. [UNESP]Fuchs, G. E.Nunes, C. A.2019-10-062019-10-062019-04-01Journal of Materials Engineering and Performance, v. 28, n. 4, p. 2427-2438, 2019.1544-10241059-9495http://hdl.handle.net/11449/188989This study analyzes the effects of replacing Ta by Nb (at.% basis) in the phase transformation temperatures, Scheil solidification behavior, and microstructural mechanical features of a Nb-modified as well as conventional Mar-M247 superalloys. Both alloys were directionally solidified at a withdrawal rate of 18 cm/h under a thermal gradient of about 80 °C/cm. DSC results were compared to thermodynamic simulations of phase transformation temperatures and showed a good correlation. The replacement of Ta by Nb has not altered the solidification path of Mar-M247, keeping the sequence L → L + γ → L + γ + MC → L + γ + MC + γ/γ′ eutectic. Due to the segregation of Hf and Zr to the very last liquid to solidify, a low melting point γ/Ni 5 (Hf,Zr) constituent was observed. The as-solidified microstructures of both Mar-M247(Nb) and Mar-M247 were constituted of columnar dendrites of gamma matrix (γ) phase with cuboidal gamma-prime (γ′) precipitates. In addition, γ/γ′-eutectic was observed in the interdendritic region along with MC carbides in blocky, script (blocky dendritic), needle-like and fine nodular morphologies. Both alloys contained about 1.5 vol.% of MC carbides. The MC carbides in Mar-M247(Nb) and Mar-M247 are, respectively, Nb-rich and Ta-rich, with only a limited amount of Hf being detected in the MC phase. The yield stress of Nb-modified Mar-M247 showed higher values up to 750 °C. For higher temperatures, above 800 °C, a conventional Mar-M247 presented a higher value of yield stress.2427-2438engMar-M247 superalloyNb-modified Mar-M247thermodynamic simulationArtigo10.1007/s11665-019-04014-1Acesso aberto2-s2.0-8506443201515140195362246320000-0003-4172-3689