Microstructural and Mechanical Characterization of Directionally Solidified Conventional and Nb-Modified Mar-M247 Superalloy
- 19 Downloads
This 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/Ni5(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.
KeywordsMar-M247 superalloy Nb-modified Mar-M247 thermodynamic simulation
The authors acknowledge CAPES (Brasília, Brazil) for funding and supporting this project (Program RIPS/Pró-Engenharias).
- 1.E.W. Andersson, Factors Affecting the Supply of Strategic Raw Materials with Particular Reference to the Aerospace Manufacturing Industry, Durham Univ (United Kingdom) Dept of Geography, 1984.Google Scholar
- 2.J.R. Stephens, R.L. Dreshfield, and M.W. Nathal, Replacing Critical and Strategic Refractory Metal Elements in Nickel-Base Superalloys, [NASA’s COSAM program], 1983.Google Scholar
- 4.M.V. Nathal and L.J. Ebert, Influence of Composition on the Microstructure and Mechanical Properties of a Nickel-Base Superalloy Single Crystal, Superalloys, 1984, 1984, p 125–133Google Scholar
- 5.Z. Meng, G. Sun, and M. Li, The Strengthening Effect of Tantalum in Nickel-base Superalloys, Superalloys, 1984, 1984, p 563–572Google Scholar
- 6.J.K. Tien, J.P. Collier, and G. Vignoul, “The Role of Niobium and Other Refractory Elements in Superalloys,” Superalloys 718—Metallurgy and Applications, E.A. Loria, Ed., The Minerals, Metals and Materials Society, 1989, p 553–566.Google Scholar
- 7.J.R. Brinegar, J.R. Mihalisin, and J. VanderSluis, The Effects of Tantalum for Columbium Substitutions in Alloy 713C, Superalloys, 1980, 1984, p 53–61Google Scholar
- 8.J.R. Kattus, Nickel Base Alloys (MAR-M-247), Aerospace Structural Metals, 1999, p 1–8.Google Scholar
- 9.K. Harris, G.L. Erickson, and R.E. Schwer, MAR M 247 Derivations—CM 247 LC DS Alloy CMSX Single Crystal Alloys Properties & Performance, Superalloys, 1984, 1984, p 221–230Google Scholar
- 10.T.E. Strangman, G.S. Hoppin, III, C.M. Phipps, R.E. Schwer, and K. Harris, Development of Exothermically Cast Single-Crystal Mar-M 247 and Derivative Alloys, Superalloys, 1980, 1980, p 215–224Google Scholar
- 12.FIZ Karlsruhe, Inorganic Crystal Structure Database (ICSD) Scientific Manual, 2008, p 1–14.Google Scholar
- 13.“TTNI8: Thermotech Ni-Based Superalloys Database-Version 8, Thermo-Calc Software, Accessed 03-01-2018.Google Scholar
- 15.S. Milenkovic, I. Sabirov, and J. Llorca, Effect of the Cooling Rate on Microstructure and Hardness of MAR-M247 Ni-Based Superalloy, Mater. Lett., Elsevier B.V., 2012, 73, p 216–219, https://doi.org/10.1016/j.matlet.2012.01.028.
- 17.Z. Weiguo, L. Lin, and F. Hengzhi, Effect of Cooling Rate on MC Carbide in Directionally Solidified Nickel-Based Superalloy under High Thermal Gradient, CHINA FOUNDRY, 2012, 9(1), p 1–14Google Scholar
- 18.Z.H. Yu, L. Liu, X.B. Zhao, W.G. Zhang, J. Zhang, and H.Z. Fu, Effect of Solidification Rate on MC-Type Carbide Morphology in Single Crystal Ni-Base Superalloy AM3, Trans. Nonferrous Met. Soc. China (English Ed., The Nonferrous Metals Society of China, 2010, 20(10), p 1835–1840, https://doi.org/10.1016/s1003-6326(09)60382-4.
- 23.R. Sellamuthu and A.F. Giamei, Measurement of Segregation and Distribution Coefficients in Mar-M200 and Hafnium-Modified Mar-M200 Superalloys., Metall. Trans. A, Phys. Metall. Mater. Sci., 1986, 17 A(3), p 419–428.Google Scholar
- 26.E. Guo, Z. Han, and S. Yu, Influence of Niobium on Steady-State Creep Behaviour of Ni-Cr-Ti Type Wrought Superalloy, Superalloys, 1984, 1984, p 583–590Google Scholar
- 27.S.L. Shang, C.L. Zacherl, H.Z. Fang, Y. Wang, Y. Du, and Z.K. Liu, Effects of Alloying Element and Temperature on the Stacking Fault Energies of Dilute Ni-Base Superalloys, J. Phys. Condens. Matter, 2012, 24(50).Google Scholar
- 28.B. Gan and S. Tin, Assessment of the Effectiveness of Transition Metal Solutes in Hardening of Ni Solid Solutions, Mater. Sci. Eng. A, Elsevier B.V., 2010, 527(26), p 6809–6815, https://doi.org/10.1016/j.msea.2010.06.071.