Abstract
The constitutional liquation of NbC wrought alloy 718 is discussed in terms of a diffusion couple between NbC and they matrix in a pseudo-ternary of γ-NbC-Laves. Theoretical arguments are presented to show that the diffusion path cannot be a straight line connecting the terminal compositions. Experimental results indicate the existence of the NbC-γ diffusion couple and also support the hypothesis that the diffusion path is not a straight line connecting NbC and γ. Consequently, the temperature at which carbide liquation can occur is below the equilibrium NbC solidus, and hence, carbide liquation is constitutional in nature. The lowest temperature at which carbide liquation initiates depends upon the extent of deviation of the diffusion path from the straight line path. The dependence of the relative volume fractions of carbide and Laves phase in cast alloys on Nb/C ratio is explained using the γ-NbC-Laves pseudo-ternary. The Laves phase present in cast alloys is shown to liquate at the terminal eutectic temperature of the alloy, which could be lower than the carbide liquation temperature.
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D.S. Duvall and WA. Owczarski:Weld. J., Sept. 1967, vol. 46 (9), pp. 423s-432s.
B. Weiss, G.E. Grotke, and R. Stickler:Weld. J., Oct. 1970, vol. 49 (10), pp. 471s-487s.
J.J. Pepe and W.F. Savage:Weld. J., Dec. 1970, vol. 49 (12), pp. 545s-553s.
J.A. Brooks:Weld. J., Nov. 1974, vol. 53 (11), pp. 517s-523s.
W.A. Baeslack III, S.J. Savage, and F.H. Froes :J. Mater. Sci. Lett., 1986, pp. 935-39.
J.J. Pepe and W.F. Savage:Weld. J., Sept. 1967, vol. 46 (9), pp. 411s-422s.
R.G. Thompson and S. Genculu:Weld. J., Dec. 1983, vol. 62 (12), pp. 337s-345s.
W.A. Baeslack III and D.E. Nelson:Metallography, 1986, vol. 19, pp. 371–79.
P.J. Valdez and J.B. Steinman:Effect of Minor Elements on the Weldability of High-Nickel Alloys, Welding Research Council, New York, NY, 1969, pp. 93–120.
E.G. Thompson:Weld. J., Feb. 1969, vol. 48 (2), pp. 70s-79s.
T.J. Kelly:Trends in Welding Research, ASM, Metals Park, OH, 1986.
H.L. Eiselstein:Advances in the Technology of Stainless Steels and Related Alloys, ASTM STP 369, ASTM, Philadelphia, PA, 1965, pp. 62–79.
G.A. Knorovsky, M.J. Cieslak, T.J. Headley, A.D. Romig, and W.F. Hammetter:Metall. Trans. A, 1989, vol. 20A, pp. 2147–56.
G.K. Bouse:Superalloy 718 Metallurgy and Applications, TMS, Warrendale, PA, 1989, pp. 69–77.
B. Radhakrishnan and R.G. Thompson:Metall. Trans. A, Dec. 1989, vol. 20A, pp. 2866–68.
R. Vincent:Acta Metall., July 1985, vol. 33 (7), pp. 1205–16.
D.B. Williams:NORELCO Reporter, 1982, vol. 29 (3), pp. 6–41.
B. Radhakrishnan and R.G. Thompson:Recent Trends in Weld- ing Science and Technology, TNR '89, ASM INTERNA-TIONAL, Metals Park, OH, 1990, pp. 637–48.
J.M. Poole, K.R. Stultz, and J.M. Manning:Proc. Int. Symp. on the Metallurgy and Applications of Superalloy 718, Pittsburgh, PA, June 12–14, 1989, TMS, Warrendale, PA, 1989, pp. 219–28.
B. Radhakrishnan and R.G. Thompson:Metallography, 1988, vol. 21, pp. 453–71.
D. Mayo: Masters Thesis, University of Alabama at Birmingham, Birmingham, AL, 1987.
J.S. Kirkaldy and D.J. Young:Diffusion in the Condensed State, The Institute of Metals, London, 1987, p. 366.
J.B. Clark:Trans. TMS-A1ME, 1963, vol. 227, pp. 1250–51.
A. Pasparakis, D.E. Coates, and L.C. Brown:Acta Metall., 1973, vol. 21, pp. 991–1001.
A.D. Rmig, Jr., J.C. Lippold, and M.J. Cieslak:Metall. Trans. A, 1988, vol. 19A, pp. 35–50.
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Radhakrishnan, B., Thompson, R.G. A phase diagram approach to study liquation cracking in alloy 718. Metall Trans A 22, 887–902 (1991). https://doi.org/10.1007/BF02658999
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DOI: https://doi.org/10.1007/BF02658999