Phase instabilities and carbon additions in single-crystal nickel-base superalloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 348; no. 1; pp. 111 - 121
• Main Authors: Tin, S., Pollock, T.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.05.2003; Elsevier
• Subjects: Cellular precipitation; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase instabilities; Physics; Precipitation; Single-crystal Ni-base superalloys; Solid-phase precipitation; Topologically close-packed phases; Cellular precipitation; Phase instabilities; Single-crystal Ni-base superalloys; Topologically close-packed phases; Nickel base alloys; Scanning electron microscopy; Segregation; Topologically close-packed phases: Phase instabilities; Experimental study; Superalloys; Carbon additions; Optical microscopy; Monocrystals; Precipitation; Impurities; Dendrites; Phase stability; Carbides; Transition element alloys
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(02)00637-8

The phase stability of a number of experimental single-crystal nickel-base superalloys with elevated levels of rhenium, tungsten and tantalum (Ta) has been studied. Carbon additions of 0.1 wt.% were found to enhance the phase stability of the as-cast alloys, with respect to inhibiting the formation of topologically close-packed (TCP) phases. In addition to forming a variety of primary Ta-rich MC carbides upon solidification, intentional carbon additions also affected the segregation behavior of the constituent refractory elements. Comparison of experimentally measured distribution coefficients assessed via application of a Scheil-type analyses revealed reduced segregation of the refractory elements associated with precipitation of TCP phases in the carbon-containing alloys.