Effects of Nb/Ti Ratio on the Microstructures of Two Experimental Ni-Based Cast Superalloys

Abstract:

Effects of Nb/Ti ratio on the microstructures of two experimental Ni-based cast superalloys of the Nb/Ti ratio 0.46 and 0.03 were investigated. The Nb/Ti ratio had a significant effect on the dendritic microstructures, especially the γ precipitate, of the two alloys under the as-cast condition. The amount and composition of primary MC carbides were closely related to the Nb/Ti ratio for that the Nb atoms have a stronger tendency to form the MC carbides than the Ti atoms. During thermal exposure, the primary MC carbides gradually degraded through two reactions: firstly MC + γ M₆C + γ and then MC + γ M₂₃C₆ + γ. The Nb/Ti ratio had little influence on the reaction formation but obvious influence on the decomposition degree of the primary MC carbides decomposition. In addition, the second M₆C and M₂₃C₆ carbides on the boundaries (GBs) gradually formed a continuous chain during thermal exposure. The γ-free zones appeared along the GBs as the growth of the second carbides and γ precipitates on the GBs when thermal exposure time last up to 3000 h.

• Periodical: Materials Science Forum (Volumes 747-748)
• Pages: 629-635
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.747-748.629
• Online since: February 2013
• Authors: W. Sun, X.Z. Qin, W. Wang, T.T. Wang, Yong An Guo, J.T. Guo, Lang Hong Lou, Lan Zhang Zhou
• Keywords: Microstructural Evolution, Nb/Ti Ratio, Ni-Based Cast Superalloy, Thermal Exposure

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