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The Formation of Nial Phase and Layered Carbon Precipitates During Ni3Al/SiC Solid State Reactions

Published online by Cambridge University Press:  26 February 2011

T. C. Chou
Affiliation:
Lockheed Missiles and Space Company, Research and Development Division, O/93–10, B/204, Palo Alto, CA 94304
T. G. Nieh
Affiliation:
Lockheed Missiles and Space Company, Research and Development Division, O/93–10, B/204, Palo Alto, CA 94304
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Abstract

Solid state reactions of Ni3A1 with SiC have been studied at 1000°C. Three layered reaction products consisting of NiAl Ni5,4Al1Si2, and Ni(5.4−x)A11Si2+C were formed in the reaction zone. The Ni5.4AllSi2 layer showed carbon precipitation free, while modulated carbon bands were formed in the Ni(5.4−x)A11Si2+C layer. Carbon precipitates were found to exist in either a disordered or partially ordered (graphitic) state, depending upon their locations from the SiC reaction interface. The NiAl layer showed dramatic contrast difference compared to the Ni3Al and Ni5.4Al1Si2 layers, and was bounded by the Ni3Al/NiAl and NiAl/Ni5.4A1lSi2 phase boundaries. The kinetics of the NiAl formation was limited by diffusion, and the growth rate constant was measured to be 2 × 10−10cm2/s. The thickness of the reaction zone on the Ni3Al side was always greater than that on the SiC side, suggesting that the decomposition of the SiC may be a rate limiting step for the SiC/Ni3Al reactions. An Al-rejection model, based on a lower solid solubility of Al in the Ni-Al-Si ternary phase than in the Ni3A1 intermetallic compound, is proposed to explain the formation of NiAl phase. The rate limiting step for the Ni3Al/SiC reactions is discussed in light of discontinuous decomposition of SiC, which leads to the formation of alternating C and Ni(5 4−x)Al1Si2 layers in the reaction zone. Preliminary results on C precipitation behavior in NiAl/SiC system are reported.

Type
Research Article
Copyright
Copyright © Materials Research Society 1991

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