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Influence of solidification rate on precipitation and microstructure of directional solidification IN792 + Hf superalloy

Published online by Cambridge University Press:  31 January 2011

W. R. Sun ,
Z. Q. Hu ,
J. H. Lee ,
S. M. Ceo  and
S. J. Choe
W. R. Sun
Affiliation:
Department of Superalloys and Special Castings, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110015, People's Republic of China
Z. Q. Hu
Affiliation:
State Key Laboratory of Rapidly Solidified Nonequilibrium Alloy, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110015, People's Republic of China
J. H. Lee
Affiliation:
Department of Metallurgy and Materials Science, Changwon National University, 9 Sarim-Dong, Changwon, Kyungnam, 641–773, Korea
S. M. Ceo
Affiliation:
High Temperature Materials Laboratory, Korea Institute of Machinery and Materials, 66 Sangnam Dong, Changwon, Kyungnam, 641–010, Korea
S. J. Choe
Affiliation:
High Temperature Materials Laboratory, Korea Institute of Machinery and Materials, 66 Sangnam Dong, Changwon, Kyungnam, 641–010, Korea
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Abstract

The effect of solidification rate on the precipitation and microstructure of directional solidification IN792 + Hf alloy was studied. The solidification sequence and the initial precipitation temperature of different phases were determined by the observation of the quenched microstructure combined with the differential thermal analysis measurement. The script carbide was turned into faceted carbide with the drop of solidification rate. It was concluded by microstructure analysis that the faceted carbide was pushed by the γ solid front before it was captured. The incorporation of γ phase into the faceted carbide was due to the dendrite growth of the carbide toward one point and the mergence of the dendrites. Some long carbide bars were formed along the grain boundaries by continual reaction of eutectic (γ + MC carbide) at a solidification rate of 0.5 μm/s. Two zones, the γ′ forming elements enriched zone and depleted zone, were found in the residual liquid area. Eutectic γ/γ′ nucleated in the γ′ forming elements enriched zone. The η-phase precipitation was controlled by the ratio of (Ti + Hf + Ta + W)/Al in the residual liquid. The growth of eutectic γ/γ′ increased the ratio and induced the η-phase precipitation. A lower solidification rate decreased the ratio by sufficient diffusion and hence efficiently suppressed the η-phase precipitation.

Type
Articles
Information
Journal of Materials Research , Volume 14 , Issue 10 , October 1999 , pp. 3873 - 3881
Copyright
Copyright © Materials Research Society 1999

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