Study of Microsegregation and Laves Phase in INCONEL718 Superalloy Regarding Cooling Rate During Solidification
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BASED on its good strength and excellent resistance to oxidation at elevated temperatures, INCONEL718,* *INCONEL718 is a trademark of Special Metals Corporation, Huntington, WV.
a nickel-iron base and Nb-strengthened superalloy, is widely used for key structural castings in aircraft turbine.[1,2] In order to reduce the weight of aircraft turbine, complex thin-wall components of the INCONEL718 alloy are usually adopted and manufactured by investment casting.[3,4] Because of the positional variation and structural differences, the cooling rates of
LISHIBAO LING, WEI ZHOU, and MAODONG KANG, Ph.D. Candidates, are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, No. 800 Dongchuan Road, Shanghai 200240, P.R. China. YANFENG HAN, Lecturer, HAIYAN GAO, Associate Professor, and DA SHU, Professor, are with the Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai Jiao Tong University. Contact e-mail: yfhan@ sjtu.edu.cn JUN WANG, Professor, is with the Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai Jiao Tong University, also with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, No. 800 Dongchuan Road, Shanghai 200240, P.R. China. BAODE SUN, Professor, Dean, is with the School of Materials Science and Engineering, Shanghai Jiao Tong University, also with the Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai Jiao Tong University, also with the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University. Manuscript submitted June 23, 2014. Article published online October 30, 2014 354—VOLUME 46A, JANUARY 2015
whole castings vary locally. As a result, some solidification defects, such as solute segregation and undesirable Laves phase, randomly form during solidification. The segregation and Laves phase increase the hot tearing sensitivity of INCONEL718 alloy castings and harmfully influence their final properties owing to the depletion of potent solution strengthening elements for Ni-rich matrix.[5,6] Therefore, the cooling rate is one of the most important technological parameters that should be controlled during manufacturing complex thin-wall components. It is known that the Laves phase is the product of a nonequilibrium eutectic reaction, L fi c + Laves, at the end of INCONEL718 alloy solidification, and its formation depends on the local nonequilibrium conditions of solidification and corresponding Nb redistribution.[7] Both experiment and modeling methods have been employed to investigate the solute concentration profile and eutectic phase along dendrite arms in the INCONEL718 microstructure.[8–10] However, the cooling rate complicatedly influences solidification parameters, and it is difficult to establish a quantitative relationship between the cooling rate and the fraction of Laves phase in the eutectic region in the INCONEL718 castings. Bower et al.[11] and Flemings[12] proclaimed that the cooling rate has little effect on the d
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