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Article

Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations

by
Baohui Zhu
1,†,
Zhenzhen Chen
2,3,†,
Yanfei Cao
2,*,
Yanchang Liu
1,
Xiuhong Kang
2,
Yun Chen
2,
Hongwei Liu
2,
Paixian Fu
2,
Yikun Luan
2 and
Dianzhong Li
2,*
1
State Key Laboratory of Special Rare Metal Materials, Northwest Rare Metal Materials Research Institute Ningxia Co., Ltd., Shizuishan 753000, China
2
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
3
School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Materials 2021, 14(4), 796; https://doi.org/10.3390/ma14040796
Submission received: 11 January 2021 / Revised: 2 February 2021 / Accepted: 3 February 2021 / Published: 8 February 2021
(This article belongs to the Special Issue Mechanical and Metallurgical Characterizations of Advanced Alloys)
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Abstract

Channel segregation (CS) is the most typical defect during solidification of NbTi alloy. Based on numerical simulation and experimental characterizations, we deeply elucidated its characteristics, formation mechanism, effecting factor and prediction criterion. According to acid etching, industrial X-ray transmission imaging, 3D X-ray microtomography and chemical analysis, it was found that in a casing ingot, by He cooling, finer grain size, weaker segregation and slighter CS can be obtained compared with air-cooled ingot. The simulation results of macrosegregation show that CS is caused by the strong natural convection in the mushy zone triggered by the thermo-solutal gradient. Its formation can be divided into two stages including channel initiation and growth. In addition, due to the stronger cooling effect of the He treatment, the interdendritic flow velocity becomes smaller, consequently lowering the positive segregation and CS and improving the global homogenization of the final ingot. Finally, to predict the formation of CS, the Rayleigh number model was proposed and its critical value was found to be 15 in NbTi alloy for the first time. When it is lower than the threshold, CS disappears. It provides an effective tool to evaluate and optimize the solidification parameters to fabricate the homogenized NbTi ingot in engineering practice.
Keywords: NbTi alloy; channel segregation; simulations; experimental characterizations; criterion NbTi alloy; channel segregation; simulations; experimental characterizations; criterion

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MDPI and ACS Style

Zhu, B.; Chen, Z.; Cao, Y.; Liu, Y.; Kang, X.; Chen, Y.; Liu, H.; Fu, P.; Luan, Y.; Li, D. Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations. Materials 2021, 14, 796. https://doi.org/10.3390/ma14040796

AMA Style

Zhu B, Chen Z, Cao Y, Liu Y, Kang X, Chen Y, Liu H, Fu P, Luan Y, Li D. Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations. Materials. 2021; 14(4):796. https://doi.org/10.3390/ma14040796

Chicago/Turabian Style

Zhu, Baohui, Zhenzhen Chen, Yanfei Cao, Yanchang Liu, Xiuhong Kang, Yun Chen, Hongwei Liu, Paixian Fu, Yikun Luan, and Dianzhong Li. 2021. "Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations" Materials 14, no. 4: 796. https://doi.org/10.3390/ma14040796

APA Style

Zhu, B., Chen, Z., Cao, Y., Liu, Y., Kang, X., Chen, Y., Liu, H., Fu, P., Luan, Y., & Li, D. (2021). Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations. Materials, 14(4), 796. https://doi.org/10.3390/ma14040796

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