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Open AccessArticle

Effect of C Addition on as-Cast Microstructures of High Nb Containing TiAl Alloys

by Jinhu Liu 1, Fuqiang Zhang 2, Hai Nan 1,3,4, Xin Feng 1,3,4 and Xianfei Ding 1,3,4,*
1
Cast Titanium Alloy R&D Center, Beijing Institute of Aeronautical Materials, Beijing 100095, China
2
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
3
Beijing Engineering Research Center of Advanced Titanium Alloy Precision Forming Technology, Beijing Institute of Aeronautical Materials, Beijing 100095, China
4
BAIMTEC Material Co., Ltd., Beijing 100094, China
*
Author to whom correspondence should be addressed.
Metals 2019, 9(11), 1201; https://doi.org/10.3390/met9111201
Received: 10 October 2019 / Revised: 28 October 2019 / Accepted: 5 November 2019 / Published: 7 November 2019
Two high Nb-containing TiAl alloys, Ti46.6Al7.5Nb0.5Si0.2B (Alloy A) and Ti46.1Al7.4Nb5C0.5Si0.2B (Alloy B), were prepared by graphite mold casting. As-cast microstructures of the two alloys were characterized to clarify the effect of carbon addition. The results show that 5 at.% carbon addition can change the primary solidification phase from β phase to α phase. The as-cast microstructure of Alloy A consists of a fully α2 + γ lamellar structure and interdendritic eutectic silicide with a volume fraction of 2.3%. However, in Alloy B, the lamellar structure only forms in the dendritic stem and the massive γ is observed in the interdendritic regions. Two types of carbides, Ti2AlC and TiC, are produced in Alloy B. A large number of randomly distributed primary Ti2AlC particles with volume fraction of 14.9% are observed in both the dendritic and interdendritic regions. Irregularly shaped TiC remains inside of the large Ti2AlC particle, suggesting TiC carbides transformed to Ti2AlC during cooling. The addition of carbon also changes the morphology of the silicides from a eutectic structure to a blocky structure in the massive γ matrix or at the interface of the Ti2AlC and the γ matrix. High level of niobium greatly increases the solid solution limit of carbon, since C content in the matrix is much higher than the solid solubility of that in the TiAl binary system. The hardness of the matrix increases from 325 HV to 917 HV caused by the addition of carbon.
Keywords: TiAl alloy; carbides; microstructure; solidification; vickers hardness TiAl alloy; carbides; microstructure; solidification; vickers hardness
MDPI and ACS Style

Liu, J.; Zhang, F.; Nan, H.; Feng, X.; Ding, X. Effect of C Addition on as-Cast Microstructures of High Nb Containing TiAl Alloys. Metals 2019, 9, 1201.

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