Formation of columnar lamellar colony grain structure in a high Nb-TiAl alloy by electron beam melting

W. Kan; B. Chen; H. Peng; Y. Liang; J. Lin

doi:10.1016/j.jallcom.2019.151673

Formation of columnar lamellar colony grain structure in a high Nb-TiAl alloy by electron beam melting

W. Kan
, B. Chen
, H. Peng
, Y. Liang
, J. Lin

College of Engineering, Environment & Science

Research output: Contribution to journal › Article › peer-review

55 Citations (Scopus)

Abstract

The grain morphology and texture control in electron beam melted (EBM) Ti-47Al-8Nb γ-TiAl alloy is considered. The EBM process window to obtain a columnar lamellar colony (CLC) grain structure was defined following a critical assessment of thermal gradient and liquid-solid interface velocity by using numerical simulation. Experimentally, an epitaxial grain growth during solidification of Ti-47Al-8Nb has been realised by using the optimum EBM parameter sets. The length of the CLC grain structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). The texture analysis and phase identification performed using electron backscatter diffraction (EBSD) provided important insights in understanding the solidification and phase transformation processes during the EBM fabrication. It was found that the solidification path for EBM high Nb-TiAl alloy involves the high-temperature α-phase field (i.e. L+β→α and α→α₂+γ phase transformation processes). The epitaxial growth of prior β grains and the anchoring effect of residual B2-phase are very likely to be responsible for the formation of CLC microstructure.

Original language	English
Article number	151673
Journal	Journal of Alloys and Compounds
Volume	809
Early online date	2 Aug 2019
DOIs	https://doi.org/10.1016/j.jallcom.2019.151673
Publication status	Published - 15 Nov 2019

Funding

This work was funded by China NSFC ( 51831001 and 51671016 ) and the State Key Laboratory for Advanced Metals and Materials, USTB ( 2017-ZD03 ). Bo Chen acknowledges UK EPSRC for financial support through grants EP/P025978/1 and EP/R043973/1 to facilitate this international research collaboration. He further extends his sincere thank you to Prof. Sheng-kai Gong, Beihang University , in providing additional financial support.

Keywords

Electron beam melting
Finite element modelling
Microstructure
Solidification
Titanium aluminides

ASJC Scopus subject areas

Mechanics of Materials
Mechanical Engineering
Metals and Alloys
Materials Chemistry

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10.1016/j.jallcom.2019.151673

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title = "Formation of columnar lamellar colony grain structure in a high Nb-TiAl alloy by electron beam melting",

abstract = "The grain morphology and texture control in electron beam melted (EBM) Ti-47Al-8Nb γ-TiAl alloy is considered. The EBM process window to obtain a columnar lamellar colony (CLC) grain structure was defined following a critical assessment of thermal gradient and liquid-solid interface velocity by using numerical simulation. Experimentally, an epitaxial grain growth during solidification of Ti-47Al-8Nb has been realised by using the optimum EBM parameter sets. The length of the CLC grain structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). The texture analysis and phase identification performed using electron backscatter diffraction (EBSD) provided important insights in understanding the solidification and phase transformation processes during the EBM fabrication. It was found that the solidification path for EBM high Nb-TiAl alloy involves the high-temperature α-phase field (i.e. L+β→α and α→α2+γ phase transformation processes). The epitaxial growth of prior β grains and the anchoring effect of residual B2-phase are very likely to be responsible for the formation of CLC microstructure.",

keywords = "Electron beam melting, Finite element modelling, Microstructure, Solidification, Titanium aluminides",

author = "W. Kan and B. Chen and H. Peng and Y. Liang and J. Lin",

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doi = "10.1016/j.jallcom.2019.151673",

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AU - Kan, W.

AU - Chen, B.

AU - Peng, H.

AU - Liang, Y.

AU - Lin, J.

PY - 2019/11/15

Y1 - 2019/11/15

N2 - The grain morphology and texture control in electron beam melted (EBM) Ti-47Al-8Nb γ-TiAl alloy is considered. The EBM process window to obtain a columnar lamellar colony (CLC) grain structure was defined following a critical assessment of thermal gradient and liquid-solid interface velocity by using numerical simulation. Experimentally, an epitaxial grain growth during solidification of Ti-47Al-8Nb has been realised by using the optimum EBM parameter sets. The length of the CLC grain structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). The texture analysis and phase identification performed using electron backscatter diffraction (EBSD) provided important insights in understanding the solidification and phase transformation processes during the EBM fabrication. It was found that the solidification path for EBM high Nb-TiAl alloy involves the high-temperature α-phase field (i.e. L+β→α and α→α2+γ phase transformation processes). The epitaxial growth of prior β grains and the anchoring effect of residual B2-phase are very likely to be responsible for the formation of CLC microstructure.

AB - The grain morphology and texture control in electron beam melted (EBM) Ti-47Al-8Nb γ-TiAl alloy is considered. The EBM process window to obtain a columnar lamellar colony (CLC) grain structure was defined following a critical assessment of thermal gradient and liquid-solid interface velocity by using numerical simulation. Experimentally, an epitaxial grain growth during solidification of Ti-47Al-8Nb has been realised by using the optimum EBM parameter sets. The length of the CLC grain structure reached up to ∼600 μm (compared to the powder layer thickness of 70 μm). The texture analysis and phase identification performed using electron backscatter diffraction (EBSD) provided important insights in understanding the solidification and phase transformation processes during the EBM fabrication. It was found that the solidification path for EBM high Nb-TiAl alloy involves the high-temperature α-phase field (i.e. L+β→α and α→α2+γ phase transformation processes). The epitaxial growth of prior β grains and the anchoring effect of residual B2-phase are very likely to be responsible for the formation of CLC microstructure.

KW - Electron beam melting

KW - Finite element modelling

KW - Microstructure

KW - Solidification

KW - Titanium aluminides

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VL - 809

JO - Journal of Alloys and Compounds

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M1 - 151673

ER -

Formation of columnar lamellar colony grain structure in a high Nb-TiAl alloy by electron beam melting

Abstract

Funding

Keywords

ASJC Scopus subject areas

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