Precipitation Behavior of Ordered B2/&#x003c9;o Phases in Electron Beam Additive Manufacturing Process of High-Nb TiAl Alloys

WANG Xianghui; XIANG Henggao; ZHENG Gong; CHANG Chen; XIONG Anhui; CHEN Yang

doi:10.3969/j.issn.1674-6457.2026.08.020

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Journal of Netshape Forming Engineering ›› 2026, Vol. 18 ›› Issue (8) : 218-228. DOI: 10.3969/j.issn.1674-6457.2026.08.020

Additive Manufacturing

Precipitation Behavior of Ordered B2/ω_o Phases in Electron Beam Additive Manufacturing Process of High-Nb TiAl Alloys

WANG Xianghui, XIANG Henggao, ZHENG Gong, CHANG Chen, XIONG Anhui, CHEN Yang^*

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Abstract

The work aims to fabricate high-niobium TiAl alloy specimens with electron beam additive manufacturing (EBAM) technology to investigate the microstructure and phase distribution of the formed specimens under different energy density parameters and analyze the phase transformation pathways and underlying mechanisms during the EBAM process, providing theoretical support and experimental basis for optimizing the EBAM process of high-niobium TiAl alloys and improving their mechanical properties. Characterization techniques including SEM, EBSD, TKD, and TEM were utilized for in-depth analyses of microstructure, precipitate morphology, and crystallographic orientation, followed by a systematic investigation of the precipitation behavior, evolution, and formation mechanism of ordered B2 phase and ω_o phase during the EBAM of high-niobium TiAl alloys. A high energy density input during the EBAM process led to significant Al volatilization (up to 6.50 wt.%) in the high-niobium TiAl alloy and destabilized the initial coarse lamellar structure, resulting in not only lamellar degradation but also the process of parallel decomposition and precipitation of ordered B2/ω_o phases. Eventually, an α2/γ/(B2/ω_o) mixed structure coexisting with α₂ phase, γ phase, and B2/ω_o phase formed inside the specimen, wherein each phase presented specific morphological characteristics and distribution patterns. High energy density (HE) input during the EBAM process leads to severe volatilization of Al elements and instability of coarse lamellar colonies, while a high forming temperature induces the degradation of lamellar colonies and the B2/ω_o solid-state phase transformation. The B2/ω_o phase transformation proceeds via spinodal decomposition expense of the α₂ phase and the γ phase, exhibiting the following orientation relationship: {0001}α₂//{111}γ//{110}B2//{$ 11 \overline{2} 0$}ω_o,<$ 11 \overline{2} 0$>α₂//<$1 \overline{1} 0$>γ//<$1 \overline{1} 1$>B2//<0001>ω_o. The α₂+γ→B2/ω_o solid-state phase transformation involves an intermediate phase transformation, where the B2 phase precipitates first, followed by the subsequent precipitation of the ω_o phase from the 6 equivalent crystal planes of {110} in the B2 phase. The phase transformation path is determined to be: α₂+γ→B2→ω_o, and the precipitation of the B2/ω_o phase is a diffusion-controlled process, with Nb, as a strong ω_o-stabilizing element, exhibits segregation.

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TiAl alloy / electron beam additive manufacturing / microstructure / solid-state phase transformation / B2/ω_o phase

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WANG Xianghui, XIANG Henggao, ZHENG Gong, CHANG Chen, XIONG Anhui, CHEN Yang. Precipitation Behavior of Ordered B2/ω_o Phases in Electron Beam Additive Manufacturing Process of High-Nb TiAl Alloys[J]. Journal of Netshape Forming Engineering. 2026, 18(8): 218-228 https://doi.org/10.3969/j.issn.1674-6457.2026.08.020

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Funding

The National Natural Science Foundation of China (12202201); The Natural Science Foundation of Jiangsu Province (BK20220918); Key Project of State Key Laboratory of Light Superalloys (sysjj2025201); The Postdoctoral Fellowship Program (Grade B) of China Postdoctoral Science Foundation (GZB20260042)