目的 通过电子束增材制造技术成形高铌TiAl合金试样,探究不同能量密度参数下成形样品的显微组织与物相分布特征,分析其在增材制造过程中的相转变路径及内在作用机理,为优化高铌TiAl合金电子束增材制造工艺、提升成形样品的力学性能提供理论支撑与实验依据。方法 结合SEM、XRD、EBSD、TKD和TEM等表征技术,深入分析电子束增材制造高铌TiAl合金显微组织、析出相形态及晶体学取向等信息,对增材制造过程中高铌TiAl合金的有序B2相与ωₒ相的析出行为、演化规律及形成机制进行系统研究。结果 当电子束增材制造过程中输入高能量密度（HE）时,会导致高铌TiAl合金中Al元素严重烧损,Al损量（质量分数）达6.50%;同时,初始粗大片层团组织稳定性遭到破坏,出现片层退化现象,并伴随平行分解析出有序B2/ωₒ相的过程,最终在试样内部形成α2相、γ相、B2/ωₒ相共存的α2/γ/(B2/ωₒ)混合组织,且各相在空间分布上呈现特定的形貌特征与分布规律。结论 电子束增材制造过程中较大的能量密度输入导致Al元素烧损严重,粗大片层团失稳;而高的成形温度则进一步诱导了高能量密度试样中片层团退化和B2/ωo固态相转变过程,其中,固态相转变过程主要发生平行分解同时消耗α2相和γ相,其取向关系为：{0001}α2//{111}γ//{110}B2//{$ 11 \overline{2} 0$}ωo,<$ 11 \overline{2} 0$>α2//<$1 \overline{1} 0$>γ//<$1 \overline{1} 1$>B2//<0001>ωo。α2+γ→B2/ωo固态相变存在中间相变,先析出B2相,ωo相再从B2相的{110}6个等效晶面析出,其相变路径为：α2+γ→B2→ωo,同时B2/ωo相的析出是一个扩散控制的过程,其中,Nb作为强ωo稳定元素会发生偏聚。
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 ωo 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/ωo phases. Eventually, an α2/γ/(B2/ωo) mixed structure coexisting with α2 phase, γ phase, and B2/ωo 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/ωo solid-state phase transformation. The B2/ωo 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$}ωo,<$ 11 \overline{2} 0$>α2//<$1 \overline{1} 0$>γ//<$1 \overline{1} 1$>B2//<0001>ωo. The α2+γ→B2/ωo solid-state phase transformation involves an intermediate phase transformation, where the B2 phase precipitates first, followed by the subsequent precipitation of the ωo phase from the 6 equivalent crystal planes of {110} in the B2 phase. The phase transformation path is determined to be: α2+γ→B2→ωo, and the precipitation of the B2/ωo phase is a diffusion-controlled process, with Nb, as a strong ωo-stabilizing element, exhibits segregation.
关键词
TiAl合金 /
电子束增材制造 /
显微组织 /
固态相变 /
B2/ωo相
Key words
TiAl alloy /
electron beam additive manufacturing /
microstructure /
solid-state phase transformation /
B2/ωo phase
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基金
国家自然科学基金（12202201）; 江苏省自然科学基金（BK20220918）; 高温轻合金及应用技术全国重点实验室重点项目（sysjj2025201）; 2026年度国家资助博士后研究人员计划B档资助（GZB20260042）
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