TB18合金组织无析出区的形成机理

Formation Mechanism of Precipitation-Free Zone in TB18 Alloy Structure

摘要:

以TB18合金棒材为对象，通过显微组织表征、成分分析及相结构分析，探究未析出区的形成机理。结果表明：经870 ℃×120 min固溶+525 ℃×240 min时效处理后，TB18合金棒材横截面中间以内区域存在不连续白色亮斑状纯β相无析出区；在等温时效过程中，α_s相优先在β晶界析出并长大，部分无析出区随时效时间增加有所减少但仍有保留。成分分析显示，无析出区中Mo含量偏高、Nb含量偏低，且存在Ti-Nb团簇；固溶时，亚稳β相分解为富β稳定元素的β′′相和贫β稳定元素的β′相，β′相可作为α相形核衬底，而富β稳定元素区域及Ti-Nb团簇会抑制α相析出，最终形成无析出区。本研究为TB18合金工艺优化提供理论依据。

Abstract:

TB18 alloy bars were used as the research object, and the formation mechanism of the precipitation-free zone (PFZ) was investigated through microstructure characterization, composition analysis, and phase structure analysis. Results show that after solution treatment of 870 °C×120 min+aging treatment of 525 °C×240 min, discontinuous white bright spot-like pure-β PFZs exist in the middle region of the cross-section of TB18 alloy bars. During the isothermal aging, the α? phase is preferentially precipitated and grows at the β grain boundaries. With the prolongation of aging time, PFZs are decreased to a certain extent but still remain. Composition analysis reveals that in PFZs, Mo content is relatively higher, Nb content is relatively lower, and Ti-Nb clusters exist. During solution treatment, the metastable β phase decomposes into β′′ phase which is rich in β-stabilizing elements and β′ phase which lacks β-stabilizing elements. The β′ phase can serve as a nucleation substrate for the α phase, whereas the regions rich in β-stabilizing elements and Ti-Nb clusters will inhibit the precipitation of α phase, ultimately leading to the formation of PFZs. This study provides a theoretical basis for the process optimization of TB18 alloy.