Design of novel β-solidifying TiAl alloys with adjustable β/B2-phase fraction and excellent hot-workability
Design of novel β-solidifying TiAl alloys with adjustable β/B2-phase fraction and excellent hot-workability
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DOI：
10.1002/adem.200800164
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发表时间：
2008-08-01
影响因子：
3.6
通讯作者：
Bartels, Arno
中科院分区：
文献类型：
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作者：
Clemens, Helmut;Wallgram, Wilfried;Bartels, Arno
20多年来，用于航空发动机和汽车部件的γ-TiAl基合金的研究和开发一直是多个研发项目的目标。[1-3]铝化钛由于其具有显着减轻部件重量的潜力而被考虑用于未来的先进航空发动机。尽管已经取得了显着的进展，但时至今日，铝化钛尚未应用于航空发动机零件。基础材料研究设计和生产技术均已达到先进成熟状态。但总体而言，有限的拉伸延展性、较差的裂纹扩展阻力以及缺陷、损坏和长期循环载荷以及暴露于热氧化气氛对疲劳寿命的不利影响是航空发动机部件可靠性和寿命问题领域的主要问题。还需要了解不同相关损伤和缺陷的来源以及对特定钛铝合金和航空发动机部件的寿命预测的影响。扩大铸锭材料、铸件和锻件生产规模的尝试尚未达到可重复性和可承受性所需的目标。铝化钛锭和零件的大规模生产需要进一步的合金和工艺开发才能成为可靠的技术。目前的钛和镍合金表现出平衡的性能，并满足当前设计实践的所有要求。金属间γ-TiAl基合金无疑是满足所需热和机械规格的最有希望的候选材料之一。特别是高Nb含量的TiAl合金，其基本成分为Ti-(42-45) Al-(5-10) Nb-(0-0.5) B（所有成分均以at%表示），称为TNB合金，因其高蠕变强度、良好的室温延展性、良好的疲劳性能和优异的抗氧化性而备受关注。 [1-7] Nb降低了γ-TiAl中的堆垛层错能，延迟了扩散过程并改性[4,6,8]基于Ti-(42-45)Al的铸造合金通过体心立方β相凝固，表现出各向同性、等轴和无织构的微观结构，具有适度的微观偏析，而包晶合金（通过六方α相凝固）表现出各向异性的微观结构以及显着的织构和偏析。[9] Imayev 等人最近报道了具有细化铸造微观结构的 γ-TiAl 基合金的合金设计概念。[10]提高TiAl合金热加工性的合金设计策略是利用热机械加工和附加合金元素的组合，在高温下诱导无序β相作为延性相。[11-17]具有bcc晶格的无序β相提供了足够数量的独立滑移系统。因此，它可以改善高温下的变形能力，例如在进行轧制和锻造等工艺时。许多作者 [11, 14–18] 已经证明，通过与 Nb、Ta、Mo 或其他元素合金化来稳定 β 相，可以提高热加工性，并可以通过利用多种固态转变来调整新型微观结构。然而，众所周知，β相或其有序对应物B2可以分解成多个产物相，例如分解成ω、ω’和ω”，它们具有较低的晶体对称性并且非常脆。[14, 19–21]为了避免TiAl合金中出现此类有害相，分解过程及其对Al含量和三元的依赖性......
The research and development of γ-TiAl based alloys for aero-engine and automotive components have been the target of several R & D projects since more than 20 years.[1–3] Titanium aluminides are considered for future advanced aero-engines due to their potential of significant component weight savings. Although, remarkable progress has been made, today, titanium aluminides have not been applied for aeroengine parts. Both fundamental materials research and design as well as production technologies have achieved an advanced state of maturity. But overall, the limited tensile ductility, poor crack propagation resistance and detrimental effects of defects, damage and long term cycling loads as well as exposure to hot oxidizing atmospheres on the fatigue life are the mayor concerns in the area of aero-engine components reliability and lifetime issues. There are further needs of understanding the source and effect of the different relevant damages and defects on the life-prediction for a particular titanium aluminide alloy and aero engine component. The attempts of scaling up the production of ingot materials, castings and forgings, have not yet met the required targets of reproducibility and affordability. Large-scale production of titanium aluminides ingots and parts requires further alloy and process development to become a reliable technology. Current titanium and nickel alloys exhibit balanced properties and achieve all requirements of the current design practices.Intermetallic γ-TiAl based alloys are certainly among the most promising candidates to fulfill the required thermal and mechanical specifications. Especially, TiAl alloys with high Nb-contents showing a baseline composition of Ti-(42-45) Al-(5-10) Nb-(0-0.5) B (all compositions are stated in at%), termed TNB alloys, have attracted much attention because of their high creep strength, good ductility at room temperature, good fatigue properties, and excellent oxidation resistance.[1–7] Nb reduces the stacking fault energy in γ-TiAl, retards diffusion processes and modifies the structure of the oxidation layer.[4, 6, 8] Cast alloys based on Ti-(42-45) Al, which solidify via the body-centered cubic β-phase, exhibit an isotropic, equiaxed and texture-free microstructure with modest micro-segregation, whereas peritectic alloys (solidification via the hexagonal α-phase) show anisotropic microstructures as well as significant texture and segregation.[9] Alloy design concepts for γ-TiAl based alloys showing refined cast microstructures were recently reported by Imayev et al.[10] An alloy design strategy to improve the hot-workability of TiAl alloys is to exploit a combination of thermo-mechanical processing and additional alloying elements to induce the disordered β-phase at elevated temperatures as ductile phase.[11–17] The disordered β-phase with bcc lattice provides a sufficient number of independent slip systems. Thus, it may improve the deformability at elevated temperature, where, for example, processes such as rolling and forging are carried out. A number of authors [11, 14–18] have demonstrated that, by stabilizing the β-phase through alloying with Nb, Ta, Mo or other elements, an improvement in hot-workability can be achieved and novel types of microstructures can be adjusted by exploiting a multitude of solid-state transformations. However, it is known that the β-phase or its ordered Counterpart B2 can decompose into several product phases, for example into ω, ω’and ω”, which possess lower crystal symmetry and are extremely brittle.[14, 19–21] In order to avoid the appearance of such harmful phases in TiAl alloys the decomposition process and its dependence on Al content and ternary …