【作者】 邱从章；

【导师】 刘咏； 赵继成；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 含B2相的γ-TiAl基合金在高温下有良好的变形能力,是一种具有重要应用前景的新型高温材料。本文设计了新型含B2相的Ti-Al-Fe-Mo系合金,系统、深入地研究了TiAl合金体系的成分、结构、组织与性能的相关性,建立了该TiAl合金的凝固过程和不连续动态再结晶诱导超塑性变形的模型,较好地改善了γ-TiAl基合金变形难的问题,并成功制备出TiAl基合金薄板材,为开发具有良好成型性和高温性能的新型TiAl基合金材料提供了重要参考。利用X射线衍射(XRD)、扫描电镜(SEM)、电子探针微区分析(EPMA)、差热分析(DSC)、透射电镜(TEM)等分析手段,开展了相关的研究工作及理论分析,主要探讨含B2相的TiAl基合金三个方面的内容,其中包括B2的形成：研究体系的相平衡与扩散,确定在TiAl基合金中β稳定性元素Mo和Fe的成分与其组织的相关性；B2相的可控性：研究优化设计含B2相的TiAl合金的成分和热处理工艺,调控B2相的含量和分布；以及B2相的作用：研究含B2相的TiAl合金的热变形能力,并探讨诱导TiAl合金发生超塑性行为的机理。取得如下成果：1)采用多元扩散偶技术研究900℃多元Ti-Al-Fe-Mo系的相关系,建立了近γ相区域的局部等温截面相图以及相平衡与扩散的数据库,探讨了Ti、Al、Fe和Mo元素在不同相中的扩散能力,确定了近γ相区域含B2相的单相区、双相和三相共存区中各元素成分分布,并研究了Ti-Mo、Ti-Al等体系的成分-结构-性能的相关性,为设计含B2相的TiAl合金提供重要依据。2)确立了含B2相的TiAl基合金的凝固过程模型。研究β稳定性元素Mo和Fe的成分与Ti-45A1基合金的组织之间的相关性,B2相随Mo和Fe含量的增加而增多,经优化设计后的Ti-45Al-3Fe-2Mo合金具有组织细小、热变形行为良好的特点,其凝固过程为L→L+βprimary→βprimary+α→α→α+(α’+γ)→(α’+γ)层片+(β’+γ)等轴→(α2+γ)层片+(B2+γ)等轴。3)建立了含B2相的TiAl合金的热变形行为机制和热加工图。Ti-45A1-3Fe-2Mo合金是一种温度、应变速率敏感的材料,高温压缩变形时的本构方程为ε=e23.118[sinh(0.0138σ)]3.45exp(-292.43/RT)。热加工图表明温度800℃左右时,压缩变形的应变速率应低于0.056s-1,在800-1100℃压缩过程中应变速率不应高于0.18s-1。当应变速率较高时,应根据加工图选择适当较高的变形温度。4)建立了含B2相的TiAl合金的不连续动态再结晶诱导超塑性的变形机制和模型。Ti-45Al-3Fe-2Mo合金为含B2相的TiAl合金,在790。C具有良好的低温超塑性变形行为；B2相的不连续动态再结晶,有利于层片晶团的扭转和拉长以及晶界滑移等共同软化与应变硬化的协调往复作用,缓解变形带来的应力集中,延缓孔洞的产生、聚合和连接,促使合金发生超塑性变形,直至超过材料的极限而断裂。本文含图88幅,表22个,参考文献162篇。更多还原

【Abstract】 B2-containing TiAl alloy (the y-based TiAl alloy, which contains a certain amount of B2phase) has arisen worldwide concerns due to its excellent properties, including good workability and high-temperature performances. A novel B2-containing Ti-Al-Fe-Mo alloy has been developed in this research. And the relationship among composition, microstructure and properties of the Ti-Al-Fe-Mo system has been studied systematically. Models of the solidification process (SP) and discontinuous dynamic recrystallization (DDRX)-induced low-temperature superplasticity of this alloy have also been set up. Eventually thin-gage foils of the B2-containing TiAl alloy were successfully fabricated via hot rolling.A large number of experimental and theoretical analyses were performed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), electron probe micro-analysis (EPMA), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The following aspects of B2-containing TiAl alloy were studied:(a) the formation of B2phase——to understand the relationship between composition and microstructure by investigate the phase equilibrium and diffusion of Ti-Al-Fe-Mo system;(b) the controllability of the status of B2phase——to adjust and modify the content and distribution of B2phase by optimal designing the composition of B2-containing TiAl alloy and following heat treatment;(c) the effect of B2phase——to analyze the mechanism of thermal deformation and superplasticity of B2-containing TiAl alloy. Results are shown as below:1) The high-throughput diffusion multiples and EPMA has been used to analyze the Ti-Al-Fe-Mo diffusion system at900℃. The partial composition phase diagram and the database of Ti-Al-Fe-Mo phase equilibrium and diffusion have been established, which can be used for the design of new B2-containing TiAl alloy. There are different diffusion coefficients of the elements (including Ti, Al, Fe, and Mo) in different phases (B2, a2, and y phase). The distribution of the elements in various regions nearby y phase field has been discussed.2) The relationship between the content of β stabilizers (Mo and Fe) and the microstructure of the Ti-45A1based alloy has been understood. With the increasing amount of Mo or/and Fe content, the B2phase grows gradually. In the Ti-45Al-3Fe-2Mo alloy, the grains are significantly refined to about12μm, and this alloy shows a very good hot workability at elevated temperatures. Its solidification process (SP) can be described as:L→L+βprmary→βprimary+α→α→α+(α’+γ)→lamellar (α’+γ)+equiaxed (β’+γ)→lamellar (α2+γ)+equiaxed (B2+y).3) The hot deformation mechanism and the processing map (PM) of the B2-containing TiAl alloy were established. Ti-45Al-3Fe-2Mo alloy is sensitive to temperature and strain rate since its flow stress decreases with temperature and increases with strain rate. The relationship among the strain rates, flow stress, and temperature could be expressed by the function: ε=e23.118[sinh(0.0138σ)]3.54exp(-292.43/RT). The PM shows that the strain rate should be lower than0.056s-1when compressed at800℃, and not higher than0.18s-1at the temperature between800and1100℃. A higher temperature should be selected according to the PM when compressed at higher strain rates.4) The mechanism of DDRX-induced low-temperature superplastic deformation of the B2-containing TiAl alloy was discussed. The low-temperature superplastic deformation takes place during tensile deformation of Ti-45Al-3Fe-2Mo alloy at790℃. For the existence of B2phase, the reciprocating cooperation between strain hardening and softening by DDRX, kinking and elongating of lamellar, and grain boundary sliding (GBS) has been promoted. The reciprocating cooperation is conductive to reduce the stress concentration and release the accumulation energy, which is helpful for postponing the occurrence, aggregation and concatenation of cavitations. This cooperation results in the B2-containing TiAl alloy exhibiting large plastic strain, not breaking until the material is stressed beyond its strength limit.更多还原