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The stability of microstructure and the fatigue deformation mechanism of duplex aluminides containing fine precipitates under cyclic loading.

循环加载下含有细小析出物的双相铝化物的显微组织稳定性及疲劳变形机制

基本信息

批准号：
09305045
负责人：
UMAKOSHI Yukichi
金额：
$ 24.45万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

TiAl alloys are known to be a candidate for high-temperature structure materials because of high strength at high temperatures, low density and superior oxidation resistance. Fatigue propertiy is one of the most important factors for industrial application. In this project, the stability of microstructure and the deformation behavior of TiAl alloys containing fine dispersed precipitates were examined under cyclic loading, and the following summary and conclusions were reached.(1) In TiAl alloys ordinary dislocations perform the to-and-fro motion in γ matrix under cyclic loading and the vein structure composed of highly dense dislocations are formed, resulting in strong cyclic hardening. In the γ matrix, domain boundaries and γ/αィイD22ィエD2 phase boundary act as a strong barrier for the motion of dislocations and the cyclic hardening is accelerated.(2) The persistent slip bands (PSB) are formed depending on the type of γ domains. They act as a nucleation site for a micro-crack and develop … More into a failure of specimens. Formation of the PSB is closely related to twinning. Addition of Nb in TiAl alloys increases the stacking fault energy and suppressed the formation of twninning resulting in improving fatigue life.(3) Refinement of lamellae increased yield stress and improves the ductility of TiAl alloys in monotonic deformation. The refinement of lamellae is effective in suppressing the crack propagation and improvement of fatigue life.(4) In the γ matrix of Al-rich TiAl alloys, fine precipitates of AlィイD25ィエD2TiィイD23ィエD2, r-AlィイD22ィエD2Ti and h-AlィイD22ィエD2Ti with the LlィイD20ィエD2-based superstructures appear. These precipitates are homogenelously distributed and induce improvement of high-temperature strength and creep reststance.(5) When 1/2<110> ordinary and <110> superlattice dislocations enter AlィイD22ィエD2Ti and AlィイD25ィエD2TiィイD23ィエD2 precipitates, an anti-phase boundary (APB) is created behind the dislocation. Since APB energy created by the ordinary dislocation is higher than that by superlattice dislocation, the motion of ordinary dislocation is strongly interrupted by the precipitates and the superlattice dislocation is operative.(6) The h-AlィイD22ィエD2Ti and AlィイD25ィエD2TiィイD23ィエD2 precipitates maintain the good coherency with the LlィイD20ィエD2 matrix.These precipitates exhibit good thermal stability. Less

TiAl合金具有高温强度高、密度低、抗氧化性好等优点，被认为是一种理想的高温结构材料。疲劳性能是影响其工业应用的重要因素之一。本课题对含有细小弥散析出相的TiAl合金在循环载荷下的组织稳定性和变形行为进行了研究，得出了以下结论：(1)在循环载荷作用下，TiAl合金中的普通位错在γ基体中往复运动，形成由高密度位错组成的脉状组织，导致强烈的循环硬化。在γ基体中，磁畴边界和γ/αィイD22ィエD2相界对位错的运动起到很强的阻挡作用，加速了循环硬化。(2)持久滑移带的形成取决于γ磁畴的类型。它们充当微裂纹的形核位置，并形成…更多的是样本的失败。PSB的形成与孪晶密切相关。Nb的加入增加了TiAl合金的层错能，抑制了孪晶的形成，提高了疲劳寿命。(3)片晶的细化提高了TiAl合金的屈服应力，改善了TiAl合金的单调变形塑性。(4)在富铝TiAl合金的γ基体中，出现了AlィイD25ィエD2TiィイD23ィエD2、r-AlィイD22ィエD2Ti和h-AlィイD22ィエD2Ti的细小析出相，并具有LlィイD20ィエD2基超结构。(5)当1/2&lt；110&gt；普通位错和&lt；110&gt；超晶格位错进入AlィイD22ィエD2Ti和AlィイD25ィエD2TiィイD23ィエD2析出时，位错后形成反相界。(6)h-AlィイD22ィエD2Ti和AlィイD25ィエD2TiィイD23ィエD2析出相与LlィイD20ィエD2相具有良好的共格特性，表现出良好的热稳定性。较少