多因素对裂纹稳定扩展的互影响及表征

发布时间：2018-01-02 14:00

  本文关键词：多因素对裂纹稳定扩展的互影响及表征　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

  更多相关文章： 镍基高温合金 疲劳裂纹扩展 多组织因素 Paris区

【摘要】：涡轮盘用镍基高温合金的服役环境对其损伤容限设计提出了更为严格的要求,因此对裂纹整体扩展过程中具有较大占比的Paris区就显得尤为重要。如何表征和评价裂纹扩展的稳定性,并对多组织因素和环境因素叠加的互关联影响程度进行表征将是一个急需解决的问题。为此,本文系统研究了高温下裂纹在Paris区的扩展特征,就单一组织、多组织因素和环境因素对裂纹扩展规律进行深入的分析,为合金在高温下的损伤容限设计提供可靠的思路和方向。通过对粉末镍基高温合金(FGH4096.FGH4097.FGH4098)及变形高温合金GH4738裂纹扩展曲线及高温下裂纹在Paris区的扩展机制进行系统分析,表明Paris区存在慢速扩展和快速扩展两个特征明显不同的裂纹扩展区间,揭示了其本质为一条与应力加载方向垂直的主裂纹以穿晶为主的慢速扩展方式,转变为一条沿晶扩展的主裂纹伴随产生多发二次沿晶裂纹的快速扩展方式。基于此,提出了稳定扩展韧性△KT和稳定扩展寿命系数Ds概念及△KT-Ds关系构建的裂纹稳定扩展特征图,以表征裂纹在高温下扩展的稳定性。系统研究了晶粒尺寸、晶界碳化物以及γ’相析出特征对合金裂纹扩展速率、扩展各阶段寿命以及扩展稳定性的影响规律。表明增大合金的晶粒尺寸、晶界碳化物的析出及减少二次γ’相的尺寸均能有效的提高裂纹扩展寿命,增加稳定扩展韧性AKT和稳定扩展寿命系数Ds。同时构建了多组织因素交互影响模型,从而获得不同组织特征对裂纹扩展影响的权重,为高稳定裂纹扩展合金设计优先考虑哪种组织因素提供了依据。通过对不同温度及加载应力下GH4738.GH4720Li及FGH4098等合金的裂纹扩展规律分析,观察到在某个温度或加载应力下裂纹扩展寿命显著下降的温度或应力敏感现象。进而揭示了裂纹扩展寿命在敏感温度范围显著下降的本质是由于裂纹扩展速率升高及稳定扩展韧性△KT显著降低而导致,温度对合金的晶界、一次γ’相界以及滑移带的影响都会显著影响稳定扩展韧性AKT的变化；应力敏感现象的本质是由于增加初始AK显著降低了相对的稳定扩展韧性(△KT-△K),导致疲劳裂纹在扩展较短的距离下便进入快速扩展区。综上,本文通过对大量典型镍基高温合金疲劳裂纹扩展行为分析的基础上,提出了对Paris区再划分的裂纹稳定扩展特征图,对多组织和环境因素的影响规律进行了系统阐述,为设计具有高的裂纹扩展稳定性的组织和评价服役条件提供了实验和理论依据及可行的研究方法。
[Abstract]:The service environment of nickel-based superalloy for turbine disc puts forward more stringent requirements for the design of damage tolerance. Therefore, it is particularly important to have a large proportion of the Paris region in the whole process of crack growth. How to characterize and evaluate the stability of crack growth. It will be an urgent problem to characterize the degree of mutual correlation between multiple organizational factors and environmental factors. Therefore, the characteristics of crack propagation in Paris region at high temperature are systematically studied in this paper. On the basis of single structure, multi-structure factors and environmental factors, the law of crack growth is analyzed deeply. It provides a reliable way of thinking and direction for the design of damage tolerance of the alloy at high temperature. Through the analysis of the powder nickel-based superalloy FGH4096.FGH4097.FGH4098). The crack growth curve of deformed superalloy GH4738 and the mechanism of crack propagation in Paris region at high temperature were systematically analyzed. It is shown that there are two distinct crack growth zones in the Paris region with distinct characteristics of slow growth and rapid growth. It is revealed that the nature of the crack is a slow growth mode of the main crack which is perpendicular to the direction of stress loading and is mainly transgranular. The main crack is transformed into a fast propagating mode with multiple secondary intergranular cracks. The concept of stable growth toughness KT and stable propagation life coefficient Ds and the characteristic diagram of crack stability growth constructed by KT-Ds relation are presented. In order to characterize the stability of crack propagation at high temperature, the grain size, grain boundary carbides and 纬 'phase precipitation characteristics on the crack growth rate of the alloy were systematically studied. It is shown that increasing grain size, precipitation of grain boundary carbides and reducing the size of secondary 纬 'phase can effectively improve the crack propagation life. At the same time, the interaction model of multiple microstructure factors was constructed to obtain the weight of the influence of different microstructure characteristics on crack growth. It provides the basis for the design of high stable crack propagation alloy which kind of structure factors are preferred. Crack of GH4738.GH4720Li and FGH4098 alloys under different temperature and loading stress. Expansion law analysis. It is observed that the temperature or stress sensitivity of crack growth life decreases significantly at a certain temperature or under loading stress. It is further revealed that the essence of the decrease in crack growth life in the sensitive temperature range is due to the increase of crack growth rate. High and stable extension toughness KT decreased significantly. The effect of temperature on grain boundary, primary 纬 'phase boundary and slip band will significantly affect the change of stable ductile AKT. The essence of stress-sensitive phenomenon is that increasing initial AK significantly reduces the relative stable propagation toughness (KT-KN), which leads fatigue crack to enter the rapid growth zone at a short distance. Based on the analysis of fatigue crack growth behavior of a large number of typical nickel-based superalloys, the characteristic diagram of crack stability growth in the Paris region is proposed in this paper. The effects of multi-structure and environmental factors are systematically expounded, which provides experimental and theoretical basis and feasible research methods for the design of structures with high crack growth stability and the evaluation of service conditions.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG132.3
，

本文编号：1369510