本文關鍵詞：多因素對裂紋穩(wěn)定擴展的互影響及表征　出處：《北京科技大學》2017年博士論文　論文類型：學位論文

  更多相關文章： 鎳基高溫合金 疲勞裂紋擴展 多組織因素 Paris區(qū)

【摘要】：渦輪盤用鎳基高溫合金的服役環(huán)境對其損傷容限設計提出了更為嚴格的要求,因此對裂紋整體擴展過程中具有較大占比的Paris區(qū)就顯得尤為重要。如何表征和評價裂紋擴展的穩(wěn)定性,并對多組織因素和環(huán)境因素疊加的互關聯(lián)影響程度進行表征將是一個急需解決的問題。為此,本文系統(tǒng)研究了高溫下裂紋在Paris區(qū)的擴展特征,就單一組織、多組織因素和環(huán)境因素對裂紋擴展規(guī)律進行深入的分析,為合金在高溫下的損傷容限設計提供可靠的思路和方向。通過對粉末鎳基高溫合金(FGH4096.FGH4097.FGH4098)及變形高溫合金GH4738裂紋擴展曲線及高溫下裂紋在Paris區(qū)的擴展機制進行系統(tǒng)分析,表明Paris區(qū)存在慢速擴展和快速擴展兩個特征明顯不同的裂紋擴展區(qū)間,揭示了其本質(zhì)為一條與應力加載方向垂直的主裂紋以穿晶為主的慢速擴展方式,轉(zhuǎn)變?yōu)橐粭l沿晶擴展的主裂紋伴隨產(chǎn)生多發(fā)二次沿晶裂紋的快速擴展方式�；诖�,提出了穩(wěn)定擴展韌性△KT和穩(wěn)定擴展壽命系數(shù)Ds概念及△KT-Ds關系構建的裂紋穩(wěn)定擴展特征圖,以表征裂紋在高溫下擴展的穩(wěn)定性。系統(tǒng)研究了晶粒尺寸、晶界碳化物以及γ’相析出特征對合金裂紋擴展速率、擴展各階段壽命以及擴展穩(wěn)定性的影響規(guī)律。表明增大合金的晶粒尺寸、晶界碳化物的析出及減少二次γ’相的尺寸均能有效的提高裂紋擴展壽命,增加穩(wěn)定擴展韌性AKT和穩(wěn)定擴展壽命系數(shù)Ds。同時構建了多組織因素交互影響模型,從而獲得不同組織特征對裂紋擴展影響的權重,為高穩(wěn)定裂紋擴展合金設計優(yōu)先考慮哪種組織因素提供了依據(jù)。通過對不同溫度及加載應力下GH4738.GH4720Li及FGH4098等合金的裂紋擴展規(guī)律分析,觀察到在某個溫度或加載應力下裂紋擴展壽命顯著下降的溫度或應力敏感現(xiàn)象。進而揭示了裂紋擴展壽命在敏感溫度范圍顯著下降的本質(zhì)是由于裂紋擴展速率升高及穩(wěn)定擴展韌性△KT顯著降低而導致,溫度對合金的晶界、一次γ’相界以及滑移帶的影響都會顯著影響穩(wěn)定擴展韌性AKT的變化；應力敏感現(xiàn)象的本質(zhì)是由于增加初始AK顯著降低了相對的穩(wěn)定擴展韌性(△KT-△K),導致疲勞裂紋在擴展較短的距離下便進入快速擴展區(qū)。綜上,本文通過對大量典型鎳基高溫合金疲勞裂紋擴展行為分析的基礎上,提出了對Paris區(qū)再劃分的裂紋穩(wěn)定擴展特征圖,對多組織和環(huán)境因素的影響規(guī)律進行了系統(tǒng)闡述,為設計具有高的裂紋擴展穩(wěn)定性的組織和評價服役條件提供了實驗和理論依據(jù)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 緯 '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 緯 '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 緯 '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.
【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG132.3
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本文編號：1369510