本文選題：CLAM鋼 + 真空環(huán)境　； 參考：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年博士論文

【摘要】：聚變實(shí)驗(yàn)堆包層在穩(wěn)定運(yùn)行和服役過(guò)程中承受恒定載荷作用的同時(shí),還可能承受脈沖載荷等復(fù)雜載荷的綜合作用,使結(jié)構(gòu)材料產(chǎn)生蠕變-疲勞交互損傷,因此,針對(duì)包層結(jié)構(gòu)材料開(kāi)展蠕變-疲勞損傷行為及機(jī)理研究對(duì)聚變堆包層的設(shè)計(jì)與優(yōu)化具有重要的科學(xué)意義和工程價(jià)值。本文以中國(guó)抗輻照低活化結(jié)構(gòu)鋼(CLAM鋼)為研究對(duì)象,開(kāi)展了高溫550℃、真空5x10-3 Pa下應(yīng)變控制的低周疲勞和蠕變-疲勞實(shí)驗(yàn)研究,旨在探究CLAM鋼的低周疲勞和蠕變-疲勞力學(xué)行為和失效機(jī)理,獲得保載時(shí)間、應(yīng)變幅和保載方式對(duì)CLAM鋼真空蠕變-疲勞力學(xué)行為的影響規(guī)律與機(jī)制,確保CLAM鋼在聚變實(shí)驗(yàn)堆、甚至未來(lái)聚變堆服役環(huán)境下的安全運(yùn)行。本論文主要研究?jī)?nèi)容與結(jié)論如下:首先,研究了高溫真空環(huán)境下CLAM鋼在不同應(yīng)變幅控制下的疲勞力學(xué)行為。結(jié)果表明:循環(huán)載荷下,峰值應(yīng)力持續(xù)軟化。0.5%應(yīng)變幅疲勞失效后,CLAM鋼位錯(cuò)密度由2.4×1014m-2降為0.2×1014m-2,板條寬度由0.7μm粗化為1.3μm�；谖诲e(cuò)強(qiáng)化和亞晶強(qiáng)化理論,位錯(cuò)密度降低和板條粗化造成應(yīng)力下降。前奧氏體晶粒尺寸和析出物尺寸變化不大,對(duì)應(yīng)力軟化的貢獻(xiàn)不大。基于疲勞壽命與彈/塑性應(yīng)變關(guān)系分析,建立CLAM鋼的Manson-coffin模型,疲勞壽命隨應(yīng)變幅增大而減小,并同其他RAFM鋼真空環(huán)境中疲勞壽命相當(dāng)。同時(shí),對(duì)比CLAM鋼在真空環(huán)境和大氣環(huán)境中的疲勞壽命,真空環(huán)境中的疲勞壽命更優(yōu)。分析裂紋擴(kuò)展軌跡顯示,真空環(huán)境存在兩種裂紋萌生擴(kuò)展模型。其次,在研究高溫真空環(huán)境下低周疲勞行為的基礎(chǔ)上,引入峰值載荷保載,分析了壓縮保載方式下的蠕變-疲勞交互力學(xué)行為。壓縮保載方式下,CLAM鋼產(chǎn)生循環(huán)軟化和應(yīng)力松弛現(xiàn)象,除板條粗化分解、亞晶形成和位錯(cuò)密度下降的影響以外,析出物的粗化和亞晶向晶粒轉(zhuǎn)化同樣產(chǎn)生影響,并基于EBSD分析和位錯(cuò)滑移/攀移分析,揭示了大角度晶界的形成機(jī)制。保載對(duì)裂紋萌生和蠕變空洞形核的促成是蠕變-疲勞較純疲勞壽命下降的微觀原因。另外,保載時(shí)間和應(yīng)變幅的增大,產(chǎn)生更為明顯的應(yīng)力松弛,并造成蠕變-疲勞壽命下降。低應(yīng)變幅控制下的蠕變-疲勞壽命較純疲勞壽命下降54%,而高應(yīng)變幅控制下壽命下降39%,這說(shuō)明低應(yīng)變幅控制下的蠕變-疲勞更容易發(fā)生交互作用。最后,引入拉伸保載并同壓縮保載對(duì)比,進(jìn)一步研究了不同保載方式對(duì)CLAM鋼蠕變-疲勞力學(xué)行為的影響。結(jié)果表明:拉伸保載方式下,CLAM鋼仍會(huì)產(chǎn)生循環(huán)軟化和應(yīng)力松弛現(xiàn)象。CLAM鋼的蠕變疲勞對(duì)拉伸保載更為敏感,這不同于大氣環(huán)境下的壓縮保載敏感性。除去氧化這一外部因素的影響,應(yīng)力松弛是保載方式敏感性的根本原因,而平均應(yīng)力并非主導(dǎo)因素。通過(guò)斷裂行為分析顯示,拉伸保載較壓縮保載更能促進(jìn)主裂紋的擴(kuò)展,且在穩(wěn)態(tài)擴(kuò)展階段拉伸保載更容易形成空洞和次級(jí)裂紋,促進(jìn)裂紋的進(jìn)一步擴(kuò)展并加速材料的斷裂失效。
[Abstract]:In the process of stable operation and service, the cladding of the fusion experimental reactor can withstand the complex load of the complex loads such as pulse load, which can cause the creep fatigue interaction damage of the structural material. Therefore, the design of the creep fatigue damage behavior and mechanism of the cladding material is designed for the design of the fusion reactor cladding. It is of great scientific significance and engineering value. In this paper, the low cycle fatigue and creep fatigue test of strain controlled low activation structural steel (CLAM steel) in China (CLAM steel) at high temperature and vacuum 5x10-3 Pa are studied. The purpose is to explore the low cycle fatigue and creep fatigue mechanical behavior and failure mechanism of CLAM steel. The influence law and mechanism of the loading time, the amplitude and the loading mode on the vacuum creep fatigue mechanical behavior of CLAM steel, and ensure the safe operation of the CLAM steel in the fusion experimental reactor and even the future fusion reactor. The main contents and conclusions of this paper are as follows: first, the different amplitude control of CLAM steel in the high temperature and vacuum environment is studied. The results show that under cyclic loading, the dislocation density of CLAM steel is reduced from 2.4 x 1014m-2 to 0.2 x 1014m-2, and the width of the slats is reduced from 2.4 x to 1014m-2, and the width of the strip is reduced from 0.7 mu m to 1.3 Mu based on the theory of dislocation strengthening and subcrystal strengthening, and the decrease of dislocation density and the roughening of the slats. The size of the grain size and the size of the precipitates have little change, and the contribution to the force softening is little. Based on the analysis of the relationship between the fatigue life and the elastic / plastic strain, the Manson-coffin model of CLAM steel is established. The fatigue life decreases with the increase of the strain amplitude, and is equivalent to the fatigue life of other RAFM steels in vacuum environment. At the same time, the comparison of the CLAM steel in the vacuum environment and the large size of the steel is compared. The fatigue life in the air environment is better than the fatigue life in the vacuum environment. Analysis of the crack propagation path shows that there are two crack initiation and propagation models in the vacuum environment. Secondly, on the basis of the low cycle fatigue behavior under the high temperature vacuum environment, the peak load is introduced and the creep fatigue interactive mechanics under the compression loading method are analyzed. Under compression loading, CLAM steel produces cyclic softening and stress relaxation. In addition to the influence of slats coarsening, subcrystal formation and dislocation density decline, the coarsening of precipitates and subgrains are also affected by grain transformation. Based on EBSD analysis and dislocation slip / climb analysis, the formation mechanism of large angle grain boundary is revealed. The formation of crack initiation and creep cavity nucleation is the microcosmic cause of creep fatigue more than pure fatigue life. In addition, the increase of loading time and strain amplitude, more obvious stress relaxation and creep fatigue life decrease. The creep fatigue life under the control of low strain amplitude is 54% lower than that of pure fatigue life, and high strain amplitude The reduced life decreased by 39%, which indicates that the creep fatigue is easier to interact with the low strain amplitude control. Finally, the influence of the loading and compression loading on the creep fatigue mechanical behavior of CLAM steel is further investigated. The results show that the CLAM steel will still produce cyclic softening and softening under the tensile loading. The creep fatigue of.CLAM steel is more sensitive to tensile loading, which is different from the compression loading sensitivity under the atmospheric environment. The stress relaxation is the root cause of the sensitivity of the loading mode except for the external factors of oxidation. The average stress is not the dominant factor. The tensile loading is more compressed through the fracture behavior analysis. Loading can promote the expansion of the main crack, and it is easier to form cavitation and secondary cracks in the steady state expansion stage, which can promote the further expansion of the crack and accelerate the fracture failure of the material.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TL64

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