本文關(guān)鍵詞：CoCrFeNiMn系高熵合金高溫變形與斷裂行為研究　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 高熵合金 熱機(jī)處理 微結(jié)構(gòu) 拉伸性能 鋸齒流變 蠕變

【摘要】：多主元高熵合金作為一種新型的合金材料,它是由五種或五種以上主要元素構(gòu)成且每種元素的原子百分比在5-35%之間。由于該合金多主元特性產(chǎn)生的高熵效應(yīng)、晶格畸變效應(yīng)、緩慢擴(kuò)散效應(yīng)等,使合金在結(jié)構(gòu)上易于形成簡(jiǎn)單的固溶體結(jié)構(gòu)(面心立方、體心立方或兩相混合),而非復(fù)雜的金屬間化合物。另外在一些熱處理?xiàng)l件下可能在基體中伴隨生成納米析出相。這種特殊結(jié)構(gòu)產(chǎn)生的固溶強(qiáng)化、析出強(qiáng)化效果使高熵合金表現(xiàn)出優(yōu)異的力學(xué)性能,例如較高的拉伸強(qiáng)度和延展性,優(yōu)異的抗高溫蠕變性能和熱穩(wěn)定性等。然而,關(guān)于高熵合金高溫變形和斷裂行為發(fā)生的機(jī)理尚無(wú)完善的論述,需要進(jìn)行深入的研究。本文利用真空電磁感應(yīng)熔煉方法制備并澆鑄了 CoCrFeNiMn高熵合金。為了研究熱機(jī)處理工藝對(duì)合金組織演化和力學(xué)性能的影響,對(duì)合金進(jìn)行了均勻化熱處理、冷軋和再結(jié)晶退火等工序。對(duì)熱機(jī)處理態(tài)的合金進(jìn)行室溫和高溫的拉伸試驗(yàn),通過(guò)變形微結(jié)構(gòu)觀察和理論分析研究了鋸齒流變行為,并對(duì)合金高溫拉伸蠕變的變形機(jī)理進(jìn)行了探討。為了研究A1元素的添加對(duì)合金微結(jié)構(gòu)和力學(xué)性能的影響,通過(guò)同樣的工藝路線制備了AlxCoCrFeNiMn(x=0.4,0.5,0.6)高熵合金(記為Al0.4、Al0.5和Al0.6)。對(duì)不同Al含量合金的相組成、組織結(jié)構(gòu)和拉伸性能進(jìn)行了表征和分析,并選取Al0.5合金對(duì)其高溫拉伸蠕變行為進(jìn)行了研究。研究發(fā)現(xiàn),熱機(jī)處理后CoCrFeNiMn高熵合金由粗大的樹(shù)枝晶偏析結(jié)構(gòu)轉(zhuǎn)變?yōu)槌煞志鶆虻牡容S晶結(jié)構(gòu),在此過(guò)程中保持單一的面心立方相不變。軋制比例越高,再結(jié)晶溫度越低,得到的等軸晶粒越細(xì)。其中最細(xì)晶粒的合金(軋制比40%,退火溫度900℃/1h),平均晶粒尺寸為25μm,室溫下抗拉強(qiáng)度達(dá)到580MPa,延伸率為56%左右。合金在中溫區(qū)表現(xiàn)出優(yōu)異的動(dòng)態(tài)應(yīng)變強(qiáng)化能力,應(yīng)變強(qiáng)化指數(shù)在500℃達(dá)到0.42。與此同時(shí)在300～600℃溫度區(qū)間觀察到了顯著的鋸齒流變行為,鋸齒類型隨著溫度的升高或應(yīng)變率的降低發(fā)生A→A+B→B→B+C→C的轉(zhuǎn)變。其中最大鋸齒幅度出現(xiàn)在3×10-4s-1/600℃的C型鋸齒(～6.7MPa)和500℃/1×10-5 s-1的B+C型鋸齒(～8.9MPa)。對(duì)室溫、400℃和600℃的缺陷組織觀察發(fā)現(xiàn),低應(yīng)變下(～1%)較低密度的短直位錯(cuò)呈平行堆積排列,高應(yīng)變下(～20%)較高密度的糾纏位錯(cuò)呈胞狀結(jié)構(gòu)分布。400℃和600℃時(shí)出現(xiàn)大量的位錯(cuò)彎曲和扭折,證明了位錯(cuò)被溶質(zhì)原子"釘扎"的過(guò)程。基于溶質(zhì)拖拽模型和準(zhǔn)靜態(tài)時(shí)效模型,在300～500℃溫度區(qū)間,鋸齒流變的激活能為116 kJmol-1,說(shuō)明位錯(cuò)的"釘扎"受溶質(zhì)原子經(jīng)位錯(cuò)管道擴(kuò)散過(guò)程控制;在500～600℃溫度區(qū)間,激活能為295 kJmol-1,位錯(cuò)與溶質(zhì)原子的相互作用受多原子協(xié)同晶格擴(kuò)散控制,其中擴(kuò)散最慢的Ni元素對(duì)變形速率起主要作用。具有25μm晶粒尺寸的合金高溫蠕變行為表現(xiàn)出兩個(gè)不同特征的應(yīng)力區(qū)域。低應(yīng)力區(qū)的應(yīng)力指數(shù)為5-6,平均激活能為268 kJmol-1;而在高應(yīng)力區(qū),應(yīng)力指數(shù)為8.9-14,平均激活能為380 kJmol-1。微結(jié)構(gòu)分析觀察到大量割階結(jié)構(gòu),表明蠕變過(guò)程中發(fā)生了位錯(cuò)攀移。另外,高應(yīng)力區(qū)還觀察到顯著的動(dòng)態(tài)再結(jié)晶現(xiàn)象,并且在晶界處產(chǎn)生了大量的納米析出相(M23C6和富含Cr的σ相)。因此,低應(yīng)力區(qū)和高應(yīng)力區(qū)的蠕變均為晶格擴(kuò)散控制的位錯(cuò)攀移機(jī)制,但是高應(yīng)力區(qū)明顯升高的應(yīng)力指數(shù)是由于蠕變過(guò)程中動(dòng)態(tài)再結(jié)晶和晶界析出的共同作用導(dǎo)致的。對(duì)熱機(jī)處理后的AlxCoCrFeNiMn(x=0.4,0.5,0.6)高摘合金的微結(jié)構(gòu)研究發(fā)現(xiàn),富含AlNi的體心立方相隨著A1含量的升高而增多,合金的平均晶粒尺寸隨著Al含量的升高而減小。體心立方相的強(qiáng)化作用和晶粒尺寸的"Hall-Petch"作用使Al0.6合金的室溫屈服強(qiáng)度和最大強(qiáng)度分別達(dá)到348MPa和801MPa。與CoCrFeNiMn合金類似,Alx合金在中溫區(qū)(300～600℃)表現(xiàn)出了較高的動(dòng)態(tài)應(yīng)變強(qiáng)化能力,這與此溫度區(qū)間發(fā)生的鋸齒行為有關(guān)。Al0.5合金的蠕變行為表現(xiàn)出與溫度有關(guān)的轉(zhuǎn)變。500℃和550℃應(yīng)力指數(shù)為2.6-3,平均蠕變激活能為201 kJmol-l,說(shuō)明合金的蠕變由溶質(zhì)原子管道擴(kuò)散控制的位錯(cuò)黏滯性滑移過(guò)程主導(dǎo):600℃和650℃的應(yīng)力指數(shù)為4.6-5.4,平均蠕變激活能為411 kJmol-1,說(shuō)明蠕變過(guò)程為元素品格擴(kuò)散控制的位錯(cuò)攀移機(jī)制。
[Abstract]:Multi element high entropy alloy as a new alloy material, which is composed of five or more than five kinds of main elements and the atomic percentage of each element in the range of 5-35%. Due to the high entropy effect of the alloy multi principal element properties, lattice distortion effect, slow diffusion effect, which is easy to form a solid alloy the solution structure is simple in structure (FCC, BCC or mixed), rather than complex intermetallic compounds. In addition some heat treatment conditions may be accompanied by the generation of nano precipitates in the matrix. The solid solution strengthening the special structure, the effect of precipitation strengthening high entropy alloy performance the excellent mechanical properties, such as high tensile strength and ductility, excellent high temperature creep resistance and thermal stability. However, the mechanism of the occurrence of high entropy alloy high temperature deformation and fracture behavior is not perfect in this need For further research. In this paper, using vacuum induction melting and casting method for preparation of CoCrFeNiMn high entropy alloy. In order to study the effect of heat treatment on microstructure evolution and mechanical properties of the alloy, homogenizing heat treatment, cold rolling and recrystallization annealing process. The tensile test at room temperature and high temperature thermomechanical treatment of alloy the state, through the deformation microstructure observation and theoretical analysis of the serrated flow behavior and deformation mechanism of the alloy, high temperature tensile creep are discussed. The effects of adding A1 on the microstructure and mechanical properties of the alloy, through the same process to prepare AlxCoCrFeNiMn (x=0.4,0.5,0.6) high entropy alloy (remember for Al0.4, Al0.5 and Al0.6). The phase composition of Al alloy with different content of structure, microstructure and tensile properties were characterized and analyzed, and selected the Al0.5 alloy on its high temperature tensile The creep behavior was studied. The study found that after thermomechanical treatment of CoCrFeNiMn high entropy alloy into uniform components such as crystal structure from coarse dendrite segregation structure, in the process of maintaining the FCC single phase constant. The higher the proportion of rolling, recrystallization temperature is low, the equiaxed grains get finer. One of the most fine grain alloy (rolling ratio 40%, annealing temperature of 900 DEG /1h), the average grain size is 25 m, the tensile strength at room temperature reached 580MPa, the elongation rate is about 56%. The alloy in medium temperature region showed excellent ability to strengthen the dynamic strain, strain hardening index at 500 DEG C to 0.42. at the same time 300 to 600 DEG C temperature range was observed for the serrated flow significantly, sawtooth type with the increase of temperature or strain rate decreasing change A - A+B - B - B+C - C. The maximum amplitude of serration appeared in type C 3 * 10-4s-1/600 C saw The tooth (~ 6.7MPa) and B+C /1 * 10-5 500 C zigzag S-1 (~ 8.9MPa). The room temperature, observed defects 400 degrees and 600 degrees, under low strain (~ 1%) short straight low density of dislocations in parallel packed high strain (~ 20%) higher dislocation entanglement a large number of dislocation density and bending torsion cell structure distribution of.400 DEG C and 600 DEG C, proved that the process of dislocation pinning by solute atoms. The solute drag model and quasi static model based on time, at 300 to 500 DEG C temperature range, the serrated flow activation energy of 116 kJmol-1, said Ming dislocation pinning by solute atoms by dislocation pipe diffusion process control; at 500 to 600 DEG C temperature range, the activation energy is 295 kJmol-1, the interaction of dislocations and solute atoms by atomic coordination lattice diffusion control, the diffusion of Ni element on the slow deformation rate plays a major role. With 25 m grain ruler High temperature creep behavior "showed two different regional stress characteristics. Low stress index was 5-6, the average activation energy of 268 kJmol-1; while in high stress area, the stress index was 8.9-14, the average activation energy observed in large cut order structure of 380 kJmol-1. micro structure analysis that happened in the process of creep, dislocation climb. In addition, the high stress region also observed significant dynamic recrystallization phenomenon, and at the grain boundaries resulting in a large number of nano precipitates (M23C6 and Cr rich phase). Therefore, the low stress area and high stress zone are dislocation creep lattice diffusion controlled climb mechanism, but the high stress area significantly increased the stress index is the result of the interaction of dynamic recrystallization during creep and grain boundary precipitation. The heat treated AlxCoCrFeNiMn (x=0.4,0.5,0.6) micro structure study found that high pick alloy, rich in the body of AlNi Cubic phase with increasing content of A1 increased, the average grain size of the alloy decreases with the increase of Al content. The BCC phase strengthening and the grain size of the "Hall-Petch" of the Al0.6 alloy at room temperature yield strength and maximum strength reached 348MPa and 801MPa. and CoCrFeNiMn alloy is similar to that of Alx alloy at medium temperature area (300 ~ 600 DEG C) showed a higher ability to strengthen the dynamic strain, the occurrence and the temperature interval of.Al0.5 alloy creep behavior of sawtooth behavior related to temperature change of.500 degrees and 550 degrees of stress index was 2.6-3, the average creep activation energy of 201 kJmol-l, indicating the dislocation creep controlled alloy by the solute diffusion pipeline viscosity slip leading process: 600 degrees and 650 degrees of the stress index was 4.6-5.4, the average creep activation energy of 411 kJmol-1, the creep process is diffusion controlled character elements The mechanism of dislocation climbing.

【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
【分類號(hào)】：TG139

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1 付建新;CoCrFeNiMn系高熵合金高溫變形與斷裂行為研究[D];中國(guó)科學(xué)技術(shù)大學(xué);2017年

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本文編號(hào)：1404703