發(fā)布時間：2018-02-16 22:08

  本文關(guān)鍵詞： 高熵合金 合金化 組織結(jié)構(gòu) 析出強化 力學(xué)性能　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：高熵合金是上世紀(jì)90年代提出的一種全新的合金設(shè)計理念,其每種組成元素比例接近,但一般不超過35%。由于高混合熵效應(yīng),高熵合金一般形成簡單固溶體,其晶格中存在較大的畸變,并因此衍生出了一系列特點,比如微觀結(jié)構(gòu)熱穩(wěn)定性高,擴散緩慢等,因而具有許多獨特的性能。目前高熵合金的研究仍然處于起步階段,許多科學(xué)問題亟待解決。首先,現(xiàn)有的高熵合金力學(xué)性能的研究,過多地集中在了室溫壓縮以及硬度上,而關(guān)系到能否實際應(yīng)用的拉伸性能,卻較少報道；其次,缺乏對成分-組織-性能關(guān)聯(lián)的系統(tǒng)研究；最后,由于高熵合金突出的高溫相穩(wěn)定性以及遲滯擴散等特點,其在高溫材料領(lǐng)域,具有極大的應(yīng)用潛力,但是相應(yīng)的研究仍十分匱乏。本論文以塑性優(yōu)異、結(jié)構(gòu)簡單的面心立方(fcc) FeCoNiCr(Mn)系高熵合金為基礎(chǔ)展開研究。首先,系統(tǒng)探索了A1元素在FeCoNiCrMn高熵合金中的合金化作用,發(fā)現(xiàn)A1的添加導(dǎo)致了合金微觀組織從fcc向bcc(體心立方)的轉(zhuǎn)變,而B2相的形成是拉伸強度提高及塑性降低的主要原因；其次,研究了FeCoNiCrMn高熵合金在1023～1123 K高溫下的流變行為,發(fā)現(xiàn)其變形過程為擴散所主導(dǎo),而微觀組織變化表明其固溶體結(jié)構(gòu)在低應(yīng)力下不夠穩(wěn)定需要引入其它強化機制：再次,在上述結(jié)果基礎(chǔ)上,通過同時引入合金化元素Ti和A1,成功地在FeCoNiCr高熵基體中析出了均勻彌散的納米Y’第二相,在保持塑性優(yōu)良的前提下,由于析出強化的作用顯著提高了室溫拉伸強度；隨后又研究了Ti和Al含量以及熱處理工藝對其組織結(jié)構(gòu)和力學(xué)性能的影響,發(fā)現(xiàn)了γ’和Heusler相的析出競爭關(guān)系,確定了最優(yōu)合金成分(FeCoNiCr)94Ti2A14;最后,研究了優(yōu)化后合金的高溫流變及蠕變性能,發(fā)現(xiàn)其穩(wěn)態(tài)應(yīng)變速率降低了約2個數(shù)量級,但是其硬脆的Heusler相及軟弱的界面區(qū)域?qū)е氯渥儔勖燥@不足。此外,本研究還初步探索了FeCoNiCrMn在不同模式(拉伸、壓縮及扭轉(zhuǎn))下的動態(tài)變形行為。結(jié)果表明,晶粒細化(36μm)極大地促進了形變孿晶的發(fā)生,從而獲得了優(yōu)異的綜合力學(xué)性能。
[Abstract]:High entropy alloy is a new design concept of alloy put forward in -10s. The proportion of each component element is close, but generally does not exceed 35.As a result of high mixing entropy effect, high entropy alloy generally forms simple solid solution. There is a large distortion in the lattice, and a series of characteristics have been derived, such as high thermal stability of microstructure, slow diffusion and so on, so it has many unique properties. At present, the study of high-entropy alloys is still in its infancy. Many scientific problems need to be solved. First, the existing research on mechanical properties of high-entropy alloys is focused on room temperature compression and hardness, but the tensile properties related to their practical application are seldom reported. There is no systematic study on the relationship between composition, microstructure and properties. Finally, high entropy alloys have great potential for application in the field of high temperature materials due to their outstanding high temperature phase stability and hysteresis diffusion. However, the corresponding research is still very scarce. This thesis is based on the high entropy alloy FeCoNiCr-Mn-based, which has excellent plasticity and simple structure. Firstly, the alloying effect of A1 element in FeCoNiCrMn high entropy alloy is systematically explored. It is found that the addition of A1 leads to the transformation of microstructure from fcc to BCC, while the formation of B2 phase is the main reason for the increase of tensile strength and the decrease of plasticity. Secondly, the rheological behavior of FeCoNiCrMn high entropy alloy at 1023 ~ 1123K is studied. It is found that the deformation process is dominated by diffusion, while the microstructure changes indicate that the instability of the solid solution structure under low stress requires the introduction of other strengthening mechanisms: thirdly, on the basis of the above results, By introducing alloying elements Ti and A1 at the same time, the uniformly dispersed second phase of nanometer Y 'was successfully precipitated in the high entropy matrix of FeCoNiCr. The tensile strength at room temperature was obviously increased because of the effect of precipitation strengthening on the premise of keeping good plasticity. Then the effects of Ti and Al contents and heat treatment on the microstructure and mechanical properties of the alloy were studied. The precipitated competition relationship between 緯 'and Heusler phase was found, and the optimum alloy composition, FeCoNiCrTi94Ti2A14, was determined. The rheological and creep properties of the optimized alloy at high temperature are studied. It is found that the steady strain rate of the alloy decreases by about two orders of magnitude, but the creep life of the alloy is slightly inadequate due to the hard and brittle Heusler phase and the weak interface region. The dynamic deformation behavior of FeCoNiCrMn in different modes (tensile, compression and torsion) was also preliminarily investigated. The results show that the grain refinement (36 渭 m) greatly promotes the occurrence of deformation twins, and the excellent comprehensive mechanical properties are obtained.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TG139

【參考文獻】

相關(guān)期刊論文 前1條

1 劉源;李言祥;陳祥;陳敏;;多主元高熵合金研究進展[J];材料導(dǎo)報;2006年04期

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本文編號：1516544