本文選題：納米量熱 + 金屬微滴��； 參考：《上海大學(xué)》2017年博士論文

【摘要】：隨著現(xiàn)代社會的發(fā)展和科學(xué)技術(shù)的進(jìn)步,金屬材料在極端非平衡條件下的相變越來越引起人們的重視。納米量熱作為一種新興的量熱技術(shù),具有高達(dá)107 K/s的加熱冷卻速度,可以原位獲取金屬材料在極端非平衡條件下的相變行為。相對于傳統(tǒng)熱分析技術(shù),其熱容靈敏度在納米量級,可以檢測到微弱的相變信息。除熱力學(xué)和動力學(xué)外,納米量熱結(jié)合其它表征手段,可以對相變進(jìn)行全方面的研究。這不僅有助于揭示極端非平衡相變的內(nèi)部機(jī)理,還可以為新材料開發(fā)和改性提供直觀的實(shí)驗(yàn)證據(jù)。本文在前期非平衡形核研究的基礎(chǔ)上,利用Sn基合金微滴和Ce_68Al_10Cu_20Co_2(at.%)大塊非晶在極端冷卻和加熱條件下的凝固、玻璃化轉(zhuǎn)變、晶化以及熔化現(xiàn)象進(jìn)行了系統(tǒng)研究差示快速掃描量熱儀(Differential fast scanning calorimetry,DFSC)實(shí)現(xiàn)了單個(gè)Sn基合金微滴在10~4 K/s級別的原位冷卻,凝固組織得以細(xì)化,析出相分布均勻。在Sn3.5Ag微滴中,15000 K/s的冷卻速度可以獲得0.22 Tm的過冷度。借助于聚焦離子束(Focused ion beam,FIB)和高分辨透射電子顯微鏡(High resolution transmission electron microscopy,HRTEM),成功對其凝固組織進(jìn)行了表征。在此條件下,微滴析出相都在100 nm以下,沒有大塊針狀A(yù)g_3Sn的形成�？焖倌讨�,b-Sn基體和Ag_3Sn之間形成納米擴(kuò)散偶并存在高達(dá)10~9/m的濃度梯度,可以降低形核驅(qū)動力,提高過冷熔體的穩(wěn)定性,形成SnAg非晶。在Sn_3.0Ag_0.5Cu微滴中,通過對20000 K/s冷卻速度下“凍結(jié)”的不同尺寸、不同形貌析出相的表征,闡明了Ag_3Sn的生長機(jī)理。結(jié)果表明,晶粒內(nèi)部Ag_3Sn形成初期為球形,其((?)02)晶面作為擇優(yōu)生長面沿[(?)03]方向生長,變?yōu)榘魻�。但是受限于生長時(shí)間,尺寸仍在納米級別。納米量熱實(shí)現(xiàn)了Ce_68Al_10Cu_20Co_2大塊非晶從0.083 K/s到14000 K/s加熱速度下的晶化動力學(xué)研究。加熱速度增加,晶化溫度升高,晶化激活能降低,傳統(tǒng)Kissinger方程不再適用。通過計(jì)算玻璃化轉(zhuǎn)變溫度和熔點(diǎn)之間的晶體生長速度,發(fā)現(xiàn)了低溫熔體中生長速度和粘性流動發(fā)的去耦合,即不再遵循Stokes-Einstein方程,而Ediger關(guān)系可以在低溫段表述此變化,即Dμη~(-0.865)。結(jié)合經(jīng)典形核理論可以獲得Ce_68Al_10Cu_20Co_2過冷熔體的形核率,以此判斷加熱和冷卻過程中晶化行為的不對稱性,即加熱晶化由生長控制,冷卻晶化由形核控制。由此進(jìn)一步排除Ce晶體首先析出的可能性。隨著加熱速度的提高,Ce_68Al_10Cu_20Co_2晶化路徑發(fā)生變化,因此普通差示掃描量熱儀(Differential scanning calorimetry,DSC)和快速加熱下的晶化產(chǎn)物差異明顯。在Ce_68Al_10Cu_20Co_2金屬玻璃中,以Al原子為中心的二十面體為基本原子結(jié)構(gòu)。相對于直接形成晶體,亞穩(wěn)的Al_13Co_4準(zhǔn)晶與非晶具有更高的結(jié)構(gòu)相似性,因此會首先析出,作為金屬玻璃微結(jié)構(gòu)和最終晶化產(chǎn)物的過渡相。納米量熱設(shè)備極高的冷卻速度可以實(shí)現(xiàn)Ce_68Al_10Cu_20Co_2非晶的原位制備。當(dāng)冷卻速度從100 K/s增大到50000 K/s,先后獲得晶體、晶體-非晶混合組織以及完全非晶三種不同凝固組織。通過后續(xù)再加熱可以確定凝固組織微結(jié)構(gòu)對玻璃化轉(zhuǎn)變、晶化以及熔化的影響。研究表明,金屬玻璃形成由籠統(tǒng)地抑制晶化進(jìn)一步細(xì)分為形核和晶體生長兩方面。具體而言,10000 K/s的冷卻速度可以抑制冷卻過程中晶化的發(fā)生,即傳統(tǒng)意義上的臨界冷卻速度。而在50000 K/s的冷卻速度下,不僅晶化被完全抑制,均勻形核的發(fā)生也被限制。原位冷卻形成的Ce_68Al_10Cu_20Co_2非晶在玻璃化轉(zhuǎn)變溫度附近退火10-3-10~4 s,實(shí)現(xiàn)了微結(jié)構(gòu)的有序化轉(zhuǎn)變。通過計(jì)算再加熱過程中的晶化焓和整體潛熱,實(shí)現(xiàn)了對等溫形核和晶化動力學(xué)的定量分析,結(jié)合結(jié)構(gòu)表征,證實(shí)了Ce_68Al_10Cu_20Co_2的二次晶化機(jī)制。在等溫退火過程中產(chǎn)生的有序團(tuán)簇表現(xiàn)出了明顯的尺寸效應(yīng),形成低溫熔化峰。玻璃態(tài)的晶化由均勻形核和非均勻形核共同作用,而過冷熔體中,異質(zhì)形核成為影響晶化的主要因素。當(dāng)非晶中形成大量納米晶,二者界面會存在高致密度的原子團(tuán)簇,可從整體上提高殘余非晶的玻璃化轉(zhuǎn)變溫度,即提高其動力學(xué)穩(wěn)定性。
[Abstract]:With the development of modern society and the progress of science and technology, the phase transition of metal materials in extreme non equilibrium conditions has attracted more and more attention. As a new calorimetric technology, nano calorimetry has a heating cooling rate of up to 107 K/s, and the phase transition behavior of metal materials in the extreme non equilibrium condition can be obtained in situ. In the traditional thermal analysis technology, its heat capacity sensitivity is at the nanometer scale, and the weak phase change information can be detected. In addition to thermodynamics and dynamics, nano calorimetry combined with other characterization methods can make full research on the phase transition. This not only helps to reveal the internal mechanism of the extreme non equilibrium phase transition, but also can be developed and modified for the new material. On the basis of the previous nonequilibrium nucleation research, this paper systematically studies the differential rapid scanning calorimeter (Differential fast scanning) using Sn based alloy micro droplets and Ce_68Al_10Cu_20Co_2 (at.%) bulk amorphous alloy under extreme cooling and heating conditions, glass transition, crystallization and melting phenomena. Calorimetry, DFSC) realized the in-situ cooling of a single Sn based alloy microdrop at the 10~4 K/s level. The solidification structure was refined and the precipitation phase was uniformly distributed. In the Sn3.5Ag microdrop, the cooling rate of 15000 K/s could be obtained by the cooling rate of 0.22 Tm. N transmission electron microscopy, HRTEM), the solidification structure has been successfully characterized. Under this condition, the precipitates of the microdroplets are below 100 nm, and no large acicular Ag_3Sn is formed. In the rapid solidification, the nano diffusion couple between the b-Sn matrix and Ag_3Sn is formed and the concentration gradient of up to 10~9/m can be found, which can reduce the driving force of the nucleation. The stability of the supercooled melt formed SnAg amorphous. In the Sn_3.0Ag_0.5Cu droplet, the growth mechanism of Ag_3Sn was clarified by the characterization of the different sizes of freezing at 20000 K/s cooling rate and the precipitation of different morphologies. The results showed that the formation of Ag_3Sn in the grain was spherical at the initial stage, and ((?) 02) as the preferred growth surface along [(?) 03] direction] The crystallization kinetics of Ce_68Al_10Cu_20Co_2 bulk amorphous from 0.083 K/s to 14000 K/s was studied. The heating rate increased, the crystallization temperature increased, the crystallization activation energy decreased, and the traditional Kissinger equation was no longer applicable. The crystal growth rate between the glass transition temperature and the melting point has been found. The decoupling of the growth speed and the viscous flow in the melt is found, that is, the Stokes-Einstein equation is no longer followed, and the Ediger relationship can be expressed at the low temperature section, namely, D UA ~ (-0.865). The form of the Ce_68Al_10Cu_20Co_2 supercooled melt can be obtained by combining the classical nucleation theory. The nucleation rate is used to determine the asymmetry of crystallization behavior during heating and cooling, that is, the heating crystallization is controlled by the growth and the cooling crystallization is controlled by the nucleation. Thus the possibility of the first precipitation of the Ce crystal is eliminated. With the increase of the heating speed, the crystallization path of the Ce_68Al_10Cu_20Co_2 is changed, so the common differential scanning calorimeter (Different The crystallization products of the ial scanning calorimetry, DSC) and the rapid heating are distinct. In the Ce_68Al_10Cu_20Co_2 metal glass, the twenty surface body centered on the Al atom is the basic atomic structure. Compared with the direct formation of the crystal, the metastable Al_13Co_4 quasicrystal has a higher structural similarity with the amorphous, so it will first precipitate, as a metal glass. The transition phase of the glass microstructures and the final crystallization products. The high cooling rate of the nano calorimeter can be prepared in situ of the Ce_68Al_10Cu_20Co_2 amorphous. When the cooling rate is increased from 100 K/s to 50000 K/s, the crystal, crystal - amorphous and completely amorphous three different solidification structures are obtained. The subsequent reheating can be confirmed. The effects of solidification microstructure on glass transition, crystallization and melting are determined. The study shows that the formation of metallic glass is further subdivided into two aspects: nucleation and crystal growth. Specifically, the cooling rate of 10000 K/s can inhibit the crystallization of the crystal during the cooling process, that is, the critical cooling rate in the traditional sense. At the cooling rate of 50000 K/s, not only the crystallization is completely suppressed, but the homogeneous nucleation is also restricted. The Ce_68Al_10Cu_20Co_2 amorphous formed by the in-situ cooling is annealed 10-3-10~4 s near the glass transition temperature, which realizes the ordering transformation of the microstructures. The quantitative analysis of temperature nucleation and crystallization kinetics, combined with structural characterization, confirmed the two crystallization mechanism of Ce_68Al_10Cu_20Co_2. The ordered clusters produced in the process of isothermal annealing showed a significant size effect and formed a melting peak at low temperature. The crystallization of the glass state was combined with homogeneous nucleation and non-uniform nucleation, while the supercooled melt was different. The mass nucleation is the main factor affecting the crystallization. When a large number of nanocrystals are formed in the amorphous, there will be a high density cluster of atoms in the two interface, which can improve the glass transition temperature of the residual amorphous from the whole, that is, to improve its dynamic stability.
【學(xué)位授予單位】：上海大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TG111

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