本文選題：塊體非晶合金 + 非均勻性��； 參考：《湘潭大學》2016年博士論文

【摘要】：塊體非晶合金(BMG)因具有獨特而優(yōu)異的物理、化學和力學性能引起了人們極大的關注。BMG不僅在國防、航空航天、機械和電子電力等領域有著廣闊的應用前景,同時它也是研究非晶材料的結構、玻璃轉變和變形機理等基本科學問題的理想研究對象。目前人們已成功開發(fā)了眾多的非晶合金系,有的已在工程中得到了應用。然而較低的玻璃形成能力(GFA)和室溫塑性仍然是很多非晶合金系應用的主要障礙。洞悉非晶合金的微觀結構是理解玻璃形成和變形本質,并進一步開發(fā)性能更優(yōu)的非晶合金的關鍵。本文以Zr-Cu-Al、Zr-Ni-Al和Zr-Cu-Al-Nb等Zr基塊體非晶合金為研究對象,應用第一性原理分子動力學(AIMD)模擬結合實驗結果的方法,對非晶合金的微觀結構與玻璃形成以及流變行為的關系進行了系統(tǒng)深入的研究。全文工作和主要結果總結如下:1、基于經(jīng)典結晶理論研究了非晶合金的流變性能與GFA的影響。結果表明,合金的等溫轉變曲線“鼻尖”溫度T_n處的黏度與GFA成正比,同時晶化開始溫度Tx處的黏度與GFA成反比或液相線溫度T_l對應的黏度與GFA成正比。由此得到了新的GFA參數(shù)ψ0=(T_g-T_0)/(T_n-T_0)+(T_g-T_0)/(T_l-T_0),其中T_g為玻璃轉變溫度,T_0為理想玻璃轉變溫度。2、用AIMD研究了Zr_(55-x)Cu_(45)Al_x(x=3,7,12 at.%)非晶合金的玻璃轉變過程,并用Honeycutt-Andersen的鍵型指標和Voronoi多面體等方法分析了其原子結構,以及結構變化對微觀流變性能和玻璃形成的影響。我們發(fā)現(xiàn)該合金系中添加少量(x=3,7)Al時,以Al為中心的二十面體團簇比以Cu或Zr為中心的團簇要穩(wěn)定。不管是在熱起伏還是在外力作用下,這些以Al為中心的團簇都是最穩(wěn)定的團簇,可視為該合金系中的基本結構單元;當x=7時,這些穩(wěn)定原子團簇以共點、共線或共面的方式互相連接形成的二十面體中程序的空間骨架結構,使其整體結構更穩(wěn)定,原子平均擴散能力更低,GFA更強。3、對(Zr_(0.5)Cu_(0.4)Al_(0.1))_(100-x)Nb_x(x=0,3,6 at.%)非晶合金的實驗和AIMD模擬研究結果表明,少量的(3 at.%)Nb的添加后,形成了以Nb為中心的(類)二十面體以及以Al為中心的(類)二十面體原子團簇穩(wěn)定結構。這兩種穩(wěn)定團簇在合金中互相聯(lián)接和匹配形成了一種更穩(wěn)定緊密的結構,而且也增加了結構總體的非均勻性程度,導致其彈性模量、強度以及宏觀塑性的提高;而較多的(6 at.%)Nb添加后,一些穩(wěn)定Nb團簇取代了Al團簇,一定程度降低了這種結構的非均勻性程度,并導致其宏觀強度的下降和微觀流動性能的提高。4、對Zr_(67)Ni_(33-x)Al_x(x=8,15,21 at.%)非晶合金的AIMD研究表明:該合金系內部存在著以Ni為中心和以Al為中心的兩類團簇,其中以Ni為中心的團簇主要為0 3 6、0 3 6 1、0 2 8和0 2 8 1這幾種Bernal多面體。而以Al為中心的主要為配位數(shù)為12的0 2 8 2、0 3 6 3、0 0 12 0和配位數(shù)為13的0 110 2、0 3 6 4等(類)二十面體。(類)二十面體的穩(wěn)定性一般高過這些Bernal多面體,隨著Al含量的提升,以Al為中心的(類)二十面體含量也在不斷提高。這就使得合金的強度和彈性模量逐漸提高,而結構的非均勻性程度和流動性能逐漸降低。5、對Zr-Cu-Al(-Nb)和Zr-Ni-Al非晶進行單軸壓縮的第一性原理模擬結果顯示,合金塑性流動時應力-應變關系出現(xiàn)了原子尺度的“鋸齒流變”狀的變化。我們發(fā)現(xiàn),隨著應變的增加,1551鍵對和(類)二十面體團簇含量不斷減少。1551鍵對含量變化與這種鋸齒狀的應力變化具有一定的對應關系。進一步的分析表明在外應力作用下,相對穩(wěn)定的(類)二十面體團簇轉變成為更易流動的無序或類似液態(tài)的原子團簇,應力的陡降直接原因是合金內這些穩(wěn)定團簇含量的減少。這說明具有五次對稱結構的(類)二十面體穩(wěn)定團簇在合金抵抗塑性流動時扮演了類似骨架的角色。
[Abstract]:The bulk amorphous alloy (BMG) has attracted great attention because of its unique and excellent physical, chemical and mechanical properties..BMG not only has a broad application prospect in the fields of national defense, aerospace, mechanical and electronic power, but it is also ideal for the study of the basic scientific problems of the structure of amorphous materials, glass transition and deformation mechanism. At present, many amorphous alloys have been developed successfully, and some have been applied in engineering. However, the low glass forming ability (GFA) and room temperature plasticity are still the main obstacles for many amorphous alloys. The microstructure of the amorphous alloys is the essence of the formation and deformation of the glass, and the further development of the amorphous alloy. The key of amorphous alloys with better performance is to study the relationship between the microstructure of amorphous alloys and the relationship between the microstructure of amorphous alloys and the rheological behavior of Zr based bulk amorphous alloys, such as Zr-Cu-Al, Zr-Ni-Al and Zr-Cu-Al-Nb, with the method of first principle molecular dynamics (AIMD) simulation combined with experimental results. The full text work and the main results are summarized as follows: 1, based on the classical crystallization theory, the influence of the rheological properties of amorphous alloy and GFA is studied. The results show that the viscosity of the temperature T_n at the tip temperature of the alloy is proportional to the GFA, and the viscosity of the Tx at the beginning of the crystallization temperature is inversely proportional to the GFA or the viscosity of the liquid phase temperature T_l. The new GFA parameter 0= (T_g-T_0) / (T_n-T_0) + (T_g-T_0) / (T_l-T_0) is obtained, in which T_g is the glass transition temperature, T_0 is the ideal glass transition temperature.2. The glass transition process of the amorphous alloy of 45 is studied AIMD, and the key type index and the polyhedron are used. The atomic structure and the effect of structural changes on the microrheological properties and glass formation were analyzed. We found that when a small amount of (x=3,7) Al was added to the alloy system, the twenty - hedral clusters centered on the Al were more stable than the clusters centered on Cu or Zr. These clusters of Al centered clusters, regardless of the thermal fluctuations and external forces, were in the center. The most stable cluster is considered as the basic structural unit in the alloy system. When x=7, these stable clusters are interconnected with each other in a common, coplanar or coplanar way to form the space skeleton of the twenty plane. The overall structure is more stable, the atomic average diffusion capacity is lower, the GFA is stronger.3, and (Zr_ (0.5) Cu_ (0.4) Al_ (0) (0). The experimental and AIMD simulation results of Nb_x (100-x) Nb_x (x=0,3,6 at.%) amorphous alloys show that a small amount of (3 at.%) Nb is added to form a Nb centered (class) twenty - hedral and a Al centered (class) twenty - hedral cluster stable structure. The two stable clusters are linked and matched in the alloy to form a more stable form. The tight structure is fixed, and the degree of inhomogeneity of the structure is increased, which leads to the increase of its modulus, strength and macro plasticity; and after adding more (6 at.%) Nb, some stable Nb clusters replace the Al clusters, which reduces the uneven uniformity of the structure to a certain extent, and leads to the decrease of the macro intensity and the microscopic flow. The improvement of dynamic performance.4, the AIMD study of Zr_ (67) Ni_ (33-x) Al_x (x=8,15,21 at.%) amorphous alloy shows that there are two clusters of clusters with Ni centered and Al centered in the alloy system, of which Ni centered clusters are mainly 03 6,0 36, 28 and 0281. 12 028 2,0 36 3,0 0120 and 0110 2,0 364 (class) twenty of the coordination number 13. (class) the stability of the twenty face is generally higher than these Bernal polyhedron. With the increase of Al content, the content of the Al centered (class) twenty surface body is also increasing. This makes the strength and modulus of the alloy increase gradually, and the structure of the structure. The inhomogeneity and flow performance gradually decrease.5. The first principle simulation of the uniaxial compression of Zr-Cu-Al (-Nb) and Zr-Ni-Al amorphous shows that the stress strain relationship in the plastic flow of the alloy appears at the atomic scale "sawtooth rheology". We find that with the increase of strain, 1551 bond pairs and (class) twenty sides mass Further analysis shows that under the action of external stress, the relatively stable (class) twenty - face clusters change into more easily disordered or similar liquid clusters, and the direct cause of the stress drop is in the alloy. This shows that the content of stable clusters decreases. This shows that the (class) twenty - hedral stable cluster with five symmetric structures plays a similar role as a skeleton in the alloy resistance to plastic flow.

【學位授予單位】：湘潭大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG139.8

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相關期刊論文 前1條

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本文編號：1895437