快凝條件下液態(tài)Cu-Zr合金團簇結(jié)構(gòu)遺傳與演化特性的模擬研究
發(fā)布時間：2019-01-09 07:23
【摘要】：非晶合金的玻璃形成能力與其熔體局域原子結(jié)構(gòu)有著內(nèi)在的、直接的聯(lián)系。因此,研究快凝條件下液態(tài)合金中團簇結(jié)構(gòu)的遺傳與演化特性,不僅可以加深對玻璃轉(zhuǎn)變現(xiàn)象的認識,還有助于從結(jié)構(gòu)的角度理解玻璃形成能力。為此,本文采用分子動力學(xué)方法,模擬研究了不同條件下液態(tài)Cu-Zr合金的快速凝固過程;運用雙體分布函數(shù)、Honeycutt-Andersen(H-A)鍵型指數(shù)、擴展原子團類型指數(shù)(CTIM)等方法對系統(tǒng)的微結(jié)構(gòu)特征進行了表征和分析;進一步采用原子軌跡逆向跟蹤方法探究了快凝合金液體和過冷液體中團簇結(jié)構(gòu)的遺傳與演化特性,揭示了團簇結(jié)構(gòu)遺傳性與玻璃形成能力間的內(nèi)在關(guān)系。本文的主要研究內(nèi)容如下:采用Finnis-Sinclair(F-S)多體勢,首先模擬研究了液態(tài)Cu50Zr50合金在5K/ns冷速下的快速凝固過程。結(jié)果表明:合金液體和快凝固體中主要的原子組態(tài)是(1212/1551)規(guī)則二十面體和(12 8/1551 2/1541 2/1431)缺陷二十面體,它們中比例最高的均是以Cu原子為中心的Cu6Zr7原子團,其次為Cu7Zr6和Cu8Zr5團簇。由(1212/1551)規(guī)則二十面體基本團簇以穿透共享模式鉸鏈形成的二十面體中程有序的尺寸分布在液相和玻璃固相中分別呈現(xiàn)出13,19,23,…和13,19,23,25,29,37,…的幻數(shù)特征。團簇的演化與跟蹤分析發(fā)現(xiàn):沒有任何團簇能從液體直接遺傳到固態(tài)玻璃合金,二十面體團簇遺傳的起始溫度Tonset位于Tm~Tg過冷液相區(qū)。二十面體團簇的遺傳以完全和直接遺傳為主,其遺傳分數(shù)fi在Tg附近顯著增加。在Tg以下,(12 12/1551)規(guī)則二十面體團簇的完全遺傳分數(shù)fp遠高于其核遺傳分數(shù)fc與碎片遺傳分數(shù)fs。相對于(12 8/1551 2/1541 2/1431)缺陷二十面體,(12 12/1551)規(guī)則二十面體具有更高的結(jié)構(gòu)穩(wěn)定性和更強的結(jié)構(gòu)遺傳能力,但僅有少部分在遺傳過程中能保持化學(xué)成分不變。通過部分遺傳,某些二十面體中程有序也能夠從過冷液體中被遺傳到玻璃合金。進一步研究了不同冷速和壓力條件下快凝Cu56Zr44合金中二十面體團簇的遺傳特性及其與玻璃形成能力間的關(guān)系。隨著冷速?增加,約化玻璃轉(zhuǎn)變溫度Trg隨著lg?線性上升,但二十面體的團簇化程度降低,特別是在300K~Tg溫度區(qū)間。提高?不僅可以增加Tg以上的fp和fs,而且Tonset也會隨之升高。當(dāng)γ105K/ns時,(12 12/1551)規(guī)則二十面體團簇的結(jié)構(gòu)遺傳甚至可以出現(xiàn)在Cu56Zr44合金的液相區(qū)。壓力P對二十面體團簇的遺傳行為和可遺傳能力也有顯著的影響。隨著P的增加,不僅Tonset會隨之升高,而且Tg以上溫度區(qū)間的fi也顯著增加,特別是fp。依賴于P的玻璃形成能力可以用相對遺傳起始溫度?Tc和約化遺傳過冷度Ks來近似地估計。最后本文系統(tǒng)地研究了液態(tài)CuxZr100-x合金快速凝固過程中二十面體團簇結(jié)構(gòu)遺傳性與玻璃形成能力間的關(guān)系。結(jié)果發(fā)現(xiàn):二十面體團簇,特別是二十面體中程有序?qū)uxZr100-x金屬玻璃的形成起主要作用。二十面體團簇的遺傳性是快凝Cux Zr100-x合金的固有屬性,但Tonset僅出現(xiàn)在Tm~Tg過冷液相區(qū)。以過冷液體中遺傳而來的二十面體團簇作為參考,發(fā)現(xiàn)過冷液體中的二十面體中程有序到快凝固體的直接和連續(xù)遺傳與CuxZr100-x玻璃合金的形成密切相關(guān)。遺傳的相對數(shù)量fcore(T)和fatom(T)不僅是玻璃轉(zhuǎn)變的度量,而且300K的數(shù)值fcore(300K)和fatom(300K)可以用來大致地估計快凝過程中CuxZr100-x合金玻璃形成能力隨Cu濃度x的變化。選擇Tonset與臨界轉(zhuǎn)變溫度Tc的差分作為評估參數(shù),發(fā)現(xiàn)它們的局域最大值與實驗上具有最佳玻璃形成能力的合金有很好的成分對應(yīng)關(guān)系。
[Abstract]:The glass forming ability of the amorphous alloy has intrinsic and direct contact with its melt local atomic structure. Therefore, the study of the genetic and evolutionary characteristics of the cluster structure in the liquid alloy under the fast setting conditions can not only deepen the understanding of the glass transition phenomenon, but also help to understand the glass forming ability from the angle of the structure. In this paper, the rapid solidification process of liquid Cu-Zr alloy under different conditions was studied by using the molecular dynamics method. The microstructure characteristics of the system were characterized and analyzed by means of the two-body distribution function, the honeycutt-Andersen (H-A) key type index and the extended radical type index (CTIM). The genetic and evolutionary characteristics of the cluster structure in the liquid and subcooled liquid of the fast-setting alloy and the subcooled liquid are further investigated by the method of the reverse tracking of the atomic trajectory, and the intrinsic relation between the structure of the cluster and the formation of the glass is revealed. The main contents of this paper are as follows: Finnis-Sinclair (F-S) multi-body potential is used to simulate the rapid solidification process of liquid Cu50Zr50 alloy at 5K/ ns cooling rate. The results show that the main atomic configurations of the alloy liquid and the fast-solidified body are (1212/ 1551) and (12 8/ 1551 2/ 1541 2/ 1431), the most of which are Cu6Zr7 radicals centered on the Cu atom, followed by the Cu7Zr6 and Cu8Zr5 clusters. The ordered size distribution of the icosahedron formed by the (1212/ 1551) regular icosahedral base cluster to penetrate the shared mode hinge exhibits 13, 19, 23,... in the liquid phase and the glass solid phase, respectively. and 13, 19, 23, 25, 29, 37,... The magic number characteristic. The cluster evolution and follow-up analysis found that no cluster of clusters can be directly inherited from the liquid to the solid-state glass alloy, and the initial temperature Tonset of the icosahedral cluster is located in the subcooled liquid-phase region of Tm-Tg. The genetic fraction of the icosahedral cluster is mainly and directly inherited, and the genetic fraction fi of the icosahedral cluster is significantly increased in the vicinity of the Tg. Under the Tg, the total genetic fraction fp of the icosahedral cluster in the (12 12/ 1551) rule is much higher than that of the nuclear genetic fraction fc and the fragment genetic fraction fs. Relative to (128/ 1551 2/ 1541 2/ 1431) the two decahedron, (12 12/ 1551), the icosahedron has higher structural stability and stronger structural genetic ability, but only a small part can keep the chemical composition unchanged during the genetic process. By partial inheritance, some icosahedron can also be inherited from the subcooled liquid to the glass alloy in order. The genetic characteristics of icosahedral clusters in fast-setting Cu56Zr44 alloys under different cold and pressure conditions and their relationship with the formation of glass are further studied. With the cooling rate? An increase in the glass transition temperature Trg with lg? The linear increase, but the degree of clustering of the icosahedron decreases, especially in the 300K-Tg temperature range. Improved? Not only can the fp and fs above Tg be increased, but the Tonset will also increase. In the case of 105K/ ns, the structural inheritance of the (12 12/ 1551) regular icosahedral cluster can even appear in the liquid phase of the Cu56Zr44 alloy. The pressure P also has a significant effect on the genetic behavior and the genetic ability of the icosahedral cluster. As the P increases, not only the Tonset increases, but the fi of the temperature range above Tg is also significantly increased, in particular fp. P-dependent glass-forming ability can be used relative to the initial temperature? The Tc and the epigenetic subcooling degree Ks are estimated approximately. In the end, the relationship between the structure of the icosahedral cluster and the formation of the glass in the process of rapid solidification of the liquid CuxZr100-x alloy is studied systematically. The results show that the formation of the CuxZr100-x metal glass in the icosahedron cluster, especially the icosahedron, plays a major role in the formation of the CuxZr100-x metal glass. The hereditary character of the icosahedral cluster is the intrinsic property of the fast-setting Cux Zr100-x alloy, but the Tonset only appears in the subcooled liquid phase of Tm ~ Tg. The direct and continuous inheritance of the icosahedron in the subcooled liquid to the fast-solidified body is closely related to the formation of the CuxZr100-x glass alloy. The relative number of fcore (T) and ftom (T) of the heredity is not only a measure of glass transition, but also the value fcore (300K) and ftom (300K) of 300K can be used to estimate the change of the glass forming ability of the CuxZr100-x alloy with the concentration of Cu in the fast-setting process. The difference between Tonset and critical transition temperature Tc is chosen as the evaluation parameter, and the local maximum value is found to have a good relationship with the alloy with the best glass forming ability.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG139.8
[Abstract]:The glass forming ability of the amorphous alloy has intrinsic and direct contact with its melt local atomic structure. Therefore, the study of the genetic and evolutionary characteristics of the cluster structure in the liquid alloy under the fast setting conditions can not only deepen the understanding of the glass transition phenomenon, but also help to understand the glass forming ability from the angle of the structure. In this paper, the rapid solidification process of liquid Cu-Zr alloy under different conditions was studied by using the molecular dynamics method. The microstructure characteristics of the system were characterized and analyzed by means of the two-body distribution function, the honeycutt-Andersen (H-A) key type index and the extended radical type index (CTIM). The genetic and evolutionary characteristics of the cluster structure in the liquid and subcooled liquid of the fast-setting alloy and the subcooled liquid are further investigated by the method of the reverse tracking of the atomic trajectory, and the intrinsic relation between the structure of the cluster and the formation of the glass is revealed. The main contents of this paper are as follows: Finnis-Sinclair (F-S) multi-body potential is used to simulate the rapid solidification process of liquid Cu50Zr50 alloy at 5K/ ns cooling rate. The results show that the main atomic configurations of the alloy liquid and the fast-solidified body are (1212/ 1551) and (12 8/ 1551 2/ 1541 2/ 1431), the most of which are Cu6Zr7 radicals centered on the Cu atom, followed by the Cu7Zr6 and Cu8Zr5 clusters. The ordered size distribution of the icosahedron formed by the (1212/ 1551) regular icosahedral base cluster to penetrate the shared mode hinge exhibits 13, 19, 23,... in the liquid phase and the glass solid phase, respectively. and 13, 19, 23, 25, 29, 37,... The magic number characteristic. The cluster evolution and follow-up analysis found that no cluster of clusters can be directly inherited from the liquid to the solid-state glass alloy, and the initial temperature Tonset of the icosahedral cluster is located in the subcooled liquid-phase region of Tm-Tg. The genetic fraction of the icosahedral cluster is mainly and directly inherited, and the genetic fraction fi of the icosahedral cluster is significantly increased in the vicinity of the Tg. Under the Tg, the total genetic fraction fp of the icosahedral cluster in the (12 12/ 1551) rule is much higher than that of the nuclear genetic fraction fc and the fragment genetic fraction fs. Relative to (128/ 1551 2/ 1541 2/ 1431) the two decahedron, (12 12/ 1551), the icosahedron has higher structural stability and stronger structural genetic ability, but only a small part can keep the chemical composition unchanged during the genetic process. By partial inheritance, some icosahedron can also be inherited from the subcooled liquid to the glass alloy in order. The genetic characteristics of icosahedral clusters in fast-setting Cu56Zr44 alloys under different cold and pressure conditions and their relationship with the formation of glass are further studied. With the cooling rate? An increase in the glass transition temperature Trg with lg? The linear increase, but the degree of clustering of the icosahedron decreases, especially in the 300K-Tg temperature range. Improved? Not only can the fp and fs above Tg be increased, but the Tonset will also increase. In the case of 105K/ ns, the structural inheritance of the (12 12/ 1551) regular icosahedral cluster can even appear in the liquid phase of the Cu56Zr44 alloy. The pressure P also has a significant effect on the genetic behavior and the genetic ability of the icosahedral cluster. As the P increases, not only the Tonset increases, but the fi of the temperature range above Tg is also significantly increased, in particular fp. P-dependent glass-forming ability can be used relative to the initial temperature? The Tc and the epigenetic subcooling degree Ks are estimated approximately. In the end, the relationship between the structure of the icosahedral cluster and the formation of the glass in the process of rapid solidification of the liquid CuxZr100-x alloy is studied systematically. The results show that the formation of the CuxZr100-x metal glass in the icosahedron cluster, especially the icosahedron, plays a major role in the formation of the CuxZr100-x metal glass. The hereditary character of the icosahedral cluster is the intrinsic property of the fast-setting Cux Zr100-x alloy, but the Tonset only appears in the subcooled liquid phase of Tm ~ Tg. The direct and continuous inheritance of the icosahedron in the subcooled liquid to the fast-solidified body is closely related to the formation of the CuxZr100-x glass alloy. The relative number of fcore (T) and ftom (T) of the heredity is not only a measure of glass transition, but also the value fcore (300K) and ftom (300K) of 300K can be used to estimate the change of the glass forming ability of the CuxZr100-x alloy with the concentration of Cu in the fast-setting process. The difference between Tonset and critical transition temperature Tc is chosen as the evaluation parameter, and the local maximum value is found to have a good relationship with the alloy with the best glass forming ability.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG139.8
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