快凝条件下液态Cu-Zr合金团簇结构遗传与演化特性的模拟研究
发布时间：2019-01-09 07:23
【摘要】：非晶合金的玻璃形成能力与其熔体局域原子结构有着内在的、直接的联系。因此,研究快凝条件下液态合金中团簇结构的遗传与演化特性,不仅可以加深对玻璃转变现象的认识,还有助于从结构的角度理解玻璃形成能力。为此,本文采用分子动力学方法,模拟研究了不同条件下液态Cu-Zr合金的快速凝固过程;运用双体分布函数、Honeycutt-Andersen(H-A)键型指数、扩展原子团类型指数(CTIM)等方法对系统的微结构特征进行了表征和分析;进一步采用原子轨迹逆向跟踪方法探究了快凝合金液体和过冷液体中团簇结构的遗传与演化特性,揭示了团簇结构遗传性与玻璃形成能力间的内在关系。本文的主要研究内容如下:采用Finnis-Sinclair(F-S)多体势,首先模拟研究了液态Cu50Zr50合金在5K/ns冷速下的快速凝固过程。结果表明:合金液体和快凝固体中主要的原子组态是(1212/1551)规则二十面体和(12 8/1551 2/1541 2/1431)缺陷二十面体,它们中比例最高的均是以Cu原子为中心的Cu6Zr7原子团,其次为Cu7Zr6和Cu8Zr5团簇。由(1212/1551)规则二十面体基本团簇以穿透共享模式铰链形成的二十面体中程有序的尺寸分布在液相和玻璃固相中分别呈现出13,19,23,…和13,19,23,25,29,37,…的幻数特征。团簇的演化与跟踪分析发现:没有任何团簇能从液体直接遗传到固态玻璃合金,二十面体团簇遗传的起始温度Tonset位于Tm~Tg过冷液相区。二十面体团簇的遗传以完全和直接遗传为主,其遗传分数fi在Tg附近显著增加。在Tg以下,(12 12/1551)规则二十面体团簇的完全遗传分数fp远高于其核遗传分数fc与碎片遗传分数fs。相对于(12 8/1551 2/1541 2/1431)缺陷二十面体,(12 12/1551)规则二十面体具有更高的结构稳定性和更强的结构遗传能力,但仅有少部分在遗传过程中能保持化学成分不变。通过部分遗传,某些二十面体中程有序也能够从过冷液体中被遗传到玻璃合金。进一步研究了不同冷速和压力条件下快凝Cu56Zr44合金中二十面体团簇的遗传特性及其与玻璃形成能力间的关系。随着冷速?增加,约化玻璃转变温度Trg随着lg?线性上升,但二十面体的团簇化程度降低,特别是在300K~Tg温度区间。提高?不仅可以增加Tg以上的fp和fs,而且Tonset也会随之升高。当γ105K/ns时,(12 12/1551)规则二十面体团簇的结构遗传甚至可以出现在Cu56Zr44合金的液相区。压力P对二十面体团簇的遗传行为和可遗传能力也有显著的影响。随着P的增加,不仅Tonset会随之升高,而且Tg以上温度区间的fi也显著增加,特别是fp。依赖于P的玻璃形成能力可以用相对遗传起始温度?Tc和约化遗传过冷度Ks来近似地估计。最后本文系统地研究了液态CuxZr100-x合金快速凝固过程中二十面体团簇结构遗传性与玻璃形成能力间的关系。结果发现:二十面体团簇,特别是二十面体中程有序对CuxZr100-x金属玻璃的形成起主要作用。二十面体团簇的遗传性是快凝Cux Zr100-x合金的固有属性,但Tonset仅出现在Tm~Tg过冷液相区。以过冷液体中遗传而来的二十面体团簇作为参考,发现过冷液体中的二十面体中程有序到快凝固体的直接和连续遗传与CuxZr100-x玻璃合金的形成密切相关。遗传的相对数量fcore(T)和fatom(T)不仅是玻璃转变的度量,而且300K的数值fcore(300K)和fatom(300K)可以用来大致地估计快凝过程中CuxZr100-x合金玻璃形成能力随Cu浓度x的变化。选择Tonset与临界转变温度Tc的差分作为评估参数,发现它们的局域最大值与实验上具有最佳玻璃形成能力的合金有很好的成分对应关系。
[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.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：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.
【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG139.8
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