液态Ta快凝过程中团簇的遗传及其与局域对称性的关联

Heredity of clusters in liquid Ta rapid solidification process and its correlation with local symmetry

金属玻璃是液态金属在某种程度上的“冻结”,探明液态金属的结构特征及其在快凝过程中的演化特性,有助于理解玻璃转变和玻璃形成能力的微结构机制.为此,本文采用分子动力学,模拟研究了液态金属Ta的快凝过程.并用双体分布函数、最大标准团簇、遗传跟踪等方法,对快凝Ta的微结构特征及其演化特性进行了表征和分析.结果表明,快凝金属Ta的原子组态是各种Kasper团簇及变形结构,其中占比最高的是Z13 Kasper团簇.连续遗传起始温度和阶段遗传分数均可用来表征团簇结构遗传能力的大小.最大标准团簇的对称性可以采用局域对称性参数(LSP)来定量表征,局域五次对称参数(LSP_(5))越大其遗传能力越强.各类团簇在能量区间出现的频率均服从高斯分布,其平均原子势能期望值(E^(j)_(exp))与LSP呈近似线性关系,且E^(j)_(exp)随LSP_(5)的增大而降低.高的局域五次对称性降低了团簇的平均原子势能,从而增强了这类团簇的结构遗传能力.

Metallic glass(MG)has received intensive attention in the fields of amorphous physics and materials science,owing to its excellent mechanical properties,good corrosion resistance,and large elastic deformation limit.Comparing with traditional oxide glass,the limited glass-forming ability(GFA)seriously restricts the application of MG in engineering.Therefore,the GFA has been a hot scientific issue in the field of amorphous material research.Recently,scientists have fully realized that GFA is closely related to the local atomic structure in liquid as well as its evolution features.Since the MG is called the“freezing”liquid,exploring the correlation of local atomic structures between liquid phase and solid phase under rapid solidification conditions is helpful in understanding the microstructural mechanism of GFA.Therefore,the rapid solidification process of liquid Ta is investigated via molecular dynamics simulation.The pair correlation function(PDF),the largest standard cluster(LSC),and the reverse atomic trajectory tracking methods are used to characterize and analyze the microstructure and its evolution during the rapid solicitation of liquid Ta.The results show that the local atomic configurations of the rapidly solidified Ta are various Kasper clusters as well as their distorted configurations,among of which[1/444,10/555,2/666]deformed icosahedron(or Z13 cluster)accounts for the highest proportion.The trend of hereditary ability of clusters revealed by the onset temperature of continuous heredity is consistent well with that by the fraction of staged heredity.The geometric symmetry of clusters can be quantitatively characterized by using the local symmetry parameter(LSP).The hereditary ability of clusters is closely related to their LSP.The local five-fold symmetry is beneficial to enhancing hereditary ability,while local four-and six-fold symmetry are disadvantageous for that.The probability of clusters with the same LSC index emerging in the energy range follows the Gaussian distribution,and the expected average atomic potential E^(j)_(exp)E^(j)_(exp)energy is almost linearly related to the LSP,and decreases with the increase of LSP_(5).The high local five-fold symmetry reduces the average atomic potential energy of LSC,thereby enhancing its configurational heredity.These findings have guiding significance in improving GFA through regulating the local symmetry of liquid monatomic metals or alloys.