冷速对快凝Ni_(50)Zr_(50)合金团簇结构遗传与演化特性的影响

Heredity and Evolution of Cluster in Rapid Solidification of Liquid Ni_(50)Zr_(50)Alloy under Different Cooling Rates

采用分子动力学方法,模拟研究6个不同冷速下液态Ni_(50)Zr_(50)合金的快速凝固过程,用双体分布函数、原子团类型指数、遗传跟踪等方法对快凝合金的微结构特征与演化特性进行表征和分析。结果表明:Ni_(50)Zr_(50)玻璃合金中数目最多的原子组态是Z11 Kasper团簇,而非二十面体。快凝合金中的特征团簇趋向于聚合在一起形成中程序,其数目随冷速的降低而增加。基本团簇的结构遗传均起始于T_(m)~T_(g)的过冷液相区,其中Z11 Kasper团簇在T_(g)以上的附近温区具有最高阶段遗传分数。提高冷速有利于过冷液相区中基本团簇的阶段遗传分数增加和遗传的起始温度升高。冷速诱导的Ni_(50)Zr_(50)合金玻璃形成能力(GFA)的提高可以归因于特征团簇(如Z11 Kasper团簇)遗传能力的增强。

Amorphous alloys have been severely restricted to widespread commercial application by their limited glass-forming ability(GFA).Since it is essentially a“freezing liquid”to some extent,studying the correlation of the atomic structures in solid with those in liquid during the rapid solidification of liquid alloys is expected to provide new insights for GFA.Therefore,the rapid solidification processes of liquid Ni_(50) Zr_(50) alloy under six different cooling rates are simulated using molecular dynamics(MD)methods.The microstructure as well as its evolution of the rapidly solidified Ni_(50) Zr_(50) alloys are characterized and analyzed with pair distribution function(PDF),cluster-type-index method(CTIM),and reverse atomic trajectory tracking method.The results show that the most numerous atomic configurations in Ni_(50) Zr_(50) metallic glass is(112/14418/15511/1661),i.e.,Z11 Kasper cluster,rather than icosahedra.The characteristic clusters in rapidly solidified Ni_(50)Zr_(50) alloys tended to aggregate to form medium-range orders(MROs),and their numbers increase with the decrease of cooling rate.The configurational heredity of basic clusters emerges in the supercooled liquid region of T_(m)-T_(g).Among the typical clusters,Z11 Kasper cluster possesses the highest fraction f of staged heredity in a wide temperature range above T_(g).Raising cooling rate is beneficial for increasing f of basic clusters in the supercooled liquid region and increasing onset temperature of configuration heredity.The GFA of Ni_(50)Zr_(50) alloy induced by raising cooling rate can be attributed to the enhanced hereditary ability of characteristic clusters such as Z11 Kasper cluster.