Cu-12％Al合金熔体内中程有序原子团簇

通过高温X射线衍射仪研究了Cu 12％Al（质量分数，下同）合金熔体结构，并用纯铜作对比实验.在1250 ℃时，发现Cu 12％Al合金熔体结构因子曲线上18.5 nm－1位置有预峰出现.随着温度的下降，预峰变得更加明锐.预峰的出现是液体中存在中程有序的标志.通过熔态旋淬法获得该合金的快速凝固条带，对条带进行固态X射线衍射分析，其结构是具有有序体心立方晶格的Cu3Al.熔体内的中程有序结构单元尺寸与快凝Cu3Al（111）晶面面间距d111数值一致.由双体分布函数得到的最近邻原子距离、配位数.结合原子团簇结构单元的几何模型，计算得出该体心立方的棱边长(a=3.00 10－10m)与文献中所提供的固态晶格常数（a=2.95 10－10 m）基本吻合.可证明该合金熔体中存在以DO3结构为基本单元的中程有序原子团簇，在液相线以上200 ℃温度范围内这种中程有序都能稳定存在，并随着温度的下降，中程有序的相关尺寸逐渐增大.

Medium-Range Order Structure Clusters in Cu-12%Al Elloys Melt

Using X ray diffraction, the structure factors of molten Cu 12％(mass fraction)Al alloys and pure copper have been investigated. Distinct prepeak(the prepeak occurs at values of scattering vector Q=18.5 nm－1) has been found in the structure factor of Cu 12％Al alloys melt at 1250 ℃. The prepeak in the liquid alloy increases with decreasing temperature. The prepeak is a sign of medium range order. Rapid solidified ribbons prepared by the single roller melt spinning technique have been investigated with X ray scattering. The phase in the ribbons is Cu3Al with superstructure. The structural unit size of medium range order clusters in liquid equals to intercrystal face distance d111 of Cu3Al. According to the nearest neighbor distance and coordination number, obtained from the pair correlation function, and basic unit model of cluster, the length of cubic edge can be calculated, which meets the parameter of the crystalline structure given by literature. So it is speculated that there are DO3 structure clusters in the liquid Cu 12％Al alloy. This stable medium range order can exist up to nearly 200 ℃ above liquidus and the structural correlation length increases with decreasing temperature.