Al-Ni二元系中一种新型缺陷点阵

本文从点阵间隔、密度以及衍射强度的测量详尽地研究了Al-Ni合金在δ相区内的结构变化。点阵间隔的量度表明:在不到4原子百分数的狭隘均匀范围内,α和c初则随Ni含量的增加而递减,过理想成分Ni₂Al₃以后,则又随Ni含量的增加而递增;也就是说,α和c在理想成分处同时出现最小值。密度和衍射强度的数据无可辩驳地指出这样一个事实:当Ni含量少于理想成分时,每晶胞所含的原子数恒为5,Al原子无规地替代了在赝立方体心位置上的部分Ni原子;当Ni含量超出理想成分时,每晶胞所含的原子数多于5,多余的Ni原子无规地填充到原来在理想结构中所空出的部分体心位置上去。决定这些变化的主要困素是基本结构单位内所含的平均价电子数,在δ相区内,每基本结构单位即每赝立方体的平均价电子数不能小于3。δ相和同一系统中的β相适成互补的对应关系,它是合金相缺陷点阵的一种新类型。

A NEW TYPE OF DEFECT LATTICE IN THE Al-Ni SYSTEM

A thorough investigation of the structural changes in the δ phase of Al-Ni alloys has been taken by measuring the lattice spacings, densities, and intensities of diffraction lines. The determination of the lattice spacings shows that, within the narrow homogeneity range less than four atomic per cent, a and c decrease at first with the increase of the Ni content, while after the ideal composition Ni₂Al₃, they increase with the increase of the Ni content; in other words, both a and c reach minimum simultaneously at the ideal composition. All density and intensity measurements prove unequivocally that when the Ni content is less than that in the ideal composition, the number of atoms contained in each unit cell always remains five, the Al atoms substituting at random some of the Ni atoms at the centres of the pseudo-cubes; and when the Ni content exceeds that in the ideal composition, the number of atoms per unit cell is more than five, the superfluous Ni atoms filling up randomly part of the interstices forming centres of the pseudo-cubes in the ideal structure.The principal factor governing these changes is the mean number of valence electrons in the fundamental structural unit. In the δ phase, the mean number of valence electrons per fundamental structural unit, the pseudo-cube, could not be greater than three.Complementary to the corresponding β phase in the same system, the δ phase forms a new type of defect lattice in alloy phases.