B2基准晶类似相的结构及摩擦行为

Structure and tribological property of B2-based approximants

研究了具有B2及其超结构的一类特殊准晶类似相．以Al－Cu－Mn和Al－Cu合金系为例介绍其相种类，并且证实它们均为等电子浓度相类似相，并分析了这些相的晶体结构，揭示了其与准晶的联系．发现了与Al－Cu类似相有关的B2化学孪晶模式，即180°/[111]操作，该模式可导致生成具有五边形局部原子排列和B2结构的五次孪晶．报道了Al－Cu－Fe合金系中成分不同的B2相的摩擦性能，发现价电子浓度e／a对摩擦因数有明显影响，e／a值接近1．86的样品（即Al－Cu－Fe准晶的e／a）具有接近准晶的摩擦因数，而e／a偏离越大，摩擦因数就越大．这说明具有准晶价电子浓度的B2结构才可能是准晶类似相．

The present paper deals with a special group of approximants having B2 superstructures. Recent work on structural features of the B2-superstructure approximants issummarized. Experimental results obtained in Al-Cu-Mn and Al-Cu systems are presented,where a series of B2-based approximants are observed. These phases all have similar valenceelectron concentrations, in full support of the e/α-constant definition of approximants. Specialemphasis is laid on the chemical twinning modes of the B2 basic structure in relation to the Al-Cuapproximants. It is revealed that the B2 twinning mode responsible for the formation of localpentagonal atomic arrangement is of 180°/[111] type. This is also the origin of 5-fold twinningof the B2 phase on quasicrystal surfaces. Crystallographic features of phases B2, τ2, τ3, γ, andother newly discovered phases are also discussed. In all these phases, local entagonalconfigurations are revealed. Dry friction properties are presented of some AICuFe samples containing the B2-type phases. The results indicate that the B2 phase having their valence rationear that of the quasicrystal possesses low friction coefficient under various loads, comparablewith the annealed quasicrystalline ingot. Such a result indicates that the B2-type phase with e/αnear that of quasicrystal is indeed an approximant.