Structure and tribological property of B2-based approximants

Abstract

The present paper is concerned with a special group of approximants with B2 superstructures. In the first part, recent work on structural features of the B2 superstructure approximants is summarized. Experimental results obtained in AI-Cu-Mn and AI-Cu systems are presented, where a series of B2-based approximants are observed. These phases all have similar valence electron concentrations, in full support of the e/a-constant definition of approximants. Special emphasis is laid on the chemical twinning modes of the B2 basic structure in relation to the AI-Cu approximants. It is revealed that the B2 twinning mode responsible for the formation of local pentagonal atomic arrangements is of 180°/[111] type. This is also the origin of 5-fold twinning of the B2 phase on quasicrystal surfaces. Crystallographic features of phases B2, ~2, z3, y, and other newly discovered phases are also discussed. In all these phases, local pentagonal configurations are revealed. In the second part, dry trihological properties of some AICuFe samples containing the B2-type phases are presented. The results indicated that the B2 phase having their valence ratio near that of the quasicrystal possesses low friction coefficient under various loads, comparable with the annealed quasicrystalllne ingot. Such a result indicates that the B2-type phase with e/a near that of quasicrystal is indeed an approximant, which is in full support of the valence electron criterion for approximants.

Stability of mechanically alloyed vacancy ordered phase in Al70Cu15Ni15alloy during annealing

“…These structures can be described in terms of basic B2 (CsCl) type of cell with the ordering among transition metals and vacancy along the [111] direction. Dong et al [6] have carried out extensive investigations on the occurrence of B2 phase, which resulted in the realization that the valence electron concentration of the B2 phase is similar to that of a quasicrystal. The B2 phase and related VOPs were found to co-exist extensively with the quasicrystalline phases, particularly in Al-Cu-TM (Ni, Co, TM= transition metal) systems and they follow a well-defined orientation relationship [7][8][9][10].…”

Formation of a new F.C.C. τ2 phase in rapidly quenched Al55Cu35V10 alloy

“…phase, no such modulations are observed. However, Dong et al [7] have designated this phase in Al-Cu-Mn system as τ2 phase and have shown a close structural relation with icosahedral and decagonal phases. (121) is 16°±1°.…”

“…For this class of approximants, it has been proposed that there is an electronic structural correspondence between quasicrystalline and crystalline structure. Dong et al [6,7] have extensively studied the e/a (valance electron per atom) constant line in the ternary phase diagram of Al-Cu-Fe, Al-Cu-Mn, Al -Cu-(Fe,Cr) [6,7]. For example, it has been shown for Al-Cu-Fe system that the monoclinic Al 13 Fe 4 , icosahedral phase Al 62.…”

Mechanical Milling: a Top Down Approach for the Synthesis of Nanomaterials and Nanocomposites

“…The decagonal quasicrystals have some structural similarity with several well known stable crystalline structures, for example Al 13 Fe 4, Al 3 Ni, Al 3 Ni 2 and B2 phases. All the crystalline Al 3 Ni, Al 3 Ni 2 and B2 phases can exist along with decagonal near the temperature of the decagonal phase formation [189]. The fraction of decagonal phase (FDP) has been calculated by comparing the integrated intensities of the most intense XRD peak of the D phase.…”