Amorphous alloys, and the partially or fully crystallised materials derived from them, can have properties attractive for a diverse range of applications. In some cases, their wear resistance can be of primary concern, in others, it is an important secondary property. The distinctive mechanical properties of amorphous alloys make their wear resistance of fundamental interest also. This review focuses on the influence of a variety of factors in wear testing, on the mechanisms of wear, on the characteristics of different categories of amorphous alloy, and on the effects of partial or complete crystallisation. It is shown that amorphous alloys can have very good resistance to sliding and abrasive wear. The wear resistance of related quasicrystalline phases is also considered.

Wear resistance of amorphous alloys and related materials

The experimental aspects of the plastic deformation of icosahedral quasicrystals are reviewed. Macroscopic experiments, which involve the general investigation of stress-strain curves and the determination of the thermodynamic activation parameters of the deformation process are described. Investigations of the microstructure of plastically deformed samples, studied by means of transmission electron microscopy are presented. Important parameters such as the dislocation density, the Burgers vectors of dislocations, and slip systems are analyzed. Additionally, the results of in-situ straining experiments giving direct insight into the dynamics of the deformation process are presented. Direct conclusions on the nature of the plastic deformation process are drawn, and the current view of the deformation mechanism based on the specific structure of this class of materials is consistently discussed in terms of a qualitative ‘cluster friction model’.

The plasticity of icosahedral quasicrystals

The plastic deformation of icosahedral Al-Pd-Mn single quasicrystals has been studied by in situ straining experiments in a high-voltage electron microscope at elevated temperatures. The results provide the first direct evidence for dislocation motion in quasicrystals. The dislocation velocity, for an applied stress of 390 MPa, was determined as 7×10−7ms−1. It was found that the dislocation motion takes place in planes which are perpendicular to threefold and fivefold lattice directions.

In-situ observation of dislocation motion in icosahedral Al-Pd-Mn single quasicrystals

Single element quasicrystalline monolayers were prepared by depositionof antimony and bismuth on the fivefold surface of icosahedralAl71.5Pd21Mn8.5 and the tenfold surface of decagonal Al71.8Ni14.8Co13.4.Elastic helium atom scattering and low energy electron diffraction ofthe monolayers show Bragg peaks at the bulk derived positions of theclean surfaces, revealing highly ordered quasicrystalline epitaxialfilms. Their adatom densities of (0.9+/-0.2)x10(15) cm(-2) and(0.8+/-0.2)x10(15) cm(-2) on Al-Pd-Mn and Al-Ni-Co, respectively,correspond to roughly one adatom per Al atom of the quasicrystallinesubstrate surfaces.

https://juser.fz-juelich.de/record/19463/files/13431.pdf

Quasicrystalline epitaxial single element monolayers on icosahedral Al-Pd-Mn and decagonal Al-Ni-Co quasicrystal surfaces

Al[sbnd]Pd[sbnd]Mn single-quasicrystals have been plastically deformed at temperatures between 730 and 800°C up to different strain values and analysed in the transmission electron microscope. Dislocations were created during deformation. The dislocation density ranged between 1·7 × 107 cm−2 in undeformed samples and 7·8 × 108cm−2in material deformed at 732°C. Six-dimensional dislocation Burgers vectors were determined employing the convergent-beam electron diffraction technique. 87% of these Burgers vectors were oriented parallel to twofold directions in three-dimensional physical space. Their moduli were 0·113, 0·183 and 0·296nm. The ratio of the phason to the phonon component of the Burgers vectors was found to increase with increasing strain. A variety of slip systems was observed. In most cases the respective slip plane normals were parallel to fivefold and threefold directions.

Study of plastically deformed icosahedral Al-Pd-Mn single quasicrystals by transmission electron microscopy

Single quasicrystals of Al 7 0Pd 21 Mn 9 were plastically deformed by 25% under compression at 750 o C. Both these samples as well as control samples of as-grown and heat-treated material were investigated by transmission electron microscopy. It was found that upon deformation the dislocation density increases by about 2 orders of magnitude. This provides the first direct evidence for quasicrystal deformation by a dislocation mechanism. The dislocation were found to have twofold and fivefold Burgers vector directions in physical space

M Wollgarten

Papers

Direct evidence for plastic deformation of quasicrystals by means of a dislocation mechanism