Influence of Grain Orientation on Friction and Wear Behavior in Quasicrystalline Alloys
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Influence of Grain Orientation on Friction and Wear Behavior in Quasicrystalline Alloys ALAN DUCKHAM, DAN SHECHTMAN* and BENJAMIN GRUSHKO† National Institute of Standards and Technology, MSEL, Gaithersburg, MD 20899 *Department of Materials Engineering, Technion, Haifa, Israel † Institute of Solid-State Research, Jülich, Germany ABSTRACT The influence of grain orientation on the friction and wear behavior of single-phase quasicrystalline alloys is investigated. Pin-on-disc wear tests and friction coefficient measurements have been performed on bulk samples of icosahedral phase AlPdMn and decagonal phase AlNiCo alloys. Wear behavior has been evaluated by optical microscopy, scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Coefficient of friction values of the decagonal AlNiCo alloy are found to be widely scattered (between 0.03 and 0.55) compared to the far more consistent values of the icosahedral alloys. This is explained by considering the significant variation in wear behavior that is observed between different – sometimes adjacent – oriented grains in the decagonal specimens. INTRODUCTION The inherent low surface energies of quasicrystalline alloys suggest their potential use in low friction and wear resistant applications. To date a considerable amount of work has been performed on evaluating the tribological properties of various quasicrystalline coatings manufactured by various thermal spraying [1,2] and vapor deposition [3] processes. The analysis of this work has been complicated by the fact that often these coatings are comprised of several phases. For example in the Al-Cu-Fe-Cr system, the icosahedral phase, the decagonal phase, several approximants to the decagonal phase and several crystalline phases can possibly form for a fairly narrow region of the phase diagram. A more fundamental understanding of the properties of quasicrystalline alloys could be achieved by measuring the properties of individual phases. To this aim, wear testing to measure friction coefficients and wear resistance of single-phase icosahedral, decagonal and crystalline alloys has been conducted. EXPERIMENTAL PROCEDURE The details of the bulk single-phase cast specimens that were studied are listed in Table I. The specimens consisted of four Al-Pd-Mn icosahedral alloys (all single crystals), an Al-Ni-Co decagonal alloy (large grained polycrystals) and an Al-Fe intermetallic crystalline alloy (a single crystal). The cylindrically shaped specimens were sectioned into circular discs suitable for wear testing. They were subjected to standard metallographic grinding and polishing procedures with 1 µm diamond paste used in the final polish. The specimens were initially characterized by X-ray diffraction (XRD) to confirm that they were indeed single-phase. Specimens were then subjected to unlubricated pin-on-disc wear tests [4] during which friction data was collected for the calculation of coefficient of friction values. Multiple tests were performed on each specimen. Each test consisted of 400 revolution
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