Phase Transitions in Quasicrystals Induced by Friction and Wear
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Phase Transitions in Quasicrystals Induced by Friction and Wear
Chuang DONG1, Jinsong Wu1, Liming Zhang1, Jean-Marie Dubois2, Pierre Brunet2, Qinggang Zhou1, Dehe Wang1, and Huichen Zhang3 1 State Key Laboratory for Materials Modification by Laser, Ion and Electron Beams, Department of Materials Engineering, Dalian University of Technology, Dalian 116024, China 2 LSG2M, Ecole des Mines, Parc de Saurupt, 54042 Nancy, France 3 Materials Research Institute, Dalian Maritime University, Dalian 116024, China ABSTRACT Certain ductility may occur during friction tests on quasicrystalline materials that are intrinsically brittle. This is, at least in part, due to a solid-state phase transition from the icosahedral to a BCC phase. The present paper first summarizes phase transition features of quasicrystals and then examines the microstructural mechanism of scratch indentation on an icosahedral Al-Cu-Fe sample. The last part of this paper is devoted to a discussion of the correlation of this phase with respect to quasicrystals. 1. INTRODUCTION Quasicrystalline materials find their applications mainly in surface-related fields. The most famous example is non-stick quasicrystalline coating on cookware [1] which utilizes low surface energy [2], high hardness [3, 4], high wear and corrosion resistance, and low friction coefficient properties [5, 6]. Although the related patent was deposited more than ten years ago [1] and the commercial product is already on the market today, the basic understanding about the complicated surface behaviors of this kind of materials is still a subject of extensive research. On the one hand, the surface crystallographic and electronic structures of quasicrystalline and approximant phases have gained tremendous progress [7]. It is now known that the ideal surface of quasicrystal can be regarded as the extension of the bulk structure and retains the special electronic structure. However, the surface in practices is contaminated with oxides and other phases. Beeli et al have observed that a cubic phase of B2 structure (β phase in the following) is formed on the surface of quasicrystalline grains [8]. The surface of quasicrystals is also subject to a phase transition to the β phase in case of ion bombardment [9-11]. Therefore, the true surface is quite complicated and exerts influences over many surface properties such as surface energy and tribology. On the other hand, the surface properties of quasicrystalline materials, mostly tribological for practical reasons, are dependent upon the surface structure and are still to be fully understood. One of the questions that arise from tribological tests is the presence of apparent ductility after repeated sliding passes [12, 13]. Therefore a microstructure investigation of scratch process is necessary to clarify the mechanism. We have confirmed that one of the deformation mechanisms is a stress-induced phase transition, leading to the K7.5.1
formation of a BCC phase, or disordered β phase [14]. Therefore, phase transitions in quasicrystals not only are imp
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