| Quasicrystals materials are characterized by low coefficient of friction,low surface energy,non-sticky,high hardness/elasticity ratio and chemical and thermal stabilities,making them important for wear related applications.In this work,the Al62.0Cu25.5Fe12.5 icosahedral quasicrystal was chosen as abrasive material,to compare with conventional hard abrasives such as diamond,alumina and silica,to wear against copper,2024 aluminum alloy and 304 stainless steel.Special attention was paid to the characteristic smearing mechanism brought by quasicrystal abrasive wearing,i.e.,flattening the surface at the least surface removal.The enhanced passivation of stainless steel was also noticed.The main contents and conclusions of this paper include the following:（1）After comparing the abrasive polishing behaviors of Al62.0Cu25.5Fe12.5 icosahedral quasicrystals,alumina,silica,and diamond abrasives on soft metals such as Cu and Al alloys and a austenite stainless steel,focusing on the smearing-type plastic deformation.It is pointed out that the QC abrasive shows dominating smearing mechanism,in sharp contrast to all the other three abrasives,as reflected by large indent size shrinking with respect to surface removal depth,etc.△R/△h,which we define as the smearing coefficient,in accordance with the proposed geometrical models for cutting and smearing wear.This parameter assesses the degree of smearing-type wearing in a quantitative manner.A larger smearing coefficient leads to a more smearing-dominant wearing.（2）The characteristic smearing mechanism of Al62.0Cu25 5Fe12.5 icosahedral quasicrystal abrasive produces an obvious surface hardening effect,with the nano-hardness of 304 stainless steel is 0.25～0.40 GPa,that of copper 0.12～0.21 GPa,all higher than after conventional abrasives polishing.The quasicrystal abrasive wear produces a flattened surface with the least surface removal when used to polish the soft metals,thus opening up new application fields for quasicrystals in particle form,where low-wearing and fine surface finishing are demanded.（3）The Al62.0Cu25.5Fe12.5 icosahedral quasicrystal abrasive polishing produces a pronounced passivation enhancement on 304 stainless steel,in comparison with three kinds of conventional hard abrasives.This is the direct result of severe surface plastic deformation upon polishing using quasicrystal abrasives following a characteristic smearing-dominant polishing mechanism.According to measurements on electrochemical impedance,Mott-Schottky,and potentiodynamic polarization,the quasicrystal-polished surfaces exhibit the most stable and homogeneous oxide film,which well resists Cl-ions corrosion attack.The effect becomes more pronounced after longer time passivation immersion treatment.The degree of corroded damage is much reduced compared with the conventional abrasives in neutral corrosion environment.（4）In alkaline corrosion environment（KOH+NaOH+3.5%NaCI solution）,the passive film on 304SS pretreated with the Al62.0Cu25.5Fe12.5 quasicrystal abrasive polishing exhibits the largest impendence,18.543×105Ωcm2,and the lowest admittance Y2,both arising from the inner passivation film.The Mott-Schottky results indicate the least defect density on the passivated surface and a highly dense passivation film formed quite rapidly in the alkaline environment.The cyclic polarization results confirm the rapid passivation and further reveal better resistance against localized pitting corrosion and self-recovering capability.The above-mentioned results open up new application fields for quasicrystals as abrasive materials,especially in relevance to surface flattening and passivation enhancement. |
