Self-lubricating,low-friction,wear-resistant Al-based quasicrystalline coatings

After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a γ-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (µ ≤ 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.     

Solution-based synthesis of AgI coatings for low-friction applications

Thin films of AgI have been synthesized from Ag surfaces and elemental I₂ using a rapid and simple solution-based method. The effect of using ultrasound during the synthesis was studied, as well as the influence of the nature of the solvent, the I₂ concentration, the time, the temperature, and the sonication power. The films were characterized using X-ray diffraction, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy, and found to consist of β-AgI, possibly along with some γ-AgI. It was found that sonication increases the film thickness and grain size. The nature of the solvent has a profound effect on the film growth, with mixtures of water and ethanol leading to thicker coatings than films synthesized using either component in its pure form. Selected coatings were tribologically tested, and the AgI coating was seen to lower the friction coefficient significantly compared to a reference Ag surface under otherwise identical conditions. Long lifetimes (over 30000 cycles) were seen against a Ag counter surface. Tracks and wear scars were studied using SEM and Raman spectroscopy, and it was found that the friction level remains low as long as there is AgI in the points of contact. This method is found to be a simple and fast way to deposit AgI on Ag with large possibilities of tuning the thickness and grains sizes of the resulting films, thereby optimizing it for the desired use.     

Quasicrystalline materials

The report in late 1984 of phases in rapidly cooled aluminium alloys whose electron diffraction patterns exhibit icosahedral symmetry has stimulated intensive research into the structure and properties of quasicrystalline materials. Here I review our current understanding of quasicrystalline materials and quasiperiodic tilings, and in particular I discuss in detail the interpretation of transmission electron microscopy observations of quasicrystalline phases.     

Quasicrystalline Phase in As-cast Mg-Zn-Y-Zr Alloy

An icosahedral phase in as-cast Mg 5. 78Zn-0.89Y-0.48Zr (wt-%) alloy has been identified with transmission electron microscope (TPM) The selected area diffraction patterns (SADP) from the phase show a five-fold symmetry of a quasicrystalline structure. The energy dispersive X-ray spectra (EDXS) indicate that the quaternary phase has a chemical composition of 67.6Zn-1 9.4Mg-8,1 Y-4 9Zr in at -%     

Sputter deposited low-friction and tough Cr-Si3N4 nanocomposite coatings on plasma nitrided M2 steel

Nanocomposite coatings of Cr-Si₃N₄ exhibiting low friction and high toughness were prepared on plasma nitrided AISI M2 steel substrates using an unbalanced magnetron sputtering system. The surface morphology and cross-sectional microstructure of the Cr-Si₃N₄ nanocomposite coatings were studied using field emission scanning electron microscopy (FESEM) techniques. Cr-Si₃N₄ nanocomposite coatings prepared at 48 at.% Cr exhibited a dense microstructure with nanoindentation hardness and toughness values of 18 GPa and 2.0 MPam^½, respectively. Nanoscratch measurements indicated that Cr-Si₃N₄ nanocomposite coatings exhibited good adhesion with a maximum critical load of 150 mN. Ball-on-disc reciprocating tests at a load of 2 N showed that Cr-Si₃N₄ nanocomposite coatings prepared at 48 at.% Cr exhibited an average friction coefficient of 0.30. FESEM studies of the wear tracks indicated that there was no significant wear loss and the Cr-Si₃N₄ nanocomposite coatings exhibited only mild wear due to oxidation.     

含准晶相Al－Cu－Fe合金的球磨非晶化研究

应用球磨方法使含准晶相的Ａｌ６５Ｃｕ２０Ｆｅ１５合金转变为非晶相。利用Ｘ射线结构分析和扫描电镜研究了经不同时间球磨的合金粉末的相结构及形貌。结果表明，Ａｌ－Ｃｕ－Ｆｅ二十面体准晶相比合金中的少量晶体相更易于非晶化，且在非晶化过程中没有中间相生成。应用高温差热分析仪（ＤＴＡ）和Ｘ射线衍射技术（ＸＲＤ），分别研究了该非晶粉末的晶化特性。     

Al-Cu-Fe-Cr准晶增强铝基复合材料的研究

采用常规铸造法制备了四元系Al-Cu-Fe-Cr准晶,利用XRD、SEM和TEM等分析手段,分析了准晶和其类似相的微观组织以及在热处理后的相转变。以ZL101合金为基体,Al-Cu-Fe-Cr准晶颗粒为增强体,通过机械搅拌的方法制备了Al-Cu-FeCr准晶/ZL101复合材料,分析复合材料的微观组织和成分,并研究其力学性能。结果表明:铸态准晶合金组织中含有Al65Cu20-Fe10Cr5相(I+d)、准晶I相、λ-Al3Fe相以及少量的η-AlCu和θ-Al2Cu相,经880℃×30min热处理水淬后,λ相消失,得到了高纯度的Al65Cu20Fe10Cr5相和准晶I相;复合材料中由于准晶和基体之间的相互扩散,使得准晶相失稳发生分解;随着准晶含量的增加,复合材料的抗拉强度增加,延伸率减小,但由于Cr元素的加入使针状的β-Fe相转变成汉字状或骨骼状的α-Fe相,对复合材料的延伸率有提升作用。     

Development and Oxidation Behavior of Al-Cu-Fe Quasicrystalline Coating on Ti Alloy

An oxidation resistant Al-Cu-Fe quasicrystalline coating was fabricated on substrate of Ti alloy by low pressure plasma spraying (LPPS) method. As-sprayed Al-Cu-Fe coating has a rapidly solidified lamellar microstructure consisting of quasicrystalline phase and crystalline phase. The formation of quasicrystalline coating is related to the annealing. The results from the ox!dat!on experiments showed that Al-Cu-Fe quasicrystalline coating improved the oxidation resistance of Ti-base alloys. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al-Cu-Fe quasicrystalline coating after oxidation consisted of Al2O3. Oxidation occurs Ieading to a change of concentration and phase transformation in the coating surface. Selective oxidation of AI transforms the quasicrystalline phase into the phase.     

Influence of Processing on the Microstructure of Alloys Which Contain Quasicrystalline Phases

In this investigation a microstructural characterization of the phases obtained in ternary and quaternary alloys was undertaken. One of the main objectives of this study was to explore the possibility of quasicrystalline phases formation under normal casting conditions from the liquid melt. The alloys investigated, were melted in an induction furnace and subsequently cast into a wedge shaped copper mould, which resulted in different cooling velocities in the same ingot. The thick and thin sections of the ingots were characterized by: Optical microscopy, x-ray diffractometry, chemical analysis using EDS and atomic absorption spectroscopy.     

Low Temperature Electronic Transport in Al–Cu–Ru Quasicrystalline Alloys

Electrical resistivities of several quasicrystalline (QC) icosahedral Al–Cu–Ru alloys have been measured between room temperature and mK temperatures. None of the Al–Cu–Ru samples exhibited “insulating” behaviors in their resistivities. One sample had a large resistivity of ≈49,000 μΩ cm at room temperature. Its resistivity increased with decreasing temperatures by a factor of 3.2 and exhibited a maximum around 2 K. Fitting discrepancies between the experimental magnetoconductivity data and the weak localization and electron–electron interaction theories suggest that the weak localization theory poorly describes the electronic conduction behavior of this highly resistive quasicrystalline sample.     

准晶薄膜与涂层的制备、性能和应用

本文综述了近年来准晶薄膜的制备方法、性能及其应用等方面的研究工作。准晶薄膜的制备方法主要有物理汽相沉积法和热喷涂法两大类。准晶薄膜具有优异的力学、热学与光学等性能,已经应用于不粘锅涂层、热障涂层和太阳能吸收器等。     

Quasicrystalline phase formation during heat treatment in mechanically alloyed Al65Cu20Fe15 alloy

Abstract

Quasicrystalline phase formation during heat treatment in the mechanically alloyed Al₆₅Cu₂₀Fe₁₅ powders was studied by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The mechanical alloying was performed at speed of 300 rev min^–1 for times up to 70 h. It was found that mechanical alloying of the Al₆₅Cu₂₀Fe₁₅ powders did not result in the quasicrystalline (QC) icosahedral phase (i-phase) formation. The long time milling resulted in the formation of a cubic Al (Cu,Fe) solid solution phase (β-phase). The cubic Al (Cu,Fe) solid solution identified as β-phase was observed to be present as one of the major phases in the Al₆₅Cu₂₀Fe₁₅ alloy. The formation of the quasicrystalline icosahedral phase (i-phase) was only observed for short time milled powders after additional annealing at temperature above 500°C. The present investigation also showed that a tetragonal Al₂Cu phase (θ-phase) forms with short time milling. The tetragonal Al₇Cu₂Fe₁ phase (w-phase) was observed after heat treatment of the short time milled and unmilled powders. The present investigation indicated that an effective process to prepare the quasicrystalline materials was using a combination of short time milling and subsequent annealing.     

Role of Disclinations and Nanocrystalline State in the Formation of Quasicrystalline Phases on Mechanical Alloying of Cu-Fe Powders

1. IntroductionCu-Fe ajloys are potential candidate materials foruse as bearings, bushes and other atifriction components. They are also being considered for manywide ranging applications such as automotive components, fferelitial geajrs for garden tractors, pistonrings for small bore engines, camshaft drive sprockets,and pressure plates for steering systems[1]. However,the near total immiscibility of Cu and Fe in the phasediagram pose a major limitation to the preparation ofthese alloys by c…