Al-Cu-Fe QUASICRYSTALLINE PHASE FORMATION BY MECHANICAL ALLOYING

Al-Cu-Fe alloys were prepared from elemental powders in a high-energy planetary ball mill. A sequence of solid state reactions resulting in quasicrystal (QC) phase formation takes place during heating of the as-milled powder. These reactions were studied by both differential scanning calorimetry and x-ray diffraction methods. Mechanically alloyed powders were consolidated by cold and hot pressing, as well as by explosive compaction. After annealing at sufficiently high temperatures, the consolidated samples are single-phase QC, except the ones consolidated by explosion. The high reactivity of the as-milled alloys causes the appearance of high porosity of the consolidated samples after the annealing.     

Phase Transformations in Low-Fe Alloys of the Al-Cu-Fe System

Microstructure and phase transformation in the Al-Cu-Fe alloys of the approximate compositional range of 20-50 at.% Cu and 2 - 10 Fe at.% have been investigated from samples quenched from their respective temperatures by means of different thermal analysis, magnetothermal analysis, scanning electron microscopy, electron probe analysis and powder X-ray diffraction. Representative phase transformations categorized as polymorphic, discontinuous precipitation,quasi-binary eutectoid, and ternary transitional U-type phase transformation are presented. These phase transformations were found to have a common feature which consumes the β phase and appears the φ phase. A schematic diagram was proposed to demonstrate the transition processes with decreasing temperature.     

磁控溅射制备Al-Cu-Fe薄膜不同溅射时间的生长行为

采用磁控溅射法在硅基材上制备了Al-Cu-Fe薄膜,采用原子力显微镜(AFM)和X射线衍射仪(XRD)研究了不同溅射时间下Al-Cu-Fe薄膜的生长行为。结果表明,随着溅射时间的延长,Al-Cu-Fe薄膜的β晶相的衍射峰半峰宽逐渐减小,而λ晶相的衍射峰半峰宽则逐渐增大。Al-Cu-Fe薄膜的生长依次经历了小岛形核阶段、小岛结合阶段、连续薄膜阶段、晶粒长大阶段等4个阶段。另外,随着溅射时间的延长,Al-Cu-Fe薄膜的粗糙度呈现出先增大后减小的趋势。     

PHASE TRANSFORMATION IN RAPIDLY SOLIDIFIED AI-Cu-Fe ALLOY

By means of rapid solidification, two Al_(65)Cu_(20)Fe_(15) powders were prepared with water and liquid N_2 as the respective cooling agent. Both powders are composed of a qnasicrystalline icosahedral phase and a crystalline hexagonal phase, with the water-cooled alloy having a higher crystalline phase content. In the isothermal an nealing process, the crystalline phase in the water-quenched alloy begins to decrease at 500℃ and then disap pears at 600～700℃. At about 800℃, new crystalline phases form, and at 900℃, the quasicrystalline phase disappears. Conversely, in the liquid N_2 quenched alloy, the quasicrystalline phase starts to decrease at about 500℃. and the hexagonal phase decomposes into new crystalline phases. At 700～800℃, the quasicrystalline phase disappears. For the water-cooled sample, the quenching at 100～200C makes the crystalline to quasicrystalline phase transformation start at a lower temperature and the crystallization of the quasicrystal occur at a higher temperature. For the liquid N_2 quenched alloy, the quenching at 100～400℃, did not affect its phase transformation at high temperature.     

Diffusion during annealing of Al/Cu/Fe thin films

The Al-Cu-Fe system is interesting due to the existence of the quasicrystalline phase Al_62.5Cu₂₅Fe_12.5 as well as its approximant phases. A two-step procedure of thin film preparation is considered: deposition of a multilayer structure of individual elements and consequential annealing. To analyze the diffusion processes trilayers of individual elements were deposited by sputtering with a total thickness of about 400 nm. Afterwards, the samples were annealed in tube furnace in inert atmosphere. Rutherford backscattering spectrometry, Auger electron spectrometry and X-ray diffraction were used to quantify the depth profiles. The results point out to a three-stage process as a function of rising temperature: first Al and Cu form the γ-Al₄Cu₉ compound layer; second the aluminium spreads throughout the film with copper and iron mainly divided. The β-Al(Cu,Fe) phase is observed. Complete homogenization is followed afterwards.     

Effect of starting powders on the control of microstructural development of Al-Cu-Fe quasi-crystalline plasma-sprayed coatings

Powders and plasma-sprayed coatings of an Al₆₃Cu₂₅Fe₁₂ alloy containing a quasi-crystalline phase were characterized by X-ray diffraction, electron microscopy, and differential thermal analysis. The relationships between powder and coating microstructures were examined. Powders were produced by casting and crushing and by gas atomization. Both techniques produced powders with multiple phases; cubic and monoclinic ternary structures were formed along with the face-centered icosahedral quasi-crystalline phase. These phases were also produced in the plasma-arc-sprayed coatings formed using different starting powders. Cooling rates during powder processing greatly affected the phase equilibria and scale of segregation of this alloy. Finer grain sizes in the plasma-sprayed coatings were obtained from the more chemically homogeneous gas-atomized powders.     

Formation and Oxidation Behavior of Al—Cu—Fe Quasicrystal

Al62.5Cu25Fe12.5 alloy was prepared by arc melting .It was found that the formation of quasicrystalline phase is related to the condition of annealing,such as temperature and duration.Weight gain of Al-Cu-Fe quasicrystal during the oxidation at 700 and 800℃ in dry air was measured by means of thermal balance.The oxidation kinetics showed that the quasicrystal has good oxidation resistance.Only α-Al2O3 was formed on Al62.5Cu25Fe12.5 quasicrystal.The surface morphologies of Al-Cu-Fe quasicrystal after isothermal oxidation for different times were observed.     

Particle size effects on chemistry and structure of Al-Cu-Fe quasicrystalline coatings

Gas atomized Al₆₃Cu₂₅Fe₁₂ powders of varying size fractions were plasma sprayed onto hot (~600 °C) and cool (~25 °C) substrates using Mach I and subsonic plasma gun configurations. The chemical composition and phase contents of coatings were determined. Furthermore, coatings were annealed in vacuum at 700 °C for 2 h to observe phase changes. It was found that finer particles (e.g., <25 μm) tend to vaporize Al during spraying, which shifts the coating composition away from the quasicrystalline (ψ) single-phase region in the Al-Cu-Fe phase diagram. Coatings deposited on hot substrates were denser, richer in theψ phase, and harder than the corresponding coatings deposited onto cool substrates.     

Al65Cu20Fe15合金的凝固组织及二十面体准晶的生成

用Ｘ射线能谱分析、电子背散射衍射和粉末Ｘ射线衍射等技术研究了Ａｌ６５Ｃｕ２０Ｆｅ１５合金的铸锭及其退火后的显微组织和相组成。发现铸锭中的初生晶是λ－（Ａｌ,Ｃｕ）１３Ｆｅ４,呈明显的枝晶结构。     

Al-Cu-Fe准晶薄膜/涂层的研究进展

综述了目前制备Al-Cu-Fe准晶薄膜/涂层的方法,并分析了其影响因素.重点评述了Al-Cu-Fe准晶薄膜/涂层的组织及其转变,介绍了Al-Cu-Fe准晶薄膜/涂层的性能及其应用,并指出了其今后研究趋势.