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.     

Rietveld refinement,microstructure and high-temperature oxidation characteristics of low-density high manganese steels

Three forged low-density high manganese steels Mn28Al10,Mn28Al8 and Mn20Al10 were used as experimental materials in this study.The forged microstructure and external oxidation characteristics at 1323 K and 1373 K for 5–25 h in air were investigated by microstructural observation and X-ray diffraction(XRD)technique.The phase compositions and abundance in the forged and oxidized samples were quantitatively obtained by Rietveld method on the basis of XRD pattern analysis.The results showed that an austenitic microstructure formed in steels Mn28Al10 and Mn28Al8,and 18.02 wt%ferrite could be found in Mn20Al10.The relative amount of ~5.28 wt%-carbide(Fe_3AlC_(0.5))in Mn28Al10 was far greater than that in Mn28Al8 and Mn20Al10.The oxidation kinetics of forged steels oxidized at 1323 K for 5–25 h had two-stage parabolic rate laws;and the oxidation rate of the first stage was lower than that of the second stage.When they were oxidized at 1373 K for 5–25 h,the oxidation kinetics followed only a parabolic law and the oxidation rates were respectively greater than those at 1323 K for 5–25 h.When they were oxidized at 1323 K for 25 h,detached external scales contained Fe_2MnO_4and-Fe_2O_3oxides.-Al_2O_3and(Fe,Mn)_2O_3oxides could only be indexed in steels Mn28Al8 and Mn28Al10,respectively.When they were oxidized at 1373 K for 25 h,Fe_2MnO_4,Fe_3O_4,-Fe_2O_3 and-Al_2O_3oxides could all be indexed in the external detached scales.The main phase of detached external scales was Fe_2MnO_4;and the relative amount of-Al_2O_3in steel Mn28Al8 was higher than that in steels Mn28Al10 and Mn20Al.The external oxidation layers of these three forged steels oxidized at 1323 K and 1373 K for 25 h were essentially followed the sequence of-Al_2O_3,Fe_2MnO_4,Fe_3O_4,FeMnO_3,and Fe_2O_3from the substrate to the outside surface.The forged Mn28Al10 steel with austenitic microstructure and a certain amount of-carbide(~5.28 wt%in the present work)possessed a better combination of strength,ductility,specific strength,and oxidation rate when compared to that of the forged Mn28Al8 and Mn20Al10 steels.     

Sliding Friction of Al-Cu-Fe-B Quasicrystals

Dry sliding friction between the Al_59Cu_25.5Fe_12.5B_3 quasicrystals (QCs)/coating of the diamond-like carbon (DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters (temperature, sliding velocity, applied load, atmosphere) on friction and wear of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning electron microscopy (SEM). The results showed that for QCs, the friction coefficient and roughness of worn surface were influenced by the parameters, especially greatly by the temperature. With rise of the applied load and sliding velocity, the friction coefficient decreased. The dominant wear mechanism at 350℃ was delamination for QCs. The cracks formed on the worn surface during the friction. Moreover, phase transformation was not observed on worn surface of QCs at 350℃. All the results are discussed and explained.     

Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu

By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.     

Distribution of Microelements and Their Influence on the Corrosion Behavior of Aluminum Foil

The distribution of microelement Fe, Si, Cu and Mg in the surface layer of aluminum foil annealed at 300℃ and 500℃ were determined by secondary ion mass spectrometer. The corrosion structure produced by electrochemical etching was also observed. It was found that the Mg concentration at external surface was increased exponentially over the fourth degree and promoted by higher annealing temperature, which will increase the number of corrosion pits inside the large grains, and therefore the specific capacity of the foils for electrolytic capacitors. The similar effects of microelement Fe, Si and Cu were not so strong.     

Pack Aluminizing of Copper

Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.     

Oxidation Resistance of the Aluminide Coating Formed on Carbon Steels

Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.     

Microstructures and Mechanical Properties of Vacuum Brazed Ti_3Al/TiAl Joints Using Two Ti-based Filler Metals

Vacuum brazing of Ti3Al-based alloy to Ti Al was firstly carried out by Ti—15Cu—15Ni(wt%) filler metal.A continuous Ti3 Al band, Ti2 Ni and Ti2Cu/Cu3 Ti phases formed and the joint showed a shear strength of53.8–112.4 MPa at room temperature. For the improvement of the joint strength, a new Ti—Zr—Cu—Ni—Fe filler alloy was designed, and its wettability on Ti3 Al and Ti Al substrate was studied with the sessile drop method. After holding for 20 min at 1010 °C the Ti—Zr—Cu—Ni—Fe filler showed a low contact angle of20° and 21° on (Ti)_3Al and Ti Al substrate, respectively. The joint brazed with this novel filler mainly consisted of Ti-rich area, (Ti)_3Al reaction layer and residual filler metal. With the increase of the brazing temperature, the amount of residual filler metal decreased and the (Ti)_3 Al reaction layer thickened. The (Ti)_3Al/Ti Al joint brazed with Ti—Zr—Cu—Ni—Fe filler exhibited a lower hardness than that brazed with Ti—Cu—Ni filler. The corresponding joints brazed at 950 °C for 5 min presented the shear strength of257.6 ± 33.6 MPa at room temperature and 304.8 ± 9.9 MPa at 600 °C.     

Preparation and Characterization of Multilayered Al/Fe-Mo-Si-B Alloy with Nanostructure

The bulk multilayered Al/Fe-Mo-Si-B alloy with nanostructure was prepared by annealing the alternate layers consisting of metal Al and amorphous (Fe0.99,Mo0.01)78 Si9B13 alloy ribbons for 30 min at 873 K under pressure of 3~5.5 GPa. The structures and grain sizes of the Fe-MoSi-B nanocrystalline alloy were measured and analyzed. It was found that the pressure could restrain the growth of the grains and influence the formation of phases. The dependence of grain sizes for α-Fe(Mo,Si) and Fe2B on pressure was given. The morphologies of Al/Fe-Mo-SiB nanocrystalline alloy intedeces were observed by SEM. Two intedecial phases formed at various pressures were established by TEM and EDAX, and an unknown Fe-rich one with nanostructure was also observed. The dependence of the intedecial phases on pressure and its formation and growth mechanism were discussed     

High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy

A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-Al alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.     

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.     

Laser plasma spectroscopy of Al-Cu-Fe quasicrystal an d alloy

Electron number density and temperature were determined from laser-induced plasmas produced by irradiating Al-Cu-Fe targets of a quasicrystal and of an alloy of similar composition. The Al(I) atomic emission spectra of the two systems were measured as a function of the distance from the target and of the time delay after laser irradiation. Differences of plasma characteristics were observed for laser ablation of quasicrystal and alloy targets, and the results were interpreted on the basis of different plasma formation mechanisms for the two systems.     

超音气体雾化Al-Si合金粉末表面氧化和吸附特性

利用超音速气体雾化法制备Al-17Si-6Fe-4.5Cu-0.5Mg合金粉末，借助X射线光电子能谱（XPS）对粉要态合金表面氧化和吸附特性进行了研究，并对粉末表面层结构进行了分析。结果表明：粉末表面氧化主要以Al和Mg元素的氧化为主，氧化层成分主要为Al2O3，Al(OH)3和MgO，而合金中的Si,Fe及Cu元素很少氧化。除此之外，在粉末表面化还吸附一层含Cl元素的碳氢有机化合物污染层，测定表明粉末表面氧化层和吸附层总厚度约为2nm。     

Al-Ni-Fe系铸态合金中的准晶相

系统研究了Al72.5Fe14.5Ni13和Al71Fe5Ni24铸态合金的相组成，发现其中分别存在D—Al72．6Fel4．6Nil2．8和D'—Al70．5Fe10Nil9．5两种十次准晶，它们各自与AlFe和AlNi二元十次准晶相关．实验结果与三元准晶相图的电子浓度特征吻合，说明三元准晶相图的电子浓度特征对确定三元准晶的理想成分和探索准晶新成分有一定的指导作用．     

Activation of Al–Cu–Fe quasicrystalline surface: fabrication of a fine nanocomposite layer with high catalytic performance

A fine layered nanocomposite with a total thickness of about 200 nm was formed on the surface of an Al₆₃Cu₂₅Fe₁₂ quasicrystal (QC). The nanocomposite was found to exhibit high catalytic performance for steam reforming of methanol. The nanocomposite was formed by a self-assembly process, by leaching the Al–Cu–Fe QC using a 5 wt% Na₂CO₃ aqueous solution followed by calcination in air at 873 K. The quasiperiodic nature of theQC played an important role in the formation of such a structure. Its high catalytic activity originated from the presence of highly dispersed copper and iron species, which also suppressed the sintering of nanoparticles.     

Cu对粉末冶金Fe3Al基复合材料性能的影响

研究了Cu含量对粉末冶金Fe3Al基复合材料的烧结性能和力学性能的影响,分析了施加载荷和改变转速对加入不同量铜粉末冶金Fe3Al基复合材料的摩擦磨损性能的影响,并借助电子显微镜和能谱分析了不同铜含量Fe3Al基复合材料的磨损机理.结果表明:加入12%的Gu可使Fe3Al基复合材料具有良好的烧结性能和力学性能;载荷和转速对复合材料的磨损形式受铜的加入量的影响;铜的加入影响复合材料的磨损形式和磨损机理,当含铜量较少时,复合材料以磨粒磨损为主,随加入铜的量的增多,其磨损形式变为磨粒磨损和轻微的粘着磨损形式,加入大量铜时,则以粘着磨损为主.     

Novel Ti based metal matrix composites reinforced with Al–Cr–Fe quasicrystals approximants

In this work, Ti/Al–Cr–Fe metal matrix composites were fabricated with Ti as matrix and Al–Cr–Fe quasicrystal approximants as reinforcements using spark plasma sintering. In all samples a Ti₃Al ring forms around each Al–Cr–Fe particle as a bonding layer between Ti and Al–Cr–Fe particles. In the sample sintered with a holding time of 5 min, there are only TiAl regions present at the Ti₃Al/Al–Cr–Fe interface. However, in the samples sintered with a holding time of 10, 15 or 20 min, TiAl, Ti(Al,Cr)₂ and L1₂ regions were detected at the Ti₃Al/Al–Cr–Fe interface. The addition of Al–Cr–Fe particles into the Ti matrix was found to improve the mircrohardness to 460 HV and increase the wear resistance by more than 50%.     

Evolution of microstructure induced by calcination in leached Al–Cu–Fe quasicrystal and its effects on catalytic activity

Effects of calcination on catalytic activity for steam reforming of methanol (SRM) over an Al–Cu–Fe quasicrystal (QC) leached with NaOH aq. have been investigated in terms of microstructure with X-ray diffraction and transmission electron microscope (TEM). Calcination at 600 °C in air drastically improved the catalytic activity of the leached QC. TEM observations on cross-section of the samples revealed that cubic Cu _x Fe_3-x-y Al _y O₄ spinel was formed at the outermost layer of the leached QC after calcinations. Prior to the catalytic reaction, the Cu _x Fe_3-x-y Al _y O₄ spinel decomposed to a composite where fine Cu nanoparticles dispersed in (Fe,Al)₃O₄ matrix under H₂ treatment at 300 °C. Drastic increase in catalytic activity is responsible for the fine Cu nanoparticles in the composite. The Cu nanoparticles sit along the same orientation with (Fe,Al)₃O₄, e.g., Cu [013]//(Fe,Al)₃O₄ [013] and Cu [200]//(Fe,Al)₃O₄ [400]. This orientation relationship may stabilize the Cu nanoparticles through a bonding of Cu–O–Fe.