Spray Atomized and Codeposited Al-Li Based Metal-matrix Composites Processing and Properties

In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. Relatively high rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during flight and upon impacting with the substrate. The processing method uses codeposition of the metallic semi-solidified droplets (metallic matrix) with the injected reinforcement ceramic particles. In the present paper, the microstructures, mechanical properties, interfacial properties, thermal stability and aging behaviour of spray atomized and codeposited Al-Li-X MMC's (injected X=SiC, Al2O3) are reported and correlated to the processing conditions.

Analysis of Solidification in Spray Atomized and Codeposited Metal-matrix Composites Part Ⅱ:Reinforcement Injection and Deposition

The influence of the injection of reinforcing particles (for the production of metal matrix composites and of the droplets-to-substrate heat transfer on the resulting microstructural uniformity of spray atomized and codeposited composite material is analyzed. The reinforcement particles injection velocity has to be limited between an upper and a lower critical values. in order to ensure entrapment into the matrix droplets in flight. The thermal history of the injected droplets during the deposition stage is calculated with the assumption that the in-flight solidifying droplets reach the substrate while containing still at least 20% liquid volume fraction, in order to avoid porosity of the deposited material. The substrate to pouring-tube orifice distance where that condition is achieved depends strongly on the atomization pressure and the convective heat transfer coefficient of the substrate. It is demonstrated that 'tailoring' the microstructures and the reinforcement volume percent in the deposited material is feasible. The critical process parameters : the atomization pressure, the melt flow rate. the substrate to pouring-tube orifice distance, the reinforcement particles injection location and rate can all be adequately chosen in order to obtain any desired microstructure, grain size, reinforcement volume percent, with the additional benefit, if wanted, of rapid solidification processing

Analysis of Solidification in Spray Atomized and Codeposited Metal-matrix Composites Part Ⅰ: Atomization

Fluid mechanics, heat transfer and liquid-to-solid phase transformation are assessed in optimizing the spray atomization and codeposition process parameters for size refinement and microstructural uniformity of the deposited material. Atomization gas velocities, atomized droplets velocities, convective heat transfer coefficients, thermal histories of the solidifying droplets, freezing rates, fraction solid evolution and solid-liquid interface propagation velocity are calculated. The influence, on the deposit microstructural features, of process parameters like the atomization gas pressure, the pouring tube orifice diameter, the geometrical features of the atomization device,the potency of , pre-existing or injected as reinforcement, nucleation sites, the wetting angle between the liquid melt bnd impurity particles acting as preferred nucleation sites, the in-flight distance of the solidifying droplets in the atomization chamber, i5 evaluated. As a result of the evaluation, appropriate choice of the adjustable process parameters for the production of powders and/or deposits with desired grain size and microstructure, can be made.

Electrochemical codeposition of Mg-Li-Gd alloys from LiCl-KCl-MgCl_2-Gd_2O_3 melts

Mg-Li-Gd alloys were prepared by electrochemical codeposition from LiCl-KCl-MgCl 2 -Gd 2 O 3 melts on molybdenum electrode with constant current density at 823 and 973 K. The microstructure of the Mg-Li-Gd alloys was analyzed by X-ray diffraction （XRD）, optical microscopy （OM） and scanning electron microscopy （SEM）. The results show that magnesium and gadolinium deposit mainly in the first 30 min, and the alloy obtained contains 96.53% Mg, 0.27% Li and 3.20% Gd （mass fraction）. Then, the reduction of lithium ions occurs quickly. The composition of alloy can be adjusted by controlling electrolysis time or Gd 2 O 3 concentration in LiCl-KCl melts. With the addition of Gd into Mg-Li alloys, the corrosion resistance of the alloys is enhanced. XRD results suggest that Mg 3 Gd and Mg 2 Gd can be formed in Mg-Li-Gd alloys. The distribution of Gd element in Mg-Li-Gd alloys indicates that Gd element mainly distributes at the grain boundaries of Mg-Li-Gd alloys.

Preparation and oxidation behaviour of electrodeposited Ni-CeO_2 nanocomposite coatings

Ni-CeO2 nanocomposite coatings with different CeO2 contents were prepared by codeposition of Ni and CeO2 nanoparticles with an average particle size of 7 nm onto pure Ni surfaces from a nickel sulfate. The CeO2 nanoparticles were dispersed in the electrodeposited nanocrystalline Ni grains （with a size range of 10-30 nm）. The isothermal oxidation behaviours of Ni-CeO2 nanocomposite coatings with two different CeO2 particles contents and the electrodeposited pure Ni coating were comparatively investigated in order to elucidate the effect of CeO2 at different temperatures and also CeO2 contents on the oxidation behaviour of Ni-CeO2 nanocomposite coatings. The results show that the as-codeposited Ni-CeO2 nanocomposite coatings have a superior oxidation resistance compared with the electrodeposited pure Ni coating at 800 °C due to the codeposited CeO2 nanoparticles blocking the outward diffusion of nickel along the grain boundaries. However, the effects of CeO2 particles on the oxidation resistance significantly decrease at 1050 °C and 1150 °C due to the outward-volume diffusion of nickel controlling the oxidation growth mechanism, and the content of CeO2 has little influence on the oxidation.

Preparation of Gd-Ni alloy film in urea-NaBr melt

Electroreduction of Ni(Ⅱ) to metallic Ni in urea NaBr melt at 373 K is irreversible in one step. Gd(Ⅲ) is not reduced to Gd alone, but can be inductively codeposited with Ni(Ⅱ). The amorphous Gd Ni alloy films were obtained by potentiostatic electrolysis and galvanostatic electrolysis. With the cathode potential shift to negative direction and the increase of current density, the content of gadolinium in the alloy increases first, and then drops down gradually. The molar ratio of Gd(Ⅲ) to Ni(Ⅱ) and the time also influence the content of Gd. Crystalline GdNi 3 alloy was obtained after heat treatment of the deposit. [

Electrochemical Behaviors of Fe^(2+) and Sm^(3+)in Urea-NaBr Low Temperature Melt and Their Inductive Codeposition

The cyclic voltammetry, chronopotentiometry and chronoamperometry were used to study the behaviors of Fe 2+ on Pt, Cu, Ag and Ti electrodes in urea NaBr melt at 373 K. Electroreduction of Fe 2+ to metallic Fe is irreversible in one step. The exchange current density determined on Ti electrode is 2 68×10 -5 A·cm -2 . Sm 3+ does not reduce to Sm alone, but can be inductively codeposited with Fe 2+ . Sm Fe alloy film contained over 90% Sm (mass fraction) can be obtained by potentiostatic electrolysis and galvanostatic electrolysis on Cu substrate. The Sm content in the alloy is related to the cathode potential, current density and the Sm 3+ /Fe 2+ molar ratio. The surface state of the Sm Fe deposit was studied by scanning electron microscopy.

Electrochemical behavior of electroplated Zn-P alloy

The electroplating behavior of Zn P alloy on copper from light acid chloride solutions (LACS) was investigated using cyclic voltammetry and linear potential sweep method. It is found that, under the experimental conditions, the concentrations of H 3PO 3 and ascorbic acid in LACS change the codeposition mechanism of Zn P alloy, the addition of H 3PO 3 into LACS promotes the three dimentional (3 D) instantaneous nucleation/growth, while the addition of ascorbic acid promotes the two dimentional (2 D) instantaneous nucleation and layer by layer growth. H 3PO 3 and zinc ions inhibit the deposition each other. The experimental results also show that H 3PO 3 in the LACS can be reduced on the cathode individually, and low pH value of the LACS promotes the reduction of H 3PO 3.

Study on Electrodeposition of Ho-Co Alloy in Dimethylsulfoxide

Co deposition of Ho with Co was studied in dimethylsulfoxide (DMSO) by cyclic voltammetry and potentiostatic deposition at room temperature. The cyclic voltammogram shows that the codeposition of Ho with Co can be attributed to induced codeposition mechanism, for the codeposition potential is more negative than the deposition potential of Co but positive than that of Ho. For the potentiostatic deposition used in Ho Co alloys preparation, the results indicate that in the range of selected concentration the potential is the main factor determining the content of Ho in Ho Co alloys, while the composition of Ho 3+ and Co 2+ in electrolyte solution has less influence. According to the analysis of X ray diffraction, EDAX, and scanning electron microscopy, uniform, compact and amorphous films on Cu can be obtained at -1 8 V (vs.SCE) in 0 165 mol·L -1 Ho(NO 3) -0 135 mol·L -1 CoCl 2 DMSO solution.

Electrodeposition of La-Ni Alloy Powders in Dimethylsulfoxide (DMSO)

The brown metallic luster La-Ni alloy powders were prepared by potentiostatic electrolysis technique in dimethylsulfoxide solution at room temperature. The atomic rate of La and Ni in alloy powders are 11∶1 and 10∶1. The size of metal grains is about 0.1 to 100 μm. It shows that the micrometer powders of rare earth alloys can be obtained by controlling electrodeposition conditions. The peak potentials of -2.81 and 1.75 V are attributed to reduction of La 3+ and Ni 3+ ions, respectively. The peak potentials at -2.20 and -0.168 V are the oxidation peaks of lanthanum and nickel, respectively. When potential is more negative than -1.74 V, La(Ⅲ) and Ni(Ⅱ) will codeposit. Increasing cyclic times, the value of peak current is decreasing, and the reduction peak of La(Ⅲ) was finally disappeared.

Pulse Plating of Copper-ZrB_(2) Composite Coatings

Copper-zirconium diboride （ZrB2） composite coatings were fabricated using pulse plating technique to acquire a new type of EDM （electro-discharge machining） electrode material. The effects of pulse parameters, i.e., the average current density, the frequency and the duty cycle, on the incorporation of ZrB2 particles in the copper matrix were investigated. The amount＇of codeposited ZrB2 particles had a maximum at average current density of 3 A/din2 and increased with decreasing duty cycle as well as current frequency of the pulse current used for deposition. The hardness of the coatings increased with increasing ZrB2 percentage, whereas the incorporation of ZrB2 particles had little effect on the resistivity of the composites.

Electrolytic Codeposition of Y(Ⅲ) and Al(Ⅲ) and Surface Metalliding in Molten Fluorides—Oxides Systems

The mechanism of the electrolytic codeposition of Y Al alloy in molten LiF AlF 3 Al 2O 3 YF 3, LiF YF 3 Y 2O 3 AlF 3 and LiF YF 3 Y 2O 3 Al 2O 3 systems was investigated by means of cyclic voltammetry. The electrodeposited products were analysed by X ray diffraction. The results show that the electrolytic codeposition of Y Al alloy in the LiF YF 3 Y 2O 3 Al 2O 3 system without AlF 3 can be achieved at the same potential for Y(Ⅲ) and Al(Ⅲ) which have great difference in deposition potential. It is beneficial to codeposition of Y(Ⅲ) and Al(Ⅲ) when temperature rises. The potential of beginning codeposition is about -0.85 V ( vs Pt reference electrode), but only at the potential of -0.95 V or more negative can Y based Al alloy containing a great amount of yttrium be obtained.

Studies on Electrolytic Codeposition of Lanthanum-Cobalt in Urea Melt

The electrolytic codeposition of lanthanum-cobalt in the melt consisting of urea-NaCl-NaAc-CoCl2-LaCl3 was studied by means of cyclic voltammetry, electron probe analyser, X-ray diffraction. Cathodic potential, current density, La3+/Co2+ molar ratio in the melt and the electrode substrates all exercise influence on the content of lanthanum deposied. The deposites consist of cobalt and lanthanum, but they don't form any intermetallic compound.

MODELING OF THE PROCESS OF COMPOSITE ELECTRODEPOSITION

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Electroreduction of Co(Ⅱ) and La(Ⅲ)in UreaMelt

Electroreduction of Co(Ⅱ)to metallic cohalt in urea melt is irrevsible in one step.The transfer coeffi-cient of electrode reaction of Co(Ⅱ)+2e=Co(O)and the diffusion coefficient of Co(Ⅱ)were determined.The lanthanum can be inductively codeposited with cobalt. The contents of lanthanum in cobalt-lanthanum de-posts increase with the shift of electrode potential to the negative direction and the raise of La(Ⅲ)/Co(Ⅱ)mo-lar ratio in the melt. The cyclic voltammetry,open circuit potential-time curve after potentiostatic electrolysisand electron probe analyas were used.

Catalytic Effect of SCN^- on Electrodeposition of Zinc-Nickle Alloy

The electrodeposition of zinc nickle alloy was obtained on a copper cathode of 1×1cm 2. The deposited alloys are quantitatively analyzed by atomic absorption spectrometry. The morphology of the deposits was observed by means of scanning electron microscopy(SEM).We observed that the electrodeposition of zinc nickle alloy is an anomalous codeposition. The catalytic effects of SCN - on the electrochemical behavior of Ni deposition and hydrogen discharge are obvious. SEM analysis shows that the surface morphology of the coating appears to be more compact and homogeneous with the increase of SCN - concentration.

Electrochemical codeposition of typical α+β phases Mg-Li alloys from the molten LiCl-KCl-MgCl_2 system

Electrochemical codeposition of Mg-Li alloys on molybdenum electrodes was investigated in LiCl-KCl（50 wt.%：50 wt.%） melts containing different concentrations of MgCl2 at 973 K.Cyclic voltammograms show that the underpotential deposition of lithium on pre-deposited magnesium leads to the formation of liquid Mg-Li alloys.The deposition potentials of Mg（II） and Li（I） ions gradually near each other with MgCl2 concentration decreasing.Mg-Li alloys with typical α ＋ β phases could be obtained by potentiostatic electrolysis from LiCl-KCl melts containing 5 wt.% MgCl2 at -2.25 V vs.Ag/AgCl（cathodic current density 1.70 A·cm-2） for 2.5 h.α phase, α ＋ β phases, and β phase Mg-Li alloys with different lithium contents were obtained by potentiostatic electrolysis from LiCl-KCl melts with the different concentrations of MgCl2.The samples were characterized by X-ray diffraction and scanning electron microscopy.

Electrochemical formation of Mg-Li-Y alloys by co-deposition of magnesium, lithium and yttrium ions in molten chlorides

An electrochemical approach for the preparation of Mg-Li-Y alloys via co-reduction of Mg, Li, and Y on a molybdenum electrode in LiCl-KCl-MgCl2-YCl3 melts at 943 K was investigated. Cyclic voltammograms （CVs） illuminated that the underpotential deposition （UPD） of yttrium on pre-deposited magnesium led to the formation of a liquid Mg-Y alloy, and the succeeding underpotential deposition of lithium on pre-deposited Mg-Y led to the formation of a liquid Mg-Li-Y alloy. Chronopotentiometry measurements indicated that the order of electrode reactions was as follows： discharge of Mg（II） to Mg-metal, electroreduction of Y on the surface of Mg with formation of ε-Mg24＋xY5 and after that the discharge of Li＋ with the deposition of Mg-Li-Y alloys. X-ray diffraction （XRD） indicated that Mg-Li-Y alloys with different phases were formed via galvanostatic electrolysis. The microstructure of different phases of Mg-Li-Y alloys was characterized by optical microscope （OM） and scanning electron microscopy （SEM）. The analysis results of inductively coupled plasma atomic emission spectrometer （ICP-AES） showed that the chemical compositions of Mg-Li-Y alloys corresponded with the phase structures of the XRD patterns, and the lithium and yttrium contents of Mg-Li-Y alloys depended on the concentrations of MgCl2 and YCl3 .

Electrochemical study on preparation of Mg-Li-Yb alloys in LiCl-KCl-KF-MgCl_2-Yb_2O_3 melts

This paper presented a novel study on electrochemical codeposition of Mg-Li-Yb alloys in LiCl-KCl-KF-MgCl2-Yb2O3 melts on molybdenum. The factors of the current efficiency were investigated. Electrolysis temperature had great influence on current efficiency; the highest current efficiency was obtained when electrolysis temperature was about 660 oC. The content of Li in Mg-Li-Yb alloys increased with the high current densities. The optimal electrolytic temperature and cathodic current density were around 660 oC and 9.3 A/cm2, respectively. The chemical content, phases, morphology of the alloys and the distribution of the elements were analyzed by X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry, respectively. The intermetallic of Mg-Yb was mainly distributed in the grain boundary of the alloys, presented as reticulated structures, and refined the grains. The lithium and ytterbium contents in Mg-Li-Yb al-loys could be controlled by changing the concentration of MgCl2 and Yb2O3 and the electrolysis conditions.