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.

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

Effect of corrosion behavior of cast and extruded ZK60 magnesium alloys processed via friction extrusion

The increasing demand for high-strength,corrosion-resistant magnesium alloys in transportation has led to the development of new processing techniques.In this work,cast and extruded ZK60 magnesium alloys were processed using the innovative solid-phase process,Friction Extrusion(FE).The microstructure was analyzed using Scanning Electron Microscopy(SEM),and Energy Dispersive Spectroscopy(EDS),showing a marked reduction in grain size,uniform solute distribution(Zn and Zr),and second phases after FE processing.Moreover,optical micrographs and Electron Backscatter Diffraction(EBSD)were employed to further evaluate the alloy microstructure.The corro-sion resistance and electrochemical behavior were analyzed using potentiodynamic polarization,Scanning Electrochemical Cell Impedance Microscopy(SECCIM),and atomic emission spectroelectrochemistry analysis(AESEC).Time evolution surface imaging and post-corrosion microstructures were also analyzed to support the understanding of underlying corrosion mechanisms.Corrosion initiation and propagation in FE-processed samples followed grain boundary patterns,differing from cast and extruded ZK60 behaviors.Electrochemical measurements and in-situ time-dependent optical imaging demonstrated that FE processing enhanced corrosion potential,reduced corrosion current,and increased cathodic activity.Additionally,FE processing reduced the disparity in pitting potential between cast and extruded samples,resulting in intermediate pitting potentials.Higher Mg and lower Zn dissolution was observed in the lower anodic currents for FE-processed samples.During aggravated anodic current cycles,Mg dissolution equalized,but the Zn/Mg dissolution ratio increased for FE-processed extruded samples,suggesting less cathodic activation and better resistance to further pitting.

A first-principle calculation of structural,mechanical and electronic properties of titanium borides

The first-principle calculations are performed to investigate the structural,mechanical and electronic properties of titanium borides （Ti2B,TiB and TiB2）.Those calculated lattice parameters are in good agreement with the experimental data and previous theoretical values.All these borides are found to be mechanically stable at ambient pressure.Compared with parent metal Ti （120 GPa）,the larger bulk modulus of these borides increase successively with the increase of the boron content in three borides,which may be due to direction bonding introduced by the boron atoms in the lattice and the strong covalent Ti-B bonds.Additionally,TiB can be regarded as a candidate of incompressible and hard material besides TiB2.Furthermore,the elastic anisotropy and Debye temperatures are also discussed by investigating the elastic constants and moduli.Electronic density of states and atomic Mulliken charges analysis show that chemical bonding in these titanium borides is a complex mixture of covalent,ionic,and metallic characters.

Efficient Separation of Ar and Kr from Environmental Samples for Trace Radioactive Noble Gas Detection

Radioactive noble-gas isotopes, SSKr （half-life tl/2=10.8 y）, 39Ar （tl/2=269 y）, and SlKr （t1/2-229,000 y）, are ideal tracers and can be detected by atom trap trace analysis （ATTA）, a laser-based technique, from environmental samples like air and groundwater. Prior to ATTA measurements, it is necessary to efficiently extract krypton and argon gases from samples. Using a combination of cryogenic distillation, titanium chemical reaction and gas chromatography, we demonstrate that we can recover both krypton and argon gases from 1-10 L ＂air-like＂ samples with yields in excess of 90% and 98%, respectively, which meet well the requirements for ATTA measurements. A group of testing samples are analyzed to verify the performance of the system, including two groundwater samples obtained from north China plain.

The effect of nozzle layout on droplet ejection of a piezo-electrically actuated micro-atomizer

We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.

PRECIPITATION HARDENING OF ELINVAR ALLOY

The microstructural evolution and precipitation hardening of an Elinvar alloy doped with Ti and Al during isothermal aging at 700℃ have been investigated by atom probe field ion microscopy and microhardness measurements.The γ′ precipiates are spherical and coherent with the matrix.The chemical composition of the precipitates are(Ni_(0.53)Fe_(0.47)_3 (Ti_(0.(?))Al_(0.4)). During aging,a Lifshitz-Wagner type dissolution and coarsening reaction of the precipitates has been observed,The hardness of the material varies with the aging time and reaches maxi- mum when the average diameter of the precipitates was about 11 nm.

Control of Nickel Alloy Structural Change by the Atomic Emission Spectroscopy Method

The aim of the work was the assessment of capability for the change control in the structure of a compact material of pelletized heatproof nickel alloy grade EP741NP using the atomic emission method. The proposed method of evaluation is based on the statistical significance of the analytical response differences during atomic emission spectroscopy of solid specimens taken from one sample before and after heat treatment using the instruments AtomComp 81 and ARL 4460 with a high-voltage spark excitation. For calculations, the ratio of the line intensity of the analyzed element to the line intensity of the main sample component (in our case Ni2254) was used. The difference confidence estimation was made by the averages comparison method in a variance analysis. The study results are presented on the effect of material structure on analytical response during atomic emission spectroscopy of solid specimens. It was proved that the samples before and after heat treatment give statistically differing results while analyzed.

Theoretical Study on N-H…O Blue-shifted H-Bond for HNO…H2O2 Complex

A theoretical study on the blue-shifted H-bond N-H…O and red-shifted H-bond O-H…O in the complex HNO…H2O2 was conducted by employment of both standard and counterpoise-corrected methods to calculate the geometric structures and vibrational frequencies at the MP2/6-31G（d）, MP2/6-31 ＋ G（d,p）, MP2/6-311 ＋ ＋ G（d,p）, B3LYP/6-31G（d）, B3LYP/6-31 ＋G（d,p） and B3LYP/6-311 ＋ ＋G（d,p） levels. In the H-bond N-H…O, the calculated blue shift of N-H stretching frequency is in the vicinity of 120 cm^-1 and this is indeed the largest theoretical estimate of a blue shift in the X-H…Y H-bond ever reported in the literature. From the natural bond orbital analysis, the red-shifted H-bond O-H…O can be explained on the basis of the dominant role of the hyperconjugation. For the blue-shifted H-bond N-H…O, the hyperconjugation was inhibited due to the existence of significant electron density redistribution effect, and the large blue shift of the N-H stretching frequency was prominently due to the rehybridization of spn N-H hybrid orbital.