Zhang Bangwei

An analytic MEAM model for all BCC transition metals

A new pair potential is proposed, and a new analytic MEAM is developed by adding a modification term to total energy with the pair potential. The model can reproduce the shear moduli of all BCC transition metals accurately, especially the negative Cauchy pressure for the metal Cr. The mono- and di-vacancy formation and migration energies for all BCC transition metals are calculated with the model. The calculations are in agreement with the available experimental data.

Properties of electroless Ni-W-P amorphous alloys

This paper describes work performed to determine some of the properties of the electroless Ni-W-P amorphous deposits. Phosphorus contents were varied up to 32 at.%, and the amorphous structure was found to be present at phosphorus contents above 5 at.%. Irrespective of P content, all the deposits exhibited excellent adhesion to metallic substrates. The addition of even small amounts of W provided greatly increased hardness compared with the plain Ni-P deposits. The wettability properties of the Ni-W-P deposits were found to be comparable to those of Ni-P and N-B-P deposits but inferior to those of Ni-B deposits

The structure and infrared spectra of nanostructured MgO-Al2O3 solid solution powders prepared by the chemical method

Alumina ceramics has been used widely as an industrial material because of its high heat resistance and excellent wear resistance. Nanosize metal oxide used as raw materials would decrease the sintering temperature of ceramics and enable their physical and chemical properties to be developed fully. This paper studies the synthesis of nanostructured alumina-magnesia powders. The whole compositional range for the binary Al2O3-MgO system is studied. The powder samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA) and infrared spectroscopy (IRS). The results show that the nanostructured alumina-magnesia powders form solid solutions in a wide range of composition. In the alumina-rich side, the gamma-Al2O3 phase is found and the maximum amount of magnesia that can be incorporated is 30%. In the magnesia-rich side, the MgO phase is present and the range of solid solutions is from 0 to 20 wt% Al2O3 It is also found that the lattice parameter a(0) of gamma-Al2O3 increases with increase in the amount of magnesia, but the lattice parameter of the MgO phase decreases with increase in the amount of alumina. The grain size increases linearly with the amount of magnesia added and is smaller than 3.6 nm for alumina solid solution. It changes in a parabolic manner with the amount of alumina and is smaller than 15 nm for magnesia solid solution. The specific surface is about 140 m(2) g(-1) for the powders. The heat decomposition temperature of the precursor determined by DTA is not changed with increase in the amount of magnesia in the gamma-Al2O3 solid solution range. The heat decomposition temperature increases with increase in the amount of alumina in the MgO solid solution range. In the range of mixed phase, it is greater than those in the range of two solid solutions. The results for IRS of the nanostructured alumina-magnesia powders are discussed

Preparation and thermal properties of amorphous Fe–W–B alloy nano-powders

Abstract Amorphous Fe–W–B alloy nano-powders were obtained by chemical reduction for the first time. The powders have nearly spherical morphology with a size of 30–100 nm. The effect of the preparation condition on the composition of the powders has been studied systematically. The crystallisation temperature and activation energy of crystallisation for the powders were also studied. The thermal properties can be attributed to the strengthening of partial bonds formed by overlapping the s–p hybrid orbitals of boron atoms with the s–p–d orbitals of iron and tungsten atoms.

Amorphous forming ability in the ternary Cu–Sn–P system by mechanical alloying

Highly pure (99.9%) copper, tin and phosphorus powders of 250 mesh were thoroughly mixed to obtain the required ternary Cu86-xSnxP14 (x=2-15) alloy compositions. These mixtures were milled in a planetary ball mill. The powder samples at different intervals of milling were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). It has been found that a powder mixture of Cu84Sn2P14 amorphized after 28 h of mechanical alloying, but still some crystalline phase could be seen. When the period of milling was greater than 28 h, the intensity of thr crystalline Bragg reflexes increased with further milling. The period of complete amorphization for Cu86-xSnxP14, X=4, 5, 8 and 10 an 28, 20, 12 and 32 h, respectively. However, no typical amorphous phase was detected for the Cu71Sn15P14 mixture powders. The results show that the amorphization tendency increases first then decreases with increase of tin content, but no amorphous phase forms after the content of tin is greater than 15 wt%. The glass forming composition range in this alloy system is 4-10 wt% Sn. The amorphous forming ability for the ternary system is explained by the formation theory of amorphous alloys by one of the present authors. The formation enthalpies of the system are also calculated using Miedemas model, in order to explain the glass forming composition range

PREDICTION OF BINARY TRANSITION TRANSITION-METAL AMORPHOUS-ALLOYS BY MECHANICAL ALLOYING

The glass forming ability of binary TM-TM (TM = transition metal) alloys produced by mechanical alloying is studied with both two-dimensional maps of Miedemas coordinates and combinative coordinates. The former is constructed of Miedemas coordinates, the differences of electronegativities Delta phi and electron densities Delta n(ws)(1/3); the latter is constructed of the ratio Delta phi/Delta n(ws)(1/3) and size factor(R(1) - R(2))/R(2). In these maps, binary systems which formed amorphous phase are clearly separated from the non-formed systems by a curve. The equations of the curves are y = 3.825x, and y = 2.52x(-1/4) for the pure Miedema coordinates and combinative coordinates, respectively.

Investigation of magnetic properties for Fe - Ni - P - B nanosize amorphous alloy powders prepared by chemical reduction

Quaternary Fe-Ni-P-B nanosize amorphous alloy powders were prepared successfully by chemical reduction. The nanosize powders had a diameter in the range 20-200 nm. The magnetic properties were studied. The saturation magnetization of the alloy powders decreased with increasing nickel or iron in the iron-based or nickel-based alloys, respectively, which meant that there was a minimum for the magnetization versus Fe content plot. On the contrary, the coercivity,of the alloy powders increased with increasing nickel or iron in the iron-based or nickel-based alloys, respectively, that is to say there was a maximum for the coercivity versus Ni content plot. The dependences of the saturation magnetization and coercivity of the alloy powders on annealing temperature were studied. It was also found that the remanence-to-saturation ratio was not larger than 0.15 even after heat treatment.

INVESTIGATION OF RAPIDLY QUENCHED CU100-XPX ALLOYS

Rapidly quenched Cu100-xPx (x = 4.0-19.6 at%) alloy ribbons were prepared by melt spinning. The characteristics of the alloys were investigated by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The results indicate that rapid quenching of the Cu-P system results in the formation of a microcrystalline structure of alpha-Cu and Cu3P but no amorphous phase. On the other hand, rapid quenching also leads to the supersaturated solid solution of phosphorus in alpha-Cu, and the degree of supersaturation increases with the phosphorus concentration.

Calculations of the thermodynamic properties for binary hcp alloys with simple embedded atom method model

The simple embedded atom method model for hcp metals developed by Johnson has been applied to calculate the thermodynamic properties of all binary alloy systems for the eleven transition hcp metals. It has been shown that the agreement with the calculation results from Miedema thermodynamic theory and with the available experimental data is general good, but the agreement with the experimental data for the formation energy of Co-Y alloys is weak, which implies that a more better model for hcp metals is needed.