Experimental and mathematical modeling of metal spray forming process

The metal spray forming process was examined using mathematical simulation and verified through the prototyping evaluation at Baosteel＇ s test and development facilities. The mathematical model comprised of four sections, including jet gas flow in the deposition chamber;single droplet behavior along its trajectory path;probability and statistical analysis of droplet mass behavior, and forecast of the shape and temperature distribution of the billet during the spray forming process.

Three-and two-dimensional calculations for the interface anisotropy dependence of magnetic properties of exchange-spring Nd2Fe(14)B/α-Fe multilayers with out-of-plane easy axes

Hysteresis loops,energy products and magnetic moment distributions of perpendicularly oriented Nd2Fe(14)B/α-Fe exchange-spring multilayers are studied systematically based on both three-dimensional(3D)and one-dimensional(1D)micromagnetic methods,focused on the influence of the interface anisotropy.The calculated results are carefully compared with each other.The interface anisotropy effect is very palpable on the nucleation,pinning and coercive fields when the soft layer is very thin.However,as the soft layer thickness increases,the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises.Negative interface anisotropy decreases the maximum energy products and increases slightly the angles between the magnetization and applied field.The magnetic moment distributions in the thickness direction at various applied fields demonstrate a progress of three-step magnetic reversal,i.e.,nucleation,evolution and irreversible motion of the domain wall.The above results calculated by two models are in good agreement with each other.Moreover,the in-plane magnetic moment orientations based on two models are different.The 3D calculation shows a progress of generation and disappearance of vortex state,however,the magnetization orientations within the film plane calculated by the 1D model are coherent.Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.

An electron spin resonance study of Eu doping effect in La_(4/3)Sr_(5/3)Mn_2O_7 single crystal

The effect of Eu3＋ ion doping in the La sites of single-crystal La4/3Srs/3Mn2O7 was investigated. Electron spin resonance （ESR） was applied to La4/3Sr5/3Mn2O7 and （Lao.8Euo.2）4/3Sr5/3Mn2O7 single crystals. A phase separation and phase transitions were observed from the ESR spectra data. Between 350 K and 300 K, both paramagnetic resonance （PMR） and anisotropic ferromagnetic resonance （FMR） lines were observed in the ab plane and the c axis direction, suggesting a coexistence of the paramagnetic （PM） phase and the ferromagnetic （FM） phase. The magnetization measurement reveals a spin-glass-like behavior in single-crystal （Lao.8Euo.2）4/3 Sr5/3Mn2O7 below the temperature of spin freezing Tf （- 29.5 K）.

Magnetic and transport properties of bilayered manganites La_(1.2)Sr_(1.8)Mn_(2-x)Ga_xO_7(x=0,0.08)

The magnetic and electrical properties of nonmagnetic Ga＋3 ion substitution for Mn site are investigated in the bilayer manganite La1.2Sr1.8Mn2-xGaxO7. When the Mn is substituted by Ga, the ferromagnetic property obviously weakens, the magnetic transition temperature decreases and a spin-glass behaviour occurs at low temperature. Meanwhile, doping causes the resistivity to dramatically increase, the metal-insulator transition temperature to disappear, and a greater magneto-resistance effect to occur at low temperature. These effects result from the fact that Ga substitution dilutes the magnetic active Mn-O-Mn network and weakens the double exchange interaction, and further suppresses ferromagnetic ordering and metallic conduction.

Spray Deposition Behavior and Numerical Simulation of Growth of Tubular Preform in Spray Forming Process

Analysis on the deposition behavior of spray on deposition surface was made and an optimization method for the movement parameters （u, ω） of substrate was obtained. Simultaneously, a mathematical model of growth of tubular preform, specifically aimed at the kind of atomizer that is fixed and with a tilt angle was established. By in- tegrating the optimization method and the mathematical model, the growth process and shape of preform were simu- lated. The results show that the tilt angle of atomizer plays an important role on the dimensions and shapes of tubular preforms and it can provide a guidance for the development of spray forming equipment.

Thermodynamic Behaviors of Nb and P in Dephosphorization of Niobium-bearing Hot Metal with BaO-based Slag

The Bayan Obo iron ore contains valuable metallic elements such as niobium and rare earth elements. However, developing appropriate metallurgical processes to achieve effective dephosphorization of Nb-bearing hot metal meanwhile retaining Nb in the steel products remains a challenge. We carried out a thermodynamic study on dephosphorization of Nbbearing hot metal and investigated the effects of the initial [C] content and the dephosphorization temperature on oxidation behaviors of [Nb] and [P]. In particular, we focused on thermodynamic analysis of dephosphorization of Nb-bearing hot metal with highly basic BaO-based slag. The results showed that the highly basic BaO-based slag system is more suitable for dephosphorization under oxidative conditions, and increasing the [C] content favors dephosphorization of Nb-bearing hot metal without oxidizing [Nb]. Moreover, the values of equilibrium oxygen activity for oxidation reactions of [Nb] and [P] are increased as the dephosphorization temperature increases. Considering the hot metal containing 0.02% of [Nb] in Baotou Steel, thermodynamic calculations indicated that the content of [P] can be reduced to 0.02%–0.05% and [Nb] remains unoxidized when dephosphorization occurs at the cconditions of T=1573–1673 K, [C]=4.0%, [Nb]=0.02%, aP2O5=10-24, aNb2O5=10-10.

Hydrogen storage properties of mechanically milled La_2Mg_(17-x)wt.%Ni(x=0,50,100,150 and 200) composites

Melting method was used to obtain La2Mg17 alloy, and then Ni powder was added by mechanical alloying method. The kinetics of hydriding process and electrochemical properties of La2Mg17-X wt.%Ni （x=0, 50, 100, 150, 200） composites were investigated. X-ray diffraction （XRD） and scanning electron microscopy （SEM） analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders. The research of hydrogen absorption properties found that La2Mg17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content, reached to 5.796 wt.% at 3 MPa, and up to 5.229 wt.% merely in 2 min, which revealed that the amorphous phase reduced the H occupation of the lattice clearance, resulting in the decline of hydrogen absorption capacity. The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 ℃, however, the cycle stability decreased considerably./~ series of ki- netic measurements demonstrated that the controlling steps of electrochemical process of La2Mg17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk （x=50, 100） to hydrogen diffusion on both alloy bulk and surface （x=150, 200）.