Xingjun Liu

Experimental determination and thermodynamic calculation of phase equilibria in the Fe-Mn-Al system

The phase equilibria among the face-centered cubic (fcc), body-centered cubic (bcc), and βMn phases at 800, 900, 1000, 1100, and 1200 °C were examined by electron probe microanalysis (EPMA), and the A2/B2 and B2/D03 ordering temperatures were also determined using the diffusion couple method and differential scanning calorimetry (DSC). The critical temperatures for the A2/B2 and B2/D03 ordering were found to increase with increasing Mn content. Thermodynamic assessment of the Fe−Mn−Al system was also undertaken with use of experimental data for the phase equilibria and order-disorder transition temperatures using the CALPHAD (Calculation of Phase Diagrams) method. The Gibbs energies of the liquid, αMn, βMn, fcc, and ε phases were described by the subregular solution model and that of the bcc phase was represented by the two-sublattice model. The thermodynamic parameters for describing the phase equilibria and the ordering of the bcc phase were optimized with good agreement between the calculated and experimental results.

Design and formation mechanism of self-organized core/shell structure composite powder in immiscible liquid system

Under the guidance of the calculation of phase diagrams method, the self-organized Cu alloy/stainless steel composite powders with a core/shell microstructure were developed based on the gas atomization process, and the formation evolution of self-organized core/shell structure composite powders was modeled by the phase field method. This paper gives a more detailed explanation for the formation of self-organized core/shell structure composite powders from the viewpoints of thermodynamics and kinetics. Such core/shell structure composite powders have good combination of high strength and corrosion resistance (Fe-rich phase) and high electric and thermal conductivities (Cu-rich phase) with many potential advanced applications in electronic devices.

Self-organization of core-shell and core-shell-corona structures in small liquid droplets

It was recently discovered that core-shell and core-shell-corona microstructures in immiscible liquid alloys, which were previously obtained only in outer space, can be fabricated under gravity condition on earth using conventional gas atomization. The origin was attributed solely to Marangoni motion driven by temperature-dependence of interfacial energy. We found in this letter, with the aid of computer simulation, that coupled processes of spinodal decomposition, decomposition-induced fluid flow, collision and collision-induced-collision among second-phase droplets all play critical rules at different stages in the formation of these structures. Their contributions relative to the Marangoni effect are analyzed as function of system size.

Ni56Mn25-xCrxGa19 (x=0, 2, 4, 6) high temperature shape memory alloys

National Natural Science Foundation of China [50771086]; Program for New Century Excellent Talents in University (NCET), China [NCET-09-0676]; Program for New Century Excellent Talents in Fujian Provincial University (NCETFJ), China; Fujian Provincial Dep

Thermal stability, crystallization behavior, Vickers hardness and magnetic properties of Fe–Co–Ni–Cr–Mo–C–B–Y bulk metallic glasses

Abstract Thermal stability, crystallization behavior, Vickers hardness and magnetic properties of the Fe 41 Co 7– x Ni x Cr 15 Mo 14 C 15 B 6 Y 2 ( x =0, 1, 3, 5) bulk metallic glasses were investigated. The Fe 41 Co 7– x Ni x Cr 15 Mo 14 C 15 B 6 Y 2 ( x =0, 1, 3, 5) metallic glasses were fabricated by copper mold casting method. The thermal stability and crystallization behavior of the metallic glass rods were investigated by differential scanning calorimetry and isothermal experiments. Hardness measurements for samples annealed at different temperatures for different time were carried out at room temperature by the Vickers hardness tester, and magnetic measurements were performed at different temperatures by the vibrating sample magnetometer. It is shown that the addition of Ni does not play a positive role for enlarging Δ T x and GFA from parameter γ (= T x /( T g + T l )), and it can, however, increase the activation energy in the initial stage of crystallization by changing the initial crystallization behavior. The minor addition of Ni can refine the crystal grain obtained from the full crystallization experiment. The primary crystallization causes the decrease of hardness in these alloys, and as the crystallization continues, the hardness in all samples increases instead due to the precipitation of carbide and boride. The annealing temperature has an obvious effect on magnetic properties of these alloys, and the minor addition of Ni can effectively prevent the alloy annealed at high temperature to transform from paramagnetic to ferromagnetic state.

Microstructure, mechanical and shape memory properties of Ti-55Ta-xSi biomedical alloys

National Natural Science Foundation of China [50771086]; Program for New Century Excellent Talents in University, China; Program for New Century Excellent Talents in Fujian Province University, China; Fujian Provincial Department of Science and Technology

Thermodynamics and liquid phase separation in the Cu-Co-Nb ternary alloys

Ministry of Education of China [707037]; Ministry of Science and Technology of China [2009DFA52170, 2009AA03Z101]; Fujian Provincial Department of Science Technology [2009I0024]; Xiamen City Department of Science Technology [3502Z20093001]; Aviation Scien

Giant phase shift effect in Tb0.3Dy0.7Fe2/Pb(Zr,Ti)O3 laminated composite

In this letter we present a magnetic field-induced giant phase shift effect under resonant frequency in the bilayered magnetoelectric composite of Tb0.3Dy0.7Fe2(Terfenol-D) and Pb(Zr,Ti)O3. When the bias magnetic field is varied from 0.1 T to 0.3 T, the phase shift of the magnetoelectric effect under 83.2 kHz was as large as 180°, which implies a complete transformation from capacitor behavior to inductor behavior. The phase shift was analyzed in the polar coordinates, and the mechanism of this giant phase shift was considered as the ΔE effect of Terfenol-D. This giant phase shift effect may benefit existing phase modulation techniques.

Thermodynamic calculation of phase diagram and phase stability with nano-size particles

In the present paper, the surface tensions and interfacial energies for pure metals and alloys for different structures were predicted by combining with the evaluated thermodynamic parameters in the framework of the CALPHAD (Calculation of Phase Diagrams) method. It is shown that the calculated results are in good agreement with the existing experimental data. On the basis of the predicted values of surface tension and interfacial energy, the phase stability and phase diagram with nano-size particles can be calculated by considering the Gibbs-Thomson equation. The calculated results for pure Fe indicate that the fcc phase is more stable with the decreasing of size of particles, which is in agreement with the experimental data reported, and the phase diagram with nano-size particle can be calculated.

A Novel Self-Assembling Al-based Composite Powder with High Hydrogen Generation Efficiency.

In this study, a novel self-assembling hydrogen generation powder comprised of 80Al-10Bi-10Sn wt.% was prepared using the gas atomization method and then collected in an air environment. The morphological and hydrolysis properties of the powders were investigated. The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries. The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C. Furthermore, at 30 °C, the powders exhibited a hydrogen conversion yield of 91.30% within 16 minutes. The hydrogen produced by this powder could be directly used in proton exchange membrane fuel cells. The mechanisms of the hydrolysis reactions were also analyzed.