Jiajia Han

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.

Atomic-Level Mechanisms of Nucleation of Pure Liquid Metals during Rapid Cooling.

To obtain a material with the desired performance, the atomic-level mechanisms of nucleation from the liquid to solid phase must be understood. Although this transition has been investigated experimentally and theoretically, its atomic-level mechanisms remain debatable. In this work, the nucleation mechanisms of pure Fe under rapid cooling conditions are investigated. The local atomic packing stability and liquid-to-solid transition-energy pathways of Fe are studied using molecular dynamics simulations and first-principle calculations. The results are expressed as functions of cluster size in units of amorphous clusters (ACs) and body-centered cubic crystalline clusters (BCC-CCs). We found the prototypes of ACs in supercooled liquids and successfully divided these ACs to three categories according to their transition-energy pathways. The information obtained in this study could contribute to our current understanding of the crystallization of metallic melts during rapid cooling.

Portable water-using H2 production materials converted from waste aluminum

ABSTRACT This study investigates the feasibility of using waste aluminum as a substitute to pure aluminum for preparing portable water-using hydrogen production materials by gas atomization process. The H2 production performances of waste aluminum H2 production materials in different reaction conditions considering reaction temperature, reaction aqueous solution and water adding method were investigated. The results show that such materials can achieve a high Al/H2 conversion and a stable H2 flow rate for practical fuel cell electricity generation. In addition, the recycling of activation agents and Al(OH)3 can be realized.

Experimental investigation of phase equilibria in the Zr–Cu–Ni ternary system

Abstract The phase equilibria in the Zr–Cu–Ni ternary system are investigated combined with X-ray diffraction, electron probe micro-analysis and differential scanning calorimetry. Two isothermal sections of the Zr–Cu–Ni ternary system at 1 000 °C and 1 100 °C are experimentally established. Most of the binary intermetallic compounds, e. g. Zr7Ni10, ZrNi, ZrNi5, Zr14Cu51, and Zr2Cu9, show a remarkable ternary solubility. A new ternary compound named τ3 (Zr31.1–30.7 · Cu28.5–40.3Ni40.4–29.0) is detected at 1 000 °C and dissolved at 1 020 °C because the nearby large liquid phase field further expands. The newly determined phase equilibria will provide important information for both thermodynamic assessment and alloy design of Zr-based metallic glass.

Improvement of the Thermal Stability of Laminated Magnetoelectric (ME) Composites

In order to search for ME laminated composites with a good thermal stability, the temperature dependent ME coefficient in two kinds of laminates bonded by welding, namely, Ni/Pb(Zr,Ti)O3/Ni and Metal-glass/Pb(Zr,Ti)O3/Metal-glass were investigated. The ME effect of all laminated composites at temperature range from −20 to 100 °C was measured. Results showed that both two laminates bonded by welding exhibited very good thermal stability. A new phenomenon was found that the ME charge coefficient slowly increased with increasing temperature, which resulted from the increase of piezoelectric layer’s capacitance. These ME laminated composites bonded by welding supposed a good performance at high temperature, which were suitable for high temperature applications.

Influence of microstructural features on thermal expansion coefficient in graphene/epoxy composites.

In this paper, theoretical calculations were conducted to determine the coefficient of thermal expansion (CTE) based on the effective medium approach using Green’s function method. The influences of microstructural features were investigated, including volume fraction, aspect ratio, and the orientation of graphene fillers. Calculated results demonstrated strong anisotropy of CTE when all graphene sheets in the composite were aligned in the in-plane direction due to the large difference between the elastic moduli of the graphene and epoxy. The in-plane CTE in the graphene/epoxy composite can be effectively reduced with small additions of graphene additive. Orientation dispersion among the graphene fillers significantly decreases the anisotropy of CTE. Accounting for the influences of all microstructural features, simulation results closely align with current experimental results. This work will provide a general guideline and a solid foundation for the optimal design and preparation of graphene/polymer composites.