Qingsen Meng

Interface kinetics of combustion–diffusion bonding of Ni3Al/Ni and TiAl/Ti under direct current field

The bonding of TiB2–Ni and TiC–Ni composites to, respectively, Ni and Ti substrates was investigated by field-activated and pressure-assisted synthesis. Bonding and in situ synthesis was utilized to prepare (TiB2)pNi/Ni3Al/Ni (Composition 1) and (TiC)pNi/TiAl/Ti (Composition 2) joining structures. The effect of applied current on the kinetics of formation of the diffusion layer between the substrate (Ni or Ti) and the respective intermetallic layer (Ni3Al or TiAl) was investigated. For both compositions, the current was shown to have a marked influence of the activation energy of formation of the layer, decreasing it by as much as 31xa0%. Calculations of adiabatic temperatures suggest a possible current contribution to interdiffusion, as has been reported previously.

Enhancing the zT Value of Bi-Doped Mg2Si0.6Sn0.4 Materials through Reduction of Bipolar Thermal Conductivity

Solid solutions of Mg2Si0.6Sn0.4-xBix with 0 ≤ x ≤ 0.03 were prepared by a one-step synthesis and consolidation method, using MgH2 as a starting material. The thermoelectric properties of these samples were evaluated over the temperature range 300-775 K. Figure of merit, zT, values were determined over this range for all compositions and found to increase with temperature reaching a value of 1.36 at 775 K for samples with x = 0.02. Examination of the components of the total thermal conductivity showed that the bipolar thermal conductivity is suppressed by an increase in the band gap, resulting from solid solution formation, and by low minority carrier mobility. The suppression of the bipolar thermal conductivity is believed to be the consequence of charged grain boundaries.

Preparation and scratch test of AlMgB14 modified by TiB2

In this paper, the AlMgB14 and AlMgB14–TiB2 composites were synthesized by means of mechanical alloying and the field-activated and pressure-assisted synthesis process. The effect of temperature and pressure on the purity and property of products was discussed. The results show that the process of preparing AlMgB14 bulk materials is optimized as follows: synthesis temperature 1,400–1,500xa0°C, heating rate 100xa0°C·min−1, axial pressure 60xa0MPa, heat preservation 8–10xa0min, optimum starting powders’ ratio Al: Mg: Bxa0=xa00.1915:0.1363:0.6722, and adding excessive 3xa0wt% Al. The abrasion resistance of AlMgB14 composites with varying amounts of TiB2 was studied using single-point diamond scratch tests with loads ranging from 10 to 100xa0N in 10 N increments. The scratch width increases almost linearly with the applied load and decreases with TiB2 proportion increasing up to 70xa0wt%. With its advantages of fast heating, short reaction time, energy conservation, and high purity, this method offers a new way to synthesize AlMgB14 and AlMgB14–TiB2 composites.

Thermoelectric transport properties and structure of Mg2Si0.8Sn0.2 prepared by ECAS under different current intensities

Thermoelectric materials Mg2Si0.8Sn0.2 were sintered under three different conditions including no electricity sintering (NCS), low electricity sintering (LCS), and high electricity sintering (HCS). Thermoelectric performance and microstructure of three group samples were measured and compared. The results indicate that the application of electric current during the sintering process changes the microstructure and significantly increases the density of samples, and increases the electric conductivity and the power factor. The electric current activated/assisted sintering is an effective way to obtain thermoelectric materials with excellent performance.