热压烧结制备Cu/FeCoCr复合材料的显微组织及热物理性能

利用相图计算的CALPHAD方法和超音雾化制粉技术,在CuFeCoCr体系中设计并制备了一系列微米级复合粉体。通过热压烧结方法在烧结温度为950℃,烧结压力为45 MPa的工艺条件下成功获得块体复合材料。研究了块体复合材料中Cu含量对显微组织,热导率,热膨胀系数以及显微硬度的影响。结果表明:CuFeCoCr块体复合材料均由fcc富铜相和fcc富铁钴铬相组成。该系列复合材料经600℃时效处理8 h后,其热膨胀系数变化范围为5.83×10-6~10.61×10-6 K-1,热导率变化范围为42.17~107.53 W·m-1·K-1。其中Cu55(Fe0.37Cr0.09Co0.54)45复合材料表现出良好的综合性能,即其热膨胀系数和热导率分别为9.08×10-6K-1和91.09 W·m-1·K-1,与电子封装半导体材料的热膨胀系数相匹配。     

Thermodynamic modelling of the ternary Bi-Ga-Te system for potential application in thermoelectric materials

Thermoelectric materials have drawn widespread attention because they can enable the direct conversion between electric and thermal energy. Over the years, different materials such as skutterudites, clathrates, intermetallic alloys, eutectic alloys, chalcogenides have been explored for Thermoelectric (TE) applications. Amongst the eutectic alloys, the Bi-Ga-Te system exhibits promising potential as a TE material. Accordingly, in this study, we performed the thermodynamic optimization and critical evaluation of binary Bi–Ga, Bi–Te, Ga–Te, and ternary Bi-Ga-Te systems using the CALPHAD method. It is observed that the Ga–Te system shows asymmetric liquid solution properties with strong negative enthalpy of mixing, whereas the Bi–Te liquid exhibits the symmetric regular solution behavior. Moreover, the Bi–Ga liquid solution has a positive enthalpy of mixing. Therefore, Modified Quasichemical Model (MQM) using pair approximation was utilized to describe the diversified thermodynamic properties of liquid solution in sub-binaries by taking into account the Short-Range Ordering (SRO). By merging the binary optimization results with a proper interpolation method, the liquid solution properties and phase diagram information in the Bi-Ga-Te ternary system were also reproduced successfully without any adjustable ternary parameter. Several ternary eutectic compositions were suggested for designing TE alloy with enhanced properties using the developed database.     

Comparative study on the viscosity modeling of the Ag–Au–Cu liquid alloys

With the new CALPHAD-type model proposed in our previous work, the viscosity of the Ag–Au–Cu system was re-optimized. Comparisons were made in the calculated viscosities of the Ag–Au and Ag–Cu liquid alloys at 1373 K among different models. It was found that the CALPHAD-type models perform better than the empirical models. The calculated viscosities of the Ag–Au–Cu liquid alloys with and without ternary interaction parameters were both compared with the calculation results of the previous CALPHAD-type model. Considering ternary interaction, the best fitness with the experimental data could be obtained by our model. The good performance in reproducing the measured viscosities of binary and ternary systems evidences the validity of the new model.     

Thermodynamic assessments of the U–Nb–Mo and U–Nb–Cr ternary systems

The thermodynamic assessments of the U–Nb–Mo and U–Nb–Cr systems have been performed by using the CALPHAD (Calculation of Phase Diagrams) method on the basis of critical evaluation of phase diagram data reported in literature. The reported individual solution phases, i.e. liquid, (αU), (βU), γ, δ and two intermetallic compounds, i.e. MoU₂ and NbCr₂, have been modeled. The modeling covers the whole composition range and a wide temperature range. By utilizing the available thermodynamic parameters of the sub-binary systems, the U–Nb–Mo and U–Nb–Cr systems have been thermodynamically assessed and a series of self-consistent parameters have been obtained for the first time, which can reproduce most of the phase diagram and thermodynamic data to provide guidance for the design of nuclear fuels.     

Predicting the density of molten alloys using computational thermodynamics

The density of a molten alloy can be calculated from the quotient of its molar mass divided by its molar volume. The molar volume of a molten alloy, however, often deviates from the average of the molar volumes of its constituents. The deviation is caused mainly by the affinity (or lack of it) between dissimilar atoms, which can be quantified by the enthalpy of mixing. Up to now, the link between the enthalpy of mixing and the volume change has been determined empirically through the regression of experimental measurements of alloy densities. In the present study, the derivative of molar volume with respect to enthalpy was deduced and the molar volumes of molten alloys were computed entirely based on the properties of pure elements and the enthalpy of mixing of the alloys. The very slight increase in the packing density due to the size difference of different atoms was also considered. The effect of cluster formation due to short range ordering was also addressed. Over six hundred data points were used in validations. Excellent agreements were achieved between the calculated values and the experimental measurements.     

Thermodynamic assessment of the Ga–Se–Te system

In this study, the Ga–Te binary system was reassessed by means of the CALPHAD method using a modified lattice stability parameter for Te as well as experimental data for this binary system. The two-sublattice ionic solution model was applied for the liquid phase, and the intermediate phases were described by the sublattice model. A set of self-consistent thermodynamic parameters was optimized for all the phases in the Ga–Te binary system, which reproduced the phase diagram and the thermodynamic properties well. Using the reevaluated Ga–Te system, previously assessed Ga–Se system, and modified Se–Te system, a critical evaluation of the Ga–Se–Te ternary system was performed. The calculated vertical sections, isothermal sections, and liquidus projection agreed reasonably well with the experimental data. Immiscibility in the liquid phase was observed, and the origin of this behavior is discussed from a thermodynamic perspective.