Li-bin Liu

Thermodynamic optimization of Mg-Nd system

Based on the reported experimental data, the phase diagram of Mg-Nd binary system was optimized using the CALPHAD approach. Gibbs energies of the disordered BCC_A2 and ordered BCC_B2 phases were modeled with a single expression based on a 2-sublattice model. Liquid and terminal solutions, such as dHCP and HCP, were modeled as substitational solutions. Intermediate phases Mg2Nd, Mg3Nd and Mg41Nd5 were treated as stoichiometric compounds. The optimization was carried out in the Thermo-Calc package. A set of thermodynamic parameters is obtained. Calculated phase diagram, enthalpies of formation and Gibbs energies of formation are in reasonable agreement with the experimental data.

Thermodynamic re-assessment of Fe-Ti binary system

The Fe–Ti binary system was re-assessed using the CALPHAD method in order to improve the capability of being extrapolated to a ternary or higher-order system. Compared with previous assessments, the main focus was put on the thermodynamic description of the two intermetallic compounds Fe2Ti and FeTi. The C14_Laves phase Fe2Ti was described by the two-sublattice model, which is widely used at present. By checking the homogeneity range on the boundary of the ternary systems involving the binary, the phase boundary of this compound was further confirmed. The FeTi phase with a BCC_B2 crystal structure was treated as the ordered phase of the BCC_A2 phase and a unified Gibbs energy function was used to describe both the ordered and disordered phases. Reproduction of the specific heat capacities of these compounds was another aspect paid particular attention to. Comprehensive comparisons of the calculated and experimental results regarding the phase diagram and thermodynamic properties show a good agreement between them and prove the validity of the present thermodynamic description.

Thermodynamic optimization of Bi-Ni binary system

Based on the available experimental data, the Bi-Ni binary system was optimized thermodynamically by the CALPHAD method. The solution phases, including liquid, fcc_A1(Ni) and rhombohedral_A7(Bi), were described as substitutional solution phases, of which the excess Gibbs energies were expressed with the Redlich-Kister polynomial. The intermetallic compound, BiNi, was modeled using three sublattices (Bi) (Ni, Va) (Ni, Va) considering its crystal structure (NiAs-type) and the compatibility of thermodynamic database in the multi-component systems, while Bi3Ni was treated as a stoichiometric compound. Finally, a set of self-consistent thermodynamic parameters formulating the Gibbs energies of various phases in this binary system were obtained. The calculated results are in reasonable agreement with the reported experimental data.

Thermodynamic assessment of Mg-Ga binary system

Abstract In order to obtain the thermodynamic description of the Mg-Ga binary system, the thermodynamic assessment of the system was carried out using the CALPHAD method through Thermo-calc® software package based on the evaluation of all available experimental data from the published literature. The solution phases, including liquid, hcp(Mg) and orthorhombic(Ga), were described by the substitutional solution model, of which the excess Gibbs energies were expressed with the Redlich-Kister polynomial. Meanwhile, all intermetallic compounds, Mg 5 Ga 2 , Mg 2 Ga, MgGa, MgGa 2 and Mg 2 Ga 5 , were modeled as stoichiometric compounds. A set of self-consistent thermodynamic parameters formulating the Gibbs energies of various phases in the Mg-Ga binary system were obtained finally. The much better agreement is achieved between the calculated results and the reported experimental data.

Phase equilibria in Mg-rich corner of Mg–Ca–RE (RE=Gd, Nd) systems at 400 °C

Abstract The phase equilibria in Mg-rich corner of Mg–Ca–Gd and Mg–Ca–Nd ternary systems at 400 °C were determined through the equilibrated alloy method by using XRD, SEM, EPMA and DSC. Partial isothermal sections in Mg-rich corner of Mg–Ca–Gd and Mg–Ca–Nd ternary systems at 400 °C were constructed from 13 alloys. A three-phase region of α–Mg, Mg41RE5 and Mg2Ca was determined in both ternary systems. It is formed by a similar ternary eutectic reaction L→α-Mg+Mg2Ca+Mg41RE5 at 499.6 °C and 505.6 °C, respectively. It is found that the maximum solubility of Ca in Mg5Gd is 3.68% (molar fraction) and 3% of Gd can be dissolved in Mg2Ca in the Mg–Ca–Gd system at 400 °C. While in the Mg–Ca–Nd system the maximum solubility of Ca in Mg41Nd5 is 3.57% and 1.24% of Nd can be dissolved in Mg2Ca at 400 °C. Other three-phase equilibria existing in Mg-rich corner of Mg–Ca–Gd system are α-Mg+Mg5Gd+T and Mg5Gd+Mg2Ca+T and the three-phase equilibrium in Mg-rich corner of Mg–Ca–Nd system is Mg3Nd+Mg2Ca+ Mg41Nd5.

Isothermal section of Mg–Nd–Gd ternary system at 723 K

Abstract An isothermal section of the Mg–Nd–Gd ternary system at 723 K was established by diffusion triple technique and electron probe microanalysis (EPMA). Mg 3 Gd and Mg 3 Nd form a continuous solid solution (Gd, Nd) 3 Mg, and a continuous solid solution (Gd, Nd)Mg is also formed between MgGd and MgNd. Mg 7 Gd, Mg 5 Gd, Mg 2 Gd, Mg 41 Nd 5 , (Gd, Nd) 3 Mg and (Gd, Nd)Mg are found in the ternary system. In these intermetallic phases, Mg 7 Gd has been reported to be a metastable phase in previous literatures. The solubilities of Mg, Gd and Nd in all the phases were detected. Furthermore, four three-phase equilibria, α(Mg)+Mg 7 Gd+ Mg 41 Nd 5 , Mg 7 Gd+Mg 5 Gd+Mg 41 Nd 5 , Mg 5 Gd+Mg 41 Nd 5 +(Gd, Nd) 3 Mg and (Gd, Nd) 3 Mg+(Gd, Nd)Mg+Mg 2 Gd, were identified in the isothermal section.

Thermodynamic description of Au-Ag-Si ternary system

Based on the available experimental information, the Ag-Si binary system was thermodynamically assessed using the CALPHAD method. The solution phases, including liquid, fcc-A1 and diamond-A4, were modeled as substitutional solutions, of which the excess Gibbs energies were expressed by Redlich-Kister polynomial functions. Combined with previous assessment of the Ag-Au and Au-Si binary systems, thermodynamic description of the Au-Ag-Si ternary system was performed to reproduce the reported phase equilibria. Thermodynamic properties of liquid alloys, liquidus projection and several vertical and isothermal sections of this ternary system were calculated, which are in reasonable agreement with the reported experimental data.

Thermodynamic assessment of Cu-Cd system

Abstract A thermodynamic assessment of the Cu-Cd system has been carried out by CALPHAD technique. The liquid phase, FCC_A1(Cu) and HCP_A3(Cd) terminal phases are described by a simple substitutional model, their excess Gibbs energy is formulated with the Redlich-Kister expression. The system contains four intermediate compounds, including β(Cu2Cd), γ(Cu4Cd3), δ(Cu5Cd8) and ɛ(Cu3Cd10). The δ phase is described by a two-sublattice model and the other three intermediate phases are treated as stoichiometric phases. The optimization is carried out in the Thermo-Calc package. A set of self-consistent thermodynamic parameters are obtained. The calculated phase diagram and thermodynamic properties agree well with the available experimental data.