Experimental investigation and thermodynamic description of the Ni–Ti–W system

The liquidus surface projection and isothermal sections at 1173 and 1373 K of the Ni–Ti–W system were constructed on the basis of microstructure and phase constituents of as-cast and annealed alloys, which were obtained by means of scanning electron microscopy (SEM) coupled with energy dispersion spectroscopy (EDS), X–ray diffraction (XRD). Six primary solidification regions were determined in the liquidus surface projection. Five and six three-phase regions were derived in the isothermal sections at 1173 and 1373 K, respectively. No new ternary compounds were found. Based on the present experimental data, the Ni–Ti–W system was optimized using CALPHAD (CALculation of PHase Diagram) method. The solution phases, liquid, fcc, bcc, and hcp, were treated as substitutional solution. Two compounds Ni₃Ti and NiTi₂ were treated as (Ni,Ti,W)_m(Ni,Ti,W)_n, and Ni₄W was treated as (Ni,Ti)₄W₁ by a two-sublattice model. NiTi with B2 crystal structure was treated as the ordered phase of bcc solution, and model was (Ni,Ti,W)_0.5(Ni,Ti,W)_0.5(Va)₃. A set of self-consistent thermodynamic parameters was obtained.     

Modeling of the viscosity in the AL–Cu–Mg–Si system: Database construction

The viscosity database for the Al–Cu–Mg–Si system was constructed using the CALPHAD (CALculation of PHAse Diagram)-type formalism. Viscosities of pure elements were described with the Arrhenius formula based on the experimental data. Subsequently, viscosities of the Al–Cu, Al–Si, Al–Mg and Cu–Si binary systems were assessed via CALPHAD technique and compared with the corresponding experimental data. Due to the lack of experimental data, viscosities in the Mg–Si and Cu–Mg systems were estimated by means of the Hirai's equation. The viscosities of the ternary Al–Cu–Si system were then predicted based on the binary parameters and compared with the experimental results. Using the established viscosity database for the quaternary Al–Cu–Mg–Si system, the viscosities of some commercial aluminum alloys were predicted. The reasonable agreement between calculations and experiments in Al-rich corner indicates that the CALPHAD-type database for the viscosity is valid and the database is suitable for predicting the viscosity of the commercial Al–Cu–Mg–Si based alloys.     

Computational modeling of elastic constants as a function of temperature and composition in Zr–Nb alloys

We used CALPHAD-type model to describe single crystal elastic constants of bcc solution phases in Zr–Nb system. The model parameters were evaluated by utilizing least square algorithm based on available experimental and first-principles data. The composition-polycrystalline elastic properties profiles of the Zr–Nb alloys of full composition were predicted and are in agreement with experimental data. The critical temperature corresponding to the dynamical stabilization of bcc pure Zr can be estimated to 600 K and the critical composition corresponding to the dynamical stabilization of bcc Zr–Nb alloys at room temperature is about 4 at% Nb. The current calculations present an effective strategy to design biomedical alloys using a computational method.     

Thermodynamic modeling of Cr–Nb and Zr–Cr with extension to the ternary Zr–Nb–Cr system

The total energies of Laves phases in the Cr–Nb and Zr–Cr systems have been calculated by the pseudo-potential VASP code with a full relaxation of all structural parameters. The special quasirandom structures (SQSs) have been constructed and their total energies have been calculated by the VASP code to predict the enthalpies of mixing for bcc and hcp solid solution phases. The phonon calculations for the C14 and C15 Laves phases have been performed to analyze the phase stability at elevated temperatures. The experimental study on the Zr–Cr system has been carried out at different temperatures to determine the phase boundaries. Based on these results, thermodynamic models of Cr–Nb and Zr–Cr with extension to the ternary Zr–Nb–Cr systems have been developed in this work by using the CALPHAD approach.     

Cr和Zn元素对AA3xxx合金均质化热处理微观组织演化的模拟研究

Cr和Zn作为杂质或添加合金元素对铝合金产品的最终性能有很大影响。采用基于热力学与扩散动力学的KWN模型,研究了这两种元素对AA3xxx合金均质化热处理过程中弥散相形成的影响。该研究的目的是展示数学模型对铝合会成分及工艺设计的指导作用。