Hongxiao Li

Intermetallics and phase relations of Mg-Zn-Ce alloys at 400 °C

Abstract The crystal structures, compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 °C were identified through equilibrium alloy method. For Mg-Zn-Ce system, there is a linear ternary compound ( T phase), whose chemical formula is (Mg 1- x Zn x ) 11 Ce. The range of Zn content in T phase is from 9.6% to 43.6% (molar fraction). The crystal structure of T phase is C -centered orthorhombic lattice with lattice parameters of a =0.96-1.029 nm, b =1.115-1.204 nm, c =0.940-1.015 nm. And the lattice parameters of T phase are decreasing a little with increasing Zn content. According to the results of composition and crystal structure, the maximal solubility of Zn in Mg 12 Ce is about 7.8% (molar fraction), and the chemical formula of the solid solution can be identified as (Mg 1- x Zn x ) 12 Ce. The isothermal section of Mg-Zn-Ce system in Mg-rich corner at 400 °C was constructed.

Thermodynamic assessment of Co-Cr-W ternary system

Abstract The Co-Cr-W ternary system was critically assessed using the CALPHAD technique. The solution phases including the liquid, γ-Co, ɛ-Co and α-Cr were described by a substitutional solution model. The σ, μ and R phases were described by three-sublattice models of (Co, W) 8 (Cr, W) 4 (Co, Cr, W) 18 , (Co, Cr, W) 7 W 2 (Co, Cr, W) 4 and (Co, W) 27 (Cr, W) 14 (Co, Cr, W) 12 , respectively, in order to reproduce their homogeneity ranges. A self-consistent set of thermodynamic parameters for each phase was derived. The calculated isothermal sections at 1 000, 1 200 and 1 350 °C are in good agreement with the experimental data. A eutectoid reaction of R ⇔ μ+γ-Co+σ in this ternary system was predicted to occur at 1 022 °C.

Partial phase relationships of Mg-Zn-Ce system at 350 °C

Abstract The alloys were prepared in Mg-rich corner of Mg-Zn-Ce system. Partial phase equilibrium relationships of these alloys at 350 °Cwere identified by using scanning electron microscopy(SEM), electron probe microanalysis(EPMA), X-ray diffraction(XRD) analysis and selected area electron diffraction(SAED) pattern analysis of transmission electron microscopy(TEM). Partial isothermal section of Mg-Zn-Ce system in Mg-rich corner was identified. The results show that there is one ternary compound (T-phase) in Mg-Zn-Ce system. The T-phase is a linear ternary compound in which the content of Ce is about 7.7% (molar fraction); while the content of Zn is changed from 19.3% to 43.6% (molar fraction). The crystal structure of T-phase is C-centered orthorhombic. In addition, one two-phase region of Mg+T-phase and one three-phase region of Mg+T-phase+MgZn(Ce) exist in the Mg-rich corner of Mg-Zn-Ce system at 350 °C.

Phase equilibria in the Mg-rich corner of the Mg-Zn-La system at 350°C

Abstract The phase eqyilibria in the Mg-rich corner of the Mg-Zn-La system at 350°C have been investigated by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. It has been shown that the linear compound (Mg, Zn) 17 La 2 existed in the Mg-Zn-La system at 350°C. The linear compound (so-called T phase) was with the C-centred orthorhombic crystal structure induced by the solution of significant quantities of the third element. The three-phase region α(Mg) + MgZn(La) + T and the two-phase region composed of the α(Mg) and the linear-compound T phase existed in the Mg-rich corner of the Mg-Zn-La system at 350°C.

Phase equilibria in Co-rich region of Co−Ti−Ta system

Abstract The phase equilibria in Co-rich region of Co-Ti-Ta system were studied. The microstructure and XRD analysis together with EDS determination show that L 1 2 type Co 3 Ti phase and Laves_C36_Co 3 Ta phase get equilibrium with α -Co phase from 1 000 to 1 200 °C. The Co 3 Ti phase possesses a solubility of Ta higher than 10%, and the addition of Ta stabilizes the Co 3 Ti phase. The isothermal sections of the Co-Ti-Ta system in the Co-rich region at 1 000, 1 100 and 1 200 °C were constructed according to the result.

Isothermal section of Mg-rich corner in Mg–Zn–Al ternary system at 335 °C

Abstract The phase equilibria and compositions at the Mg-rich corner of the Mg–Zn–Al ternary system at 335 °C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the α -Mg solid solution is not in equilibrium with the Mg 32 (Al, Zn) 49 ( τ ) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al 5 Mg 11 Zn 4 ( φ ). The whole composition range of the φ phase was also obtained at 335 °C, i.e., 52.5%–56.4% Mg, 13.6%–24.0% Al, 19.6%–33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg 7 Zn 3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the α -Mg solid solution.

Ternary compounds and solid-state phase equilibria in Mg-rich side of Mg−Zn−Ca system at 300 °C

Abstract The phase equilibria and compositions in Mg-rich side at 300 °C were investigated in Mg-Zn-Ca ternary system through the equilibrated alloy method by using scanning electron microscopy, electron probe microanalysis, X-ray diffraction and transmission electron microscopy. The results show that two ternary compounds T1 and T2 can be in equilibrium with the Mg-based solid solution in Mg-Zn-Ca system. T1 phase is a linear compound with the composition region (molar fraction) of 15% Ca, 20.5%-48.9% Zn and balanced Mg at 300 °C. Its hexagonal structure parameters decrease with increasing Zn content, i.e. a=0.992-0.945 nm, c=1.034-1.003 nm. T2 phase has hexagonal structure with the composition region of 26.4%-28.4% Mg, 63.2%-65.5% Zn and 7.1%-8.4% Ca. At 300 °C, the solubility of Zn in the Mg-based solid solution increases for the addition of Ca, the maximum solubility of Zn is 3.7%. Three-phase fields consisting of α-Mg+Mg2Ca+T1, α-Mg+T1+T2, α-Mg+T2+MgZn and MgZn+T2+Mg2Zn3 exist in the Mg-Zn-Ca system at 300 °C.

Thermodynamic prediction of the composition of Fe-based amorphous alloys

Abstract The liquidus univariant lines of the Fe-Nb-B ternary system have been thermodynamically calculated by means of CALPHAD method and Fe-based thermodynamic data. It is found that there are two eutectic reactions in the Fe-rich corner, that is, (1) L(Fe-3Nb-15B) → α + γ + M 2 B (1430 K), and (2) L(Fe-10Nb-27B) → FeB + Lc 14 + M 2 B (1575 K). Moreover, the eutectic points are very close to the compositions with high glass forming ability determined experimentally. This means that it is feasible to design the compositions of multicomponent bulk metallic glasses by looking for the eutectic points in the Fe-Nb-B system by means of thermodynamic calculation.