Papers by Keyword: Enthalpy of Mixing

Abstract: Cobalt-based alloys with nickel and titanium represent a promising class of materials for the development of novel amorphous and high-temperature-resistant alloys. The targeted design of such materials requires detailed knowledge of the thermodynamic properties of liquid alloys. In this work, high-temperature calorimetry was employed to investigate the partial enthalpy of mixing of titanium in the Co–Ni–Ti liquid alloys along the cross-sections x_Co/x_Ni = 3, x_Co/x_Ni = 1/3, and x_Co/x_Ni = 1 at 1873 K and in the concentration range x_Ti = 0–0.6. The partial mixing enthalpy of titanium exhibits negative values, indicating strong interatomic interactions among the components in the melt. The integral mixing enthalpy Δ_mH over the entire compositional triangle was described using the Redlich–Kister–Muggianu formalism. The Δ_mH function shows pronounced negative values, emphasizing the significant role of CoTi and NiTi binary interactions. The associate solution model (ASM) was applied to describe the temperature and composition dependence of the thermodynamic mixing functions in the liquid Co–Ni–Ti alloys. The integral enthalpy Δ_mH, excess entropy Δ_mS^ex, excess Gibbs energy Δ_mG^ex, and Gibbs energy Δ_mG of mixing were evaluated in the temperature range 800–1873 K. It was shown that these thermodynamic functions exhibit increasing negative deviations from ideality upon cooling of the melts. Within the ASM framework, the degree of chemical short-range order in the Co–Ni–Ti liquid alloys was assessed as the total mole fraction of associates Σx_assoc in the solution. It was demonstrated that the Σx_assoc is significant and increases with decreasing temperature. The amorphization composition range for the Co–Ni–Ti liquid alloys was predicted based on our previously proposed empirical criterion related with Σx_assoc. The predicted range of x_Ti ≈ 0.2–0.8 is in satisfactory agreement with known compositions of amorphous alloys in the edged binary systems.

Abstract: This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models. While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.

Abstract: With the effects of electronic structure and atomic size being introduced, a revised model to calculate the viscosity of the bulk metallic glass alloys was proposed and the viscosity of ternary Zr-Al-Cu, Zr-Ni-Al and quaternary Zr-Al-Ni-Cu systems are calculated in this paper, and the computed results agree well with the empirical one. The sequence of viscosity of different systems is: V_Zr-Al-Cu <V_Zr-Al-Ni<.V_Zr-Al-Ni-Cu. To Zr-Al-Cu and Zr-Ni-Al, the highest viscosity locates in the composition range of X_Zr=0.37-0.86, X_Cu=0-0.40 and X_Zr = 0.45-0.79, X_Al = 0.12-0.50, respectively. And to the Zr-Ni-Al-Cu system with 66.67% Zr, the highest viscosity is obtained in the region of X_Al= 0.63-0.80, X_Ni = 0.14-0.24.