Papers by Keyword: CALPHAD

Abstract: Heusler alloys have been considered as one of the most promising thermoelectric materials for electrical power generation in a temperature range of 500–800 °C. Establishment of phase diagrams allows one to predict formation, equilibria, and stability of phases in of these ternary alloys. In this work we report on the simulation and investigation of phase diagram and phase equilibria in ternary Ti-Fe-Sb system which is of considerable interest for thermoelectric applications. The simulation was carried out using the CALPHAD method in Pandat software. The existence of the thermoelectric Heusler TiFe_1.5Sb phase was revealed in a temperature range from 970 to 1070 K. The equilibria between TiFe_1.5Sb and other phases were determined. The entropy of formation was calculated for the phases existing at 970, 1020 and 1070 K using a fitting approach. A narrow equilibrium region containing pure body centered cubic Fe and TiFe_1.5Sb was found.

Abstract: A coupling interface between phase-field model with finite interface dissipation and the CALPHAD (CALculation of PHAse Diagram) thermodynamic and atomic mobility databases is developed. It robotizes the procedures that provides the composition and temperature dependent properties in multicomponent and multi-phase systems. Based on the developed coupling interface, different CALPHAD properties can be directly coupling in the phase-field simulation.

Abstract: In this paper, a new vanadium nitrogen (V-N) microalloyed high strength weathering steel with the yield strength and tensile strength higher than 550 MPa and 650 MPa was designed and developed by using thermodynamic model of nitrogen solubility and phase diagram database of CALPHAD. Based on the established thermodynamic model, the effect of C content on nitrogen solubility in molten steel was investigated. The nitrogen solubility increases with the decrease of C content and the increase of temperature. In order to obtain higher N content in steel, C content must be controlled at a low range of 0.03~0.04%. Furthermore, an allowable concentration range of C and N was selected based on the phases quantity prediction of VN/V(C,N), (Cr, Fe)₇C₃, AlN and γ through the CALPHAD approach. Consequently, five new weathering steels were designed with variations of (C+N) content or N/C ratio. And then the four selected steels were cast, hot rolled and air cooled. The tensile tests at the room temperature show that the yield strength and tensile strength of steel with 0.032% C and 0.038%N satisfy the requirements of new generational weathering steel.

Abstract: Multicomponent diffusion in metallic melts is a very important phenomenon during the solidification/casting process of the metallic alloys. However, there exist extremely limited reports on the diffusivity information in multicomponent metallic liquids. In this chapter, a universal and effective phenomenological approach to predict the composition– and temperature–dependent diffusivities in liquid multicomponent systems is systematically proposed. The presently proposed phenomenological method is then adopted to construct the diffusivity/mobility databases of liquid solders, cemented carbides, Co–Cr–Fe–Mn–Ni high entropy alloys and Al–Ce–Ni alloys. Then, the accurate diffusivity/mobility data are further utilized to perform the simulations of the dissolutions of the substrate into the solders, the gradient layer formation of the cemented carbides, the diffusion behavior of liquid Co–Cr–Fe–Mn–Ni high entropy alloys and the rapid solidification of Al–Ce–Ni system. The simulated results indicate that the presently proposed phenomenological method is applicable to investigate the diffusion kinetics in multicomponent metallic melts.

Abstract: The Ginzburg-Landau (G-L) model possesses the thermodynamic foundation of energy minimization and is available for many dynamic formalisms, thus holds great potential for investigating the complex materials behaviors. The common ingredient in energy spawns the real-time control of diffusion potential and chemical mobility by integrating G-L model with CALPHAD technique. The coupling between martensitic transformation and dislocation evolution is achieved by mean of continuous mechanism. The updated G-L model is then validated against the martensitic transformation coupled with composition redistribution in Fe-C binary system. The modeling allows some deeper insights into the mechanisms of coupling effects behind the observed phenomena. It has been proven that the partitioning of carbon in steels is an ordinary diffusion governed by instantaneous diffusion potential and chemical mobility. The rough twin boundaries and retained austenite within the martensite should be attributed to the effect of dislocations. Although the developed model in this chapter has deficiencies, it sheds some lights on the integration of multi-physics models for a complex phase transformation.

Abstract: Ternary intermetallic compounds with rare earth elements and transition metals in the RE-Mn-X (X=Si, Ge, Sn etc.) ternary systems show interesting magnetic properties. As key sub-binary systems of the RE-Mn-X (X=Si, Ge, Sn etc.) ternary systems, the information of phase equilibria and thermodynamic properties of the Mn-RE (RE=Nd, Gd, Dy) binary systems are indispensable to explore the RE-Mn-X (X=Si, Ge, Sn etc.) alloys with better magnetic properties. In this work, the experimental data of phase equilibria and thermodynamic properties of the Mn-RE (RE=Nd, Gd, Dy) binary systems in the published literature were reviewed. Based on the available experimental information, thermodynamic calculation of phase equilibria of the Mn-RE (RE=Nd, Gd, Dy) binary systems was performed using the CALPHAD method. As a result, further experimental investigation and thermodynamic optimization would be still necessary in order to develop the self-consistent and compatible thermodynamic database of the RE-Mn-based alloy systems.

Abstract: The experimental data of phase equilibria and thermodynamic properties of the Fe-RE (RE=Ho, Er, Tm, Sm) binary systems were reviewed. The previous thermodynamic calculation of the Fe-RE (RE=Ho, Er, Tm, Sm) binary systems were discussed based on the comparison of the calculated phase diagram and thermodynamic properties with the experimental data. The compared results show that more experimental information of phase diagram and thermodynamic properties in the Fe-RE (RE=Ho, Er, Tm, Sm) binary systems should be determined and then thermodynamic re-calculation of these binary systems would be performed to develop compatible and available thermodynamic database of the RE-Fe-B ternary systems. It is indispensable to study the relations between alloy compositions, microstructure and magnetic properties of novel Nd-Fe-B-based permanent magnets.

Abstract: In order to design a solvent for high-purity SiC solution growth, the impurity incorporation and the carbon solubility of various solvent materials have been investigated. Among the transition metal elements, the impurity elements of Cr, Ti, V and Hf are more readily incorporate during the solution growth than the other transition metal elements. The thermodynamic calculation revealed that the Y-Si solvent has relatively large carbon solubility, which is comparable to the Cr-Si and Ti-Si solvents often used in the solution growth of bulk SiC crystals. From these results, the Y-Si solvent is expected to be a suitable solvent for the high-purity SiC solution growth. Furthermore, we have demonstrated that the Y-Si solvent can achieve lower incorporation of metal impurity in the grown crystal than the Cr-Si solvent maintaining the growth rate.

Abstract: The effect of melt superheat and oxide inclusions on the fluidity of a commercial A356 alloy has been investigated. Fluidity measurements have been performed by means of Archimedean spiral in sand moulds. The specific testing method and the experimental apparatus show a good reproducibility. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of defects occurring at the tip of the spirals. The results reveal that oxide films increase the variability in the fluidity results obtained at the same apparent experimental conditions. A long permanence in the holding furnace and the introduction of some turbulence during sampling increase the oxide formation and entrapment in the molten bath, thus decreasing the repeatability of the fluidity results. The fluidity increases linearly with superheat and it extrapolates to zero at the temperature corresponding to a fraction solid of about 23%. The initial Ti content in the alloy produces an independent crystallization during freezing of the fluidity spirals.

Abstract: The Fe-RE (RE=Gd, Tb, Dy, Lu) binary systems with the experimental data of phase equilibria and thermodynamic properties in the published literature were reviewed firstly. Based on available phase equilibria data and thermodynamic data, the Fe-RE (RE=Gd, Tb, Dy, Lu) binary systems were assessed thermodynamically using the CALPHAD method. As a result, further experimental investigations and thermodynamic calculations would be both required in order to develop thermodynamic database of the RE-Fe-B ternary systems, which is very useful to study the relations between alloy compositions, microstructure and magnetic properties of novel Nd-Fe-B-based permanent magnets.