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General Considerations
Published in D. R. F. West, N. Saunders, Ternary Phase Diagrams in Materials Science, 2020
The thermodynamic work of Josiah Willard Gibbs, carried out in the USA in the latter part of the 19th century, provided the fundamental foundation for the understanding of phase equilibria and for the representation of such equilibria in the form of equilibrium (phase) diagrams. In 1876 Gibbs published the first half of his great memoir On the Heterogeneous Equilibria of Substances in the Transactions of the Connecticut Academy of Arts and Sciences,1and the second half followed two years later. This work developed and virtually completed the theory of chemical thermodynamics, and provided basic theory for the development of physical chemistry. Also, in metallurgy Gibbs’ work provided an essential basis and guiding principle for the extensive interest in phase diagram determination and application that occurred as a major feature of the evolution of physical metallurgy around the end of the 19th century. As the 20th century progressed, experimental investigations of phase diagrams and phase transformations formed a major feature of metallurgical activity, related to alloy development and processing; in addition there has been extensive work on non-metallic systems, such as ceramics, while more recently polymeric systems have also become of considerable importance. In the latter half of the 20th century, the use of thermodynamic data and procedures for the calculation of phase diagrams (CALPHAD) has been established as a vital field.
Thermodynamics of High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
Apart from standard handbooks for Gibbs energy data of the lower-order system, an extensive and robust source for Gibbs energy is available in the Calphad approach. Calphad is regarded as the direct method for designing HEAs [39]. The phase diagrams calculation from Gibbs energy models started more than a century ago [40]. Kaufman generalized it with the idea of lattice stability [41]. The approach grew over the last few decades and is now considered to have reached maturity [42]. The Calphad approach involves two major sets of activities: one is generation of Gibbs energy databases and the other is calculation of phase diagrams and thermodynamic properties using those databases.
Application of Computational Thermodynamics for Magnesium Alloys Development
Published in Leszek A. Dobrzański, George E. Totten, Menachem Bamberger, Magnesium and Its Alloys, 2020
With a density being two-thirds that of aluminum and one-quarter of steel, magnesium (Mg) alloys are of growing importance. The development of Mg-based light alloys for vehicle structures has been promoted in light of global climate change due to greenhouse gases [1]. Computational thermodynamics, based on the CALPHAD (CALculation of PHAse Diagram) approach [2–4], is a key enabling technology to help accelerate the pace of materials research and development through building phase relations that can reduce the design-to-alloy production cycle time [5,6]. This technology has the capability to solve a vast number of materials-related problems related to phase equilibria, phase stability, and phase transformations by using well-developed CALPHAD software packages such as Thermo-Calc [7], FactSage [8], and PANDAT [9], where a modeled thermodynamic database is prerequisite for any thermodynamic analyses [1,10]. However, measured thermodynamic data from experiments, thermochemical data in particular, are scarce, and that can result in uncertainties in thermodynamic modeling, particularly the distribution of Gibbs energy into enthalpy and entropy contributions in some cases. Fortunately, the advanced computational tools available today, for instance first-principles calculations based on the density functional theory [11], can provide considerable insight into these basic materials properties. First-principles calculations have now become an important part of computational thermodynamics. This chapter will include the CALPHAD modeling and the new first-principles calculations of Mg-based alloys and compounds.
Recent progress and scientific challenges in multi-material additive manufacturing via laser-based powder bed fusion
Published in Virtual and Physical Prototyping, 2021
The CALPHAD method establishes a thermodynamic model based on the crystal structure of each component phase (i.e. gas phase, liquid phase, solid solution, and compound). The Gibbs free energy of each phase in a material system can be determined by evaluating and screening the experimental and theoretical calculation data (from first-principles calculations, statistical methods and experience, and semi-empirical formulas) of the multi-material system under certain temperature and pressure. Fitting and optimising the model parameters are essential during this step. Finally, a thermodynamic database of multi-component material systems is established using CALPHAD (Ohtani 2006). Figure 6 shows the flow of the CALPHAD method. CALPHAD is a useful thermodynamic calculation method that can be employed to determine the thermodynamic properties of multi-component systems. Moreover, it is the thermodynamic basis of material dynamics and microstructure evolution simulation. Accordingly, the CALPHAD method is widely used in the research and development of new materials and processes (Hofmann et al. 2014).
Recent progress on additive manufacturing of multi-material structures with laser powder bed fusion
Published in Virtual and Physical Prototyping, 2022
Di Wang, Linqing Liu, Guowei Deng, Cheng Deng, Yuchao Bai, Yongqiang Yang, Weihui Wu, Jie Chen, Yang Liu, Yonggang Wang, Xin Lin, Changjun Han
The calculation of phase diagram (CALPHAD) is a useful thermodynamic calculation method that can be employed to determine the thermodynamic properties of multi-component structures (Wei and Li 2021). The CALPHAD method can establish a thermodynamic model based on the crystal structure of each component phase (gas phase, liquid phase, solid solution, compound, etc.). In multi-material structures, CALPHAD can provide critical information for accurately predicting the phase formation. Therefore, the compatibility of dissimilar materials can be evaluated through CALPHAD. The transition path from one material to another can also be designed based on the results of thermodynamic calculations through CALPHAD, which can avoid the generation of undesired phases.
Irradiation behavior of HfNbTaTiV in comparison of HfNbTaTiZr and F82H
Published in Journal of Nuclear Science and Technology, 2023
Yun Zong, Ryota Ikubo, Naoyuki Hashimoto, Hiroshi Oka
To fabricate the body-centered cubic high-entropy alloys, the pure metallic elements V (99.9%), Ti (99.9%), Zr (99.9%), Nb (99.9%), Hf (99.9%), and Ta (99.95%) were utilized as raw materials and weighed using an electrical balance to a total of roughly 30 g. All HEAs (HfNbTaTiV and Senkov alloy) were manufactured by arc-melting under a high vacuum, with the buttons being rotated and heated more than ten times to ensure full melting of all specimens. The chemical compositions of the three alloys discovered with an X-ray fluorescence spectrometer are listed in Table 1. (XRF JEOL JSX3100RII). Table 2 demonstrates the heat-treatment condition. In Figure 1, the phase diagram of HfNbTaTiV was calculated using the CALPHAD methodology. CALPHAD is a phenomenological method for calculating and forecasting thermodynamic, kinetic, and other properties of multicomponent material systems [17]. The microstructures of the alloys were investigated using a scanning electron microscope (SEM, JSM-6510LA). The crystal structure of the annealed specimens was determined by X-ray diffraction (SmartLab XRD) with Cu K radiation at a speed of 6°/min. Each sample was processed and cold rolled approximately 90% to a thickness of approximately 0.25 mm to investigate the presence of ductility. The average hardness of the samples was determined at room temperature using a Vickers indenter (Struers) with testing more than ten times. The specimens were irradiated at Kyoto University’s dual-beam irradiation experimental test facility (DuET). Three HEAs were irradiated with 6.4 MeV Fe3+ ions at 300°C for 5 h. The depth profile of displacement damage calculated using the stopping and range of ions in the matter (SRIM) package is depicted in Figure 2 [18–20]. The Nano Indenter TI-950 (Hysitron) was used as the nanoindentation test device. In this study, the indentation depths were 100, 200, and 250 nm. At least 10 measurements were taken for each, and the average value was calculated. TEM observation was performed at an acceleration voltage of 200 keV to observe the microstructure after irradiation. The defect cluster data after irradiation were obtained by removing the data at around 2.5 m from the surface while accounting for FIB irradiation damage.