Phase Stability Of Solid Solutions Research Articles

Explaining the entropy forming ability for carbides with the effective atomic size mismatch

To quickly screen for single-phased multi-principal-element materials, a so-called entropy forming ability (EFA) parameter is sometimes used as a descriptor. The larger the EFA, the larger is the propensity to form a single-phase structure. We have investigated this EFA descriptor with atomic relaxations in special-quasi-random structures and discovered that the EFA correlates inversely with the lattice distortion. Large effective atomic size differences lead to multi-phase compounds, and little size differences to single-phase compounds. Instead of configurational entropy, we therefore demonstrate the applicability of the Hume-Rothery rules to phase stability of solid solutions even in compositionally complex ceramics.

БАЗА ЗНАНЬ ІНТЕЛЕКТУАЛЬНОЇ ІНФОРМАЦІЙНОЇ СИСТЕМИ ПРОГНОЗУВАННЯ ФАЗОВОЇ СТАБІЛЬНОСТІ ТВЕРДИХ РОЗЧИНІВ

This research work is devoted to the development of a knowledge base for solving the current problem of forecasting the phase stability of solid solutions. Knowledge bases mean a set of facts and inference rules that allow logical conclusion and purposeful processing of information. The most important property of information stored in knowledge bases is the reliability of specific and generalized information in the database and the relevance of the original information obtained using the rules of inference embedded in the knowledge base. The best knowledge bases include the most relevant, reliable and fresh information, have perfect information search systems, a carefully thought-out structure and format of knowledge. The expert system embodies the methodology of adapting the algorithm of successful solutions from one sphere of scientific and practical activity to another. With the spread of computer technologies, it is an identical intelligent computer program that contains the knowledge and analytical abilities of one or more experts in some field of application and is able to draw logical conclusions based on this knowledge, thereby providing a solution to specific tasks. An intelligent information system (IIS) is one of the types of automated information systems, which is a complex of software, linguistic and logical-mathematical tools for the implementation of the main task, which usually consists of data interpretation and forecasting. Data interpretation is one of the traditional tasks for expert systems. Interpretation means the process of determining the content of data, the results of which must be agreed and correct. A multivariate analysis of the data is usually assumed, and the findings from this model form the basis for probabilistic estimates. Forecasting allows you to predict the consequences of some events or phenomena based on the analysis of available data. A parametric dynamic model is usually used in the forecasting system, in which parameter values are set for a given situation. As a result of the development, a knowledge base model was built for predicting the phase stability of solid solutions using a set of production rules, predicates, functions and operators.

ЗАСТОСУВАННЯ ІНТЕРПОЛЯЦІЇ КУБІЧНИМИ СПЛАЙНАМИ В ІНТЕЛЕКТУАЛЬНІЙ ІНФОРМАЦІЙНІЙ СИСТЕМІ ПРОГНОЗУВАННЯ ФАЗОВОЇ СТАБІЛЬНОСТІ ТВЕРДИХ РОЗЧИНІВ

This research work is devoted to the use of cubic spline interpolation to solve the current problem of predicting the phase stability of solid solutions. The theory of isomorphic substitutions in Urusov crystals was used to calculate the mixing energies (interaction parameters) and critical decomposition temperatures (stability temperatures) of solid solutions. The proposed intelligent information system (IIS) automates the construction of diagrams, which allows to predict the thermodynamic stability of solid solutions. IIS also provides interactive features for user convenience. The obtained results can be useful in choosing the ratio of components in "mixed" matrices, the amount of activator in luminescent, laser and other practically important materials, as well as in matrices for immobilization of toxic and radioactive waste. The results of the application of interpolation on large segments, ie with a relatively large number of nodes, are often unsatisfactory. On the one hand, at large distances between nodes the interpolation accuracy decreases, and on the other hand, with increasing number of nodes due to the influence of high-order polynomials there are oscillations of the interpolation curve, because only in this way the curve can be forced to pass through given points. This state does not correspond to the real dependence resulting from the tabular values of the nodes. Therefore, it is proposed to use spline interpolation, which has a number of important advantages. First, it is high convergence. In contrast to Lagrange interpolation polynomials, the sequence of cubic splines on a uniform grid of nodes always converges to a continuous interpolated function. Secondly, we have minimal sensitivity to the error of the original data. Small changes in the values of the function at one or more adjacent interpolation points do not significantly affect the behavior of the spline at some distance from these points. As a consequence of the above - higher interpolation accuracy. As a result of the research the calculation of unknown coefficients for the proposed splines is formalized and the advantages of practical application of the proposed interpolation method are determined. The IIS of phase stability of solid solutions was improved using interpolation by cubic splines, as a result, the accuracy of the results was increased by 4.96%.

Інтелектуальна інформаційна система прогнозування фазової стабільності твердих розчинів

Інтелектуальна інформаційна система прогнозування фазової стабільності твердих розчинів

Effect of multicomponent alloying with Ni, Mn and Mo on phase stability of bcc Fe-Cr alloys

Fe-Cr system attracts lot of attention in condensed matter physics due to its technological importance and extraordinary physics related to a non-trivial interplay between magnetic and chemical interactions. However, the effect of multicomponent alloying on the properties of Fe-Cr alloys are less studied. We have calculated the mixing enthalpy, magnetic moments, effective chemical, strain-induced and magnetic exchange interactions to investigate the alloying effect of Ni, Mn, Mo on the phase stability of the ferromagnetic bcc Fe−Cr system at zero K. We demonstrate that the alloying reduces the stability of Fe-Cr alloys and expands the region of spinodal decomposition. At the same time, the mixing enthalpy in ternary Fe100-≿-05Cr≿Ni05 alloys indicates a stability of solid solution phase up to 6 at. % Cr. In Fe100-≿-07Cr≿Ni05Mn01Mo01 alloys, we did not find any alloy composition that has negative enthalpy of formation. Analyzing magnetic and electronic properties of the alloys and investigating magnetic, chemical and strain-induced interactions in the studied systems, we provide physically transparent picture of the main factors leading to the destabilization of the Fe-Cr solid solutions by the multicomponent alloying with Ni, Mn, Mo.

P93] Microstructure and properties of Cu-Al-Fe high-temperature shape memory alloys

Fe-Cr system attracts lot of attention in condensed matter physics due to its technological importance and extraordinary physics related to a non-trivial interplay between magnetic and chemical interactions. However, the effect of multicomponent alloying on the properties of Fe-Cr alloys are less studied. We have calculated the mixing enthalpy, magnetic moments, effective chemical, strain-induced and magnetic exchange interactions to investigate the alloying effect of Ni, Mn, Mo on the phase stability of the ferromagnetic bcc Fe−Cr system at zero K. We demonstrate that the alloying reduces the stability of Fe-Cr alloys and expands the region of spinodal decomposition. At the same time, the mixing enthalpy in ternary Fe100-≿-05Cr≿Ni05 alloys indicates a stability of solid solution phase up to 6 at. % Cr. In Fe100-≿-07Cr≿Ni05Mn01Mo01 alloys, we did not find any alloy composition that has negative enthalpy of formation. Analyzing magnetic and electronic properties of the alloys and investigating magnetic, chemical and strain-induced interactions in the studied systems, we provide physically transparent picture of the main factors leading to the destabilization of the Fe-Cr solid solutions by the multicomponent alloying with Ni, Mn, Mo.

Thermodynamic Basis of Non-equilibrium Phase Transformations of bcc β-Phase in Ti–Mo System

This study reports the experimental identification of transformation products of high temperature bcc β phase in Ti–xMo (x = 1, 7, 15, 25 wt%) alloys and aims to understand the transformations by thermodynamic modelling. The high temperature bcc β phase had undergone martensitic transformation in Ti–1Mo and Ti–7Mo alloys, resulting in acicular martensitic structure within large β grains. X-ray diffraction (XRD) analysis confirmed the martensite to be hcp (α′) and orthorhombic (α″) in Ti–1Mo and Ti–7Mo alloys respectively. Combined analysis of XRD and transmission electron microscopy (TEM) suggested the formation of fine plates of α″, omega (ω) and bcc β phases in Ti-15 and Ti-25 Mo alloys. Calculation of enthalpy of formation supported the stability of solid solution phase over the amorphous phase in the entire concentration range of Mo.

Stability of Solid-Solution Phase and the Nature of Phase Separation in Ru–Zr–O Ternary Oxide

Equilibrium phase diagram of ruthenium–zirconium oxide (Ru–Zr–O) was calculated by a combination of ab initio density functional theory and thermodynamic calculations. The phase diagrams suggest that the solubility between ruthenium oxide and zirconium oxide is very low under normal experimental conditions, in good agreement with the prior reports in literature. Also provided is the theoretical support for the reported phenomenon that doping or amorphization of Ru–Zr–O might suppress phase separation of the oxide. To study the spinodal decomposition of Ru–Zr–O, we successfully prepared an amorphous Ru0.48Zr0.52O2 film of a solid solution phase by a thermal decomposition at a low temperature (563 K). In situ transmission electron microscopy was utilized to witness the spinodal decomposition of the amorphous Ru0.48Zr0.52O2 solid solution by electron–beam annealing. The present fundamental study of the phase behavior of Ru–Zr–O provides a guideline for the phase and microstructure design of Ru-based mixed ox...

Defect and phase stability of solid solutions of Mg2X with an antifluorite structure: An ab initio study

First principles calculations are done for Mg2X (X=Si, Ge or Sn) antifluorite compounds and their solid solutions in order to investigate their pseudo-binary phase diagram. The formation energies of the end-member compounds agree qualitatively with the experiments. For X=Si and Ge, there is a complete solubility, but we observe a miscibility gap in the pseudo-binary phase diagram Mg2Si–Mg2Sn. This agrees with the most recent experiments and phase diagram assessments. Calculated electronic properties of Mg2Si1−xSnx alloys qualitatively agree with experiments and in particular the energy bandgap decreases when Si is substituted by Sn. Supercell calculations are also done in order to determine the most stable defects and the doping induced by these defects in the three end-member compounds. We find that the intrinsic n-doping in pure Mg2Si can be attributed to the presence of magnesium atoms in interstitial positions. In Mg2Ge and Mg2Sn, since other defects are stable, they can be also of p-type.

Integrated design of Nb-based superalloys: Ab initio calculations, computational thermodynamics and kinetics, and experimental results

An optimal integration of modern computational tools and efficient experimentation is presented for the accelerated design of Nb-based superalloys. Integrated within a systems engineering framework, we have used ab initio methods along with alloy theory tools to predict phase stability of solid solutions and intermetallics to accelerate assessment of thermodynamic and kinetic databases enabling comprehensive predictive design of multicomponent multiphase microstructures as dynamic systems. Such an approach is also applicable for the accelerated design and development of other high performance materials. Based on established principles underlying Ni-based superalloys, the central microstructural concept is a precipitation strengthened system in which coherent cubic aluminide phase(s) provide both creep strengthening and a source of Al for Al 2O 3 passivation enabled by a Nb-based alloy matrix with required ductile-to-brittle transition temperature, atomic transport kinetics and oxygen solubility behaviors. Ultrasoft and PAW pseudopotentials, as implemented in VASP, are used to calculate total energy, density of states and bonding charge densities of aluminides with B2 and L2 1 structures relevant to this research. Characterization of prototype alloys by transmission and analytical electron microscopy demonstrates the precipitation of B2 or L2 1 aluminide in a (Nb) matrix. Employing Thermo-Calc and DICTRA software systems, thermodynamic and kinetic databases are developed for substitutional alloying elements and interstitial oxygen to enhance the diffusivity ratio of Al to O for promotion of Al 2O 3 passivation. However, the oxidation study of a Nb–Hf–Al alloy, with enhanced solubility of Al in (Nb) than in binary Nb–Al alloys, at 1300 °C shows the presence of a mixed oxide layer of NbAlO 4 and HfO 2 exhibiting parabolic growth.