An understanding of high entropy alloys from phase diagram calculations

The concept of High Entropy Alloy (HEA) is understood from the point of view of phase diagram calculation. The role of entropy of mixing on the phase stability is discussed for both ideal and non-ideal solid solution phases. The relative stability of a solid solution phase and line compounds is illustrated using hypothetical systems. Calculated binary and multicomponent phase diagrams are used to explain the phenomena observed experimentally for HEAs. The potential of using the CALPHAD (CALculation of PHAse Diagrams) approach in aiding the design of alloys with multiple key components is also discussed.     

Multicomponent multisublattice alloys,nonconfigurational entropy and other additions to the Alloy Theoretic Automated Toolkit

A number of new functionalities have been added to the Alloy Theoretic Automated Toolkit (ATAT) since it was last reviewed in this journal in 2002. ATAT can now handle multicomponent multisublattice alloy systems, nonconfigurational sources of entropy (e.g. vibrational and electronic entropy), Special Quasirandom Structures (SQS) generation, tensorial cluster expansion construction and includes interfaces for multiple atomistic or ab initio codes. This paper presents an overview of these features geared towards the practical use of the code. The extensions to the cluster expansion formalism needed to cover multicomponent multisublattice alloys are also formally demonstrated.     

Experimental investigation and thermodynamic calculation of Ti-Hf-Mn system

The phase relationship of Ti-Hf-Mn system was studied by diffusion triple and equilibrated alloy methods. The isothermal sections at 1373, 1273 and 1173 K for this system were constructed by means of electron probe microanalysis (EPMA) and X-ray diffraction (XRD) for the first time. No ternary phase was found in the system at all these temperatures. Six, seven and seven three-phase equilibria regions have been determined at 1373, 1273 and 1174 K, respectively. In this ternary system, the intermetallic compounds TiMn₂, HfMn₂ and HfMn exhibit wide solid solution range at those three temperatures. In particular, the solution range of Ti in HfMn phase decreases with the increase of temperature, from 30.5 at% at 1173 K to 26.5 at% at 1373 K. Based on all available experimental data, the Ti-Hf-Mn system was evaluated using the CALPHAD method. The calculation results are in excellent agreement with the experimental data.     

Alloy composition and process design based on thermodynamic and kinetic simulation: The case of medium Mn steel

This paper presents a design method for alloy materials that can be applied to medium Mn steel containing Al and/or Si. By using thermodynamic calculations based on CALPHAD, a wide range of alloy composition spaces were systematically studied, and the relationship between retained austenite fraction and its stability with intercritical annealing temperature was investigated. Alloys that meet the Process Window (PW) were screened and their various characteristics of alloy elements within the process window were determined. Additionally, the study performs three different kinetic simulations of austenite growth and solute partitioning during isothermal annealing on alloys that meet PW. The prediction of the model is verified by comparing with the experimental data in the literature. The results show that the remote model is more suitable for the actual production of low temperature isothermal intercritical annealing. Therefore, the method provided in this work makes a guiding contribution to alloy development, which can determine the alloy composition and heat treatment process satisfying PW and optimize the overall properties.     

Experimental reinvestigation and thermodynamic description of Bi-Te binary system

The Bi-Te phase diagram was determined by equilibrium alloy method, combined with electron probe microanalysis (EPMA), X-ray diffraction (XRD) and thermal analysis (DSC). The experimental result shows that there is a β-phase with a large composition range at low temperature, while Bi₂Te and Bi₄Te₃ are relatively stable in the solid-liquid region. A consistent phase diagram that covers the experimental findings has been achieved. Based on the new experimental phase diagram, coupling with the reported thermodynamic data, the thermodynamic optimization of the Bi-Te binary system was carried out with the help of CALPHAD approach. A group of reasonable thermodynamic parameters was obtained.     

CALPHAD-based alloy design for advanced automotive steels - Part I: Development of bearing steels with enhanced strength and optimized microstructure

Alloy design is of prime importance for automotive steels to achieve desired properties, such as strength, hardenability and wear resistance. In the present study, CALPHAD-based computational techniques have been successfully utilized to develop advanced steels for automotive applications. The first part of this series describes an integrated computational approach for the compositional modification of bearing steels. A conventional 100CrMn6 bearing steel has been precisely redesigned to achieve strength enhancement with optimized cementite size distribution. The strength of the modified bearing steel was further improved by the addition of 0.2 wt% V using fine vanadium carbide precipitates. Experimental verification of the calculated results confirmed the reliability of the computational method employed in this study.     

Calculation of phase equilibria for an alloy nanoparticle in contact with a solid nanowire

Phase equilibria in a system constituted of an alloy nanoparticle in contact with a solid nanowire have been modelled based on the minimization of a Gibbs free energy function. The Gibbs free energy consists of a bulk, surface and interface contribution. The bulk contribution is taken from CALPHAD thermodynamic databases and the surface properties from the literature. The effect of particle size and surface and interfacial properties on the liquidus line of the Au-Ge and In-Si systems has been studied. The results are compared to the bulk phase diagram and phase equilibria calculated for nano-systems with different geometries.     

Thermodynamic modeling of the Cu-Fe-Cr and Cu-Fe-Mn systems

All the thermodynamic and phase diagram information available in the literature on the Cu-Cr system, Cu-Fe-Cr system, and Cu-Fe-Mn system were critically evaluated and used in the thermodynamic optimization to obtain a set of consistent thermodynamic model parameters for the systems. The liquid solutions for the Cu-Cr, Cu-Mn, Fe-Cr, Cu-Fe-Cr, and Cu-Fe-Mn systems were described using the Modified Quasichemical Model (MQM) with pair approximation. The solid solution phases were modeled using the Bragg-Williams random mixing model. Accurate reproduction of all the reliable phase diagram and thermodynamic property data indicates the high reliability of the present thermodynamic optimizations.     

Modelling, design and characterization of Shape Memory Alloy-based Poly Phase motor

Design and characterization of SMA wire-based Poly Phase rotary motor has not been reported in literatures. The motor presented in this paper can be used either in stepping mode or in servo mode of operation. A method of designing a balanced Poly Phase motor based on SMA wire is proposed in this paper. The motor uses SMA wire with a tension spring in series for each phase of the motor. The principle of operation of the Poly Phase motor is presented. The proposed motor has been characterized similar to a stepper motor. Various parameters of the motor have been defined. The motor can be actuated in either direction with different phase sequencing methods, which are presented in this work. The motor is modelled and simulated and the results of simulations and experiments are presented. Based on this principle a compact actuator can be realized. Generalization of the concept is done and motor up to 16 Phases are studied and the simulation results are discussed.     

PANDAT software with PanEngine, PanOptimizer and PanPrecipitation for multi-component phase diagram calculation and materials property simulation

The newly enhanced PANDAT, integrating PanEngine, PanOptimizer and PanPrecipitation, bridges thermodynamic calculation, property optimization, and kinetic simulation of multi-component systems based on CALPHAD (CALculation of PHAse Diagram) approach. This software package, in combination with thermodynamic/kinetic/thermo-physical databases, provides an integrated workspace for phase diagram calculation and materials property simulation of multi-component systems. The simulation results, which include thermodynamic, kinetic, thermo-physical properties, and microstructure related information, are critically needed in materials design, in the selection of parameters for fabrication steps such as heat treatment, prediction of performance, and failure analysis. In addition to the functionalities provided by PANDAT as a stand-alone program, its calculation/optimization engines (PanEngine, PanOptimizer and PanPrecipitation) are built as shared libraries and enable their integration with broader applications in the field of Materials Science and Engineering.     

Thermodynamic assessment of Cu–Eu and Cu–Yb system

The Cu–Eu and Cu–Yb binary systems have been assessed with CALPHAD method. Liquid, BCC and FCC phases are treated as substitutional solution phases, of which the excess Gibbs energies are modeled by Redlich–Kister polynomial functions. The binary intermetallic compounds are treated as stoichiometric phases. Thermodynamic parameters of various phases have been optimized and the calculated results are in agreement with experimental data.     

气流干燥器数学模型及分段设计计算方法

气流干燥器是化工生产中广泛应用的干燥装置。由于过程的复杂性,采用以往设计计算方法即整体平均法及试差法, 前者计算结果误差大,后者过于繁复。本文介绍一种利用气-固两相流动的有关理论及有关传热研究的试验结果,建立过程的数学模型,对气流干燥管进行分段、分区间逐次计算的方法,其计算结果与实际情况吻合较好,可以用于工程计算。     

Phase diagrams and mechanical properties of TiC-SiC solid solutions from first-principles

First-principles calculations were carried out in order to investigate the stability and properties of the random Ti_1-xSi_xC solid solutions (alloys) with both the B1 and B3 structures. Lattice parameter, total energy, formation energy, phonon spectra, and elastic properties were studied as functions of composition. The phase diagram, in particular, binodal and spinodal curves were calculated. It was established that at 0 K the B1 alloys are energetically favorable at 0 ≤ x < 0.5, while the B3 alloys are favorable at 0.5 ≤ x ≤ 1.0. It was found that the contribution to the Gibbs free energy coming from the lattice vibrations strongly reduces the critical temperature of stabilization of the solid solutions. Calculated elastic moduli, Debye temperature, and Vickers hardness do not point to any strength enhancement of the alloys compared to TiC and SiC. Analysis of the spatial distribution of the Young and shear moduli shows that the B3 alloys exhibit much more spatial anisotropy of the elastic moduli than the B1 alloys.     

The design and realization of CoViD: a system for collaborative virtual 3D design

Many important decisions in the design process are made during fairly early on, after designers have presented initial concepts. In many domains, these concepts are already realized as 3D digital models. Then, in a meeting, the stakeholders for the project get together and evaluate these potential solutions. Frequently, the participants in this meeting want to interactively modify the proposed 3D designs to explore the design space better. Today’s systems and tools do not support this, as computer systems typically support only a single user and computer-aided design tools require significant training. This paper presents the design of a new system to facilitate a collaborative 3D design process. First, we discuss a set of guidelines which have been introduced by others and that are relevant to collaborative 3D design systems. Then, we introduce the new system, which consists of two main parts. The first part is an easy-to-use conceptual 3D design tool that can be used productively even by naive users. The tool provides novel interaction techniques that support important properties of conceptual design. The user interface is non-obtrusive, easy-to-learn, and supports rapid creation and modification of 3D models. The second part is a novel infrastructure for collaborative work, which offers an interactive table and several large interactive displays in a semi-immersive setup. It is designed to support multiple users working together. This infrastructure also includes novel pointing devices that work both as a stylus and a remote pointing device. The combination of the (modified) design tool with the collaborative infrastructure forms a new platform for collaborative virtual 3D design. Then, we present an evaluation of the system against the guidelines for collaborative 3D design. Finally, we present results of a preliminary user study, which asked naive users to collaborate in a 3D design task on the new system.     

An integrated circuit design of a silicon neuron and its measurement results

A novel MOSFET-based silicon nerve membrane model and its measurement results are described in this paper. This model is designed based on a mathematical structure that is characterized by phase plane analysis and bifurcation theory. The circuit is fabricated through MOSIS TSMC 0.35 μm CMOS process. Measurement results demonstrate that our circuit shows fundamental abilities of excitable cells such as a) a resting state, b) an action potential, c) a threshold, and d) a refractoriness. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Participatory design in interactive media design education for the solution of unfamiliar design problems: a case study on a disabling environment and an emerging technology

This paper investigates the effectiveness of participatory design study in rendering the students' capability of producing innovative design solutions to problems with uncertainties with which the students have no prior experience. At the project, the students were given a case to work on augmented reality technology with which they had no previous experience and design a tactical interface for sailing boats, a field they had no competence in. While the students were asked to develop proposals for this design problem with which they were inexperienced, a two-stage study was conducted to enable them to produce ideas on the topic. This paper discusses the impacts of such a participatory method in terms of design education. At the end of our study, it was observed that the students were positively influenced by the process in which they worked collaboratively with an expert user group.