Calculation of Existence Domains and Optimized Phase Diagram for the Nb-Ti Binary Alloy System Using Computational Metho
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Calculation of Existence Domains and Optimized Phase Diagram for the Nb-Ti Binary Alloy System Using Computational Methods Abhishek Kumar Thakur1
•
Vivek Kumar Pandey1 • Vikas Jindal1
Submitted: 2 March 2020 / in revised form: 22 September 2020 / Accepted: 12 October 2020 ASM International 2020
Abstract We present the thermodynamic modeling for the Nb-Ti binary alloy system using CALPHAD (CALculation of PHAse diagram) and CE-CVM (Cluster expansioncluster variation method) focusing on the solid solution part of the system. Existence domains for the various invariant reactions between the interaction parameters of the system were calculated between BCC and HCP phases. Five different regions viz. Simple Isomorphous, Monotectoid, Simple Isomorphous with congruent maxima, Monotectoid with congruent maxima and Syntectoid were identified in the calculated existence domains, each of which has its own characteristic reactional topology. The calculated existence domains are in good agreement with the earlier thermodynamic assessments made on the Nb-Ti system. Further, we have used the first-principles calculation to generate the thermochemical data for BCC and HCP phases for the Nb-Ti system. Moreover, we have also calculated the optimized phase diagram using the calculated existence domains, earlier experimental data, and the generated thermochemical data for the Nb-Ti system. Keywords CALPHAD CE-CVM invariant reactions phase diagram thermochemical data
& Abhishek Kumar Thakur [email protected] 1
Department of Metallurgical Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India
1 Introduction Phase diagrams are extremely important in materials design and development. A clear understanding of alloy phase stability under various service conditions is fundamental and paramount importance in the efficient design and economic development of materials. These diagrams graphically represent the phase fields or the region of thermodynamic stability of various phases present in materials system under equilibrium conditions as functions of thermodynamic state variables such as composition and temperature or composition and pressure. The experimental determination of phase diagrams of the multicomponent system is laborious and expensive, since the number of experiments to be carried out increases enormously with the number of components in the alloy system. The theoretical calculations can effectively minimize the effort required for determining the phase diagrams of such systems. The knowledge of phase stability and thermodynamics of constituent subsystems can be extrapolated to determine a preliminary phase diagram of the multicomponent system of interest. This predicted phase diagram could further be used to identify the critical regimes of composition and temperature where various information can be obtained with minimal experimental effort. Recently titanium and its alloys have attracted a large number of researchers because of its excellent biocompatible propertie
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