First-principles study on the mechanical and thermodynamic properties of MoNbTaTiW
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First-principles study on the mechanical and thermodynamic properties of MoNbTaTiW Uttam Bhandari 1), Congyan Zhang 1), Shengmin Guo 2), and Shizhong Yang 1) 1) Department of Computer Science, Southern University and Agricultural & Mechanical College, Baton Rouge, Louisiana 70813, USA 2) Department of Mechanical and Industrial Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, USA (Received: 5 January 2020; revised: 18 April 2020; accepted: 21 April 2020)
Abstract: Refractory high-entropy alloys (RHEAs) are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K. In this study, the mechanical properties of MoNbTaTiW RHEA are examined by applying calculations based on first-principles density functional theory (DFT) and using a large unit cell with 100 randomized atoms. The phase calculation of MoNbTaTiW with CALPHAD method shows the existence of a stable body-centered cubic structure at a high temperature and a hexagonal closely packed phase at a low temperature. The predicted phase, shear modulus, Young’s modulus, Poisson’s ratio, and hardness values are consistent with available experimental results. The linear thermal expansion coefficient, vibrational entropy, and vibrational heat capacity of MoNbTaTiW RHEA are investigated in accordance with Debye–Grüneisen theory. These results may provide a basis for future research related to the application of RHEAs. Keywords: high-entropy alloy; MoNbTaTiW; mechanical properties; thermodynamic properties; density functional theory
1. Introduction Since the invention of the first high-entropy alloy (HEA) by Yeh et al. [1] in 2004, HEAs have attracted strong interest from both theoretical and experimental scientists. HEAs are metallic alloys made by mixing more than five elements with different contents of each element ranging from 5% to 35%, based on their molar ratios. HEAs are quite different from traditional one-metal element-based alloys. This new alloy design approach can be used to create novel metallic materials with unique properties. For many challenging industrial applications, high strength and good ductility are essential to the mechanical performance of novel HEAs. Refractory high-entropy alloys (RHEAs) constitute a group of HEAs that incorporate refractory elements, such as Mo, Nb, Ta, Ti, V, W, Re, Zr, and Hf, in constitutional compositions. The fundamental features of RHEAs include an increased temperature strength, reduced density, high melting point, high yield strength, high ductility, and high strain hardening effect [2–5]. Studies on MoNbTaTiW RHEA have been conducted since the discovery of MoNbTaW RHEA. At room temperature, MoNbTaW is very brittle [6]. To increase the strength of MoNbTaW and make it applicable at room
temperature, Han et al. [7] added Ti and experimentally studied the properties of MoNbTaTiW RHEA. They reported that the addition of Ti increases the yield st
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