Insight into the influence of alloying elements on mechanical and thermodynamic properties of Nb 3 Si: A first-principle
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-based silicides are promising ultrahigh-temperature materials. However, the structural stability and mechanical properties of Nb-based silicides are markedly influenced by Nb3Si phase. Therefore, the improvement of the stability and mechanical properties of Nb3Si is a great challenge. To solve these key problems, in this work, we apply the first-principles calculations to investigate the influence of transition metals (TM 5 Mo, Re, Ta, W, Pt, and Ir) on the structural stability, mechanical, and thermodynamic properties of Nb3Si. Two possible doped sites: Nb site and Si site are considered. We find that these alloying elements not only can stabilize the Nb3Si phase but also effectively improve the mechanical properties of Nb3Si. The calculated electronic structure shows that high elastic modulus is attributed to the formation of the TM–Si bond. Importantly, these alloying elements improve the heat capacity of Nb3Si due to the vibration of TM atoms under high temperature. Therefore, our calculated results predict that alloying elements of Re and Ir are beneficial for improving the overall performances of Nb3Si.
I. INTRODUCTION
With the development of astronautic and aeronautic industries, the applications of current high-temperature materials require that not only to satisfy the high temperature strength and good ductility but also ensure excellent thermal stability and oxidation resistance under high-temperature environments.1–6 Therefore, how to improve the overall performance of high-temperature materials is a big challenge for their applications. Among all the high-temperature materials, Nb-based silicides are promising candidates due to the high melting point, high temperature strength, high elastic stiffness, low cost, low density, and excellent oxidation resistance etc.7–13 In particular, Nbss/Nb5Si3 silicides have drawn great attention because Nb solid solutions (Nbss) can provide excellent ductility and room-temperature toughness, while for Nb5Si3, it offers an enough high-temperature strength.14–17 However, the application of Nbss/Nb5Si3 silicides is hindered by the Nb3Si phase. Earlier works have shown that the mechanical properties and thermal stability of Nbss/Nb5Si3 silicides mainly depend on the Nb5Si3 and Nb3Si.18,19 That is to say, the mechanical properties of Nbss/Nb5Si3 silicides are markedly influenced by Nb3Si. However, the utility of Nb3Si is limited by some intrinsic shortcomings: low strength and the worse stability. Although Nb3Si transforms to the Contributing Editor: Susan B. Sinnott Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.289
Nb5Si3 and Nb solid solution (Nbss) when temperature is up to 2038 K, it is again formed at 2193 K.15,20 Therefore, it is necessary to explore the solution strengthening mechanism to stabilize the Nb3Si phase. On the other hand, the high temperature strength of Nb3Si is much lower than that of Nb5Si3. The first-principles calculations have shown that the calculated bulk modulus and
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