Mechanical and electrochemical properties of Al alloyed D8m-Ta₅Si₃ nanocrystalline coatings
Date
2018
Authors
Xu, J.
Liu, W.
Xu, S.
Munroe, P.
Xie, Z.
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Journal article
Citation
Journal of Alloys and Compounds, 2018; 749:406-423
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Jiang Xu, Wei Liu, Song Xu, Paul Munroe, Zong-Han Xie
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Abstract
In this work, the structural stability, mechanical properties and electronic structure of β-Ta<inf>5</inf>Si<inf>3</inf> with different Al additions were first predicted by first-principles density functional calculations. The binary and ternary β-Ta<inf>5</inf>Si<inf>3</inf> are thermodynamically and mechanically stable, but their thermodynamic stability slightly decreases with Al additions. The elastic constants, bulk modulus (B), shear modulus (G) and Young's modulus (E) of Al-alloyed β-Ta<inf>5</inf>Si<inf>3</inf> were calculated. According to the criteria involving the bulk/shear modulus (B/G ratio) and Poisson's ratio, the D8<inf>m</inf>-structured ternary Ta<inf>5</inf>Si<inf>3</inf>, where two Si<sup>4a</sup> atoms are replaced by two Al atoms, shows improved ductility. Based on the theoretical analysis, the β-Ta<inf>5</inf>(Si<inf>0.83</inf>Al<inf>0.17</inf>)<inf>3</inf> nanocrystalline coating was deposited onto polished Ti-6Al-4V alloy substrates by double cathode glow discharge plasma method. The phase constitution, microstructure and composition of the coating were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The as-deposited coating was composed of nearly rounded D8<inf>m</inf>-β-Ta<inf>5</inf>Si<inf>3</inf> grains with an average size of ∼4 nm and exhibited strong (002) and (400) preferred orientation. After Al alloying, the hardness and the compressive residual stress of the β-Ta<inf>5</inf>Si<inf>3</inf> decreased, and the contact damage resistance and adhesion strength increased. The electrochemical corrosion properties of the β-Ta<inf>5</inf>(Si<inf>0.83</inf>Al<inf>0.17</inf>)<inf>3</inf> nanocrystalline coating were compared to the binary β-Ta<inf>5</inf>Si<inf>3</inf> coating and Ti-6Al-4V in 3.5 wt% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. It was shown that the corrosion resistance of the β-Ta<inf>5</inf>Si<inf>3</inf> was improved through the substitution of Al for Si.
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Available online 15 March 2018
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© 2018 Elsevier B.V. All rights reserved.