Abstract
In the present study, the influence of substitutional elements (Ti and Al) on the structural stability, mechanical properties, electronic properties and Debye temperature of Ta5Si3 with a D8m structure were investigated by first principle calculations. The Ta5Si3 alloyed with Ti and Al shows negative values of formation enthalpies, indicating that these compounds are energetically stable. Based on the values of formation enthalpies, Ti exhibits a preferential occupying the Ta4b site and Al has a strong site preference for the Si8h site. From the values of the bulk modulus (B), shear modulus (G) and Young’s modulus (E), we determined that both Ti and Al additions decrease both the shear deformation resistance and the elastic stiffness of D8m structured Ta5Si3. Using the shear modulus/bulk modulus ratio (G/B), Poisson’s ratio (υ) and Cauchy’s pressure, the effect of Ti and Al additions on the ductility of D8m-structured Ta5Si3 are explored. The results show that Ti and Al additions reduce the hardness, resulting in solid solution softening, but improve the ductility of D8m-structured Ta5Si3. The electronic calculations reveal that Ti and Al additions change hybridization between Ta-Si and Si-Si atoms for the binary D8m-structured Ta5Si3. The new Ta-Al bond is weaker than the Ta-Si covalent bonds, reducing the covalent property of bonding in D8m-structured Ta5Si3, while the new strong Ti4b-Ti4b anti-bonding enhances the metallic behavior of the binary D8m-structured Ta5Si3. The change in the nature of bonding can well explain the improved ductility of D8m-structured Ta5Si3 doped by Ti and Al. Moreover, the Debye temperatures, ΘD, of D8m-structured Ta5Si3 alloying with Ti and Al are decreased as compared to the binary Ta5Si3.
Highlights
In order to meet the ever-increasing demand for high performing and durable structural components to be used in harsh environments, much attention has been focused upon transition metal silicides [1,2]
The calculated results for the elastic constants show that doping with Ti simultaneously lowers the B, G, and E values of D8m -structuted
The change of the ductility of the D8m -structured Ta5 Si3 is explained according to the shear modulus/bulk modulus ratio (G/B), the Poisson’s ratio and the Cauchy’s pressure
Summary
In order to meet the ever-increasing demand for high performing and durable structural components to be used in harsh environments, much attention has been focused upon transition metal silicides [1,2]. As with many other intermetallic materials, owing to its strong covalent-dominated atomic bonds and intrinsic difficulties of dislocation movement, its low toughness poses a serious obstacle to its commercial application. To address this problem, several effective strategies have been developed, including densification [10,11], grain refinement [12], substitutional alloying [13], and the incorporation of a second reinforcing phase to form a composite [14]. Compared with additions of interstitial atoms, incorporation of substitutional atoms into Ta5 Si3 is more complex, and the site substitution of the added alloying elements in Ta5 Si3 plays an important role in influencing the electronic structure and the mechanical properties of the material. This, in turn, was used to gain insight into the effect of the two substitutional elements on the electronic structure and mechanical properties of D8m -structured Ta5 Si3
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