Mechanical and thermal properties of Yb 2 SiO 5 : First-principles calculations and chemical bond theory investigations
- PDF / 477,802 Bytes
- 11 Pages / 584.957 x 782.986 pts Page_size
- 98 Downloads / 213 Views
Ytterbium monosilicate (Yb2SiO5) is a promising candidate for environmental barrier coating. However, its mechanical and thermal properties are not well understood. In this work, the structural, mechanical, and thermal properties of Yb2SiO5 are studied by combining density functional theory and chemical bond theory calculations. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature and distortion of the structure are revealed. Meanwhile, the full set of elastic constants, polycrystalline mechanical properties, and elastic anisotropy of Yb2SiO5 are presented. In addition, the minimum thermal conductivity of Yb2SiO5 was determined to be 0.74 W m1 K1. The theoretical results highlight the potential application of Yb2SiO5 in a thermal and environmental barrier coating.
I. INTRODUCTION
Silicon-based nonoxide structure ceramics, such as Si3N4, SiC, and SiC-matrix composites, have great potential applications in gas turbine engines owing to their superior high-temperature mechanical properties, such as strength and creep resistance.1 However, a major stumbling block in realizing Si-based ceramic turbine hot section components is the recession of these materials in combustion environments because of the volatilization of silica scale by water vapor.2,3 This recession of Si-based ceramics can be prevented by an environmental barrier coating (EBC).4 EBCs are designed to protect Si-based ceramics from corrosion due to water vapor in combustion environments. Therefore, integrity of coatings during the whole duration of service at elevated temperatures is essential. In combustion conditions, flaws caused by collision of foreign particles are unavoidable and the thermal stress arose from mismatched thermal expansion coefficient (TEC) may result in spall and cracking.5 Thus, the durability of EBCs depends on the tolerance of the coatings to the external mechanical damages, which is closely related to their mechanical properties. Moreover, the thermal stress in the substrate is proportional to Young’s modulus and TEC of the given coating material.6 To minimize the thermal stress that may lead to undesirable failure and/or creep of the substrate, materials that have the similar TEC with the counterpart substrate and a low Young’s modulus are desirable.6 a)
Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/jmr.2014.201 J. Mater. Res., Vol. 29, No. 15, Aug 14, 2014
http://journals.cambridge.org
Downloaded: 02 Dec 2014
Recent experiments found that rare-earth silicates are promising candidates of EBC materials owing to their superior high-temperature stability, long durability in water vapor, and excellent chemical and mechanical compatibility with silicon-based matrix.4,7,8 Among all the studied compounds, ytterbium monosilicate (Yb2SiO5) attracted specific attention since no high-temperature polymorphs have been found for Yb2SiO5.9 Volatility tests in combustion environments have proved that Yb2SiO5 is nearly inert to the corrosion attack and show
Data Loading...
