High temperature mechanical properties of polycrystalline Y2SiO5

Rafael Cabezas-Rodriguez,Desirée Ciria,Julián Martinez-Fernandez,Guilhem Dezanneau,Fabienne Karolak,Joaquín Ramirez-Rico

doi:10.1016/j.bsecv.2021.09.008

Abstract

The high temperature mechanical properties of polycrystalline Y2SiO5 were studied in compression at temperatures in the range of 1200–1400°C, both in constant strain rate and constant stress experiments. To examine the effect of grain size on the plastic deformation, two routes were used for the synthesis and sintering of Y2SiO5: one of solid state reaction followed by conventional sintering in air, and one of sol–gel synthesis followed by spark-plasma sintering, resulting in starting grain sizes of 2.2 and 0.9μm, respectively. Ceramics obtained by these routes exhibited different high-temperature compression behavior: while the conventionally processed ceramic exhibited grain growth during mechanical testing and a stress exponent close to one, compatible with diffusional creep, the spark-plasma sintered ceramic showed no grain growth but significant cavitation, a stress exponent close to two and partially superplastic behavior. These results have implications for the design and lifetime assessment of rare earth silicate-based environmental barrier coatings.

Highlights

Ceramic matrix composites (CMCs) and silicon-based ceramics are promising candidates for high temperature structural applications such as generation gas turbine engines since they exhibit low density, excellent high-temperature mechanical properties, and good thermomechanical stability [1,2]
Two processing routes for Y2SiO5 were used in this work with the aim of obtaining ceramics with different grain sizes: solid state reaction followed by conventional sintering and sol–gel synthesis followed by spark-plasma sintering (SPS)
The presence of Y2O3 in the conventionally sintered ceramic is probably due to the addition of LiYO2 as a sintering aid, which decomposes into Y2O3 and Li2O at high temperatures, and due to incomplete reaction of Y2O3 and SiO2

Summary

Introduction

Ceramic matrix composites (CMCs) and silicon-based ceramics (such as Si3N4, SiC) are promising candidates for high temperature structural applications such as generation gas turbine engines since they exhibit low density, excellent high-temperature mechanical properties, and good thermomechanical stability [1,2]. In presence of oxygen from dry air environments, silicon-based ceramics form a protective silica scale, responsible for their excellent high temperature oxidation resistance at these conditions [3]. This SiO2 layer is susceptible of attack by impurities such as alkali salts and is unstable in the presence of water vapor, resulting in rapid ceramic recession. Yttrium silicates (e.g., yttrium orthosilicate, Y2SiO5) are promising materials for improving oxidation and erosion protection since they exhibit a high melting point, low volatilization rate, low thermal expansion coefficient, and low oxygen permeation constant [15,16]. The preparation of single-phase fully dense Y2SiO5 bulk material by these methods presents several problems [20,21,22] such as presence of secondary undesired phases, significant porosity in bulk samples, etc

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