Microstructure evolution and thermomechanical properties of plasma‐sprayed Yb₂SiO₅ coating during thermal aging

Abstract

Rare‐earth monosilicates (RE2SiO5, RE: rare‐earth elements), such as Yb2SiO5, have been developed for potential application as environmental barrier coating (EBC) materials. Yb2SiO5 coating would experience microstructure evolution under high‐temperature environment and accordingly its thermomechanical properties would be altered. In this study, Yb2SiO5 coating was fabricated by atmospheric plasma spray technique. The phase stability and microstructure change before and after thermal aging at 1300°C, 1400°C, and 1500°C were investigated. The changes in mechanical and thermal properties were characterized. The results showed that the as‐sprayed coating was mainly composed of Yb2SiO5 with a small amount of Yb2O3 and amorphous phase. Defects in the coating, including interfaces, pores, and microcracks, were greatly reduced with grain growth after thermal treatment. Thermal aging significantly modified the thermal and mechanical properties of the coating. The average CTE was increased by 13.1%, and the hardness and elastic modulus was increased by 42.4% and 49.4%, respectively, after thermal aging at 1500°C for 50 hour. The thermal conductivity of thermal‐aged coating was much higher than that of the as‐sprayed coating, which was still less than 2 W/(m·K). The influence of coating microstructure on the properties was analyzed and related to the failure mechanism of EBCs.

Thermal shock resistance of tri‐layer Yb2SiO5/Yb2Si2O7/Si coating for SiC and SiC‐matrix composites

“…Yb 2 SiO 5 and Yb 2 Si 2 O 7 powders were synthesized by solid‐state reaction method using Yb 2 O 3 and SiO 2 powders. Details of powder synthesis can be found in our previous work . The substrates commonly have appreciable influence on the thermal shock behaviors of the coating systems.…”

A comprehensive sintering mechanism for thermal barrier coatings‐Part III: Substrate constraint effect on healing of 2D pores

“…It is worth noting that the 2D pore network, instead of porosity, dominantly determines the thermal and mechanical properties of plasma‐sprayed ceramic coatings. This can be responsible for the fact that the porosity is about 10%‐15%, whereas the properties of PS ceramic coatings are <50% with respect to those of bulk materials …”

“…During thermal exposure, the thermal conductivity and elastic modulus would increase significantly, which leads to undesirable performance degradation of the TBCs. The apparent porosity seems relatively unaffected during thermal exposure .…”

Corrosion Behavior and Mechanism of Aluminum-rich CMAS on Rare-earth Silicate Environmental Barrier Coatings:

“…稀土硅酸盐的 CMAS 腐蚀行为还受到腐蚀环境 (CMAS 成分、温度和时间等)的影响。Tian 等 [18] 发现 Y2Si2O7 和 Yb2Si2O7 在 1300℃下与 CMAS 反应 生成磷灰石， 而 Lu2Si2O7 溶于 CMAS 熔体不生成磷 灰石； 1500 ℃下三种 RE2Si2O7 材料都溶解于 CMAS 熔体，同时 CMAS 沿晶界渗透导致裂纹的产生。本 研究团队 [19] [20] 研 究 了 不同组 分的 CMAS(Ca/Si = 0.635、0.478 和 0.096)对 RE2Si2O7(RE = Er、Dy、 Gd 和 Nd)块体腐蚀行为的影响，发现 CaO 含量的 增加会使腐蚀过程中生成磷灰石相。Summers 等 [21] 分别研究了 Y2Si2O7 块体在 1300 ℃与 1400 ℃以及 不同 CMAS 组分环境下的腐蚀行为，结果表明温度 主要促进反应的发生，而耐蚀性能则主要受 CMAS 组成的影响。 当飞机在不同地区服役时，硅酸盐物质沉积具 有随机性，使得 CMAS 的组分有所不同，其腐蚀行 为也有所区别。当飞机在多粉尘地带比如火山附近 服役时，在高温下其发动机主要受到空气中大量粉 尘的腐蚀。Levi 等 [22] 指出粉尘在高温下熔融形成的 CMAS 中 Al2O3 的含量较高，但目前针对高 Al2O3 含量的 CMAS 对稀土硅酸盐涂层的腐蚀行为研究 报道较少，机制尚不明确。为了探索该种 CMAS 对 稀土硅酸盐腐蚀行为的影响，本研究结合前期工作 [17] ，在不改变 Ca/Si 比(0.74)的情况下，制备了 [17] 。采用马弗炉进行热腐蚀实验， 将涂覆 CMAS 粉末的涂层样品加热至 1400 °C，分 [23][24] 。与粉体相比，三种喷 涂态涂层中不仅存在 RE2SiO5 相，还发现了对应的 RE2O3 相和非晶相。RE2O3 相是由喷涂过程中稀土 硅酸盐分解而形成，非晶相则是由粉体在等离子火 焰中熔化，然后迅速冷却导致部分晶粒未能成核和 生长而形成的 [25] 。前期研究表明，X1-Gd2SiO5、 X2-Y2SiO5 与 X2-Er2SiO5 涂层中非晶相含量分别为 56%、35%和 48%；稀土氧化物第二相含量分别为 14.58%、9.44%和 15.96% [17]…”