Mechanisms of Ytterbium Monosilicate/Mullite/Silicon Coating Failure During Thermal Cycling in Water Vapor
Mechanisms of Ytterbium Monosilicate/Mullite/Silicon Coating Failure During Thermal Cycling in Water Vapor
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DOI：
10.1111/jace.13792
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发表时间：
2015-12-01
影响因子：
3.9
通讯作者：
Wadley, Haydn N. G.
中科院分区：
文献类型：
--
作者：
Richards, Bradley T.;Begley, Matthew R.;Wadley, Haydn N. G.
采用空气等离子喷涂工艺在SiC试样上制备了Yb_2SiO_5/Al_6Si_2O_13/Si三层环境屏障涂层。的组件层的热膨胀的显着差异导致在周期性间隔泥裂纹的Yb 2SiO 5和Al 6Si 2 O 13层。当在以4.4cm/s流动的90%H2O/10%O-2环境中在1316 ℃和110 ℃之间进行热循环时，发现发生部分分层，其中断裂面位于Al 6Si 2 O 13-Si界面处的热生长氧化物（TGO）内。在试样边缘处开始分层，其中气体环境优先氧化暴露的Si粘合涂层以形成β-方石英。同时进入的气体环境，通过泥浆裂缝开始局部形成β-方石英（SiO2），其厚度是最大的直接下方泥浆裂缝。在冷却时，方石英从β转变为具有大的、受约束的体积收缩的相，这导致TGO的严重微破裂。持续的热循环最终扩展了分层裂纹并导致涂层的部分剥落。方石英TGO的形成似乎是利用Si粘结涂层的保护涂层系统中的分层寿命决定因素。
An air plasma spray process has been used to apply a model tri-layer Yb2SiO5/Al6Si2O13/Si environmental barrier coating system on SiC test coupons. Significant differences in the thermal expansion of the component layers resulted in periodically spaced mud cracks in the Yb2SiO5 and Al6Si2O13 layers. Upon thermal cycling between 1316 degrees C and 110 degrees C in a 90% H2O/10% O-2 environment flowing at 4.4 cm/s, it was found that partial delamination occurred with the fracture plane located within a thermally grown oxide (TGO) at the Al6Si2O13-Si interface. Delamination initiated at test coupon edges where the gaseous environment preferentially oxidized the exposed Si bond coat to form beta-cristobalite. Simultaneous ingress of the gaseous environment through mud cracks initiated local formation of beta-cristobalite (SiO2), the thickness of which was greatest directly below mud cracks. Upon cooling, cristobalite transformed from the beta to a phase with a large, constrained volume contraction that resulted in severe microfracture of the TGO. Continued thermal cycling eventually propagated delamination cracks and caused partial spallation of the coatings. Formation of the cristobalite TGO appears to be the delamination life-determining factor in protective coating systems utilizing a Si bond coat.