Numerical simulation of TBCs residual stresses by the growth of TGO on typical interface morphology

The effect of TGO ( thermally grown oxide) growth based on typical interface morphology on residual stresses distribution in thermal barrier coatings was analyzed by ABAQUS software. TGO oxidation kine...     

热障涂层中NiPtAl与MCrAlY粘结层表面氧化铝的生长差异研究

研究NiPtAl和MCrAlY作为粘结层的EB-PVD热障涂层不同温度循环氧化寿命差异,从涂层高温氧化角度理解氧化铝的生长差异对上述涂层不同寿命的影响原因。发现2种Pt浓度的NiPtAl涂层具有相似的氧化行为和涂层寿命,同时NiPtAl比MCrAlY作为粘结层的热障涂层表现出明显较长的循环氧化寿命。NiPtAl比MCrAlY具有较低的氧化铝生长速率和较大的临界失效厚度。NiPtAl氧化铝呈明显的等轴和柱状晶粒分布,涂层中的Pt和氧化铝晶界中Hf偏析物是影响氧化铝生长速率的重要因素。进一步证明铂能够提高氧化铝的粘结性能和热障涂层寿命,从而抵消铂的高成本进而促进NiPtAl涂层在涡轮机中的进一步广泛应用。     

Analytical electron microscopy of the mixed zone in NiCoCrAlY-based EB-PVD thermal barrier coatings: as-coated condition versus late stages of TBC lifetime

Abstract

The microstructural evolution of the alumina-zirconia mixed zone in a NiCoCrAlY-based electron beam physical vapor deposited (EB-PVD) yttria partially stabilized zirconia (Y-PSZ) thermal barrier coating (TBC) system from the as-coated condition into the advanced stages of TBC lifetime is monitored by analytical transmission electron microscopy (TEM). In the as-coated condition yttria-rich islands at the thermally-grown oxide (TGO)/TBC interface locally impede zirconia uptake of the scale during TBC deposition and give rise to the formation of an “off-plane” alumina-zirconia mixed zone textured perpendicular to the TGO/TBC interface. During prolonged isothermal/cyclic oxidation an increased chromium diffusion through the TGO scale turns the mixed zone into a reaction zone introducing a morphological instability of the mixed zone/TBC interface due to solutioning of the bottom TBC layer.

This microstructural pattern is corroborated by a triple-stage growth model for the mixed zone during three successive stages in TBC lifetime: (i) during TBC deposition, the thickness of the mixed zone increases due to predominant outward aluminum diffusion and uptake of zirconia. No columnar alumina zone (CAZ) has formed at this stage, (ii) upon completion of the transition alumina-to-corundum phase transformation the thickness of the mixed zone remains constant while the change in diffusion mechanism for an inward oxygen diffusion process now initiates parabolic growth of the columnar alumina sublayer of the TGO scale, (iii) in the late stage of TBC lifetime an marked outward chromium diffusion from the bond coat causes the mixed zone to resume growth due to TBC destabilization and the formation of a (Al, Cr)₂O₃ mixed oxide matrix phase.

A transient YCrO₃ phase is proposed for driving the destabilization of yttria-rich sections of the bottom TBC layer.     

新疆东天山地区C级GPS网的布设和精度分析

介绍东天山地区C级GPS网的布设方案、观测方法和数据处理过程;对该网中不同结点构网的异步环闭合差精度进行了对比分析,对该网高程拟合的方法、过程、结果进行介绍。     

热震中7YSZ热障涂层结构演变

采用低温超音速等离子喷涂(LT-HVOF)在镍基高温合金基体上制备了NiCoCrAlYTa粘结层, 使用大气等离子喷涂(APS)在粘结层上`制备了7wt%Y₂O₃-ZrO₂ (7YSZ) 陶瓷层。基于动态试验即热震实验研究了粘结层的扩散氧化机制, 探讨了陶瓷层的烧结及相变过程并观察了涂层的结构演变。实验结果表明: 动态热循环下随着热震次数的增加, 粘结层组元扩散氧化形成热生长氧化物(TGO)且厚度逐渐增加。此外, 粘结层组元在温度梯度下沿陶瓷层内部裂纹向高温区扩散, 最终在陶瓷层表面裂纹区域出现大量的金属氧化物, 同时粘结层组元的扩散有助于陶瓷层的烧结, 导致其显微硬度逐渐增大, 而粘结层由于Kirkendall效应, 其内部出现大量的孔洞导致其显微硬度逐渐降低。另外, 陶瓷层在相变及热循环应力的作用下表面出现了大尺度的宏观裂纹。     

EB-PVD 热障涂层TGO中氧化物混合区的形成及其影响

研究了电子束物理气相沉积热障涂层在1150～30℃之间的循环氧化行为;分析了TGO中YSZ-Al2O3混合区的形成过程及其对TGO的生长与TBCs失效的影响.TGO的向外生长和TBC沉积时形成的YSZ细晶区是形成YSZ-Al2O3混合区的两个重要条件.YSZ-Al2O3混合区对TBCs失效的影响表现在加速TGO的生长和裂纹易在该混合区形成两方面.     

天宝TGO GPS高程拟合方法初探

指出在GPS测量中高程拟合的计算方法是一个关键环节,根据天宝TGO GPS高程拟合方法的特性,通过多次实例检验,用三种方法进行了解算,验证了TGO处理高程的精度是可靠的,达到了天宝TGO GPS高程拟合方法的效果。     

VB.NET编程解决因时间过期TGO基线不解算的研究

较详细的论述了通过VB.NET编程修改RINEX文件中GPS记录的时间和记录的周数的方法和过程,达到TGO识别RINEX文件,进行基线解算的目的,本方法科学先进,可很好的节约资源投入,值得推广。     

TGO growth behaviour in TBCs with APS and HVOF bond coats

The growth of thermally grown oxide (TGO) layers and their influence on crack formation were studied for two thermal barrier coating (TBC) systems with CoNiCrAlY bond coats produced by (i) air plasma spray (APS) and (ii) high-velocity oxy-fuel (HVOF) techniques. All samples received a vacuum heat treatment and were subsequently subjected to thermal cycling in air. The TGOs were predominantly comprised of layered alumina, along with some oxide clusters of chromia, spinel and nickel oxide. However, after extended oxidation, the alumina layer formed in the APS-CoNiCrAlY bond coat transformed to chromia/spinel, while that formed in the HVOF-CoNiCrAlY bond coat remained stable. TGO thickening in the APS-CoNiCrAlY bond coat generally exhibited a three-stage growth behavior, which resembles a high temperature creep curve, whereas growth of the alumina layer in the HVOF-CoNiCrAlY bond coat showed an extended steady-state stage. Crack propagation in these two TBCs was found to be related to the growth and coalescence of oxide-induced cracking, connecting with pre-existing discontinuities in the topcoat. Hence, crack propagation during thermal cycling appeared to be controlled by TGO growth.     

Damage mechanisms and lifetime behavior of plasma-sprayed thermal barrier coating systems for gas turbines — Part II: Modeling

A phenomenological lifetime prediction tool for plasma-sprayed ZrO₂ based thermal barrier coating systems with MCrAlY bondcoat is presented. The analytical model uses a two step approach for calculating the development of delamination cracks: The initial crack growth is considered to be proportional to the thickness of the thermally grown oxide (TGO) scale on the bondcoat. After exceeding a critical TGO thickness, crack propagation is governed by linear elastic fracture mechanics taking into account stresses induced by thermal mismatch and by TGO growth. Validation using experimental data from thermal cycling tests with high temperature dwell times from few seconds up to 96 h gave evidence of the good predictive quality of the model.