热障涂层表面激光改性及其对涂层抗CMAS性能的影响

Laser Modification of Thermal Barrier Coating Surfaces and Its Effects on the CMAS Resistance of the Coating

摘要:

热障涂层是影响航空发动机涡轮叶片抗腐蚀性能的3大关键因素之一，其可大幅提高涡轮叶片的工作温度。目前，涡轮叶片最常使用的是Y₂O₃部分稳定ZrO₂（YSZ）热障涂层，但是该涂层抵抗环境沉积物（简称CMAS，其成分主要为CaO、MgO、Al₂O₃和SiO₂）腐蚀能力弱，在CMAS作用下涂层会发生相变、结构破坏及服役寿命大幅降低。为改善CMAS作用下YSZ热障涂层的相和结构稳定性，以及提高涂层的抗CMAS性能，采用脉冲Nd:YAG 激光系统对镍基高温合金基体的YSZ涂层进行表面改性，通过优化激光参数获得激光改性的热障涂层，并对其进行1 250 ℃×4 h的CMAS腐蚀试验。利用X射线衍射（XRD）、光学电镜（OM）、扫描电子显微镜（SEM）等，表征改性涂层的相组成、表面形貌、改性层微观结构、改性层/原始涂层的界面结合状态，同时分析改性涂层组织结构特征和抗CMAS腐蚀性能。结果表明，YSZ涂层表面经过激光改性后，形成了具有柱状晶结构的改性层，该层表面光滑且内部存在纵向裂纹，其厚度及与下方原始涂层的界面结合状况均受激光改性参数的影响。通过激光参数的优化，确定激光光束长度为80 mm、扫描速度为8 mm·s^-1，这有助于提高改性层/原始涂层的界面匹配性。CMAS腐蚀试验结果表明，激光改性涂层具有良好的相稳定性和结构稳定性。采用激光表面改性可提高热障涂层的抗CMAS腐蚀性能，但抗腐蚀性能提高的程度依赖于改性层的厚度和微观结构，特别是纵向裂纹的分布。

Abstract:

Thermal barrier coating is one of the three key technologies for aircraft engine turbine blades， which can significantly increase the operating temperature of turbine blades. Y₂O₃ partially stabilized ZrO₂ （YSZ） thermal barrier coating is the most widely used currently. However， it is vulnerable to corrosion by environmental deposits （mainly composed of CaO， MgO， Al₂O₃， and SiO₂， abbreviated as CMAS）. Under the action of CMAS， YSZ coating undergoes phase transformation and structural damage， leading to reducing its service life significantly. To improve the phase and structural stability of YSZ thermal barrier coatings under CMAS， and enhance their CMAS resistance， YSZ TBCs were prepared on the surface of a nickel based high-temperature alloy substrate， and their surfaces were modified using a pulsed Nd：YAG laser system. Laser parameters were optimized to obtain desirable laser modified TBC samples. The coating samples were subjected to CMAS corrosion tests under 1 250 ℃ for 4 h. X-ray diffraction （XRD）， optical electron microscopy （OM） and scanning electron microscopy （SEM） were used to characterize the phase composition， surface morphology， microstructure of the modified layer， and the interface between the modified layer and the original coating. The microstructure characteristics and CMAS resistance of the modified coating were analyzed. After laser modification， a modified layer with a columnar crystal structure was formed on the surface of the YSZ coating. The thickness of the modified layer and its bonding with the original coating were affected by the laser modification parameters. Through the optimization process， the optimal laser parameters were obtained with a beam length of 80 mm and a scanning speed of 8 mm·s^-1. The laser modified coating has a smooth surface and some longitudinal cracks， which helps to improve the interface matching between the modified layer and the original coating. Under the action of CMAS， laser modified YSZ coatings exhibit good phase stability and structural stability. Therefore， laser surface modification can improve the CMAS resistance of YSZ TBCs， but the degree of the improvement depends on the thickness and microstructure of the modified layer， especially the distribution of longitudinal cracks.