Non-destructive microwave evaluation of TBC delamination induced by acute angle laser drilling
Non-destructive microwave evaluation of TBC delamination induced by acute angle laser drilling
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DOI：
10.1088/0957-0233/18/1/021
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发表时间：
2006
影响因子：
2.4
通讯作者：
H. K. Sezer;Lin Li;Z. Wu;B. Anderson;P. Williams
中科院分区：
文献类型：
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作者：
H. K. Sezer;Lin Li;Z. Wu;B. Anderson;P. Williams
激光打孔技术已广泛应用于现代航空燃气涡轮机部件的冷却孔加工中，如涡轮机叶片、导向叶片、燃烧室和加力燃烧室等。这些部件通常由耐热镍超合金制成。高温合金基体涂有氧化钇稳定的氧化锆热障涂层（TBC），以防止它们在热发动机环境中达到过高的温度。以与表面成锐角的方式对零件钻孔是复杂的，因为（i）多个层被钻穿，（ii）孔周围的熔体喷射和热流模式是不对称的，以及（iii）钻孔距离大于垂直于表面钻孔时的距离。在作者以前的研究中，TBC的分层作为一个主要问题的角度钻孔和机制进行了讨论。分层裂纹的表征通常通过金相技术进行。它涉及使用磨料切割机对样品进行切片，用连续更细的碳化硅纸研磨至孔的中心，并抛光以允许对裂纹进行光学显微镜分析。然而，由于切割轮的阻力，热喷涂工件的夹紧和切片过程可能会在脆性涂层中引入裂纹。因此，无法确定分层是否是由于后处理切片或激光钻孔造成的。本文采用微波无损检测技术对激光打孔后热障涂层的完整性进行了检测。使用在45 MHz至110 GHz频率范围内工作的Agilent 8510 XF网络分析仪测量散射波的振幅和相位变化。结果表明，在用400 W Nd：YAG激光器进行的锐角孔激光钻孔的前缘部分，TBC/基体界面处存在1-1.5 mm长的分层。
Laser drilling has been applied to the production of cooling holes of various size and angles in the modern aerospace gas turbine components such as turbine blades, nozzle guide vanes, combustion chambers and afterburner. These parts are usually made of heat resistant nickel superalloys. The superalloy substrate is coated with yttria-stabilized zirconia thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Drilling the parts at acute angles to the surface is complicated because (i) multiple layers are being drilled through, (ii) the melt ejection and heat flow patterns around the hole are non-symmetrical and (iii) the drilling distance is greater than when drilling normal to the surface. In a previous investigation by the authors, delamination of TBC was addressed as a main problem of angled drilling and mechanisms involved were discussed. Characterization of delamination cracks was normally performed via metallographic techniques. It involves sectioning the samples using an abrasive cutting machine, grinding with successively finer silicon carbide paper up to the centre of the hole and polishing to allow optical microscopic analysis of the cracks. However, clamping and sectioning process of thermal-spray-coated workpieces can introduce cracks in brittle coatings due to the drag of the cut-off wheels. Hence, it is not possible to decide if the delamination is caused as a result of post-process sectioning or laser drilling. In this paper, a microwave non-destructive testing (NDT) technique is employed to evaluate the integrity of TBC after acute angle laser drilling. An Agilent 8510 XF network analyser operating over the frequency range of 45 MHz to 110 GHz was used to measure the amplitude and phase variations of scattered waves. The results significantly indicated the existence of delamination of 1–1.5 mm long at the TBC/substrate interface on the leading edge part of an acute-angled hole laser drilled using a 400 W Nd:YAG laser.