Abstract
In this study, a novel laser-modified drilling method was used to manufacture cooling holes through thermal barrier coatings (TBCs). Due to the “cooling processing” properties during low-frequency femtosecond (LF-fs) laser drilling, the exposure of the sidewall pores, and the interlayer clearance, the inherent characteristics of plasma-sprayed coatings induced sidewall defects in the drilled holes. After drilling, a high-frequency fs (HF-fs) laser was used to repair the sidewall pores and interlayer clearance of the drilled ceramic holes. Then, the pores and microcracks were healed by local melting using the laser. Moreover, instead of obtaining laser-induced periodic surface structures (LIPSSs), refined and homogeneous grains were produced by the HF-fs laser repair treatment at high transient pressure and temperature. The results from a high-temperature corrosion test showed that healing of the open pores and microstructural improvement in the ceramic hole walls prevented the out-diffusion of Y2O3 stabilizers and the penetration of molten salt, resulting in less corrosive products and producing corresponding phase-transformation stress. Thus, reducing the stabilizer consumption can moderate corrosion fatigue and prolong the lifetime of a cooling hole and TBCs under service.
Highlights
Higher film-cooling hole requirements have been proposed for the new generation of aircraft engines
Electro-discharge machining (EDM), because this material is insulating, which restricts its range of applications [1]
We we report in in a Ni superalloy with withwith an fs-laser, report aa method methodfor fordrilling drillingcooling coolingholes holes a Ni superalloy with an fsin which the sidewall pores and interlayer microcracks can thermally heal with the high-frequency laser, in which the sidewall pores and interlayer microcracks can thermally heal with the high-fs (HF-fs) laser
Summary
Higher film-cooling hole requirements have been proposed for the new generation of aircraft engines. Processing these film-cooling holes in aircraft engines with thermal barrier coatings (TBCs) is becoming a key issue. Laser drilling is becoming a trend in fabricating cooling holes in thermal barrier-coated turbine blades as it can drill these difficult materials with high accuracy and efficiency and it can be used with any geometry [2,3,4]. For the fs laser-drilled holes, as shown in Figure 1a–c, delamination cracks and spatter were not observed near the machined area. In order obtain excellent properties, i.e., low thermal conductivity and Young’s modulus and high strain tolerance, atmospheric plasma spraying (APS) yttria-stabilized
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