研究目的
To achieve delamination-free millisecond laser drilling of 0.75 mm diameter holes through a fundamental scientific investigation on laser drilling of TBC coated materials.
研究成果
The study concluded that delamination-free laser drilling of TBC coated materials can be achieved by removing a small length of TBC from the leading edge of the hole prior to the trepanning drilling process. For the material tested, TBC removal over a length of 280 μm can help to fully avoid the TBC delamination.
研究不足
The study acknowledges that being a thermal process, millisecond laser drilling involves increasing the temperature of the material beyond the melting temperature, and thus the thermal stress induced TBC delamination cannot be addressed either by parametric optimization or by using the multistage drilling process.
1：Experimental Design and Method Selection:
The study involved using a millisecond pulsed QCW fiber laser for drilling angular holes in TBC coated nickel superalloys. The methodology included both traditional percussion and trepanning laser drilling processes, as well as a new method called 'laser drilling post-laser TBC decoating'.
2：Sample Selection and Data Sources:
A 2 mm thick aerospace grade nickel alloy (C263) coated with a 250 μm thick yttria-stabilized zirconia (7-8 YSZ) based TBC and 100 μm thick MCrAlY based bond coat were used as test samples.
3：List of Experimental Equipment and Materials:
The lasers used were a multimode ytterbium millisecond pulsed fiber laser (YLS-2000/20000-QCW-WC) with 1070 nm wavelength. A Keyence microscope was used to examine and measure the delamination and recast layer. A thermal camera and a high-speed camera were also used.
4：Experimental Procedures and Operational Workflow:
All holes were drilled at an angle of 30° to the TBC coated C263 nickel superalloy specimens. The trepanning hole diameter was kept constant at 0.75 mm, the nozzle workpiece offset distance was kept constant at 10 mm, and the input gas pressure was kept constant at 6.5 bar.
5：75 mm, the nozzle workpiece offset distance was kept constant at 10 mm, and the input gas pressure was kept constant at 5 bar.
Data Analysis Methods:
5. Data Analysis Methods: The drilled samples were sectioned, polished, and etched to examine the coating delamination and recast layers along the mid-cross section. A Keyence microscope was used to examine and measure the delamination and recast layer.
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