MICROMACHINING ON THERMAL BARRIER COATED SUPPERALLOY USING A NANOSECOND FIBER LASER

摘要

As the advance of gas turbine engines, turbine entryrntemperature has been continuously enhanced, whichrndemands for high performance thermal barrier coatingsrnand improved cooling arrangement on turbine blades.rnIn recent years, for the purpose of improving filmrncooling efficiency on a turbine blade while reducingrnthe total volume of cooling air, film cooling holes arerndesigned with three-dimensional shaped diffuserrnopenings, such as chevron and trapezoid shaped holes.rnPrecise manufacturing of such shaped hole-openings isrna challenge especially when the metal blades arerncoated with ceramic thermal barrier coating (ZrO_2).rnCompared with traditional millisecond pulsed laserrndrilling or micro-EDM process, high frequency shortrnpulsed laser combined with high speed galvoscannerrnhas demonstrated unique advantages inrnmicromachining directly on ceramics or metals withrnhigh quality. In this study, a ns pulsed Ytterbium fiberrnlaser is used to study the physical interactions betweenrnpulsed laser beam and ceramic coating and base metalrnmaterials. Thermal ablation model was established torndetermine the ablated material volume and dimensionsrnsubjected to stationary pulses and a moving laser beam.rnResults are compared between modeling andrnexperimental data. Optimized machining parametersrnare recommended with the aim of maximum processrnefficiency with minimum thermal effects such asrnspatters, microcracks and spallation.