EFFECT OF STAND-OFF DISTANCE ON ABRASIVE WATER JET PIERCING OF CERAMIC-COATED SUPERALLOY

Abstract

The drilling of film cooling holes on gas turbine blades made out of ceramic-coated superalloy improves the efficiency of the gas turbine and prolongs the life of the turbine blade. The purpose of this study was to investigate the effects of different stand-off distances (SODs) on abrasive water jet (AWJ)-pierced holes, in which the machining time, entry and exit hole diameters, overcut, hole taper, and surface morphology were studied. In this study, the water jet pressure (WJP) of 275[Formula: see text]MPa, piercing angle of [Formula: see text], dwell time of 0.2[Formula: see text]s, and abrasive flow rates (AFRs) of 350[Formula: see text]g/min and 400[Formula: see text]g/min were considered for the AWJ piercing operations. The entry and exit hole diameters and overcut linearly increased with an increase of SOD with different abrasive flow rates. And hole taper was observed at the coating and substrate sections in which it decreased with an increase of SOD up to 2[Formula: see text]mm, and a further increase of SOD increased the hole taper. Besides, the drilled holes were found to have an absence of delamination, cracks, and thermal defects. It was also noted that there is a transformation from a brittle to a ductile mode of erosion that may occur in the high-erosion kinetic energy impact region in the YSZ material section. Based on the experimental results, it is confirmed that SOD of 2[Formula: see text]mm became an influencing factor in AWJ for piercing quality holes in the YSZ-coated superalloy.