Investigation On Mechanisms For Water-based Ultrasonic Vibration-assisted Laser Drilling With/without Magnetic Filed

In aerospace industry,in order to improve the working performance and service life of high-temperature components such as engines and combustion chambers,lots of microholes are usually manufactured on these thermal components.At present,there are two commonly used methods for manufacturing such microholes in industry,one is electrical discharge machining(EDM),the other is pulsed laser drilling.Normally,the machining quality of the EDM is relatively high,however,its machining efficiency is relatively low and its cost is relatively high.Alternatively,laser drilling has gradually become the main method for drilling micro holes because of its high drilling efficiency,wide adaptability and good economic benefits.However,because laser drilling is a thermophysical process,some defects such as recast layer,micro cracks,and residual stress inevitably occur due to laser drilling.In order to reduce or avoid these defects and improve hole quality and mechanical performance for zones surrounding drilled holes,some assistance methods have been proposed and applied for laser drilling.In this work,a novel laser drilling method assisted by water-based ultrasonic vibrations is proposed,and the magnetic field is also preliminarily considered for further research exploration.The hole quality and mechanical performance for the domains surrounding the drilled holes were improved by adding ultrasonic vibrations and magnetic field assistance.In this investigation,nickel super-alloys GH4037 and GH4049 were used for laser drilling experiments based on self-developed laser drilling facility assisted by water-based ultrasonic vibrations with/without magnetic assistance.The effects of ultrasonic vibrations on hole morphology,hole dimensions,hole wall quality,microstructure and micro hardness of domains surrounding the drilled holes were discussed using laser percussion drilling.The influence of ultrasonic vibrations on hole geometry,hole wall morphology,hole sidewall surface roughness,microstructure,micro hardness and impact toughness for zones near the drilled hole was investigated based on laser trepan drilling.The effects of ultrasonic vibrations and/or magnetic assistance on hole formation,inner sidewall morphology,microstructure and mechanical performance for areas near the drilled hole were studied.In addition,the influence of water temperatures on hole geometry,microstructure,micro hardness and residual stress for zones surrounding the hole drilled using ultrasonic-magnetic assisted percussion laser drilling were also analyzed.For percussion laser drilling,laser trepan drilling,and helical laser drilling,it is shown that ultrasonic vibrations can enhance drilling efficiency,improve hole geometry/morphology and hole sidewall quality,increase micro hardness and impact toughness for the zones surrounding the drilled holes,reduce recast layer thickness,make grains finer,and reduce residual stress.Besides,for percussion laser drilling and helical laser drilling,the addition of an external magnetic field can also increase laser drilling efficiency,improve hole quality,and reduce residual stress for the locations surrounding the drilled hole.In addition,the ultrasonic-magnetic assistance coupled into the laser drilling/trepanning process can achieve better drilling performance and hole quality.