Overlapping rate effect on laser shock processing of 1045 steel by small spots with Nd:YAG pulsed laser

Lower power lasers operating at higher frequencies, which are much more reliable and economical, have been explored for laser shock processing to improve fatigue and wearing resistance of metals. Laser shock processing with a Q-switched Nd:YAG pulsed laser was attained by the overlap of small laser spots for the treatment of AISI 1045 steel. The changes of mechanical properties of the specimen treated by different overlapping rates were investigated by both experiments and numerical simulation. Surface quality was essentially unaffected after treatment. Plastic affected depth was much shallower than that obtained with larger spot sizes, due to rapid attenuation of shock waves. Induced residual stress field was uniform on the top surface and was enhanced with the increase of overlapping rate. Surface micro-hardness reached a larger value than that reached on the untreated region and was also improved with the increase of overlapping rates. A plastically deformed martensite transformation zone was found in an extremely thin layer near the top surface due to the heat effect.