Comparison of mechanisms and effects of Nd:YAG and CO2 laser cleaning of titanium alloys

The paper compares laser cleaning trials performed using a Q-switched Nd:YAG laser, l = 1.064 mm and a continuous wave (CW) CO2 laser, l = 10.6 mm, applied to aerospace-grade, contaminated titanium alloys. The mechanisms for cleaning using each laser system are modelled to determine the mode and extent of contaminant removal. The model results are then compared with the surface chemistry and micro-structural results from the cleaning trials performed. The results show the dominant cleaning process for Nd:YAG cleaning to be by evaporation of the contaminant via conduction through surface heating, while for CO2 laser cleaning the small fraction of the beam coupling directly with the contaminant is sufficient for direct heating and selective evaporation. The results for experimental cleaning, electron beam (EB) welding and diffusion bonding align well with the model, particularly when secondary reactions are taken into account