Optical study of the effects arising from the interaction of a CO2-laser with the powder in a coaxial nozzle for laser cladding

Experimental studies of the NiCr powder interaction with the CO2-laser radiation in the conditions of free jets of a coaxial nozzle for laser cladding are carried out. Optical diagnostics is used with the video recording of moving particles and registration of the radiation spectrum. The influence of the type of working gas, i.e., air and argon, as well as laser operation modes – the continuous CW and pulse-periodic PP on plasma ignition – is studied. An increase in the average particle velocity from 3 m/s in a cold flow to 10 m/s, when exposed to a laser, was found and the maximum velocity values at the level of 50-60 m/s were registered. The phenomena of particle break-up and plasma plume formation on their surface are described. It is shown that particles rotating with a frequency of 30-40 kHz are present in the powder flow. The continuous thermal radiation of particles and the spectral lines of plasma radiation in the range of 400-900 nm are analyzed.