The influence of pulsed CO2-laser radiation on the transport of powder during laser cladding of metal

Abstract

The problem of measurement of the in-flight velocity and temperature of particles in the light field of a pulsedperiodic laser was solved using contactless detection methods. The solution of the problem is based on using a spectrometer and a complex of laser and optical means. The diagnostic technique combines two independent methods for measuring the in-flight particle velocity: a passive one, based on the registration of the natural radiation emitted by the heated particles in the gas flow, and an active one, using the effect due to laser-beam scattering. Histograms of the statistical distributions of particle velocities for two operating modes of a coaxial nozzle were presented. There is no laser radiation in the first mode. There is pulsed laser radiation in the second mode. In the experiments, various powders (Al₂O₃, Mo, Ni, Al) with particle size distributions typical of laser deposition technology and various working gases (air, nitrogen, argon) were used. СО₂-laser works in pulse-periodic mode with a mean power up to 2 kW. Pulsed power reaches several ten/hundred kilowatts. It is shown that in the field of laser radiation, powder particles acquire additional acceleration due to the evaporation and the appearance of a reactive force due to the recoil pressure of the vapors emitted from the irradiated part of the particle surface. It is shown that laser radiation can significantly affect the velocity and temperature of powder particles being transported by a gas jet. At the maximum carrier-gas velocity of up to 30 m/s, the velocities of single particles due to the laser-induced acceleration can reach the values of the order of 120 m/s.