The spectroscopy of the plasma plume induced during laser welding of stainless steel and titanium

Results of spectroscopic measurements of laser-induced plasmas under welding conditions are presented and discussed. The metals welded were stainless steel and titanium. It is shown that the intensities of the atomic lines of metals give information on the peripheral region of the plasma plume. The plasma plume parameters are found to be similar for these two metals. The ratios of intensities of the ionic and atomic lines of the metals give maximum temperatures of about 11000 K. These temperatures are several thousand kelvins higher than the temperatures determined from the atomic lines. The plasma plumes over the keyhole consist of metal vapours diluted by argon used as the shielding gas. The electron densities determined from the Stark broadening of the argon lines are about 1 x 10(17) cm(-3). The average partial pressure of the metal vapours is found to be 0.2 atm, the argon partial pressure 0.6 atm and the remaining pressure is due to electrons. Equilibrium conditions have been examined and it has been found that the plasma is in local thermal equilibrium.