Inconel625/316L functionally graded material using spectral diagnostics during laser additive manufacturing process

In this paper, the composition of Inconel625/316L functionally graded material during the additive manufacturing process was monitored on-line by laser-induced plasma optical emission spectroscopy. Several spectral lines are used to establish the quantitative relationship between relative intensity, relative intensity ratio, plasma temperature, and functional gradient material composition variation. It is shown that the change between relative strength and compositional content is similar to actual expectations. But, the relationship between the relative intensity with Inconel625 content is nonlinear. Cr-I/Ni-I relative intensity ratios almost linearly decrease with increasing Inconel625 content. The linear correlation coefficient of the best fitted curve was 0.943, and the maximum percentage error was 7.5%. The plasma temperature was obtained by the Boltzmann plot using five neutral chrome lines between 330 and 380 nm. Plasma temperature almost linearly increases with increasing Inconel625 content in a range. The linear correlation coefficient of the plasma temperature fitted straight line was 0.93, and the maximum percentage error was 2.7%. The feasibility of composition monitoring of gradient materials by spectral information during the additive manufacturing process was verified.