Composition monitoring using plasma diagnostics during direct metal deposition (DMD) process

The regression line of the line ratio data shows the better prediction of the Ni composition than that of the plasma temperature data. It is suggested that using the plasma temperature as a monitoring tool may not be suitable due to the non-linear characteristics and low sensitivity shown in the plasma temperature data. The regression line of the Ni-I (352.45 nm)/Cr-I (399.11 nm) line ratio gives the most accurate prediction compared with the regression lines for other combinations of Ni-I and Cr-I lines. The predicted Ni composition error by the Ni-I (352.45 nm)/Cr-I (399.11 nm) line ratio ranges from 0.02% to 4.5% (average 1.6%), which shows that using the line ratio for monitoring of the composition is quite reasonable. The method to predict Ni composition is also validated through the DMD experiment using as-received Inconel 718 powder with a certified Ni concentration of 50.9% (in atomic percentage). Average prediction for the Ni composition is 51.8% (error 1.6%) when the Ni-I (352.45 nm)/Cr-I (399.11 nm) line ratio is used.