Relating melt mixing, dilution and vapor emissions during directed energy deposition

• Optical emissions were captured using optical emission spectroscopy during Directed Energy Deposition processes. • Element-specific atomic emission lines could be identified in the spectral signals. • Varying powder feed rates resulted in variations of the dimensions and the elemental composition of the deposited material. • Intensity ratios of element peaks were correlated with the chemical composition and dilution of the deposited tracks. • Measurement of optical process emissions could be used for the monitoring of mixing and dilution. This study presents the results of an investigation on the influence of powder feed rate on the microstructure and composition of laser-deposited cobalt–based alloy (MetcoClad21). Optical emission spectroscopy (OES), metallographic analysis, and energy-dispersive X-ray spectroscopy (EDX) was used to characterize the samples and the process. The OES analysis was used to identify element specific atomic emission lines (peaks) within the captured optical process emissions. The elemental composition of the deposited material was observed and peak intensity ratio of certain elements were calculated in situ. The metallographic and EDX analyses were used to measure the cross–sectional–dimensions of the deposition tracks and to analyse the elemental composition of the deposited material. The results showed that the powder feed rate had a significant influence on the microstructure, the cross–sectional–dimensions and the composition within the deposition tracks. Specifically, the authors found that the Fe/Cr peak intensity ratio decreased with increasing powder feed rate, indicating a decrease in the Fe content and an increase in the Cr content of the deposited material. Hence, the peak intensity ratios could have been correlated with the track compositions and the dilution with the Fe-based substrate material. The results of this study have implications for the optimization of laser deposition processes for cobalt–based alloys by an in situ control by OES.