Thermal monitoring is essential in Laser Direct Energy Deposition (DED) to ensure the uniformity, geometry, and mechanical properties of the deposited material. Typically, thermal and optical cameras are used to observe melt pool dynamics, temperature fluctuations, and thermal cycles, which significantly influence the material’s microstructure. However, these monitoring systems face challenges, particularly due to variations in emissivity, material composition, and other factors that can lead to inaccuracies in temperature readings. Despite these challenges, previous studies have shown successful applications in single-material Laser DED.

This work investigates the thermal monitoring challenges in multi-material Laser DED with functionally graded alloys. The continuous variation in alloy composition and material transitions influences the accuracy of thermal imaging and data interpretation. Two high-frame-rate thermal cameras, covering temperature ranges from 100 to 900 °C and from 900 to 2400 °C, are employed to analyze how these factors affect recorded thermal images and temperature estimates. Additionally, an optical welding camera with integrated laser illumination can be used to provide more detailed observations of the process, offering insights into melt pool behavior and material interaction. The study explores strategies to manage these variations, including real-time calibration and image processing techniques, to improve the accuracy of temperature measurements and enhance process control. Moreover, the relationship between thermal cycles and microstructural evolution is also examined.