Investigation of heating behavior of laser beam on powder stream in directed energy deposition

This study used a high-speed camera to observe the interaction of laser beam and powder stream in directed energy deposition (DED), by which an effective method for characterizing the temperature evolution law of the incident particles is developed based on the image gray analysis. Combined with the mathematical analysis, the heating behavior of laser beam on the powder particles was investigated. It shows that by decreasing the speed and size of powder particles or increasing the laser power, the incident particle temperature reaching the deposition surface can be sufficiently increased. With the decrease of the particle speed from 9.3 m s−1 to 3.9 m s−1, the particle temperature at theoretical deposition surface is increased by 144%. In particular, the increase of the powder incident angle can significantly increase the incident temperature of powder particles. The temperature of the 65° incident particle is increased by 54.4% relative to that of the 50° incident particle. Due to the effects of the laser energy distribution along the moving trajectories, the powder particles that cross the centre axis of the laser beam and fall near the edge of the laser spot on theoretical deposition surface have the highest incident temperature. Single-pass deposition experiments show that the enhancing interaction effect between laser beam and powder stream can effectively improve deposition quality and save energy. 20% and 30% laser power were saved to obtain good deposition quality by increasing powder stream incident angle and decreasing the particle speed, respectively.