Powder incorporation and spatter formation in high deposition rate blown powder directed energy deposition

A high deposition rate blown powder directed energy deposition process is presented. Clad tracks are deposited and the process is observed by high-speed imaging. An island of unmelted powder forms inside the melt pool, in the centre of the laser spot, which can be attributed to the highly focussed powder flow and the laser beam configuration used. On contact with the melt pool, the powder grains melt to join the melt pool, or they overcome surface tension and are engulfed by the melt. Powder grains can also incorporate into a mushy zone that may be present on the powder island. The powder island appears to rotate in the melt pool and incorporates relatively slowly. The speed of rotation is connected to the size of the island, which also depends on the energy density used. Spatter can form from the edges of the melt pool or from areas around the island when molten metal droplets burst. Frames from high-speed videos are presented and reasons for the various phenomena observed are discussed.