Laser beam powder bed fusion of Inconel 718 under high power and scanning speed

The process map area of laser beam powder bed fusion for the nickel-based superalloy Inconel 718 is investigated using high laser power (600-1000 W) and scanning speeds (1500-3500 mm/s). The process map is defined by the surface morphologies (visually inspected) and relative densities of the as-built materials. The effects of the process parameters on the melting and solidification phenomena are observed by high-speed camera imaging, while those on the microstructure of the as-built parts are observed through the scanning electron micrograph (SEM). The process window to build specimens with smooth surfaces and high relative densities was in the laser power range of 700-1000 W and a scanning speed of 1500 mm/s. Notably, the relative density of the specimen built in this process window was slightly lower than that of the specimen built in the current process window of low power (100-400 W) and scanning speed (100-1500 mm/s). High-speed camera observation of the melt pool behavior revealed that the plasma plume was ejected backward in the laser scan direction, and many large spatters were ejected along the plume under the proposed higher power and scan speed conditions. Moreover, the melt pool was unstable, and the laser track displayed an irregular shape. The spatter and unstable melt pool were attributed to the keyhole evolution in the melt pool. The microstructure of the as-built parts presented features similar to those of materials built under the current process window. This research provided process parameters set under high power and scanning speed conditions and enabled the fabrication of dense materials like those produced within the conventional process window. The higher scanning velocity reduces the building time compared to the current process window.