Revisiting the influence of the scanning speed on surface topography and microstructure of IN718 thin walls in directed energy deposition additive manufacturing

Controlling the mechanical properties of metallic parts produced by additive manufacturing remains challenging. The mechanical behavior of parts is mainly related to the microstructure, which depends on process parameters and manufacturing strategies. The scanning speed is one of the key parameters that can be modulated during the process (according to the kinematic behavior of the machine tool) in order to reach different microstructures. Thus, in this work, an experimental study in laser metal powder directed energy deposition is conducted to analyze the influence of the scanning speed on the macroscopic geometry, the surface topography, and the microstructure. To do so, a series of single-layer experiments has been conducted to establish an empirical relationship between the laser power, the powder flow-rate and the scanning speed on the one hand, and the layer height and width on the other hand. In addition, six multi-layer thin-walled structures have been produced for various laser powers and scanning speeds in order to determine an association with macroscopic features, topography and microstructure. This approach opens interesting long-term perspectives to better control microstructures in DED.