Impact of Continuous Scanning Speed Variation on Microstructure in LMP-DED Additive Manufacturing

This paper deals with additive manufacturing, which enables parts with complex geometries to be produced layer by layer. For specific geometries, such as bent parts, it is necessary to vary the bead size within or between layers by modifying process parameters, such as scanning speed. However, it has been shown in the literature that modifying process parameters leads to changes in the microstructure. This paper inspects the impact of continuous variation in scanning speed on the microstructure produced with the LMP-DED additive manufacturing process. An experimental study was carried out on single-bead Inconel 718 thin walls. Scanning speed varied linearly along each bead so that at a given position in the wall, the scanning speed was the same throughout the height of the wall. An EBSD analysis of the microstructure was carried out over a length of about 20 mm for a speed variation ranging from 1125mm/min to 1875mm/min. A continuous variation in microstructure was observed from one end of the sample to the other, passing from a mix of columnar and equiaxed grains with no textured structure to large, highly textured columnar grains. These results show that it is possible to intentionally and continuously vary the microstructure of a part along its length by choosing the proper parameters and strategy. This work is preliminary to the microstructure control of a complex part.