Effect of laser scan length on the microstructure of additively manufactured 17-4PH stainless steel thin-walled parts

Components with varying dimensions are found in numerous applications. The current work examines how microstructures and phases change for additively manufactured 17-4PH thin walls as a function of laser path length, path direction, and wall thickness. Two sample sets were designed, each consisting of four walls with thicknesses of 6.4 mm to 0.8 mm. In the first set, the wall axes were parallel to the scan axes, such that the laser path length varied from layer to layer with the laser path either being parallel or perpendicular to the wall. In the second set, the walls lay at 45 degrees to the scan axes, such that the laser path had the same length in all layers and gradually decreased with wall thickness. Substantial changes in phase stability and microstructure are observed as the wall thickness decreases, with ferritic phases and coarse grains changing to fine grains and an increasing volume fraction of austenite. These changes are attributed to changes in the local temperature-time profile as the length of the laser paths change from 19 mm to 0.8 mm. These observations demonstrate the range of microstructure and phase control options available in additive manufacturing with judicious selections of part layouts on build plates and of laser beam directions.