Solidification Mode Shifting and Resultant Composite Microstructure Evolution during High Build Rate Laser Directed Energy Deposition of SS 316L

Laser‐directed energy deposition (L‐DED) using high laser power and high layer thickness can help metal additive manufacturing to achieve mass customization. The effect of varying high build rate parameters on surface topography, microstructural evolution, and mechanical properties of SS 316L alloy is investigated by varying laser power (1.5–2.1 kW), scan strategy (0°, horizontal and 90°, vertical), and layer thickness (0.6–1.1 mm) for two different part geometries (square and rectangular). The surface topography analysis reveals the presence of unmelted particles, crests, and troughs necessitating postprocessing. Interestingly, at this high build rate, each part geometry resulted in a unique microstructure for different samples–fully austenitic columnar‐equiaxed (square), fully ferrite (horizontal), and composite ferritic and columnar‐equiaxed austenitic microstructure (vertical), which are influenced by the solidification mode AF, FA, and AF + FA modes respectively, and varying thermal gradient. The composite microstructure due to shifting in solidification mode from AF in the initial layers to FA mode in the final layers of the build is reported for the first time in L‐DED SS 316L. Despite the anisotropy in microstructure, the micro‐hardness and yield strength of the L‐DED SS 316L samples were higher than the wrought sample due to finer grains and ferrite segregation in the microstructure.