On the Mechanical Performance of an L-PBF 316l Part Using the Performance-Line Instrumented Indentation Test (PL-IIT)

While L-PBF research continuously expands technologically towards more complex-shaped components and effective scanning strategies, the customization of the mechanical performance of these components to specific applications is still challenging. The presence of high process-induced residual stress levels frequently makes the current (standard) mechanical testing procedures ineffective or even inappropriate. The current engineering design principles cannot be applied to L-PBF components as the available mechanical properties are apparent (i.e., space and residual stress dependent properties). It is the aim of this work to overcome the aforementioned limitations by presenting a comprehensive methodology that can be used to determine the mechanical performance of an L-PBF 316L deposit along (five) pre-specified directions, denoted as performance lines (PLs), and in six special key regions, denoted as performance zones (PZs), through the nanoindentation test (PL-nIIT). The PLs determine the gradients of the indentation properties across the deposit, while the PZs exhibit the orientation-dependent mechanical performance in a specified number of regions of the deposit. The latter can be used for benchmarking, mechanical design, or performance customization. The frequently resorted to indentation modulus and hardness have thus been complemented with a new indentation size effect-free property (i.e., the loading stiffness rate, LSR) to help discriminate the presence of residual stress at different depths in the given deposit. A decreasing mild compressive residual stress was determined along the build direction of the deposit as revealed by the decreasing values of the relative LSR, H_IT, and E_IT (from the root to the top dome, i.e., 47.8 to 43.4, 2.57 to 2.49, and 216 to 202 GPa, respectively).