Residual stress evaluation in innovative layer-level continuous functionally graded materials produced by Powder Bed Fusion-Laser Beam

Multi-material additive manufacturing is predominantly characterized by strategies in which the transition from one material to another occurs along the building direction. This transition can be direct, with an intermediate material, or alternatively, functionally graded materials can be manufactured, in which there is a gradual composition variation. Nevertheless, recent advancements have led to the fabrication of structures where the transition in composition occurs within the same layer of construction. However, as the mechanical properties of additively manufactured samples are significantly influenced by the direction of construction, the same holds true for the direction along which the compositional variation is made. Consequently, there is a necessity to characterize the residual stresses generated in these innovative samples. Specifically, this work is focused on studying residual stresses in continuous functionally gradient materials in AISI 316L and 18Ni Maraging 300, having the composition variation within the same layer. The objectives of this study are threefold: first, to evaluate residual stresses in layer-level continuous functionally graded materials using the contour method; second, to study the influence on the residual stresses of solution annealing and aging heat treatment; and third, to examine the impact of differentiated process parameters for each material region. The results indicated that each specimen displayed areas of tensile stress concentration on the upper and lower surfaces, balanced by compression in the center. The application of heat treatment led to a decrease in the maximum tensile stress of 8% and provided a uniform and significant stress reduction within the maraging steel. Finally, the implementation of material-specific process parameters for the three composition zones in conjunction with the heat treatment resulted in a reduction in the maximum residual stress of 35% and also a significantly lower residual stress field throughout the specimen.