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Neutron diffraction was employed to measure internal residual stresses at various locations along stainless steel (SS) 17-4 PH specimens additively manufactured via laser-powder bed fusion (L-PBF). Of these specimens, two were rods (diameter=8 mm, length=80 mm) built vertically upward and one a parallelepiped (8×80×9 mm3) built with its longest edge parallel to ground. One rod and the parallelepiped were left in their as-built condition, while the other rod was heat treated. Data presented provide insight into the microstructural characteristics of typical L-PBF SS 17-4 PH specimens and their dependence on build orientation and post-processing procedures such as heat treatment. Data have been deposited in the Data in Brief Dataverse repository (doi:10.7910/DVN/T41S3V).

A new manufacturing approach in which the friction stirring phenomenon is used as a vehicle for facilitating the deformation of bulk lightweight materials into manufactured components has been recently introduced under the general concept of “bulk friction stir forming”. In a preliminary work, the concept was applied to the back extrusion process, in what was referred to as “friction stir back extrusion” or FSBE; it was shown that the concept is practically valid and FSBE is capable of producing lightweight tubular specimens. Nevertheless, the FSBE process was claimed to have several merits over conventional processes, mainly: (i) unique process capabilities and energy efficiency (ii) significant grain refinement, and thus (iii) favorable mechanical properties in the formed tubes. None of these claims were adequately addressed nor quantified in earlier work. Therefore, this work presents a comprehensive study that aims to reveal the true merits of FSBE, validate the claims, and quantify its effects on the microstructure and mechanical properties of the deformed material. The outcomes of the study are presented in three major parts, each addressing one of the abovementioned claims. Force, torque and power measurements during FSBE experiments are used to address the first claim. Detailed optical microscopy and electron back scatter diffraction work is carried out in the second part to quantify the changes to the grain structure and texture of the material. Finally, the third part presents detailed mechanical characterization using digital image correlation to quantify the effects of FSBE on the performance of the produced tubes.

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One of the key barriers to widespread adoption of additive manufacturing (AM) for metal parts is the build-up of residual stresses. In the laser-based powder bed fusion process, a laser selectively fuses metal powder layer by layer, generating significant temperature gradients that cause residual stress within the part. This can lead to parts exceeding tolerances and experiencing severe deformations. In order to develop strategies to reduce the adverse effects of these stresses, the stresses first need to be quantified. Cylindrical Nickel Alloy 625 samples were designed with varied outer diameters, inner diameters, and heights. Neutron diffraction was used to characterize the three-dimensional (3D) stress state throughout the parts. The stress state of the parts was generally comprised of tensile exteriors and compressive interiors. Regardless of part height, only the topmost scan height of each part experienced large reductions in axial and hoop stress. Improved understanding of the residual stress trends will aid in model development and validation leading to techniques to reduce negative effects of the residual stress.