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Wire arc additive manufacturing (WAAM) direct energy deposition is used to process two different duplex stainless steels (DSS) wire chemistries. Macro- and micromechanical response variables relevant to industrialization are studied using a design of the experiment (DoE) approach. The tested operation window shows that the variation of layer height and over-thickness are highly correlated with travel speed and wire feed speed and positively correlated with heat input. The maximum achieved average instantaneous deposition rate is 3.54 kg/h. The use of wire G2205, which contains 5 wt% nickel content, results in a ferrite-to-austenite ratio that is equally balanced, while wire G2209, with 9 wt% nickel, provides a lower ferrite content. The spatial distribution of Fe% is influenced by part geometry and path planning, and higher heat inputs result in coarser microstructures. The manufacturing weaving strategy generates a heterogeneous microstructure characterized by fluctuations in Fe%. Thus, understanding the effect of complex thermal history, higher-dimensional design spaces, and uncertainty quantification is required to drive metal WAAM toward full industrialization. [ABSTRACT FROM AUTHOR]

In this study, we report a micropillar stress relaxation technique employing a stable displacementcontrolled, in-situ scanning electron microscope indenter, and unusually large micropillars to precisely measure stress relaxation in electroplated nanocrystalline Ni thin films. The observed stress relaxation is significant under constant displacement: even well below the 0.2% offset yield strength, the stresses relax by ~4% within a minute; in the work hardening regime, stress relaxes by ~9% in 1 min. A logarithmic fit of the relaxation curves is consistent with an Arrhenius thermal activation of plasticity and suggests an activation volume in the vicinity of ~10 b³. The apparent and effective activation volumes diverge at lower strains, particularly in the "elastic" regime. These measurements are compared to similar measurements performed on free-standing thin film tensile coupons. Both methods yield similar results, thereby validating the applicability of pillar compression to capture time-dependent plasticity. To our knowledge, these are the first micropillar stress relaxation experiments on metals ever reported. [ABSTRACT FROM AUTHOR]

Strain-rate sensitivity (SRS) measurements using transient small-scale techniques are becoming increasingly popular for investigating nanostructured films and microcomponents since they can provide fundamental insights into the plastic deformation mechanisms within small volumes of material. Previously, researchers have typically used either nanoindentation or microcompression strain-rate jump tests on a variety of nanostructured materials and compared the resultant values with bulk compression data as a reference. However, no systematic comparison of the different transient micromechanical techniques has been performed on the same material to establish their relative merits or the consistency of their results. In this study, the SRS of nanocrystalline nickel is investigated using three independent, in situ, transient experimental techniques: miniature tension, nanoindentation, and micropillar compression. The obtained SRS exponents m measured by all techniques were found to be in good agreement, and the resulting apparent activation volume V of approximately 10 b is consistent with grain boundary diffusion processes and dislocation glide-based plasticity. [ABSTRACT FROM AUTHOR]