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This work explores the multiscale mechanical behavior of 17-4 PH stainless steel structures processed through the atomic diffusion additive manufacturing technique (ADAM). 17-4 PH stainless steel parts were fabricated with a Markforged Metal X 3D printer and characterized with respect to variable printing orientations for samples loaded in tension, shear, and bending. Sections of material were taken from each face of a bending test sample and prepared for microscopy to quantify porosity, grain size, and local stiffness and hardness. Microscale evaluation showed a porosity content of 3.3% on average across all faces. The yz face specifically showed the same sort of packing limitations often seen in other extrusion-based methods leading to greater porosity. An electron backscatter diffraction investigation showed a mean grain size of 6.5 μm with some grain alignment in the z-direction in the xz plane. Bulk material response in tension was dependent upon the print orientation of the sample. Cases where material was extruded entirely in the direction of loading saw a stiffness, strength, and strain to failure improvement of greater that 10% compared with other infill schemes. Shear testing revealed similar increases in strain to failure for samples with material extruded in only one direction compared with cross hatching at alternating orthogonal angles. Bend test results were similar in tension and compression regardless of orientation. For a sample printed with primary loading in the print plane (xy), the tensile modulus was 130–140 GPa, the tensile yield and ultimate strength were 600 MPa and 800 MPa, and the shear strength was 40.6 MPa on average.

Material extrusion (MatEx) is finding increasing applications in additive manufacturing of thermoplastics due to the ease of use and the ability to process disparate polymers. Since part strength is anisotropic and frequently deviates negatively with respect to parts produced by injection molding, an urgent challenge is to predict final properties of parts made through this method. A nascent effort is underway to develop theoretical and computational models of MatEx part properties, but these efforts require comprehensive experimental data for guidance and validation. As part of the AM-Bench framework, we provide here a thorough set of measurements on a model system: polycarbonate printed in a simple rectangular shape. For the precursor material (as-received filament), we perform rheology, gel permeation chromatography, and dynamical mechanical analysis, to ascertain critical material parameters such as molar mass distribution, glass transition, and shear thinning. Following processing, we conduct X-ray computed tomography, scanning electron microscopy, depth sensing indentation, and atomic force microscopy modulus mapping. These measurements provide information related to pores, method of failure, and local modulus variations. Finally, we conduct tensile testing to assess strength and degree of anisotropy of mechanical properties. We find several effects that lead to degradation of tensile properties including the presence of pore networks, poor interfacial bonding, variations in interfacial mechanical behavior between rasters, and variable interaction of the neighboring builds within the melt state. The results provide insight into the processing–structure–property relationships and should serve as benchmarks for the development of mechanical models.

The incorporation of carbon nanostructures into Al alloys has the potential to further improve the mechanical and electrical properties of these alloys. We report a novel one-step fabrication method of incorporating carbon in aluminum alloys by the application of a high electric current to molten Al metal containing particles of activated carbon at high temperature and under Ar atmosphere. We propose that the mechanism for carbon incorporation is similar to electromigration where the current facilitates ionization of the carbon atoms followed by polymerization of the carbon structures and the formation of graphitic chains and ribbons along preferred directions of the Al lattice. Furthermore, the current induces transformation from amorphous carbon to crystalline graphitic structures that propagate in the metal matrix. The carbon is identified by the C-K edge in electron energy loss spectra, X-ray photoelectron spectroscopy, Raman and Kelvin probe force microscopy. The stiffness is increased in these samples; hardness, on the other hand, decreases for some samples compared to reference Al alloys with no carbon. The electrical conductivity is superior to that of Al-carbon nanotube composites previously reported. The enhanced properties of Al covetics show potential for naval and aerospace applications and power transmission lines.

Molecular dynamics simulations are used to investigate lithium (Li) transport rates in symmetric tilt graphite grain boundaries (GBs). Experiments have quantified highly varied diffusion rates of L...

This work investigates the role of a carbon nanophase on the local mechanical behavior of nano-carbon metal composites (NCMCs) produced through an electrocharge-assisted process. Nanoindentation experiments on single crystal Al, Al 1350 parent alloys, and Al 1350 NCMCs revealed variable mechanical properties, caused by an interplay between microstructure and graphitic reinforcements. TEM and AFM studies also reveal nanoscale structural changes based on the incorporation of a carbon nanophase. In order to decouple the effects of the aforementioned mechanical behaviors, molecular dynamics nanoindentation simulations were performed on the (111) surface of Al and Al NCMC samples containing semi-infinite graphene nanoribbons to examine the evolution of plasticity over time. Findings indicate that the arrangement of a finite graphene nanophase within a host matrix can alter plasticity mechanisms and therefore yield strength in near-surface mechanical behaviors with little effect on elastic properties. This understanding should enable further study into tunable bulk properties of Al-based NCMCs while isolating microstructural effects and reinforcement effects of the carbon phase. Such an understanding could lead to application-specific material geometries ranging from high-performing vehicle structures to next-generation electrical devices.

Lithium-ion diffusion rates in graphitic battery anodes have been shown to vary greatly in experiments, with numerous hypotheses to explain this behavior. Here, we model several grain boundaries using molecular dynamics and quantify intercalation from the free surface. A significant variation in intercalation rates is revealed as dictated by local bond structure where the grain boundary intersects the free surface. Data presented may help explain dramatic differences in diffusion rates and permit more accurate predictions of lithium-ion battery performance.