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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The onset of alloying in Cu-Ni powders under high-shear consolidation

Friction consolidation (FC) is a solid phase processing methodology that densifies a material through high-shear deformation and pressure at elevated temperature. The method has garnered interest in the scientific community because of its ability to produce extremely refined and homogeneous microstructures, off-axis texture development, and improved material properties. This manuscript presents an investigation of Cu and Ni material mixing via evaluation of morphological evolution, grain boundary characterization, and compositional analysis to provide insights on the operational alloying mechanisms occurring under high shear and elevated temperature. Using correlative microscopy techniques, we show alloying progresses via a combination of grain boundary diffusion and interfacial roughening at heterophane boundaries. Evidence supporting Cu infiltration along Ni-Ni grain boundaries along with asymmetric diffusion of Cu into Ni grains is highlighted. The resultant, consolidated microstructure was produced directly from a powder compact in ~30 s and exhibited a submicron, equiaxed grain size.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electronic descriptors for dislocation deformation behavior and intrinsic ductility in bcc high-entropy alloys

Controlling the balance between strength and damage tolerance in high-entropy alloys (HEAs) is central to their application as structural materials. Materials discovery efforts for HEAs are therefore impeded by an incomplete understanding of the chemical factors governing this balance. Through first-principles calculations, this study explores factors governing intrinsic ductility of a crucial subset of HEAs—those with a body-centered cubic (bcc) crystal structure. Analyses of three sets of bcc HEAs comprising nine different compositions reveal that alloy chemistry profoundly influences screw dislocation core structure, dislocation vibrational properties, and intrinsic ductility parameters derived from unstable stacking fault and surface energies. Key features in the electronic structure are identified that correlate with these properties: the fraction of occupied bonding states and bimodality of the d-orbital density of states. The findings enhance the fundamental understanding of the origins of intrinsic ductility and establish an electronic structure–based framework for computationally accelerated materials discovery and design.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys

In human-made malleable materials, microdamage such as cracking usually limits material lifetime. Some biological composites, such as bone, have hierarchical microstructures that tolerate cracks but cannot withstand high elongation. Here, we demonstrate a directionally solidified eutectic high-entropy alloy (EHEA) that successfully reconciles crack tolerance and high elongation. The solidified alloy has a hierarchically organized herringbone structure that enables bionic-inspired hierarchical crack buffering. This effect guides stable, persistent crystallographic nucleation and growth of multiple microcracks in abundant poor-deformability microstructures. Hierarchical buffering by adjacent dynamic strain–hardened features helps the cracks to avoid catastrophic growth and percolation. Our self-buffering herringbone material yields an ultrahigh uniform tensile elongation (~50%), three times that of conventional nonbuffering EHEAs, without sacrificing strength.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Dual material fused filament fabrication of composite core‐shell structures with improved impact resistance and interfacial adhesion

The mechanical performance of parts produced by fused filament fabrication (FFF) has been limited due to the presence of voids and poor interlayer welding. Recent advancements in FFF have enabled the fabrication of void-free objects with strong interlayer welding through the use of semicrystalline polymer shells such as high-density polyethylene (HDPE) along with a high viscosity core polymer like acrylonitrile-butadiene-styrene (ABS). Furthermore, the zero-shear viscosity (η0) of ABS is three orders of magnitude higher than HDPE making the ABS-HDPE core-shell configuration preferable. ABS holds the shape by preventing bulk flow and part bending while HDPE promotes full surface contact across the layers. Most polymers, however, are immiscible which causes a weak weld line along the core-shell interface. Herein, maleic anhydride (MAH) is grafted to the butadiene segment of the ABS core thereby compatibilizing the interface with HDPE, improving the interfacial adhesion. Attenuated total reflectance-Fourier transform infrared spectroscopy was employed to confirm successful grafting. Using a custom-made die affording the core-shell structure, the ABS-g-MAH is shown to improve the impact resistance by 253% and 16% compared to neat HDPE and ABS specimens, respectively. Additionally, a 10% increase compared to the unmodified ABS-HDPE core-shell configuration is observed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Material property characterization of 3D printed polypropylene wood plastic composites

Abstract Wood flour (WF) at 10 wt.% and 20 wt.% loadings was used as a reinforcing filler to enhance the applicability of polypropylene (PP) for 3D printing. After performing printability tests of PP wood plastic composites (WPCs), the mechanical properties of both injection‐molded and 3D‐printed PP WPC specimens were explored. Test specimens were prepared from 3D printed hexagons for analyzing the mechanical properties. Adding WF to neat PP increased the storage modulus and the glass transition temperature while decreasing the degree of crystallinity and the coefficient of thermal expansion, while enhancing the printability of neat PP. The tensile strength, tensile modulus of elasticity, flexural strength, and flexural modulus of elasticity of injection‐molded neat PP improved by up to 21%, 59%, 30%, and 56%, respectively, with 20 wt.% WF. However, the impact strength of injection‐molded neat PP decreased by 85%, with 20 wt.% WF. After 3D printing, the tensile strength and tensile modulus of elasticity of printed neat PP increased by up to 84% and 60%, respectively, with 20 wt.% WF. The flexural strength and flexural modulus of elasticity of neat printed PP remained unchanged compared to those of PP filled with 20 wt.% WF, while the impact strength decreased by 87%. Highlights WF was used as a reinforcement in polypropylene designed for 3D printing A pilot‐scale, pellet‐fed 3D printer was used to print hollow hexagons, and then test specimens were fabricated from these hexagons for mechanical properties The tensile and flexural properties of 3D printed neat polypropylene improved, while the impact strength decreased after adding 20 wt.% WF to the neat PP.

Hwang, Sungjun↗
DOE OSTI2025

Material extrusion additive manufacturing of wood pulp-reinforced epoxy composites

Direct ink writing (DIW) is an extrusion-based form of 3D-printing that has gained popularity over the last decade. DIW uses thixotropic fluid extrusion to form a particular shape. In order to form stable structures, the rheology of the paste is important to allow for extrusion from the syringe, stability of the growing print, and prevention of unwanted seeping flow during jog moves. In this work, we use wood pulp as a bio-based filler that can provide shear thinning properties to the ink, which produces a stable ink for DIW processing. Additionally, the filler imparts improved mechanical and thermal performance compared to neat resin. The wood pulp provided the shear thinning behavior necessary for DIW printing, and pulp loadings greater than 6 wt%, provided sufficient yield stress so that the composite could self-support during printing. Nanoclay was utilized to further improve ink rheology and appearance to enable larger scale printing. Overall, this work showed successful DIW of an epoxy resin with a sustainable filler improving its stiffness and thermal properties and provides an avenue for further development of bio-based inks for DIW towards various applications.

Lamm, Meghan E. [Oak Ridge National Laboratory (OR↗