Here we introduce a novel thermo-mechanical Solid State Additive Manufacturing (SSAM) process referred to as Additive Friction Stir (AFS) manufacturing that provides a new and alternative path to ...fusion-based additive manufacturing processes for developing fully-dense, near-net shape components with a refined-equiaxed grain morphology. This study is the first to investigate the beneficial grain refinement and densification produced by AFS in IN625 that results in advantageous mechanical properties (YS, UTS, εf) at both quasi-static and high strain rate. Electron Backscatter Diffraction (EBSD) observed grain refinement during the layer deposition in the AFS specimens, where the results identified fine equiaxed grain structures with even finer grain structures forming at the layer interfaces. The EBSD quantified grains as fine as 0.27µm in these interface regions while the average grain size was approximately 1µm. Additionally, this is the first study to report on the strain rate dependence of AFS IN625 through quasi-static (QS) (0.001/s) and high strain rate (HR) (1500/s) tensile experiments using a servo hydraulic frame and a direct tension-Kolsky bar, respectively, which captured both yield and ultimate tensile strengths increasing as strain rate increased. The HS results exhibited an approximately 200MPa increase in engineering strength over the QS results, with the fracture surfaces at both strain rates aligned with the maximum shear plane and exhibiting localized microvoids.
Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling ...conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10h, and a ND content of 10wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46GPa, a 210% increase over the pristine, untreated Al powder (1.10GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.
Issues with rapid grain growth, hot cracking and poor ductility have hindered the additive manufacturing and repair of aluminum alloys. Therefore, this is the first investigation to spatially ...correlate the processing-structure-property relations of a precipitation hardened aluminum alloy 2219 (AA2219) material with respect to deposition orientations and build layers. The AA2219 material was processed by a high deposition rate (1000 cm3/h) solid-state additive deposition process known as Additive Friction Stir Deposition or MELD. An equiaxed grain morphology was observed in the three orientations, where Electron Backscatter Diffraction (EBSD) identified a layer-dependent texture with a strong torsional fiber A texture in the top of the build transitioning to weaker textures in the middle and bottom layers. Interestingly, the tensile behavior reflected the texture layer-dependence with tensile strength increasing from the bottom to the top of the deposition. However, there were no statistically significant differences in hardness measured from the top to the bottom of the deposition. Furthermore, no orientation dependence on mechanical properties was observed for compression and tension specimens tested at quasi-static (0.001/s) and high (1500/s) strain rate. Transmission Electron Microscopy (TEM) determined a lack of θ′ precipitates in the as-deposited cross-section, therefore resulting in no precipitation strengthening.
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In this study, the effect of post-deposition heat treatments on an Al–Mg–Si alloy processed with additive friction stir deposition (AFS-D), a solid-state additive manufacturing process, is examined. ...Results reveal that wrought-like microstructure and mechanical properties are achievable in AFS-D builds through the application of a post-deposition heat treatment.
A dense nanodiamond–aluminum (ND–Al) composite coating was successfully produced by low pressure cold spray (CS) deposition of ball-milled powders containing 10wt% ND. High-energy ball milling is a ...feasible means for the synthesis of composite feedstock powders as it provides excellent control over particle size distribution, crystal size, and the dispersion of ND agglomerates. The resulting CS coatings were characterized with respect to deposition efficiency, particle velocity and mechanical properties. It was found that the CS deposition produced dense, ND–Al composite coatings with increases in both hardness and elastic modulus as compared to the feedstock powders. The coating hardness of the 0.5h-milled ND–Al composite that has the highest DE (14.2%) in ND–Al composites is 3.02GPa, an 175% increase over the pristine as-received Al (1.10GPa). The highest elastic modulus of the composite coatings is 98.3GPa, a 51.5% increase over the as-received Al powder.
The microstructures and mechanical properties of high pressure die cast A383 alloys under four conditions (with and without Sr additions and heat treatment) were investigated. Sr addition is ...responsible for the increase in the elongation of high pressure die cast A383 alloys by refining the eutectic Si particles from long, needle-like morphologies to fine, fibrous ones. High cooling rates, as generated in the high pressure die casting process, also significantly contribute to the microstructural refinement of the eutectic Si particles. However, there was almost no relationship between the morphologies (size and roundness) of the eutectic Si particles and the yield strength of high pressure die cast A383 alloys. Heat treatment (aging without solution treatment) increased the yield strength of high pressure die cast A383 alloys. Sr addition combined with heat treatment was found to refine the size of aging precipitates and therefore improve the yield strength beyond the levels observed for heat treatment alone. The sludge characteristics (size, roundness and fraction) were not affected by the different heat treatments and Sr additions and had no discernible effect on the change in mechanical properties.
Large-scale metal additive manufacturing (AM) provides a unique solution to rapidly develop prototype components with net-shape or near-net shape geometries. Specifically, additive friction stir ...deposition (AFSD) is a solid-state method for large-scale metal AM that produces near-net shape depositions capable of high deposition rates. As AFSD is utilized for a broader range of applications, there is a need to understand deposition strategies for larger and more complex geometries. In particular, components with larger surface areas will require overlapping deposition passes within a single layer. In this study, the AFSD process was used to create depositions utilizing multiple passes with a varying deposition path overlap width. The effects of overlapping parallel pass depositions on the mechanical and microstructural properties of aluminum alloy 7075 were examined. The grain size and microstructural features of the deposited material were analyzed to evaluate material mixing and plastic flow in the observed overlap regions. Additionally, hardness and tensile experiments were conducted to observe the relationship between the overlap width and as-deposited material behavior. In this study, an ideal overlap width was found that produced acceptable as-deposited material properties.
Friction stir welding (FSW) can generate large residual stresses during solid state joining of oxide dispersion strengthened steels. In this work, a plate of MA956 steel was friction stir welded at ...three conditions: 500rpm/25mm per minute (mmpm), 400rpm/50mmpm and 400rpm/100mmpm. The residual stresses across these welds were measured using both x-ray and neutron diffraction techniques. The distribution and magnitude of the residual stresses agreed well between the two techniques. Longitudinal residual stresses up to eighty percent of the yield strength were observed for the 400rpm/100mmpm condition. The surface residual stresses were somewhat larger on the root side of the weld than on the crown side. Increases in the relative heat input during FSW decreased the measured residual stresses in the stir zone and the thermomechanically affected zone (TMAZ). Increasing the traverse rate while holding the rotational speed fixed increased the residual stress levels. The fatigue strength of the material is predicted to decrease by at least twenty percent with cracking most likely in the TMAZ.
The design, manufacture, and experimental analysis of structural materials capable of operation in the high temperatures, corrosive environments, and radiation damage spectra of future reactor ...designs remain one of the key pacing items for advanced reactor designs. The most promising candidate structural materials are vanadium-based refractory alloys, silicon carbide composites and oxide dispersion strengthened steels. Of these, oxide dispersion strengthened steels are a likely near-term candidate to meet required demands. This paper reviews different variants of oxide dispersion strengthened steels and discusses their capability with regard to high-temperature strength, corrosion resistance, and radiation damage resistance. Additionally, joining of oxide dispersion strengthened steels, which has been cited as a limiting factor preventing their use, is addressed and reviewed. Specifically, friction stir welding of these steels is reviewed as a promising joining method for oxide dispersion strengthened steels.
This article explores the variability in austenitic stainless steel feed-stock powders and its effect upon low-pressure cold spray deposition. Four, commercial, austenitic stainless steel powders ...were deposited using cold spray deposition with helium gas at a temperature of 230°C and a pressure of 1.7MPa. Electron microscopy and X-ray diffraction were used to characterize the microstructure of both the powders and the resultant coatings. The particle size for the powders ranged from 17 to 40μm, while the crystallites ranged from 2 to 6μm in size. Only the 304L stainless steel powder was purely austenite in phase; while the three 316L powders had ferrite contents ranging from 23 to 50%. The deposition efficiency of the four powders varied considerably from 12 to 42%, but this variation did not correlate with the ferrite content alone. The spatial location of the ferrite in the cold sprayed material was highly dependent upon the powder type used: ferrite primarily on the outside of austenite particles, mixtures of wholly ferrite and wholly austenite particles, and particles with both ferrite and austenite internally. After cold spray deposition, all of the coatings exhibited a composite microstructure containing highly deformed prior particle centers with small (300nm) crystallites near the prior particle boundaries.
•The microstructures of different commercial powders for cold spray are examined.•The ferrite content in austenitic stainless steel powders can vary considerably.•Significant refinement in crystallite size observed after cold spray deposition.•Composite deformation structure between particle centers and boundaries observed.
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