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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Effects of Sn addition on the microstructure, mechanical properties and corrosion behavior of Ti–Nb–Sn alloys

Ti and Ti alloys are widely used in restorative surgery because of their good biocompatibility, enhanced mechanical behavior and high corrosion resistance in physiological media. The corrosion resistance of Ti-based materials is due to the spontaneous formation of the TiO{sub 2} oxide film on their surface, which exhibits elevated stability in biological fluids. Ti–Nb alloys, depending on the composition and the processing routes to which the alloys are subjected, have high mechanical strength combined with low elastic modulus. The addition of Sn to Ti–Nb alloys allows the phase transformations to be controlled, particularly the precipitation of ω phase. The aim of this study is to discuss the microstructure, mechanical properties and corrosion behavior of cast Ti–Nb alloys to which Sn has been added. Samples were centrifugally cast in a copper mold, and the microstructure was characterized using optical microscopy, scanning electron microscopy and X-ray diffractometry. Mechanical behavior evaluation was performed using Berkovich nanoindentation, Vickers hardness and compression tests. The corrosion behavior was evaluated in Ringer's solution at room temperature using electrochemical techniques. The results obtained suggested that the physical, mechanical and chemical behaviors of the Ti–Nb–Sn alloys are directly dependent on the Sn content. - Graphical abstract: Effects of Sn addition to the Ti–30Nb alloy on the elastic modulus. - Highlights: • Sn addition causes reduction of the ω phase precipitation. • Minimum Vickers hardness and elastic modulus occurred for 6 wt.% Sn content. • Addition of 6 wt.% Sn resulted in maximum ductility and minimum compression strength. • All Ti–30Nb–XSn (X = 0, 2, 4, 6, 8 and 10%) alloys are passive in Ringer's solution. • Highest corrosion resistance was observed for 6 wt.% Sn content.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Micro-CT analysis and mechanical properties of Ti spherical and polyhedral void composites made with saccharose as a space holder material

The paper describes the formation, morphology and mechanical properties of Ti void composites. The Ti void composites were made using 100 and 325 mesh Ti powder for solid scaffold formation. The spherical and polyhedral voids (pores) were formed using saccharose particles (table sugar) of different shapes. The Ti void composite morphology was investigated by microcomputed tomography and scanning electron microscopy. The Ti void composites of designed porosity of 50–70% were made. Compression test was applied for mechanical properties estimation. It has been found, that Ti void composites made from 100 mesh Ti and those having spherical pores have a higher strength and elastic modulus, i.e. for the designed porosity of 50% for 100 and 325 mesh Ti void composites, a compressive strength was 32.32 and 20.13 MPa, respectively. It has been shown that this is related to better sintering of the 100 mesh Ti powders compared with the 325 mesh Ti powders. A correlation between microcomputed tomography data and mechanical properties has also been shown. The Ti void composites, made with the use of saccharose as a space holder, described in this work should be a promising material for biomedical applications, where interconnected pores and good mechanical properties are required. - Highlights: • Ti scaffolds of the porosity of 50–70% were made. • Saccharose particles as space holder were applied. • The voids in the scaffolds were designed with spherical and polyhedral shape. • The scaffold structure was investigated by SEM and micro-CT. • Micro-CT data and mechanical properties of the Ti scaffold have been correlated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microstructural characterization of a new mechanically alloyed Ni-base ODS superalloy powder

The microstructure of a new Ni-base oxide dispersion strengthened superalloy powder was studied for high temperature gas turbine applications after the mechanical alloying process. In this study, an atomized powder with a composition similar to the CMSX-10 superalloy was mechanically alloyed with yttria and Hf powders. The mechanically alloyed powder included only the supersaturated solid solution γ phase without γ′ and yttria provided by severe plastic deformation, while after the 3-step aging, the γ′ phase was precipitated due to the partitioning of Al and Ta to the γ′ and Co, Cr, Re, W, and Mo to the γ phase. Mechanical alloying modified the morphology of γ′ to the new coherent γ–γ′ nanoscale lamellar structure to minimize the elastic strain energy of the precipitation, which yielded a low lattice misfit of 0.16% at high temperature. The γ′ lamellae aligned preferentially along the elastically soft [100] direction. Also, the precipitated oxide particles were refined in the γ phase by adding Hf from large incoherent YAlO{sub 3} to fine semi-coherent Y{sub 2}Hf{sub 2}O{sub 7} oxide particles with the average size of 7 nm and low interparticle spacing of 76 nm. - Highlights: • A new Ni-base ODS superalloy powder was produced by mechanical alloying. • The nanoscale γ–γ′ lamellar structure was precipitated after the aging treatment. • Fine semi-coherent Y{sub 2}Hf{sub 2}O{sub 7} oxide particles were precipitated by addition of Hf.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Characterization of Al–Al{sub 4}C{sub 3} nanocomposites produced by mechanical milling

In this work, a mixture of Al–C–Al{sub 4}C{sub 3} nanopowder previously synthesized by mechanical milling and subsequent thermal treatment was used to reinforce the Al matrix. The nanocomposites were fabricated via high-energy ball milling and subsequent sintering process for different periods of time at 550 °C. Hardness and compression tests were performed to evaluate the mechanical properties of the nanocomposites in the as-milled and sintered conditions. According to the results the reinforcement located in the grain boundaries is responsible for the brittle behavior observed in the nanocomposites during the compression test. The combined effect of sintering and precipitation mechanisms produced an evident increase of the strength of the Al matrix at a relatively short sintering time. By using the Rietveld method the crystallite size and microstrain measurements were determined and correlated with the microhardness values. For the proper characterization of the nanoparticles present in the Al matrix, atomic force microscopy and high resolution electron microscopy were used. - Highlights: • Nanostructured Al{sub 4}C{sub 3} reinforcement was fabricated via mechanical milling and heat treatment. • We found a significant increase of the mechanical properties at short sintering times. • The formation of Al{sub 4}C{sub 3} with during sintering time restricted the excessive growth of the crystallite. • Al{sub 4}C{sub 3} located in the grain boundaries causes brittle fracture observed in compression tests. • There is a correlation between, crystallite size and microstrain values with microhardness.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Gas tungsten arc welding and friction stir welding of ultrafine grained AISI 304L stainless steel: Microstructural and mechanical behavior characterization

In the present study, an ultrafine grained (UFG) AISI 304L stainless steel with the average grain size of 650 nm was successfully welded by both gas tungsten arc welding (GTAW) and friction stir welding (FSW). GTAW was applied without any filler metal. FSW was also performed at a constant rotational speed of 630 rpm and different welding speeds from 20 to 80 mm/min. Microstructural characterization was carried out by High Resolution Scanning Electron Microscopy (HRSEM) with Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Nanoindentation, microhardness measurements and tensile tests were also performed to study the mechanical properties of the base metal and weldments. The results showed that the solidification mode in the GTAW welded sample is FA (ferrite–austenite) type with the microstructure consisting of an austenite matrix embedded with lath type and skeletal type ferrite. The nugget zone microstructure in the FSW welded samples consisted of equiaxed dynamically recrystallized austenite grains with some amount of elongated delta ferrite. Sigma phase precipitates were formed in the region ahead the rotating tool during the heating cycle of FSW, which were finally fragmented into nanometric particles and distributed in the weld nugget. Also there is a high possibility that the existing delta ferrite in the microstructure rapidly transforms into sigma phase particles during the short thermal cycle of FSW. These suggest that high strain and deformation during FSW can promote sigma phase formation. The final austenite grain size in the nugget zone was found to decrease with increasing Zener–Hollomon parameter, which was obtained quantitatively by measuring the peak temperature, calculating the strain rate during FSW and exact examination of hot deformation activation energy by considering the actual grain size before the occurrence of dynamic recrystallization. Mechanical properties observations showed that the welding efficiency of the FSW welded sample is around 70%, which is more than 20% higher than the GTAW welded sample. - Highlights: • Microstructure and mechanical properties of UFG 304L stainless steel were studied during GTAW and FSW. • Sigma phase formation mechanism was studied during FSW of 304L stainless steel. • THERMOCALC analysis was performed to obtain possible formation temperatures for sigma phase. • Nano-mechanical twins were found in the TMAZ region.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and mechanical behavior of direct metal laser sintered Inconel alloy 718

In this paper, we investigate microstructure and quasi-static mechanical behavior of the direct metal laser sintered Inconel 718 superalloy as a function of build direction (BD). The printed material was further processed by annealing and double-aging, hot isostatic pressing (HIP), and machining. We characterize porosity fraction and distribution using micro X-ray computed tomography (μXCT), grain structure and crystallographic texture using electron backscattered diffraction (EBSD), and mechanical response in quasi-static tension and compression using standard mechanical testing at room temperature. Analysis of the μXCT imaging shows that majority of porosity develops in the outer layer of the printed material. However, porosity inside the material is also present. The EBSD measurements reveal formation of columnar grains, which favor < 001 > fiber texture components along the BD. These measurements also show evidence of coarse-grained microstructure present in the samples treated by HIP. Finally, analysis of grain boundaries reveal that HIP results in a large number of annealing twins compared to that in samples that underwent annealing and double-aging. The yield strength varies with the testing direction by approximately 7%, which is governed by a combination of grain morphology and crystallographic texture. In particular, we determine tension–compression asymmetry in the yield stress as well as anisotropy of the material flow during compression. We find that HIP lowers yield stress but improves ductility relative to the annealed and aged material. These results are discussed and critically compared with the data reported for wrought material in the same condition. - Highlights: • Microstructure and mechanical properties of DMLS Inconel 718 are studied in function of build direction. • Inhomogeneity of microstructure in the material in several conditions is quantified by μXCT and EBSD. • Anisotropy and asymmetry in the mechanical response are determined by tension and compression testing.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of cobalt doping on the mechanical properties of ZnO nanowires

In this work, we investigate the influence of doping on the mechanical properties of ZnO nanowires (NWs) by comparing the mechanical properties of pure and Co-doped ZnO NWs grown in similar conditions and having the same crystallographic orientation [0001]. The mechanical characterization included three-point bending tests made with atomic force microscopy and cantilever beam bending tests performed inside scanning electron microscopy. It was found that the Young's modulus of ZnO NWs containing 5% of Co was approximately a third lower than that of the pure ZnO NWs. Bending strength values were comparable for both materials and in both cases were close to theoretical strength indicating high quality of NWs. Dependence of mechanical properties on NW diameter was found for both doped and undoped ZnO NWs. - Highlights: •Effect of Co doping on the mechanical properties of ZnO nanowires is studied. •Co substitutes Zn atoms in ZnO crystal lattice. •Co addition affects crystal lattice parameters. •Co addition results in significantly decreased Young's modulus of ZnO. •Bending strength for doped and undoped wires is close to the theoretical strength.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure, mechanical properties and microtexture of friction stir welded S690QL high yield steel

Two try-out campaigns of friction stir welding (FSW) were performed with different friction parameters to join S690QL high yield strength steel. The welds were investigated at macroscopic and microscopic scales using optical and electronic microscopy and microhardness mapping. Welds of the second campaign exhibit microstructures and mechanical properties in accordance with requirements for service use. Microtexture measurements were carried out in different zones of welds by electron backscattered diffraction (EBSD). It is shown that that texture of the bottom of the weld is similar to that of the base metal, suggesting a diffusion bonding mechanism. Finally, the mechanical properties (tensile strength, resilience, bending) were established on the most promising welds. It is shown that it is possible to weld this high yield strength steel using FSW process with satisfactory geometric, microstructural and mechanical properties. - Highlights: •1000 mm ∗ 400 mm ∗ 8 mm S690QL steel plates are joined by friction stir welding (FSW). •Maximum hardness is reduced by optimization of process parameters. •Various microstructures are formed but no martensite after process optimization. •Texture is modified in mechanically affected zones of the weld. •Texture in the bottom of the weld is preserved, suggesting diffusion bonding.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ameliorated mechanical and thermal properties of SiC reinforced Al matrix composites through hybridizing carbon nanotubes

Highlights: • The carbon nanotubes were hybridized into SiC reinforced Al based composites. • Hybridization of CNTs leads to the uniform dispersion of SiC in the Al matrix. • Hybridization of CNTs enhances the strength and ductility of the composites. • CNTs can help to decrease the coefficient of thermal expansion of the composites. - Abstract: By hybridizing carbon nanotubes (CNTs) into SiC reinforced Al matrix composites, a novel composite was fabricated to achieve excellent mechanical properties and low coefficient of thermal expansion simultaneously. The study demonstrated that the CNTs can help to acquire the uniform dispersion of SiC particles in the Al matrix, because of their interaction during ball milling and hot rolling processes. In addition, the results revealed that such design optimizes both the mechanical and thermal properties, due to homogeneous microstructure as well as tight and uniform interfaces induced by the addition of CNTs. Strengthening mechanism and Sideridis's model were used to discuss the effects of the CNTs on the mechanical and thermal properties. This study opens up an unexplored avenue for simultaneous improvement of the mechanical and thermal properties of metal matrix composites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development of nano-Y2O3 dispersed Zr alloys synthesized by mechanical alloying and consolidated by pulse plasma sintering

Highlights: • Zr-Fe-Cr-Cu-Ti-1.0wt% nano-Y{sub 2}O{sub 3} dispersed alloys are fabricated by mechanical alloying and pulse plasma sintering. • These alloys record extremely high compressive strength, Young’s modulus, and hardness. • These mechanical properties are superior as compared to other commercially available Zr based alloys. • Dispersion of nanometric FeZr{sub 2}, Y{sub 2}Ti{sub 2}O{sub 7}, Fe{sub 2}Ti, ZrCu, Cr{sub 2}Zr, Y{sub 2}O{sub 3} leads to grain boundary pinning at elevated temperature. - Abstract: In this paper, Zr alloys are synthesized with nominal compositions: 50Zr-30Fe-10Cr-5Cu-5Ti (alloy A), and 49Zr-30Fe-10Cr-5Cu-5Ti-1Y{sub 2}O{sub 3} (alloy B), 45Zr-30Fe-10Cr-10Cu-5Ti (alloy C), 44Zr-30Fe-10Cr-10Cu-5Ti-1Y{sub 2}O{sub 3} (alloy D) (all in wt%) by mechanical alloying and consolidated by pulse plasma sintering at 1173 K (900 °C), 1223 K (950 °C) and 1273 K (1000 °C) using 75 MPa uniaxial pressure applied for 5 min and 70 kA pulsed current at 3 Hz pulse frequency. The microstructure and phase evolution during mechanical alloying and sintering has been characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM & TEM) and energy dispersive spectroscopy (EDS). Mechanical properties i.e. hardness and compressive strength were determined by using nano-indentation unit and universal testing machine. The produced alloys recorded very high levels of compressive strength (1359–2456 MPa), and hardness (7.05–10.05 GPa) which measures 1.5–2.0 times more than that of other Zr alloys (2 O{sub 3}) particles which can contribute to grain boundary pinning, and improved creep and oxidation resistance at elevated temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Effects of processing defects on the dynamic tensile mechanical behavior of laser-solid-formed Ti-6Al-4 V

Highlights: • Tensile tests are conducted under coupled effects of strain rate and temperature. • Defects act as crack initiation and propagation sites for dynamic tensile fracture. • Dynamic tension-compression asymmetry is due to different behaviors of defects. • Different deformation of defects results in tensile mechanical anisotropy. • Mechanical anisotropy and asymmetry are sensitive to strain rate and temperature. - Abstract: The initial processing defects, i.e. voids, lack-of-fusion pores and inclusions, are the inevitable and unique microstructural features in the Ti-6Al-4 V (Ti64) alloy manufactured by laser solid forming (LSF). This study was to gain insight into the influences of these processing defects on the tensile thermomechanical response of the material under various strain rates of 0.001/s, 500/s, 1000/s and 3000/s, and under a wide range of temperatures from 298 K to 1273 K. The drastic effects of processing defects on the flow stress were founded to be susceptible to tensile loading and increase with the increasing strain rate. The SEM analysis was carried out to further understand the effect of initial processing defects on the dynamic fracture behavior. These processing defects, such as voids and lack-of-fusion pores, are the most vulnerable position to release impact energy instantaneously and then evolve into the initiation site and propagation path for dynamic tensile crack. The tensile crack under high strain rate and high temperature propagates through the columnar prior-β grain boundary α colony. It was analyzed that the typical tension-compression asymmetry in strength is positively associated with the strain rate in the Ti64 alloy by LSF. Such asymmetry is due to the differences in the deformation mechanism of processing defects and in the activated slip system under tensile and compressive loading. Additionally, the anisotropy of the mechanical property was discussed by examining the positive strain rate effects in two orientations (i.e., perpendicular and parallel to the crystal growth direction). This anisotropy is caused by different mechanical behaviors of lack-of-fusion defects and β grain boundary α colony in different orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and nanoindentation analysis of Mg-SiC nanocomposite powders synthesized by mechanical milling

Highlights: • Mechanical milling as an effective solution to reach a homogeneous distribution of SiC nanoparticles up to 10 vol% in Mg matrix • No deformation twinning in the nanostructured Mg matrix even after the severe plastic deformation and hard SiC nanoparticles up to 10 vol%. • Significant enhancement of nanohardness and reduced elastic modulus in the milled nanocomposite powders - Abstract: Mixtures of magnesium powder and SiC nanoparticles at various volume fractions were mechanically milled to produce nanocrystalline Mg-SiC nanocomposites. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the milled powders. The microstructural evidences revealed that mechanical milling is a proper method to achieve a uniform distribution of the SiC nanoparticles, even up to 10% in the Mg matrix. Based on the results, higher volume fraction of the SiC nanoparticles raise the value of measured microstrain and reduce the crystallite size of the Mg matrix. The TEM results pointed to the fact that no deformation twinning takes place in the nanostructured Mg matrix even after severe plastic deformation through mechanical milling and the presence of hard SiC nanoparticles up to 10 vol%. The effects of nanoparticle volume fraction on mechanical properties of the milled Mg-SiC nanocomposites were evaluated using nanoindentation tests. The results clearly showed a significant enhancement of nanohardness and reduced elastic modulus in the milled powders compared to that of the reference material namely as-received pure magnesium. It was found that the SiC nanoparticles (even up to 10 vol%), well distributed in the magnesium matrix, remarkably improve the reduced elastic modulus and nanohardness of the nanocomposite powders.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Effects of initial microstructures on serrated flow features and fracture mechanisms of a nickel-based superalloy

Highlights: • Uniaxial tensile tests are performed on a nickel-based superalloy at 473 K–973 K and low strain rates. • Effects of initial microstructures on serrated flow features, and fracture characteristics are analyzed. • The dislocation across slip in the matrix is responsible for the serrated flow. • Nucleation and growth of micro-voids is the main fracture mechanism of ST and HS superalloys. • The better tensile ductility is obtained with raising the deformation temperatures for the SAT superalloy. - Abstract: The uniaxial tensile experiments are performed on a nickel-based superalloy with different initial microstructures at intermediate temperatures (473–973) K and low strain rates (0.0001–0.001) s{sup −1}. Effects of initial microstructures on plastic deformation mechanisms, serrated flow features, and fracture characteristics are analyzed. It is clearly demonstrated that the plastic deformation mechanism of serrated flow is irrelevant to the initial microstructures, and the dislocation across slip in the matrix is responsible for the serrated flow. However, the effects of initial microstructures on fracture mechanisms are obvious, i.e., the main fracture mechanism of the ST (solution treated) and HS (solution plus γ′/γ″ phases aging precipitation) superalloys are the nucleation and growth of micro-voids, which accelerates the break of carbides and interfacial failure of carbides/matrix. While for the SAT (solution plus δ phases aging precipitation) superalloy, δ phases and carbides play a significant role in the nucleation of micro-voids. Furthermore, the increase of the deformation temperature reduces the elongation to fracture of the ST and HS superalloys. However, the better tensile ductility is obtained with raising the deformation temperatures for the SAT superalloy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mechanical characterization of Ti-6Al-4V titanium alloy at multiple length scales using spherical indentation stress-strain measurements

Recent advances in spherical indentation stress-strain protocols and analyses have demonstrated the capability for measuring reliably the local mechanical responses in polycrystalline metal samples at different length scales, ranging from sub-micron (regions within individual grains) to several hundreds of microns (regions covering several grains). These recent advances have now made it possible to study systematically the mechanical behavior of a single material system at different length scales, with tremendous potential to obtain new insights into the role of individual phases, interfaces, and other microscale constituents on the macroscale mechanical response of the material. In this paper, we report spherical indentation stress-strain measurements with different indenter sizes (microns to millimeters) on Ti-6Al-4V (Ti-64) which capture the mechanical response of single phase alpha-Ti-64, single colony (alpha-beta), few colonies, and many colonies of Ti-64. The results show that the average mechanical response (indentation modulus and yield strength) from multiple indentations remains relatively unchanged from single phase alpha to many colonies of Ti-64, while the variance in the response decreases with indenter size. In conclusion, the work-hardening response in indentation tests follows a similar behavior up to indentation zones of many colonies, which shows significantly higher work hardening rates.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Non-equilibrium simulations of hydraulic permeation: Role of mechanical boundary conditions in dense membranes

Understanding the mechanisms of water transport in reverse osmosis membranes is critical for improving membrane performance and guiding material design. While classical models describe transport as either solution-diffusion (SD)—involving concentration-driven diffusion through a homogeneous medium—or pore-flow (PF)—involving pressure-driven convection through percolated water channels—their applicability to crosslinked polyamide membranes remains debated. Here, using non-equilibrium molecular dynamics simulations, we investigate the impact of mechanical support conditions on pressure-driven water transport in polyamide membranes across varying crosslink densities and pressure differentials (1000–5000 bar). Two support conditions are considered: graphene-restrained, representing experimentally relevant supported membranes, and freeze-restrained, mimicking a self-supported structure. In graphene-restrained systems, water concentration gradients and constant pressure profiles emerge, consistent with SD theory and incompatible with PF assumptions due to the absence of percolated pores and sub-nanometer voids. In contrast, freeze-restrained systems display uniform water concentration and linearly decreasing pressure at 1000 bar, and exhibit compressibility-induced water gradients and partial percolation at 5000 bar, resembling PF-like behavior. However, the underlying assumptions of PF theory—continuous solvent pathways and pressure transmission through water-filled pores—are not met under most conditions. Our results demonstrate that accurate modeling of reverse osmosis membranes must incorporate realistic mechanical boundary conditions to distinguish between transport mechanisms. For dense polyamide membranes supported by porous substrates, graphene-restrained simulations best reflect experimental setups and support the SD model as the dominant mechanism of water permeation.

molecular dynamics↗
DOE OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of Cold Rolling on Microstructure and Mechanical Properties of Fe-30Mn-3Si-4Al-0.093C TWIP Steel

The effects of cold rolling on microstructure evolution and the associated mechanical properties of Fe-30Mn-3Si-4Al-0.093C twinning-induced plasticity (TWIP) steel are examined in this work with reduction rates of 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Through texture analysis and transmission electron microscopy (TEM) observations, it is suggested that slip, mechanical twinning, the interaction between dislocation/twin boundaries (TB), and shear band have influenced the observed mechanical behavior and development of texture. Special components of weak initial textures are preferential for mechanical twinning, resulting in an increase in strain hardening rate. By mechanical twinning, the {111}<112> orientation is rotated into a position at the vicinity of the {110}<001> Goss orientation, and the {552}<115> (Cu-twin) texture is transformed to the {110}<001> orientation. The evolution of texture is closely related to the onset of shear banding resulting from deformation twinning. The sample with 10% cold reduction exhibits a favorable combination of yield strength and ductility, indicating a considerable capacity for energy absorption. With increasing rolling reductions, the deformation of the samples becomes inhomogeneous due to the high anisotropy of the microstructure. The localized shear bands resulting from the excessive cold rolling are detrimental to the ductility of the present TWIP steel.

Shen, Yongfeng↗
DOE OSTI2020

Tunable mechanical behavior of graphene nanoribbon-metal composites fabricated through an electrocharge-assisted process

This work investigates the role of a carbon nanophase on the local mechanical behavior of nanocarbon metal matrix 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 behavior with little effect on elastic properties. Here, this understanding enables further study into tunable bulk properties of Al-based NCMCs while isolating microstructural effects and reinforcement effects of the carbon phase. Such an understanding will lead to application-specific material geometries ranging from highperforming vehicle structures to next-generation electrical devices.

36 MATERIALS SCIENCE↗