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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The effect of Cerium addition on microstructure and mechanical properties of high pressure die cast Mg-5Sn alloy

Highlights: • The alloying additive has good grain refinement effect. • The addition of Ce to the Mg-5Sn alloy led to the formation of the new intermetallic phases CeMgSn and Ce{sub 5}Sn{sub 4}. • The hardness, yield and tensile strength of Mg-5Sn alloy were improved with addition of Ce. • The elongation of Mg-5Sn was increased up to 5wt.%Ce addition, and then decreased with addition of 7 wt.%Ce. • The yield and tensile strength of the Ce added alloy were higher than those of the base alloy at elevated temperatures. - Abstract: The effect of Cerium addition to Mg-5Sn alloy and its influence on the microstructure and mechanical properties of the alloy were investigated in this work. The microstructural investigations indicate that the alloying addition of Ce leads to effective grain refinement. Also, it was observed that adding Ce to the Mg-5Sn alloy results in the formation of new phases in the alloy such as Ce{sub 5}Sn{sub 4} and CeMgSn. These intermetallic phases were considered to be effective on the enhancement of the hardness of Mg-5Sn alloy. Furthermore, the tensile test results at room temperature and elevated temperatures revealed that the yield and tensile strength of the Ce added alloy were higher than those of the base alloy. The elongation was also improved up to 5 wt% Ce addition while higher amounts decreased the elongation both at room and elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Growth of faceted SiC nanostructures using vapor phase condensation: Microstructural analysis

Highlights: • Synthesis of nanocrystalline SiC using thermal plasma route. • XRD data indicates presence of both α- and β-SiC polytypes with β-SiC as the major content. • HRTEM and SAED analysis reveals polytypic arrangement with stacking faults SiC nanoparticles. • TEM micrograph reveals presence of faceted structures such as hexagonal, triangular, triangular pyramidal structure. - Abstract: The paper emphasizes the morphological and microstructural analysis of SiC nanostructures grown by thermal plasma assisted gas phase condensation process. High Resolution Transmission Electron Microscopic and Selected Area Electron Diffraction studies are used to analyze the growth directions and the polytypic arrangement with stacking faults in the as synthesized SiC nanoparticles. The results help in understanding the hierarchical poly-types related to the observed geometries and showed the presence of both α- and β-SiC polytypes. The microstructural study is supported by X-Ray diffraction and UV–Visible absorption spectroscopic studies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Microstructure, texture and tensile behavior of pulsed electrodeposited Ni–Al composites produced using organic additive-free sulfamate bath loaded with Al nanoparticles

Highlights: • Foils of fine grained Ni with Al nanoparticles reinforcement are produced by pulsed electro-codeposition. • Ni–Al composite foils exhibit increased compressive residual stresses with increasing Al content. • Well-dispersed Al nanoparticles refine Ni matrix microstructure and induces significant texture changes. • Ultrafine grained Ni-Al composites exhibit improved hardness and tensile strength. - Abstract: Nickel and Ni–Al composites with varying Al nanoparticle content were produced by pulsed electrodeposition using an organic additive-free sulfamate bath. The as-deposited Ni–Al composites exhibited increased compressive residual stresses with increasing Al nanoparticles. Detailed microstructural investigation revealed that Al codeposition led to significant refinement of the columnar morphology and grain structure of Ni matrix along with a texture change from strong <001> to <011> fiber texture parallel to the growth direction. The as-deposited Ni with bimodal grain structure displayed good tensile strength and ductility. The microhardness and tensile strength of the Ni deposits were increased initially with Al content and then decreased at higher particle content. Particle induced grain refinement and texture changes could be related to change in the growth of upcoming Ni nuclei on to the surface of well-dispersed Al nanoparticles. Significant grain refinement and lesser internal stresses along with good particle distribution and relatively harder <011> fiber texture at lower particles concentration collectively contributed to the observed higher strengths in Ni–Al composites as compared to Ni deposits. There was substantial change in fracture morphology from spherical dimples to flat regions with increasing Al content due to agglomeration of nanoparticles at higher particle loading.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Relationship between laser energy input, microstructures and magnetic properties of selective laser melted Fe-6.9%wt Si soft magnets

Highlights: • Effect of laser energy input on magnetic properties of SLM Fe-6.9%wt.Si is described; • Magnetic properties can be described as function of as-built microstructure after stress-relief post-treatment; • Samples with density >99% and strong crystallographic texture along BD have the best magnetic properties; • At very high laser energy, a strong cube texture forms that deteriorates the magnetic properties. - Abstract: Selective Laser Melting (SLM), a powder-bed Additive Manufacturing technology, can be used in combination with high temperature post-annealing to produce high-silicon steel parts characterised by quasi-static magnetic properties comparable to those of commercial electrical steel. However, the role of the as-built microstructure on the magnetic properties is still unexplored. Therefore, in this study the effect of the energy input of the processing laser on the magnetic properties of the material is investigated. The magnetic properties are determined for 4 mm-high rings obtained using three laser energy input values that provide a good compromise in terms of porosity and crack formation. The best magnetic properties are obtained for the rings built using a value of energy input that produces a strong fibrous crystallographic texture, in which one of the crystallographic <001> axes is preferentially aligned along the build direction. Whether the magnetic properties change with sample direction as a result of the crystallographic texture will be the subject of future research.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Bi on the microstructure and mechanical properties of Sn-Zn alloys processed by rolling

Highlights: • Sn-Zn-Bi is proposed for the first time as the cladding in linear explosive device. • Bi can significantly refine the microstructure of Sn-Zn. • Bi can enhance both strength and ductility of Sn-Zn processed by rolling. • The 5 wt% Bi in Sn-3Zn leads to finest and most homogenous grains after rolling. - Abstract: Sn-Zn based alloys including Sn-3Zn, Sn-3Zn-1Bi, and Sn-3Zn-5Bi were prepared by casting and rolling, in efforts to assess their feasibility for the application as cladding materials in detonating and explosive cords. It was found that Bi significantly refined the solidification microstructure, changing the configuration of Sn-Zn eutectic from well-aligned Zn-rich precipitates/needles to misaligned Zn-rich flakes. During deformation, second phases like Zn-rich precipitates and Bi particles, and Bi solutes were effective in grain refinement since second phase particles provided more sites for nucleation and more obstacles to growth of new recrystallized grains. Tensile results revealed that Bi addition enhanced both strength and ductility of the rolled Sn-Zn-Bi alloys. The Sn-3Zn-5Bi alloy possessed superior strength and ductility (UTS: 84.4 MPa; Yield strength: 68.3 MPa; Elongation: 75.2%) due to its finest and most homogeneous equiaxed grains. Based on decent mechanical properties, the Sn-Zn-Bi alloys could be well qualified for the application as cladding materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Sn microalloying on cold rolling and recrystallization textures and microstructure of a ferritic stainless steel

Highlights: • Sn microalloying contributes to the enhancement in cold rolling texture intensity and the acceleration in cold rolling texture transformation. • Sn microalloying promotes the recrystallization process, and recrystallization occurs preferentially in steel with Sn compared with Sn-free steel. • Sn microalloying inhibits the growth of recrystallized grains, and the finer grains are obtained in steel with Sn. - Abstract: We investigated the effects of Sn microalloying on cold rolling and recrystallization textures and microstructure of a ferritic stainless steel. The as-received hot rolled sheets were cold rolled at 10%–90% reductions; the sheets cold rolled up to an 80% reduction were annealed at 740–880 °C for 5 min. For comparison, the cold rolling and recrystallization textures of the steel sheets with and without Sn were determined with the conventional X-ray diffraction method. The cold rolling and recrystallization metallographic microstructures were measured by scanning electron microscope and optical microscope, and the crystal orientation maps of the cold rolled and annealed samples were observed by electron backscattered diffraction. The micro-hardness was determined using a digital micro-hardness tester. Our results show that Sn microalloying in a medium chromium ferritic stainless steel plays multiple roles in the cold rolling and recrystallization processes. Sn micrcoalloying contributes to the enhancement in cold rolling texture intensity and the acceleration in cold rolling texture transformation. Sn microalloying is beneficial in promoting the recrystallization process. Recrystallization occurs preferentially in the ferritic stainless steel with Sn. Sn microalloying plays an important role in inhibiting the growth of recrystallized grains. The finer grains are obtained in ferritic stainless steel with Sn when annealing at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaluation of the microstructure and mechanical properties of WC particle reinforced aluminum matrix composites fabricated by friction stir processing

Highlights: • FSP was used for the preparation of aluminum matrix composites reinforced with WC particle. • WC particles were uniformly distributed in the composite. • WC particles refined the grains of aluminum matrix. • WC particles enhanced the hardness and tensile strength, but decreased the ductility. - Abstract: Tungsten carbide (WC) is an attractive reinforcing material for aluminum and its alloys. However, it is technically challenging to fabricate WC particle reinforced aluminum matrix composites (AMCs) with homogeneous distribution of WC particles by liquid state processing techniques because of large density gradient. The present work aim to produce WC particle reinforced aluminum matrix composites (AMCs) through friction stir processing (FSP) and analyze the effect of its volume fraction on the microstructural features and the mechanical behavior of the developed AMCs. Microstructural evaluation was conducted on the cross-sections of the samples by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Microhardness testing was conducted across the cross-sections of FSPed samples to obtain hardness profiles and tensile test was conducted on as-received Al and FSPed samples. The fabricated AMCs exhibited the homogeneous distribution of WC particle with no obvious particle clustering in the stir zone, irrespective of position and WC particle volume fraction. Excellent WC/Al interfacial bonding was obtained in all FSPed AMCs with obviously refined grains. The average size of WC particles after FSP was slightly reduced with the increased volume fraction. It was also found that increasing the volume fraction of WC particles favored the grain refinement, improved the hardness and strength, but decreased the ductility. This improvement in the hardness and strength was attributed to the grain refinement strengthening and homogeneous distribution of WC particles. The decreased ductility resulted from the introduction of more WC particles. Increasing the volume fraction of WC particles caused the nature of fracture to move towards brittle nature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure evolution and mechanical properties of the compressively deformed AgInCd alloy during annealing treatment

Highlights: • The microstructure of AgInCd alloy during annealing treatment is investigated. • Nanoscale deformation twins are formed in the deformed AgInCd alloy. • Deformation twins are transformed into stacking faults by detwinning mechanism. • Annealing twins show higher thermal stability than deformation twins. - Abstract: The microstructure evolution and mechanical properties of the compressively deformed AgInCd alloy during annealing treatment have been investigated in the present study. In the deformed AgInCd alloy, many deformation markings are formed and these deformation markings are mainly composed of nanoscale deformation twins. The AgInCd alloy exhibits a significant work hardening capability because of the formation of deformation twins. The recrystallization temperature of the deformed AgInCd alloy is between 300 °C and 350 °C. In the AgInCd alloy annealed at 300 °C, the deformation twins are eliminated and a large number of dark strips consisting of stacking faults are presented in the un-recrystallized regions, indicating that the deformation twins are transformed into stacking faults by the detwinning mechanism. The annealing twins show higher thermal stability than the deformation twins. The strength and microhardness of the deformed AgInCd alloy gradually decrease with the increase of annealing temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interfacial microstructure evolution and weld formation during ultrasonic welding of Al alloy to Cu

Highlights: • Surface oxide layer was fractured and dispersed around the weld interface during ultrasonic welding of Al alloy to Cu. • Mechanical mixing around the weld interface was caused by compressive deformation with ultrasonic vibration. • Once micro-bonds were generated between Al and Cu, shear deformation occurred around the weld interface. • Enhanced Cu diffusion into Al in the severely deformed region significantly contributed to the weld formation. - Abstract: Dissimilar welds of Al alloy 1050 to Cu were prepared via ultrasonic spot welding in order to understand the formation of welds and interfacial microstructures. To observe oxide layer behavior at the weld interface, the anodized Al alloy 1050 was also welded to Cu. Mechanical mixing and material flow during ultrasonic welding broke and dispersed the oxide layers into the Al matrix. This material flow is attributed to compressive deformation that occurred due to ultrasonic vibrations. Direct bonding in the Al/Cu region increased with welding time. Once micro-bonds were generated between Al and Cu, the Al matrix in the vicinity of the weld interface was severely deformed in the direction of the ultrasonic vibrations. Consequently, a recrystallized microstructure with shear texture was formed in the Al matrix. Deformation heating and severe shear deformation formed Al{sub 2}Cu intermetallic compound layers at the weld interface. The growth rate of the Al{sub 2}Cu layer was much faster than had previously been estimated based upon the peak temperature and ultrasonic welding heating time. This is likely due to the increased rate of Cu diffusion into Al in the severely deformed region.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure, texture and mechanical properties of AA 1060 aluminum alloy processed by cryogenic accumulative roll bonding

Highlights: • The Al sheets were accumulative roll bonded to five cycles at cryogenic temperature. • The microstructure, texture and mechanical properties of ARB sheets were investigated. • The texture evolution at surface layer was quantified by mathematical formulae. • The strength of the β fiber at center layer was affected by the initial texture and the strain. - Abstract: AA 1060 aluminum alloy sheet was processed to five accumulative roll bonding (ARB) cycles at cryogenic temperature. The microstructure, texture and mechanical properties of the ARB processed sheets were investigated. The results show that the surface layer of the ARB processed sheets exhibits a significant r-cube shear texture. Initial cube orientation at the surface layer was gradually rotated to the r-cube orientation during the ARB process, leading to the increase in the strength of the r-cube shear texture with ARB cycles. The texture evolution at the surface layer was quantified in terms of a simple relation between the texture volume fractions and accumulated true strain. The strength of the β fiber rolling texture and the distribution of orientation intensities along the β fiber at the center layer were strongly affected by the initial texture. As the ARB cycles increased, the initial texture was changed from the cube texture to the r-cube texture, leading to a continuous increase in the strength of the β fiber rolling texture dominated by the C orientation. The yield and ultimate tensile strength of the ARB processed sheets increased markedly after the first ARB cycle and then increased slowly with increasing ARB cycles, while the elongation decreased accordingly.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of stored strain energy heterogeneity on microstructure evolution of 90% cold rolled AISI 304L stainless steel during interrupted annealing treatment

Highlights: • Study of usefulness of stored strain energy distribution map of the material for variable temperature range. • Advantage of using stored strain energy distribution map • Variation observed in stored energy between isothermal annealing treatment and interrupted annealing treatment. - Abstract: This research work is an attempt to understand the effect of stored strain energy heterogeneity over macro-scale, induced during interrupted annealing treatment, on the micro structural evolution in a heavily cold rolled AISI 304L austenitic stainless steel. The cold rolled AISI 304L stainless steel (SS) samples were subjected to different annealing treatments. The microstructures obtained after each annealing treatment were characterized using optical and electron microscopy techniques. Further, an attempt was made to estimate the stored strain energy by a novel approach of micro hardness measurement both over small scale (area 3600 μm{sup 2}) and large scale (area ~0.25 mm{sup 2}). The stored strain energy was determined using hardness values. Using these data, spatial stored strain energy distribution contour maps were created. They were, in turn, used to characterize the local softening behavior both at micro and macro-scale levels after each interrupted annealing treatment. The results showed that, interrupted annealing treatment induces increased stored strain energy heterogeneity after each annealing interruptions. Also, it was possible to determine recrystallization kinetics of the material using stored strain energy map, which helps in designing annealing cycles for achieving ultrafine grained microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure evolution and a new mechanism of B2 phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy prepared by hot isostatic pressing

Highlights: • The microstructure evolution of Ti-47Al-2Cr-2Nb alolly was investigated in detail. • The foramtion of B{sub 2} phase can be adjusted in Ti-47Al-2Cr-2Nb alloy. • A new mechanism of B{sub 2} phase on room temperature mechanical properties of Ti-47Al-2Cr-2Nb alloy was proposed. - Abstract: The formation of B{sub 2} phase was adjusted via various hot isostatic pressing processes in Ti-47Al-2Cr-2Nb alloy. The microstructure evolution and a new mechanism of B{sub 2} phase on room temperature mechanical properties was investigated by BSE, EBSD and TEM in detail. The result shows that the formation of B{sub 2} phase leads to Cr element content decrease in γ matrix phase, which results in lattice parameter increase, namely the c/a ratio of γ matrix phase. Finally, at room temperature the mechanical properties of Ti-47Al-2Cr-2Nb alloy deteriorates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of compositional changes on microstructure in additively manufactured aluminum alloy 2139

Highlights: • Volatile elements preferentially vaporize during additive manufacturing. • Vapor losses affect precipitate habit plane in aluminum alloy 2139. • Above 0.2 wt% Mg the precipitate forms on the preferred {111} habit plane. • Higher strength is associated with precipitates on the {111} habit planes. - Abstract: A matrix of nine experiments was conducted on aluminum alloy 2139 samples made by an electron beam directed energy deposition additive manufacturing process to characterize the effect of magnesium vaporization loss on microstructure and properties. The nine-sample matrix included three different magnesium levels deposited onto material at three different temperatures. The goal was to quantify the variability in the deposited material as a function of allowable magnesium content and the local temperature of the substrate or previous layer. The results show that temperature variations in the substrate up to 100 K have no significant effect on the amount of magnesium loss; however, relatively large variations in Mg content, up to a ±0.25 wt%, can significantly affect the microstructure and mechanical properties. This is due to a change in how the precipitate phase forms, which influences the mechanism by which the alloy is strengthened.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the microstructure characterization of the AA2098-T351 alloy welded by FSW

Highlights: • The microstructural characterization of the AA2098-T351 Al-Cu-Li alloy welded by FSW was carried out. • There was strong correlation between the results of the various techniques. • DSC was an effective technique for characterization of GP zones complementing the microstructural characterization by TEM. - Abstract: The complex structure of the AA2098-T351 alloy welded by friction stir welding (FSW) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and microhardness measurements. Thermal modelling process of the FSW process was carried out by soldering thermocouples at distances of 6, 9 and 12 mm from the weld centerline, and thermocouple measurements were used as input data into the model. Finite element software COMSOL v5.2 was used for data analysis. The prevailing phases in the base metal (BM) are T1 (Al{sub 2}CuLi) θ′ (Al{sub 2}Cu), δ′/β′(Al{sub 3}(Li,Zr)) and Ω (Al{sub 2}Cu). In the heat affected zone (HAZ), either in the retreating or advancing sides, θ′ phase was not identified. In the thermomechanical affected zone (TMAZ), T1, δ′/β′, GP zones phase were detected in the retreating side, whereas T1 and Guinier-Preston (GP) zones were not observed in the advancing side. This result supports the asymmetric behavior observed in the microhardness profile of the weld. In the stir zone (SZ), GP zones, T1, δ′/β′ (Al{sub 3}(Li,Zr)) and Ω were identified.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Sr, Ce and P on the microstructure and mechanical properties of rapidly solidified Al7Si alloys

Highlights: • Rapid solidification caused formation of nanoscaled Si particle chains. • Sr or Ce induced the columnar transition zone only at extremely high cooling rate. • Enhancement of hardness is attributed to fine dispersion of eutectic Si, grain refinement and the supersaturation of Si. • Sr or Ce caused further enhancement of hardness, attributing to Si modification. - Abstract: A series of Al7Si based alloys with trace addition of Sr, Ce or P were prepared using melt-spinning at two different high cooling rates, and the microstructure as well as the hardness of the ribbons was comprehensively studied. The results show that Sr or Ce induces the formation of columnar transition zone and modifies the morphology of eutectic Si phase from dispersed particle chains to fine fibers only at extremely high cooling rate. However, P has little effect on the microstructure of either α-Al or eutectic Si. Compared with conventional casting, the Al7Si ribbons exhibit extremely high hardness due to the fine dispersion of eutectic Si, the grain refinement and the supersaturation of Si. The hardness is further enhanced by Sr or Ce addition at extremely high cooling rate, especially for columnar and equiaxed zones, attributing to the modification effect on Si phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of annealing temperature on microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel

Highlights: • Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel was investigated. • Shear bands provided recrystallization nucleation sites. • Annealing temperature can affect microstructure and texture. • r-bar increased to a maximum value (1.69) and then decreased to 1.42. - Abstract: The evolution of microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel annealed at different temperatures was investigated using a combination of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). EBSD investigations confirm that the in-grain shear bands provide more recrystallization nucleation sites to γ-fiber recrystallization grains with high Taylor factor orientations during cold rolling requiring further annealing for a more homogenous equiaxied grain structure. As the annealing temperatures increase, the grains in center layer are oriented towards {110}∥ND, and the recrystallization grains at 1050 °C are dominated by the uniform and equiaxial γ-fiber grains favourable for the improvement of r-values, while the occurrence of {100} <011> texture detrimental to r-values indicates that an exorbitant annealing temperature can reduce the intensity of γ-fiber textures affecting the formability, accordingly, the average plastic strain ratio of ferritic stainless steel increases sharply up to a maximum value (1.69) and then decreases to a certain value (1.42).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of trace amounts of added Sc on microstructure and mechanical properties of 2055 aluminum alloy

Highlights: • Effect of trace Sc on microstructure and mechanical properties in 2055 Al-alloy was investigated. • T{sub 1} is the main strengthening phase in Sc free and Sc added 2055 alloy at the aging temperature of 175°C and 200°C. • The refinement of T{sub 1} by Sc addition depends on the aging temperature. • Mechanical properties were deteriorated by Sc at the aging temperature of 175°C and improved at 200°C aging treatment. - Abstract: The effects of Sc additions and isothermal aging on the microstructure and mechanical properties of 2055 aluminum alloy have been investigated. The isothermal aging temperatures investigated were 175 °C and 200 °C. Results show that the aging temperature does not affect the type of precipitates in both Sc-free and Sc-added 2055 Al alloys. While remarkable changes in the size and number density of T{sub 1} (Al{sub 2}CuLi) precipitates have been observed. For samples aged at 175 °C for 8 h, the average length of T{sub 1} precipitates was increased from 39.9 nm to 45.6 nm, the number density decreased from 5.77 × 10{sup 22} m{sup −3} to 3.68 × 10{sup 22} m{sup −3} after Sc addition. On the contrary, when samples were aged at 200 °C for 8 h, the length decreased from 59.89 nm to 43.32 nm and number density increased from 2.13 × 10{sup 22} m{sup −3} to 3.00 × 10{sup 22} m{sup −3} by adding trace Sc. Slight deterioration of tensile strength and yield strength with higher ductility was founded at the aging temperature of 175 °C for 8 h due to the larger size and lower number density of T{sub 1} precipitates along with the formation of a W (AlCuSc) phase during the casting or homogenization processes. When aging temperature increased to 200 °C, tensile strength and yield strength were significantly improved by Sc addition without losing ductility. Highly dense fine T{sub 1} precipitates take responsible for the strength improvement, and to some extent it compensated the strength loss caused by the formation of W phase. A “vacancy-prison” mechanism was adopted to explain the effect of Sc additions on the precipitation of T{sub 1} phase as a function of aging temperature.

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↗