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At least 1,297 records · Page 72
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DOE OSTI2013

Microstructural and mechanical characterization of Al–Zn–Si nanocomposites

In this paper the addition of silicon nanoparticles into Al–Zn alloys to form metallic matrix nanocomposites by mechanical alloying process was investigated. The influence of various process parameters such as milling time and Si concentration in the Al–Zn matrix has an interesting effect on the microstructure and mechanical properties of the synthesized nanocomposites. The microstructural characterization of the nanocomposites was evaluated by transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM–EDXS) and the mechanical properties were measured by nanoindentation and micro-hardness tests. The results showed that during mechanical milling Si is added to the Al–Zn matrix achieving a uniform and homogeneous dispersion. After solidification, it forms small particles of AlZnSi with blocky morphology in interdendritic regions. The nanoindentation profiles showed that the elastic modulus and hardness properties increase with increasing milling time. However, a high concentration of Si (> 1.2 wt.%) results in a saturation of Si in the Al–Zn matrix, which adversely affects the mechanical properties. Thus, it is important to tune the milling time and concentration of Si added to the Al–Zn alloys to control the growth of brittle phases that result in reduction of the mechanical properties of the material. - Highlights: • A novel technique for addition of Si nanocomposites into Al–Zn liquid alloy is reported. • Good dispersion and homogeneity of Si in the Al–Zn matrix are obtained. • Increasing Si content above 1.2 wt.% decreases the mechanical properties of Al–Zn alloy. • The saturation point of Si in 1.2 wt.% differs from Galvalume® composition. • The Al–Zn–1.5Si alloy with addition of nanocomposite shows 5.7 GPa of hardness.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nanocrystalline Cs{sub x}WO{sub 3} particles: Effects of N{sub 2} annealing on microstructure and near-infrared shielding characteristics

In order to further improve the near-infrared shielding properties of cesium tungsten bronze (Cs{sub x}WO{sub 3}) for solar filter applications, Cs{sub x}WO{sub 3} particles were prepared by solvothermal reaction method and the effects of nitrogen annealing on the microstructure and near-infrared shielding properties of Cs{sub x}WO{sub 3} were investigated. The obtained Cs{sub x}WO{sub 3} samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and spectrophotometer. The results indicate that nanosheet-like Cs{sub x}WO{sub 3} particles with hexagonal structure began to transform into nanorods after annealed at temperature higher than 600 °C. The near-infrared shielding properties of Cs{sub x}WO{sub 3} particles could be further improved by N{sub 2} annealing at 500–700 °C. Particularly, the 500 °C-annealed Cs{sub x}WO{sub 3} samples in the N{sub 2} atmosphere showed best near-infrared shielding properties. It was suggested that the excellent near-infrared shielding ability of the 500 °C-annealed Cs{sub x}WO{sub 3} samples is correlated with its minimum O/W atomic ratio and most oxygen vacancies. Highlights: • N{sub 2} annealing could further improve the near-infrared (NIR) shielding of Cs{sub x}WO{sub 3}. • Effects of N{sub 2} annealing on microstructure and NIR shielding of Cs{sub x}WO{sub 3} were studied. • The 500 °C-N{sub 2}-annealed Cs{sub x}WO{sub 3} exhibited minimum O/W ratio and most oxygen vacancies. • The 500 °C-N{sub 2}-annealed Cs{sub x}WO{sub 3} particles exhibited best NIR shielding properties.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microstructural study and densification analysis of hot work tool steel matrix composites reinforced with TiB{sub 2} particles

Hot work tool steels are characterized by good toughness and high hot hardness but are less wear resistant than other tooling materials, such as high speed steel. Metal matrix composites show improved tribological behavior, but not much work has been done in the field of hot work tool steels. In this paper TiB{sub 2}-reinforced hot work tool steel matrix composites were produced by spark plasma sintering (SPS). Mechanical alloying (MA) was proposed as a suited process to improve the composite microstructure. Density measurements and microstructure confirmed that MA promotes sintering and produces a fine and homogeneous dispersion of reinforcing particles. X-ray diffraction patterns of the sintered composites highlighted the formation of equilibrium Fe{sub 2}B and TiC, as predicted by thermodynamic calculations using Thermo-Calc® software. Scanning electron microscopy as well as scanning Kelvin probe force microscopy highlighted the reaction of the steel matrix with TiB{sub 2} particles, showing the formation of a reaction layer at the TiB{sub 2}-steel interface. Phase investigations pointed out that TiB{sub 2} is not chemically stable in steel matrix because of the presence of carbon even during short time SPS. - Highlights: • TiB{sub 2} reinforced steel matrix composites were produced by spark plasma sintering. • TiB{sub 2} was successfully dispersed in the steel matrix by mechanical alloying. • Steel and TiB{sub 2} react during sintering forming equilibrium Fe{sub 2}B and TiC. • The new phases were investigated by means of AFM, Volta potential and XRD analyses.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Creep property and microstructure evolution of a nickel-base single crystal superalloy in [011] orientation

The creep property and microstructure evolution of a single crystal superalloy with [011] orientation were investigated at the temperatures of 700 °C, 900 °C and 1040 °C. It is shown that there exist stages of primary, steady-state, and tertiary creep under the lower temperature 700 °C. As the temperature increases to high temperatures of 900 °C and 1040 °C, steady-state creep stage is reduced or disappears and the shape of creep curves is dominated by an extensive tertiary stage. The minimum creep strain rate exhibits power law dependence on the applied stress; the stress exponents at 700 °C, 900 °C and 1040 °C are 28, 13 and 6.5, respectively. Microstructure observation shows that the morphologies of γ′ phase almost keep original shape at the lower temperature 700 °C and high applied stress. With the increasing creep temperature, γ′ precipitates tend to link together and form lamellar structure at an angle of 45° inclined to the applied stress. Transmission electron microscopy (TEM) investigations reveal that multiple < 110 > (111) slip systems gliding in the matrix channels and shearing γ′ precipitates by stacking faults or bending dislocation pairs are the main deformation mechanism at the lower temperature of 700 °C. At the high temperatures of 900 °C and 1040 °C, dislocation networks are formed at γ/γ′ interfaces and the γ′ rafts are sheared by dislocation pairs. - Highlights: • Creep properties of < 011 >-oriented single crystal superalloys were investigated. • γ′ phases become rafting at an angle of 45° inclined to the applied stress. • Creep deformation mechanisms depend on temperature and stress.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microstructure and mechanical properties of diffusion bonded W/steel joint using V/Ni composite interlayer

Diffusion bonding between W and steel using V/Ni composite interlayer was carried out in vacuum at 1050 °C and 10 MPa for 1 h. The microstructural examination and mechanical property evaluation of the joints show that the bonding of W to steel was successful. No intermetallic compound was observed at the steel/Ni and V/W interfaces for the joints bonded. The electron probe microanalysis and X-ray diffraction analysis revealed that Ni{sub 3}V, Ni{sub 2}V, Ni{sub 2}V{sub 3} and NiV{sub 3} were formed at the Ni/V interface. The tensile strength of about 362 MPa was obtained for as-bonded W/steel joint and the failure occurred at W near the V/W interface. The nano-indentation test across the joining interfaces demonstrated the effect of solid solution strengthening and intermetallic compound formation in the diffusion zone. - Highlights: • Diffusion bonding of W to steel was realized using V/Ni composite interlayer. • The interfacial microstructure of the joint was clarified. • Several V–Ni intermetallic compounds were formed in the interface region. • The application of V/Ni composite interlayer improved the joining quality.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Characterization of microstructure, texture and magnetic properties in twin-roll casting high silicon non-oriented electrical steel

An Fe-6.5 wt.% Si-0.3 wt.% Al as-cast sheet was produced by twin-roll strip casting process, then treated with hot rolling, warm rolling and annealing. A detailed study of the microstructure and texture evolution at different processing stages was carried out by optical microscopy, X-ray diffraction and electron backscattered diffraction analysis. The initial as-cast strip showed strong columnar grains and pronounced < 001 >//ND texture. The hot rolled and warm rolled sheets were characterized by large amounts of shear bands distributed through the thickness together with strong < 110 >//RD texture and weak < 111 >//ND texture. After annealing, detrimental < 111 >//ND texture almost disappeared while beneficial (001)<210 >, (001)<010 >, (115)<5 − 10 1 > and (410) < 001 > recrystallization textures were formed, thus the magnetic induction of the annealed sheet was significantly improved. The recrystallization texture in the present study could be explained by preferred nucleation and grain growth mechanism. - Highlights: • A high silicon as-cast strip with columnar structure was produced. • A thin warm rolled sheet without large edge cracks was obtained. • Microstructure and texture evolution at each stage were investigated. • Beneficial (001)<210 >, (001)<010 >, (410)<001 > recrystallization textures were formed. • The magnetic induction of annealed sheet was significantly improved.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Layered-structural monoclinic–orthorhombic perovskite La{sub 2}Ti{sub 2}O{sub 7} to orthorhombic LaTiO{sub 3} phase transition and their microstructure characterization

The layered-structural ceramics, such as lanthanum titanate (La{sub 2}Ti{sub 2}O{sub 7}), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La{sub 2}Ti{sub 2}O{sub 7} ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by the sol–gel acrylamide polymerization route. The characterizations of the samples were achieved by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). X-ray diffraction indicates that the formation of monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} nanocrystals is a necessary first step to obtain orthorhombic LaTiO{sub 3} nanocomposites (with space group Pbnm). In this work we identified that the monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} with space group P2{sub 1} transforms its structure into one with the orthorhombic space group Cmc2{sub 1} at approximately 1073 K. The microstructure associated consisted of flaky monoclinic La{sub 2}Ti{sub 2}O{sub 7} nanocomposites in comparison with round-shaped LaTiO{sub 3} nanocomposites. - Highlights: • The flaky-like La{sub 2}Ti{sub 2}O{sub 7} compound was synthesized by sol–gel acrylamide route. • Simultaneous monitoring of the DTA and XRD with temperature was performed. • Phase transformation characterization of La{sub 2}Ti{sub 2}O{sub 7} has been carried out. • The variation of the La{sub 2}Ti{sub 2}O{sub 7} and LaTiO{sub 3} grain morphology has been compared.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effects of Mo on microstructure of as-cast 28 wt.% Cr–2.6 wt.% C–(0–10) wt.% Mo irons

Microstructures of as-cast 28 wt.% Cr–2.6 wt.% C irons containing (0–10) wt.% Mo with the Cr/C ratio of about 10 were studied and related to hardness. The experimental irons were cast into dry sand molds. Microstructural investigation was performed by light microscopy, X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. It was found that the iron with about 10 wt.% Mo was eutectic/peritectic, whereas the others with less Mo content were hypoeutectic. The matrix in all irons was austenite, partly transformed to martensite during cooling. Mo addition promoted the formation of M{sub 23}C{sub 6} and M{sub 6}C. At 1 wt.% Mo, multiple eutectic carbides including M{sub 7}C{sub 3}, M{sub 23}C{sub 6} and M{sub 6}C were observed. M{sub 23}C{sub 6} existed as a transition zone between eutectic M{sub 7}C{sub 3} and M{sub 6}C, indicating a carbide transition as M{sub 7}C{sub 3}(M{sub 2.3}C) → M{sub 23}C{sub 6}(M{sub 3.8}C) → M{sub 6}C. At 6 wt.% Mo, multiple eutectic carbides including M{sub 7}C{sub 3} and M{sub 23}C{sub 6} were observed together with fine cellular/lamellar M{sub 6}C aggregates. In the iron with 10 wt.% Mo, only eutectic/peritectic M{sub 23}C{sub 6} and M{sub 6}C were found without M{sub 7}C{sub 3}. Mo distribution to all carbides has been determined to be increased from ca. 0.4 to 0.7 in mass fraction as the Mo content in the irons was increased. On the other hand, Cr distribution to all carbides is quite constant as ca. 0.6 in mass fraction. Mo addition increased Vickers macro-hardness of the irons from 495 up to 674 HV{sub 30}. High Mo content as solid-solution in the matrix and the formation of M{sub 6}C or M{sub 23}C{sub 6} aggregates were the main reasons for hardness increase, indicating potentially improved wear performance of the irons with Mo addition. - Highlights: • Mo promoted the formation of M{sub 23}C{sub 6} and M{sub 6}C in the irons with Cr/C ratio of about 10. • M{sub 23}C{sub 6} has higher Fe/Cr and Mo/Cr atm% ratios than M{sub 7}C{sub 3}. • Si content and high Mo content over about 9 atm% are characteristics of M{sub 6}C. • No M{sub 7}C{sub 3} was found at 10 wt.% Mo addition, only M{sub 23}C{sub 6} and M{sub 6}C presented. • High Mo matrices and M{sub 23}C{sub 6}/M{sub 6}C aggregates increased iron macro-hardness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructural analysis of martensite constituents in quenching and partitioning steels

A methodology to distinguish martensite formed in the first quench (M1) from martensite formed in the second quench (M2) of the Quenching and Partitioning process is presented, enabling the study of the structural characteristics of both microstructural constituents. Investigations show that M1 displays larger block size and less lattice imperfections than M2, differences that can be related to their respective carbon contents. - Highlights: • An approach to distinguish “old” from “new” martensite in Q and P steels is presented • Methodology allows separate characterization of microstructure and crystallography “Old” martensite has larger block size and more perfect lattice than the “new” one • The differences between the old and new martensite depend on their carbon contents.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of substrates on microstructure and mechanical properties of nano-eutectic 1080 steel produced by aluminothermic reaction

Nano-eutectic bulk 1080 carbon steel was prepared on glass and copper substrates by an aluminothermic reaction casting. The microstructure of the steel was analyzed by an optical microscope, transmission electron microscopy, an electron probe micro-analyzer, a scanning electron microscope and X-ray diffraction. Results show that the microstructure of the steel consisted of a little cementite and lamellar eutectic pearlite. Average lamellar spacing of the pearlite prepared on copper and glass substrates was about 230 nm and 219 nm, respectively. Volume fraction of the pearlite of the two steels was about 95%. Hardness of the steel was about 229 and 270 HV. Tensile strength was about 610 and 641 MPa and tensile elongation was about 15% and 8%. Compressive strength was about 1043 and 1144 MPa. Compared with the steel prepared on copper substrate, the steel prepared on glass substrate had smaller lamellar spacing of the pearlite phase and higher strength, and low ductility due to the smaller spacing. - Highlights: • 1080-carbon steels were successfully prepared by an aluminothermic reaction casting. • Lamellar spacing of the nanoeutetic pearlite is less than 250 nm. • The compressive strength of the steel is about 1144 MPa. • The tensile ductility of the steel is about 15%.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The effect of annealing on the transformation and the microstructure of Mn{sub 1−x}Cr{sub x}CoGe alloys

In this work the effect of different thermal treatments on the transformation behavior of Mn{sub 1−x}Cr{sub x}CoGe alloys, with x = 0.15 and 0.20 has been analyzed. The changes in the transformation temperatures have been studied by differential scanning calorimetry (DSC). The results show that the structural transition temperature depends on the previous annealing. However, under the same heat treatment no significant change is observed on the transformation temperatures when replacing Mn by Cr. The microstructural evolution has been monitored using in-situ X-ray diffraction and transmission electron microscopy. The effect of an applied magnetic field on the transformation has been explored by SQUID magnetometry. Two different magnetic transitions are found: a first order paramagnetic (PM) to ferromagnetic (FM) corresponding to the transformation observed by calorimetry and a re-entrant spin glass to ferromagnetic transition. - Highlights: • The annealing conditions determine the magnetostructural transition. • A laminar microstructure along preferential planes observed by TEM • A RSG to ferromagnetic transition at low temperatures is detected.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure evolution during annealing of TiAl/NiCoCrAl multilayer composite prepared by EB-PVD

TiAl/NiCoCrAl laminate composite sheet with a thickness of 0.4–0.6 mm as well as a dimension of 150 mm × 100 mm was fabricated successfully by using electron beam physical vapor deposition (EB-PVD) method. The annealing treatment was processed at 1123 and 1323 K for 3 h in a high vacuum atmosphere, respectively. The phase composition and microstructure of TiAl/NiCoCrAl microlaminated sheet have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the sheet characterization and results of the microstructure evolution during annealing treatment process, the diffusion mechanism of interfacial reaction in TiAl/NiCoCrAl microlaminate was investigated and discussed.

36 MATERIALS SCIENCE↗
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 OSTI2014

Metallography and microstructure interpretation of some archaeological tin bronze vessels from Iran

Archaeological excavations in western Iran have recently revealed a significant Luristan Bronzes collection from Sangtarashan archaeological site. The site and its bronze collection are dated to Iron Age II/III of western Iran (10th–7th century BC) according to archaeological research. Alloy composition, microstructure and manufacturing technique of some sheet metal vessels are determined to reveal metallurgical processes in western Iran in the first millennium BC. Experimental analyses were carried out using Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy and Optical Microscopy/Metallography methods. The results allowed reconstructing the manufacturing process of bronze vessels in Luristan. It proved that the samples have been manufactured with a binary copper–tin alloy with a variable tin content that may relates to the application of an uncontrolled procedure to make bronze alloy (e.g. co-smelting or cementation). The presence of elongated copper sulphide inclusions showed probable use of copper sulphide ores for metal production and smelting. Based on metallographic studies, a cycle of cold working and annealing was used to shape the bronze vessels. - Highlights: • Sangtarashan vessels are made by variable Cu-Sn alloys with some impurities. • Various compositions occurred due to applying uncontrolled smelting methods. • The microstructure represents thermo-mechanical process to shape bronze vessels. • In one case, the annealing didn’t remove the eutectoid remaining from casting. • The characteristics of the bronzes are similar to other Iron Age Luristan Bronzes.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A mixture of massive and feathery microstructures of Ti48Al2Cr2Nb alloy by high undercooled solidification

A mixture of massive and feathery microstructures was observed in Ti48Al2Cr2Nb alloy subjected to the undercooled solidification rather than the heat treatments in most cases. Double recalescence events and primary β solidification confirmed that massive γ phase did not directly nucleate from the undercooled melt but formed during the solid-state transformations. It is believed that small white areas (aluminium-poor) along lamellar grain boundaries may be closely related to the formation of massive γ phase and feathery γ phase. High dislocation density and stacking faults were detected in massive γ phase by transmission electron microscopy. The high energy of defects and undercooling in the solid state phase transformation can provide sufficiently high driving force for the nucleation of massive γ phase. - Graphical abstract: Display Omitted - Highlights: • A mixture of massive and feathery microstructures was observed. • Massive γ formed during the solid-state transformations. • Defects and undercooling provide driving force for the nucleation of massive γ.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure evolution in solution treated Ti15Mo alloy processed by high pressure torsion

Microstructure evolution and mechanical properties of ultra-fine grained Ti15Mo alloy processed by high pressure torsion were investigated. High pressure torsion straining resulted in strong grain refinement as-observed by transmission electron microscopy. Microhardness and light microscopy showed two distinct regions — (i) a central region with radial material flow and low microhardness (340 HV) and (ii) a peripheral region with rotational material flow and high microhardness (430 HV). Positron annihilation spectroscopy showed that the only detectable defects in the material are dislocations, whose density increases with the radial distance and the number of high pressure torsion revolutions. The local chemical environment around defects does not differ significantly from the average composition. - Highlights: • Beta-Ti alloy Ti15Mo was processed by high pressure torsion (HPT). • Lateral inhomogeneity of the microstructure and microhardness was found. • Dislocations are the only lattice defects detectable by positron annihilation. • Molybdenum is not preferentially segregated along dislocation cores.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of W on microstructure of as-cast 28 wt.%Cr–2.6 wt.%C–(0–10)wt.%W irons

Microstructures of as-cast 28 wt.%Cr–2.6 wt.%C irons containing (0–10)wt.%W with the Cr/C ratio about 10 were studied and related to their hardness. The experimental irons were cast into dry sand molds. Microstructural investigation was performed by light microscopy, X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. It was found that the irons with 1 to 10 wt.%W addition was hypereutectic containing large primary M{sub 7}C{sub 3}, whereas the reference iron without W addition was hypoeutectic. The matrix in all irons was austenite, partly transformed to martensite during cooling. The volume fractions of primary M{sub 7}C{sub 3} and the total carbides increased, but that of eutectic carbides decreased with increasing the W content of the irons. W addition promoted the formation of W-rich M{sub 7}C{sub 3}, M{sub 6}C and M{sub 23}C{sub 6}. At about 4 wt.%W, two eutectic carbides including M{sub 7}C{sub 3} and M{sub 6}C were observed together with primary M{sub 7}C{sub 3}. At 10 wt.%W, multiple carbides including primary M{sub 7}C{sub 3}, fish-bone M{sub 23}C{sub 6}, and M{sub 6}C were observed. M{sub x}C where x = 3 or less has not been found due possibly to the high M/C ratio in the studied irons. W distribution to all carbides has been determined increasing from ca. 0.3 to 0.8 in mass fraction as the W content in the irons was increased. W addition led to an increase in Vickers macro-hardness of the irons up to 671 kgf/(mm){sup 2} (HV30/15) obtained from the iron with 10 wt.%W. The formation of primary M{sub 7}C{sub 3} and aggregates of M{sub 6}C and M{sub 23}C{sub 6} were the main reasons for hardness increase, indicating potentially improved wear performance of the as-cast irons with W addition. - Highlights: • W addition at 1 up to 10 wt.%W to Fe–28Cr–2.6C produced “hypereutectic” structure. • W addition promoted the formation of W-rich M{sub 7}C{sub 3}, M{sub 6}C and M{sub 23}C{sub 6}. • M{sub 23}C{sub 6} has higher Fe/Cr and W/Cr atm% ratios than those in M{sub 7}C{sub 3}. • Si content and high W content over about 11 atm% are characteristics of M{sub 6}C. • Primary M{sub 7}C{sub 3} and aggregates of M{sub 6}C and M{sub 23}C{sub 6} increased the alloy macro-hardness.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microstructure characterization of SiC nanowires as reinforcements in composites

SiC nanowires have been rarely investigated or explored along their axial direction by transmission electron microscopy (TEM). Here we report the investigation of the cross-section microstructure of SiC nanowires by embedding them into Al matrix. Morphology of SiC nanowires was cylindrical with smooth surface or bamboo shape. Cubic (3C-SiC) and hexagonal structure (2H-SiC) phases were detected by X-ray diffraction (XRD) analysis. High density stacking faults were observed in both the cylindrical and bamboo shaped nanowires which were perpendicular to their axial direction. Selected area electron diffraction (SAED) patterns of the cylindrical and bamboo shaped SiC nanowires both in the perpendicular and parallel direction to the axial direction were equivalent in the structure. After calculation and remodeling, it has been found that the SAED patterns were composed of two sets of diffraction patterns, corresponding to 2H-SiC and 3C-SiC, respectively. Therefore, it could be concluded that the SiC nanowires are composed of a large number of small fragments that are formed by hybrid 3C-SiC and 2H-SiC structures. - Graphical abstract: Display Omitted - Highlights: • Cross-section microstructure of SiC nanowires was observed in Al composite. • Cylindrical with smooth surface or bamboo shape SiC nanowires were found. • The cylindrical and bamboo shaped SiC nanowires were equivalent in structure. • Structure of SiC nanowires was remodeled. • SiC nanowires are composed of hybrid 3C-SiC and 2H-SiC structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗