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Results for “Electron Backscatter Diffraction”

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At least 253 records · Page 14

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DOE OSTI2017

Defect features, texture and mechanical properties of friction stir welded lap joints of 2A97 Al-Li alloy thin sheets

1.4 mm 2A97 Al-Li alloy thin sheets were welded by friction stir lap welding using the stirring tools with different pin length at different rotational speeds. The influence of pin length and rotational speed on the defect features and mechanical properties of lap joints were investigated in detail. Microstructure observation shows that the hook defect geometry and size mainly varies with the pin length instead of the rotational speed. The size of hook defects on both the advancing side (AS) and the retreating side (RS) increased with increasing the pin length, leading to the effective sheet thickness decreased accordingly. Electron backscatter diffraction analysis reveals that the weld zones, especially the nugget zone (NZ), have the much lower texture intensity than the base metal. Some new texture components are formed in the thermo-mechanical affected zone (TMAZ) and the NZ of joint. Lap shear test results show that the failure load of joints generally decreases with increasing the pin length and the rotational speed. The joints failed during the lap shear tests at three locations: the lap interface, the RS of the top sheet and the AS of the bottom sheet. The fracture locations are mainly determined by the hook defects. - Highlights: • Hook defect size mainly varies with the pin length of stirring tool. • The proportion of LAGBs and substructured grains increases from NZ to TMAZ. • Weld zones, especially the NZ, have the much lower texture intensity than the BM. • Lap shear failure load and fracture location of joints is relative to the hook defects.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of gadolinium addition on microstructural evolution and solidification characteristics of Al-15%Mg2Si in-situ composite

Highlights: • The Al{sub 3}Gd is the heterogeneous nucleation of primary Mg{sub 2}Si in Al-15%Mg{sub 2}Si composite. • Addition of Gd to Al-15%Mg{sub 2}Si resulted in the formation of Al{sub 2}Si{sub 2}Gd and AlSiGd intermetallic compounds. • Absorption of Gd atoms preferentially on {100} facets of Mg{sub 2}Si crystals changed its growth manners. • Primary Mg{sub 2}Si transformed from coarse-dendritic to perfect truncated octahedral shape after treating with 1.0 wt% Gd. • Gd addition increased the nucleation and growth temperatures of primary Mg{sub 2}Si. - Abstract: The current study investigated the effects of gadolinium (Gd) addition (0, 0.3, 0.5, 1.0, and 2.0 wt%) on microstructural development and solidification characteristics of hypereutectic Al-15%Mg{sub 2}Si in-situ composite. Microstructural examinations were carried out via optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD). The results showed that an addition of 1.0 wt% Gd, changed the morphology of primary Mg{sub 2}Si from coarse dendritic to fine truncated octahedral shape. Furthermore, the average size of primary Mg{sub 2}Si particles decreased from 40 μm to 20 μm and density increased from 495 to 1167 particles/mm{sup 2}. Besides that, cooling curve thermal analysis (CCTA) technique revealed that Gd addition increased nucleation and growth temperatures of primary Mg{sub 2}Si phase. It is proposed that modification and refinement mechanism of Gd addition are mainly attributed to formation of tiny Al{sub 3}Gd particles as the heterogeneous nucleation substrates for primary Mg{sub 2}Si, which results in a refined distribution of these particles and poisoning effect by adsorbing Gd atoms, preferentially on {100} facets of Mg{sub 2}Si crystals. Moreover, it is believed that formation of Gd intermetallic compounds is responsible for refinement of primary Mg{sub 2}Si particles.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Microstructural changes and strain hardening effects in abrasive contacts at different relative velocities and temperatures

Strain hardening is commonly used to reach the full potential of materials and can be beneficial in tribological contacts. 2-body abrasive wear was simulated in a scratch test, aimed at strain hardening effects in various steels. Different working conditions were examined at various temperatures and velocities. Strain hardening effects and microstructural changes were analysed with high resolution scanning electron microscopy (HRSEM), electron backscatter diffraction (EBSD), micro hardness measurements and nanoindentation. Statistical analysing was performed quantifying the influence of different parameters on microstructures. Results show a crucial influence of temperature and velocity on the strain hardening in tribological contacts. Increased velocity leads to higher deformed microstructures and higher increased surface hardness at a lower depth of the deformed zones at all materials investigated. An optimised surface hardness can be achieved knowing the influence of velocity (strain rate) and temperature for a “tailor-made” surface hardening in tribological systems aimed at increased wear resistance. - Highlights: •Hardening mechanisms and their intensity in tribological contacts are dependent on relative velocity and temperature. •Beneficial surface hardened zones are formed at certain running-in conditions; the scientific background is presented here. •Ferritic-pearlitic steels strain hardens via grain size reduction and decreasing interlamellar distances in pearlite. •Austenitic steels show excellent surface hardening (120% hardness increase) by twinning and martensitic transformation. •Ferritic steels with hard phases harden in the ferrite phase as per Hall-Petch equation and degree of deformation.

36 MATERIALS SCIENCE↗

DOE OSTI2013

In-depth quantitative analysis of the microstructures produced by Surface Mechanical Attrition Treatment (SMAT)

Electron BackScattered Diffraction (EBSD) maps are used to characterize quantitatively the graded microstructure formed by Surface Mechanical Attrition Treatment (SMAT) and applied here to the 316L stainless steel. In particular, the analysis of GNDs – coupled with relevant and reliable criteria – was used to depict the thickness of each zone identified in the SMAT-affected layers: (i) the “ultrafine grain” (UFG) zone present at the extreme top surface, (ii), the “transition zone” where grains were fragmented under the heavy plastic deformation and, finally, (iii) the “deformed zone” where initial grains are simply deformed. The interest of this procedure is illustrated through the comparative analysis of the effect of some SMAT processing parameters (amplitude of vibration and treatment duration). The UFG and transition zones are more significantly modified than the overall affected thickness under our tested conditions. - Highlights: • EBSD maps are used to characterize quantitatively the microstructure of SMAT treated samples. • Calculation of the GND density to quantify strain gradients • A new method to depict the different zone thicknesses in the SMAT affected layer • Effects of SMAT processing parameters on the surface microstructure evolution.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Quantitative investigation of the tensile plastic deformation characteristic and microstructure for friction stir welded 2024 aluminum alloy

The effect of the microstructure heterogeneity on the tensile plastic deformation characteristic of friction stir welded (FSW) 2024 aluminum alloy was investigated for the potential applications on light weight design of vehicles. The microstructure characteristics of the FSW joints, such as the grain structure, dislocation density and the distribution of precipitation, were studied by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The tensile deformation characteristic of the FSW joints was examined using the automatic strain measuring system (ASAME) by mapping the global and local strain distribution, and then was analyzed by mechanics calculation. It is found that the tensile deformation of the FSW joints is highly heterogeneous leading to a significant decrease in global ductility. The FSW joints mainly contain two typical deformation zones, which show great effect on the regional inhomogeneous deformation. One is the nugget zone (NZ) with a region of 8 mm in width, and the other is part of the BM with a region of 10 mm in width. The BM of the joints is the weakest region where the strain localizes early and this localization extends until fracture with a strain over 30%, while the strain in the NZ is only 4%. Differences in regional strain of FSW joints, which are essentially controlled by grain structure, the distribution of precipitation and dislocation density, result in decrease on the overall mechanical properties. - Highlights: Black-Right-Pointing-Pointer Microstructure heterogeneity of welds on tensile deformation behavior is studied. Black-Right-Pointing-Pointer The welds contain two typical deformation zones, affecting the global ductility. Black-Right-Pointing-Pointer Regional strain of welds is controlled by grain structure and dislocation density. Black-Right-Pointing-Pointer Theoretical calculation is in good agreement with experimental result.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Correlation between grain boundary misorientation and M{sub 23}C{sub 6} precipitation behaviors in a wrought Ni-based superalloy

The correlation between the grain boundary misorientation and the precipitation behaviors of intergranular M{sub 23}C{sub 6} carbides in a wrought Ni–Cr–W superalloy was investigated by using the electron backscattered diffraction (EBSD) technique. It was observed that the grain boundaries with a misorientation angle less than 20°, as well as all coincidence site lattice (CSL) boundaries, are immune to precipitation of the M{sub 23}C{sub 6} carbides; in contrast, the random high-angle grain boundaries with a misorientation angle of 20°–40° provide preferential precipitation sites of the M{sub 23}C{sub 6} carbides at the random high-angle grain boundaries with a higher misorientation angle of 55°–60°/[2 2 3] turn to retard precipitation of M{sub 23}C{sub 6} carbides owing to their nature like the Σ3 grain boundaries and retard the precipitation of M{sub 23}C{sub 6} carbides. The low-angle and certain random grain boundary segments induced by twins were found to interrupt the precipitation of the M{sub 23}C{sub 6} carbides along the high-angle grain boundaries. - Highlights: ► The low angle grain boundaries and CSL boundaries are immune to precipitation. ► M23C6 precipitate preferentially at random grain boundaries within 20°–40°. ► Some certain random grain boundary segments interrupt M23C6 precipitation.

36 MATERIALS SCIENCE↗

DOE OSTI2014

EBSD analysis of (10–12) twinning activity in Mg–3Al–1Zn alloy during compression

The (10–12) twinning activity of Mg–3Al–1Zn magnesium alloy during uniaxial compression at room temperature has been investigated by electron backscatter diffraction. The results indicated that the twinning activity was closely related with two angles: one was the angle between the c-axis and the compression direction and the other was the angle between the a-axis and the titling direction in the basal plane for a given relation between the c-axis and the compression direction. These two parameters can be used to explain which twinning variant will operate under the given strain path. For the grains containing a single (10–12) twinning variant, the (10–12) twinning variant occurred in a wide range of Schmid factor values (0 < Schmid factor < 0.5) and the Schmid factor rank of 1 or 2 was the most commonly observed. By contrast, for the grains containing two (10–12) twinning variants, the (10–12) twinning activity exhibited a stronger orientation dependence and the combinations of Schmid factor ranks 1–3 and 1–2 were the most commonly observed. - Highlights: • Twinning activity of AZ31 magnesium alloy was investigated by EBSD. • (10–12) twinning shows a strong orientation dependence. • Two angles can be used to explain which twin variant will operate.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Analysis of integrity and microstructure of linear friction welded Waspaloy

Nickel-base superalloy, Waspaloy, was linear friction welded (LFWed) under different axial shortening conditions of 2.0, 3.4, and 4.6 mm. The tensile properties and microhardness of the weldments were investigated in the as-LFWed condition and compared with those in the post-weld heat treated (PWHTed) condition. Mechanical properties were related to microstructures following examination by optical microscopy, high resolution scanning electron microscopy, and electron backscatter diffraction (EBSD). Analyses of the EBSD results in terms of the misorientation angle distribution, which represents the stored energy, were performed. In the as-LFWed condition, the yield strength (YS) and ultimate tensile strength (UTS) increased with axial shortening due to greater expulsion of the softened interfacial material toward the periphery as flash. In contrast, with increasing axial shortening the total elongation initially remained constant and then decreased. This was also related to the expulsion of the softened interfacial material into the bifurcated flash. Extensive dissolution of the strengthening phase (γ′) in the weld area during linear friction welding (LFW) contributed to the lower YS and UTS in the as-welded condition compared to the PWHTed condition where the γ′ particles were recovered. After performing post-weld heat treatment (PWHT), the total elongation improved due to the relaxation of stored energy and grain growth in the thermomechanically affected zone (TMAZ). - Highlights: • Tensile property and microstructure in Waspaloy linear friction welds were studied. • Yield strength and ultimate tensile strength increased with axial shortening. • Elongation initially remained constant and then decreased with axial shortening. • Post-weld heat treat recovered dissolved γ′ particles and increased weld strength. • Stored energy relaxation during post-weld heat treatment improved weld elongation.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Grain boundary plane distributions in a cold rolled and annealed high purity iron

High purity (99.99%) iron samples were cold rolled with a thickness reduction of 87% followed by a annealing at 620 °C for 15 and 45 min, then the grain boundary plane distributions were characterized by electron backscatter diffraction and a stereology and statistics based five parameter analysis. The results showed that the grain boundary planes were mainly distributed on (1 0 0) and such distribution was enhanced obviously when the holding time of annealing increased from 15 to 45 min during which an extensive grain growth and a dramatic texture evolution took place. Further analysis indicated such distribution was largely due to the rotation of grain boundary planes of the [1 0 0] misoriented grains. Additionally, it was also observed that some random boundaries of [1 0 0] misoriented grains were changing from asymmetrical tilt into (1 0 0)/(− 1 0 0) twist when annealing proceeded from 15 to 45 min. Based on the present work and the results reported by other investigators, it was suggested that the chemistry appeared to be critical in determining the grain boundary plane distribution in iron based materials. - Highlights: •Grain boundary (GB) plane distribution (GBPD) in a high purity (99.99%) was studied. •GB planes are mainly distributed on (1 0 0) in the cold rolled and annealed samples. •Such distribution is largely due to the rotation of GB planes of [100] misoriented grains. •Some [1 0 0] asymmetrical tilt boundaries are evolving into twist ones during annealing.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Magnetic Barkhausen noise characterization of two pipeline steels with unknown history

Highlights: • The hardness, microstructure, texture and MBN of two pipeline steels were analyzed. • The angular MBN results revealed possible manufacturing histories of the two pipelines. • The MBN is closely related to the processing history, microstructure and stress state. • The use of MBN technique can help address the integrity issues in the pipeline industry. Steel samples cut from two line pipes with unknown processing history were analyzed using magnetic Barkhausen noise (MBN), electron backscatter diffraction (EBSD) and Vickers hardness techniques on the pipe surface and on sections through the wall thickness. The results show that the MBN responses vary significantly not only between the two pipe steels, but also among different thickness layers of each steel. Both steels show considerable variations in MBN at different locations on the surfaces. For one steel, the surface MBN illustrates an inverse linear relationship with respect to the hardness, while the other does not depict such a relation since the variation in hardness at different locations is very small. Across the thickness, the microstructure (phase and grain size) of both steels is quite similar, but the texture shows significant differences. Again, there is a large difference in hardness across the thickness for one steel, while the other only shows very small variation in hardness across the thickness. The variations in average MBN across the wall thickness for both steels are quite large. Angular MBN measurements on the sectioned samples revealed significant discrepancies in the magnetic anisotropy in the two steels. Based on the analysis of the angular MBN data with respect to the single and dual easy axis models, one pipe can be determined to have been manufactured through a seam welding process, while the other may have been formed by spiral welding. Due to the residual stresses in the steel samples, the effect of the crystallographic texture on the anisotropy in MBN response has essentially been suppressed.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Direct imaging of Cl- and Cu-induced short-circuit efficiency changes in CdTe solar cells

To achieve high-efficiency polycrystalline CdTe-based thin-film solar cells, the CdTe absorbers must go through a post-deposition CdCl 2 heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl 2 heat treatments are investigated using cross-sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross-sectional carrier collection profile due to these treatments that cause an increase in short-circuit current and higher open-circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of ≈350 nm. Scanning transmission electron microscope electron-energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Furthermore, each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.

14 SOLAR ENERGY↗

DOE OSTI2017

Characterization of Al-Mg Alloy Aged at Low Temperatures

For this research, long-term aged [343 K (70 °C) for 30 months and natural exposure for over 10 years] Al 5456 H116 samples were characterized using electron backscatter diffraction (EBSD), scanning transmission electron microscopy (STEM), state-of-the-art energy-dispersive X-ray spectroscopy (EDS) systems, and small-angle neutron scattering (SANS). ASTM G-67 mass loss tests of the sensitized Al 5456 alloy samples were conducted. Intragranular Mg-rich precipitates, such as Guinier–Preston (GP) zones, were confirmed in Al 5456 H116 aged at 343 K (70 °C) for 30 months, and the volume of these precipitates is 1.39 pct. β' phase is identified at the grain boundary of a navy ship sample, while high-resolution STEM results reveal no intragranular precipitates. Intergranular corrosion (IGC) of Al 5456 was found to be related to the continuity of intergranular precipitates.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Microstructure and Sn crystal orientation evolution in Sn-3.5Ag lead-free solders in high temperature packaging applications

Understanding the reliability of eutectic Sn-3.5Ag lead-free solders in high temperature packaging applications is of significant interest in power electronics for the next generation electric grid. Large area (2.5mm 2.5mm) Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates were thermally cycled between 5 C and 200 C. Sn crystal orientation and microstructure evolution during thermal cycling were characterized by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Comparisons are made between observed initial texture and microstructure and its evolution during thermal cycling. Gradual lattice rotation and grain boundary misorientation evolution suggested the continuous recrystallization mechanism. Recrystallization behavior was correlated with dislocation slip activities.

high temperature packaging↗

DOE OSTI2018

Mechanical Behavior of Commercially Pure Titanium Weldments at Lower Temperatures

Commercially pure titanium is used for low-temperature applications due to good toughness attributed to single-phase microstructure (α). Electron beam welding (EBW) and gas tungsten arc welding (GTAW) processes have been used for welding two grades of commercially pure titanium (Grade 2 and Grade 4). Martensitic microstructure is found to be finer in the case of EBW joint as compared to GTAW joint due to faster rate of cooling in the former process. Weldments have been characterized to study the mechanical behavior at ambient (298 K) and cryogenic temperatures (20 and 77 K). Strength of weldments increases with the decrease in temperature, which is found to be more prominent in case of Grade 4 titanium as compared to Grade 2. Weld efficiency of Grade 4 is found to be higher at all the temperatures (ambient, 77 and 20 K). However, ultimate tensile strength/yield strength ratio is higher for Grade 2 as compared to Grade 4. % Elongation is found to increase/retained at cryogenic temperatures for Grade 2, and it is found to decrease for Grade 4. Electron backscattered diffraction analysis and transmission electron microscopy of deformed samples confirmed the presence of extensive twinning in Grade 2 and the presence of finer martensitic structure in Grade 4. Fractography analysis of tested specimens revealed the presence of cleavage facets in Grade 4 and dimples in specimens of Grade 2. Higher strength in Grade 4 is attributed to higher oxygen restricting the twin-assisted slip, which is otherwise prominent in Grade 2 titanium.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Microstructure and mechanical properties of pure copper wire produced by shear assisted processing and extrusion

Shear assisted processing and extrusion (ShAPE) process can consolidate powdered materials and simultaneously extrude wire or tube with improved properties. We successfully produced copper wire extrusions from powder and solid materials for the first time. The extrusion pressure of ShAPE process is at least two times less than that required for conventional extrusion. We used optical microscopy to inspect and validate the integrity of extrudates. It shows that the microstructure was refined and dynamically recrystallized to equiaxial grains. Compared to the annealed copper wire, ShAPE processed wire has 80% higher yield strength, 15% higher ultimate tensile strength and 20% higher ductility. These were correlated with refined grain size and sub-structuring observed via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).

Copper, Wire, Shear Assisted Processing and Extrus↗

DOE OSTI2019

Nanoscale crystallographic characterization of nanoporous catalyst by TKD

To better understand the structure-reactivity relationships of self-supported nanoporous catalysts, a nanoscale characterization of the materials is required. Transmission Kikuchi Diffraction (TKD), or transmission electron backscatter diffraction (t-EBSD), is a recent technique used to analyze the grain crystallography and morphology of thin films and nanometer-scale materials. Using a conventional EBSD detector in a FIB-SEM instrument, we investigate nanoporous gold (npAu) samples with ligament size in the 50-70 nm range. Grains with diameters below 50 nm can be clearly resolved, but also welldefined grain boundaries extending over 3 to 4 pixels, proving the high resolution of the method. The presence of contaminations during sample preparation by FIB milling is also discussed. We conclude the results provide deeper insight than conventional EBSD technique can alone.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Growth of epitaxial CdTe thin films on amorphous substrates using single crystal graphene buffer

Traditionally, a high-quality CdTe film can only be grown on a single crystal substrate with a small lattice mismatch. We report the epitaxy of CdTe films on monolayer single crystal graphene buffered amorphous SiO 2 /Si(100) substrates, despite a 86% lattice mismatch between CdTe(111) and graphene. X-ray pole figure, electron backscatter diffraction mapping and transmission electron microscopy all confirm that the epitaxial CdTe films are composed of two domains: the primary and the Σ3 twin. The crystal quality of films is shown to improve as the post-deposition annealing temperature increases. However, the rotational misalignment in CdTe remains large even after annealing. Through density functional theory calculations on the charge transfer distribution at the interface of CdTe and graphene, it is found that the interface is dominated by the weak van der Waals interaction, which explains the large spread of in-plane orientation in CdTe films. Furthermore, the rotational misalignment in graphene itself is also confirmed to produce the large in-plane orientation spread in CdTe films. Although imperfect in epitaxy quality, this work demonstrates that monolayer single crystal graphene can buffer amorphous substrates for growing epitaxial films, and hence hints an opportunity for developing advanced thin film devices using graphene as a template.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Microstructure of TRISO Coated Particles from the AGR-1 Experiment I: SiC Grain Size and Grain Boundary Character

Pre-irradiation SiC microstructures in TRISO coated fuel particles from the AGR-1 experiment were quantitatively characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). From EBSD it was determined that only the cubic polymorph of as-deposited SiC was present and the SiC had a high fraction of CSL S3 grain boundaries. Additionally, the local area misorientation (LAM), which is a qualitative measurement of strain in the SiC lattice, was mapped for each fuel variant. The morphology of the SiC / IPyC interfaces were characterized by TEM following site-specific focused ion beam (FIB) specimen preparation. It was determined that the SiC layer had a heavily faulted microstructure typical of CVD deposited SiC and that the average grain diameter increased from the SiC/IPyC interface for all the fuel variants, except V3 that showed a constant grain size across the layer.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗