Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Electron Backscatter Diffraction”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Sublattice-specific ordering of ZnO layers during the heteroepitaxial growth at different temperatures

The effect of the substrate temperature on the sublattice ordering in ZnO layers grown by reactive pulsed magnetron sputtering on sapphire has been investigated by different techniques. The improvement of the crystal quality and heteroepitaxial growth at relatively low temperatures (550 deg. C) is verified by x-ray diffraction, high-resolution transmission electron microscopy, Rutherford backscattering spectrometry in channeling mode (RBS/C), and Raman spectroscopy. Sublattice-resolved analysis by resonant RBS/C and Raman spectroscopy reveals that the progressive transition to the single crystal phase is accomplished in a faster way for Zn- than for O-sublattice. This behavior is attributed to the preferential annealing of defects in the Zn sublattice at low temperatures when compared to those of the O sublattice.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Comprehensive study of the effect of the irradiation temperature on the behavior of cubic zirconia

Cubic zirconia single-crystals (yttria-stabilized zirconia (YSZ)) have been irradiated with 4 MeV Au{sup 2+} ions in a broad fluence range (namely from 5 × 10{sup 12} to 2 × 10{sup 16} cm{sup −2}) and at five temperatures: 80, 300, 573, 773, and 1073 K. Irradiated samples have been characterized by Rutherford backscattering spectroscopy in channeling mode, X-ray diffraction and transmission electron microscopy techniques in order to determine the disordering kinetics. All experimental results show that, whatever is the irradiation temperature, the damage build-up follows a multi-step process. In addition, the disorder level at high fluence is very similar for all temperatures. Thus, no enhanced dynamic annealing process is observed. On the other hand, transitions in the damage accumulation process occur earlier in fluence with increasing temperature. It is shown that temperature as low as 573 K is sufficient to accelerate the disordering process in ion-irradiated YSZ.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Comparison of microstructural and mechanical properties of friction stir spot welded ultra-high strength dual phase and complex phase steels

Highlights: • The microstructure and mechanical properties of FSSW of ultra high strength DP and CP steels are compared. • The stir zone (SZ) of CP steel mainly consists of bainite and martensite; no bainite is identified in the SZ of DP steel. • The cooling was not fast enough for the CP steel to suppress the effect of chemical composition on phase transformation. - Abstract: The microstructure and mechanical properties of friction stir spot welding of ultrahigh strength dual phase (DP) and complex phase (DP) steels are compared based on the experimental results. For both DP and CP steels, FSSW joints are successfully fabricated using the same process parameter set. While the microstructure of joints are characterized in detail using scanning electron microscopy, electron back scattered diffraction, and transmission electron microscopy, the mechanical property of joints are evaluated by shear tensile tests. The result of the microstructural analysis shows that the stir zone (SZ) of CP steel mainly consists of bainite and martensite, while no bainite is identified in the SZ of DP steel. The existence of bainite in the SZ of CP steel suggests that the cooling rate, which is nearly identical for both CP and DP steels, was not fast enough to suppress the effect of the alloying composition, particularly that of Mn, on the phase transformation. The result of the present study contributes to the development of solid state joining process of the ultrahigh strength steels.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Correlation Between Structural Parameters and Mechanical Properties of Al5083 Sheets Processed by ECAR

In the paper, structural parameters and mechanical properties of Al5083 alloy sheet during equal channel angular rolling (ECAR) process and their relationship are studied. In order to evaluate the effect of ECAR process, Al5083 strips were subjected to the ECAR process for 1, 2, and 3 passes through the die channel angles 110°, 120°, and 130° at two routes. The effect of the process on the microstructural evolution of samples was investigated by means of x-ray diffraction and EBSD techniques. X-ray pattern has been analyzed using Rietveld method to compute structural parameters, including microstrain, average crystallite size, and dislocation density. The results showed that the dislocation density and microstrain were increased, and crystallite size was decreased during ECAR process. It was found that the behavior of variations in mechanical properties was in accordance with the dislocation density changes. This paper revealed that the increase in the strength of ECARed samples could be attributed to reduction in high-angle grain boundaries and the increase in dislocation density. Moreover, the yield strength estimated from Taylor equation was found in accordance very well with the experimentally measured yield strength of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure, texture, and mechanical properties of friction stir welded commercial brass alloy

Microstructural evolution during friction stir welding of single-phase brass and corresponding mechanical properties were investigated. For this purpose, 2 mm thick brass plate was friction stir welded at a rotational speed of 450 rpm and traverse speed of 100 mm/min. The microstructure of the joint was studied using optical microscopy, scanning electron microscopy equipped with electron back scattered diffraction system, and scanning transmission electron microscopy. The mechanical properties were measured using hardness and tensile tests. The formation of subgrains and their transformation into new grains in conjunction with existence of A{sub 1}{sup ⁎}, A{sub 2}{sup ⁎} and C texture components revealed that the continuous dynamic recrystallization plays a dominant role in the microstructural evolution. However, grain boundary bulging, along with the formation of twin boundaries, and presence of the G texture component showed that the discontinues dynamic recrystallization may participate in the new grain formation. Furthermore, the different strengthening mechanisms, which caused the higher strength of the joint, were discussed. - Highlights: •Microstructural evolution during FSW of a single phase brass was investigated. •CDRX and DDRX were the main mechanisms of the grain structure formation during FSW. •GDRX and SRX were not contributed in grain structure formation. •The lamellas TBs were formed in the SZ of the joints. •Grain boundary, dislocation, and texture effects resulted in higher strength.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of cold rolling on the microstructural evolution of new β-typed Ti–6Mo–6V–5Cr–3Sn–2.5Zr alloys

A Ti–6Mo–6V–5Cr–3Sn–2.5Zr (wt.%) alloy was designed as a new metastable β-Ti alloy. The effect that cold rolling had on the microstructural evolution of the material was investigated via optical microscopy (OM), X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) measurements. A single β phase formed in the alloy after solution treatment at 780 °C for 30 min followed by water quenching. The solution-treated alloy was cold rolled with thickness reductions of 10%, 30%, 50% and 70%, and the hardness values increased as the thickness of the specimen decreased. The textures of the cold rolled specimen were characterized according to the 〈110〉 partial parallel to the rolling direction as the rolling reduction increased. The crystallographic orientation showed principal α-fiber textures for (111)〈110〉 and (112)〈110〉. The cold deformation led to the appearance of martensite α″ phases, particularly stress-induced martensite (SIM) α″ phases. - Highlights: • Effect of cold rolling on new β-typed Ti-6Mo-6V-5Cr-3Sn-2.5Zr alloy was studied. • A single β phase was obtained after solution treatment at 780 °C for 30 min. • α-Fiber textures became dominated with the increase in cold rolling reduction. • A stress-induced α″ martensite was caused by cold rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Evolution and Stress Corrosion Cracking Susceptibility of 12Cr Martensitic Steel Upon Long-Term Service in Power Plants

After 230,000-h long-term service at 550 °C/13.7 MPa, the microstructure of a kind of 12Cr martensitic steel was investigated using scanning electron microscopy, backscattering electron microscope and x-ray diffraction analysis. The results show that the precipitation and coarsening of carbides at grain/lath boundaries are the main cause of microstructure degradation. The static immersion tests and the slow strain rate test coupled with electrochemical impedance spectroscopy were conducted on the served steel in 1.0% NaCl solution, and it turns out that the pitting corrosion resistance and repassivation ability of the steel are significantly reduced as a result of microstructure degradation. The stress corrosion cracking susceptibility of the steel was also studied. Fracture morphology analysis shows that the secondary crack in conjunction with slip lines is a result of the coalescence of micro-cracks nucleated from the pits.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigation of UO 2 doped with Fe 2 O 3 sintered under a reducing atmosphere

Nuclear fuel produced with trace amounts of transition metal additives is of potential interest for introducing intentional signatures for accelerating nuclear forensics. In this work, we investigate the effects on microstructure, grain size, crystal structure, and stoichiometry when trace amounts of Fe in the form of Fe 2 O 3 are added to UO 2 . Sintering of compacts with different concentrations, from 250 to 3000 ppmw, was performed under a reducing atmosphere at 1773 K. The persistence of the taggant during the fuel fabrication process as well as its impact on grain size, crystal lattice, and first-neighbor chemistry was evaluated using inductively coupled plasma–optical emission spectroscopy, powder X-ray diffraction (pXRD), Raman spectroscopy, scanning electron microscopy–backscatter electron spectroscopy, energy dispersive spectroscopy, and thermogravimetric analysis. We observed that a negligible amount of Fe was lost during sintering. Our results indicate that the feedstock, Fe 2 O 3 transforms into Fe and FeO under the test sintering conditions. For all compositions, metallic Fe precipitate was found in grain boundaries as a secondary phase. In conclusion, the potential incorporation of ionic Fe into the UO 2 unit cell was determined by pXRD and Raman spectra.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Effect of build geometry on the β-grain structure and texture in additive manufacture of Ti-6Al-4V by selective electron beam melting

With titanium alloys, the solidification conditions in Additive Manufacturing (AM) frequently lead to coarse columnar β-grain structures. The effect of geometry on the variability in the grain structure and texture, seen in Ti-6Al-4V alloy components produced by Selective Electron Beam Melting (SEBM), has been investigated. Reconstruction of the primary β-phase, from α-phase EBSD data, has confirmed that in bulk sections where in-fill “hatching” is employed growth selection favours columnar grains aligned with an <001> {sub β} direction normal to the deposited powder layers; this results in a coarse β-grain structure with a strong < 001 > {sub β} fibre texture (up 8 x random) that can oscillate between a near random distribution around the fibre axis and cube reinforcement with build height. It is proposed that this behaviour is related to the highly elongated melt pool and the raster directions alternating between two orthogonal directions every layer, which on average favours grains with cube alignment. In contrast, the outline, or “contour”, pass produces a distinctly different grain structure and texture resulting in a skin layer on wall surfaces, where nucleation occurs off the surrounding powder and growth follows the curved surface of the melt pool. This structure becomes increasingly important in thin sections. Local heterogeneities have also been found within different section transitions, resulting from the growth of skin grain structures into thicker sections. Texture simulations have shown that the far weaker α-texture (∼ 3 x random), seen in the final product, arises from transformation on cooling occurring with a near random distribution of α-plates across the 12 variants possible from the Burgers relationship. - Highlights: • Distinctly different skin and bulk structures are produced by the contour and hatching passes. • Bulk sections contain coarse β-grains with a < 001 > fibre texture in the build direction. • This oscillates between a random distribution around the axis and cube reinforcement. • In the skin layer nucleation occurs off the surrounding powder bed and growth occurs inwards. • Simulations show that a weak α-texture results from a random distribution across habit variants.

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 OSTI2015

Microstructural characterization of aluminum alloys using Weck's reagent, part I: Applications

This paper focuses on the applications of a color etchant for aluminum alloys named Weck's reagent. The Al phase shows different colors from location to location after being etched by Weck's reagent. It is proved that Weck's reagent is very sensitive to the micro-segregations of Ti, Si and Mg in Al alloys so that characterization of the micro-segregations can be qualitatively realized which is usually done by electronic probe techniques. With the help of this characterization method, we are able to evaluate solid fractions for the semi-solid processed Al alloy with a better accuracy by excluding the Al grain growth during water quenching. To understand this reagent better, the color change during etching is investigated by applying different etching times at room temperature (25 °C). Among those results, 12 s shows the best color contrast after etching. Finally, we repeat the 12 second etching for four times through repeating a polishing–etching process. The result exhibits that Weck's reagent has a satisfying re-producibility with stable color and color distribution for the four times etching result. The second part of this study covers the coloring mechanism of Weck's reagent by characterizing the etched surface via various characterization methods. - Highlights: • The applications of Weck's reagent for Al alloys are introduced in detail. • Detailed relationship between micro-segregations in Al phase and the color difference revealed by Weck's reagent are studied. • Etching time has a strong influence on the color revealed by Weck's reagent. • Besides micro-segregation, grain boundaries can also be visualized by Weck's reagent, which was proved by EBSD analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation on the formation mechanism of Ti-bearing non-metallic inclusions in Fe-Al-Ti-O-N alloy by inductive separation method

Formation mechanism of Ti-bearing non-metallic inclusions was studied by inductive separation method, and characterization method was selected according to the type of each inclusion. The Al + Ti oxide was heterogeneous consisting of Al{sub 2}O{sub 3} with Ti rich oxide layer. Compositional and size distribution was characterized by automated SEM observation and EDS analysis. It is formed as the reduction of Al{sub 2}O{sub 3} by Ti in molten alloy at 1873 K. The Al-Ti oxide was homogenous. It was liquid at 1873 K characterized by EBSD. The Al/Ti molar ratio of oxide was consistent with that in each alloy as analyzed by manual SEM/EDS analysis. Its formation mechanism is proposed to be the reaction among dissolved Ti, Al, and O in molten alloy at 1873 K. TiN precipitated during solidification. The fraction of TiN smaller than 1 μm was larger in alloy2 than that in alloy1 as analyzed by automated SEM/EDS analysis. It is resulted from larger supersaturation degree in alloy2 during solidification.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure control to improve creep strength of alumina-forming austenitic heat-resistant steel by pre-strain

Highlights: • The effect of pre-strain on creep strength of AFA steel was studied. • The creep test was performed at 700°C and 200Mpa, and the aging test was carried out using box furnace at 700°C to simulate the microstructural evolution during creep. • Microstuctural evolution was observed by using SEM, EBSD, and TEM to investigate the relationship between creep strength and microstructure. - Abstract: At 700 °C and 200 MPa, the creep rupture time of W-containing alumina-forming austenitic heat-resistant (WAFA) steel increases from 1044 to 3119 h by pre-strain. Pre-strain introduces a lot of dislocation into the matrix and most of the dislocations remain stable to the end of creep without recovery and recrystallization. In addition, the dislocations have enabled secondary NbC and Laves phase to be uniformly distributed and refined. However, the dislocations lower grain boundary strength due to the coarsening of precipitates along grain boundaries Therefore, the increase in the creep rupture time in spite of deterioration of grain boundary strength is attributed to the dislocation strengthening and enhanced precipitation hardening within grains.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure, texture and mechanical properties of 6061 aluminum laser beam welded joints

Highlights: • Strong cube texture ({001}<100>) is observed in columnar dendrites. • The ratio of equiaxed dendrites shows proportional relationship with the strength. • The relations between process-microstructure-property are accurately established. - Abstract: In the present study, laser beam welding was carried out with 6061 Al alloy plate to study the microstructural evolution under various welding heat input (ηP/v = 30 J/mm, 38 J/mm, 46 J/mm, and 58 J/mm). The width of the weld metals increased continuously with the heat input values. Quantitatively correlation of the microstructure distribution with welding parameters was developed based on the EBSD results. The weld metals mainly consisted of coarse columnar dendrites and equiaxed dendrites. The ratio of equiaxed dendrites which were controlled by constitutional supercooling and heterogeneous nuclei showed directly proportional relationship with the weld strength. Strong cube texture ({001}<100>) was observed in columnar dendrites, which showed harmful effect on the weld strength. Slight softening in heat affected zone due to recrystallization was identified by nanoindentation tests. All specimens failed in weld metal and the fracture surfaces showed the characteristics of ductile fracture.

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

Formation of intermetallic structures at the interface of steel-to-aluminium explosive welds

Highlights: • The interface of Fe-Al explosive welds was characterised by SEM/EDS and EBSD. • The intermetallics formed at the weld interface are rich in Al (Fe{sub 4}Al{sub 13}, Fe{sub 2}Al{sub 5}). • The presence of intermetallic phases on the interface deeply affects the weldability. • Al-rich intermetallics increase the solidification time of the weld interface. - Abstract: The formation of intermetallic structures at the interface of carbon steel to 6082 aluminium alloy explosive welds and their influence on the weldability of these two materials were studied. The morphology, the microstructure, the chemical and phase compositions of the welds were characterised by several types of microscopy techniques. The interface characterisation proved that explosive mixtures with a lower detonation velocity were revealed as being more suitable for achieving consistent welds since jet entrapment was prevented and continuous molten layers were not formed at the weld interface. It was also found that the physical properties of the intermetallic phases generated at the weld interface have a strong influence on the weldability of steel-to-aluminium explosive welds. Specifically, it was shown that the formation of aluminium-rich intermetallic phases at the weld interface increases the solidification time of the interfacial molten material, decreasing the weldability of these two materials. The formation of these intermetallic compounds should be avoided by reducing the interaction between the flyer and the baseplate as well as by avoiding excessive molten layers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of microstructures on hot compression behavior of a Ti-43Al-2Si alloy fabricated by cold crucible continuous casting

Highlights: • TiAl alloys with different lamellar colonies were fabricated by cold crucible continuous casting. • EBSD was used to investigate the evolution of lamellae during the hot compression. • Lamellar colony boundaries promote the dynamic recrystallization process. - Abstract: To investigate the influence of lamellar orientation and colony boundary on deformation behavior, fully lamellar Ti-43Al-2Si alloys were prepared by cold crucible continuous casting and isothermal compression tests were conducted at different temperatures in the range 1373–1523 K with a strain rate of 0.01 s{sup −1}. The as-cast microstructures were elongated colony with lamellae oriented at nearly 45° to the compression direction and equiaxed colony with various lamellae orientations, respectively. The results revealed that serious cracking or sliding traces appeared on the surface of deformed specimens with elongated colony original microstructure and that their peak stresses were lower compared to those of specimens with equiaxed colony original microstructure. The relationship between deformation behaviors and as-cast microstructure was analyzed in detail. It was found that the recrystallization/globularization level is significantly lower than that in specimens with equiaxed colony original microstructure during hot deformation owing to the preferred nucleation sites in colony boundaries. Finally, the lamellae conversion process was characterized to reveal the softening mechanisms of full lamellar TiAl-based alloy during hot compression.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Characterization of bismuth nanospheres deposited by plasma focus device

A new method for producing thin layer of bismuth nanospheres based on the use of low energy plasma focus device is demonstrated. Various techniques such as scanning electron microscopy, Rutherford backscattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been used to characterize the morphology and the composition of the nanospheres. Experimental parameters may be adjusted to favour the formation of bismuth nanospheres instead of microspheres. Therefore, the formation of large surface of homogeneous layer of bismuth nanospheres with sizes of below 100 nm can be obtained. The natural snowball phenomenon is observed to be reproduced in nanoscale where spheres roll over the small nanospheres and grow up to bigger sizes that can reach micro dimensions. The comet-like structure, a reverse phenomenon to snowball is also observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗