Electron Backscatter Diffraction Study Research Articles

Deformation and damage assessment in type 316 LN stainless steel weld joint under isothermal and thermomechanical cyclic loading

Present investigation is aimed at understanding the deformation behavior and the development of damage in a type 316 LN austenitic stainless steel (SS) weld joint (WJ) under isothermal low cycle fatigue (IF) and thermomechanical fatigue (TMF). In-phase (IP) and out-of-phase (OP) TMF tests were carried out by maintaining a phasing relation of 0° and 180° respectively, between the mechanical strain and temperature cycles. Dynamic strain ageing (DSA) was found to exert a strong influence on the cyclic stress response (CSR) of the joint under both IF and TMF cycling. The CSR was observed to be higher under TMF compared to IF cycling due to the activation of additional hardening mechanisms in the former tests. The difference in fatigue life under TMF and IF is rationalized based on the development of deformation and damage through optical and scanning electron microscopy (SEM) coupled with electron backscatter diffraction (EBSD) studies. A clear demarcation of the strain distribution in the base metal (BM) and weld metal (WM) region of the joint is achieved through detailed EBSD analysis of the tested specimens. Cyclic plastic deformation and the associated development of damage take place independently in the BM and the WM parts of the joint, competing to cause the failure. The build-up of damage under IF and TMF cycling is dictated by a combination of DSA and δ-ferrite transformation, depending on the applied strain amplitude and the strain-temperature phasing employed. The observed life variations have been rationalized in terms of the substructural evolution and fracture behavior under different testing conditions.

Metallographic, mechanical and reciprocating wear characterization and behavioural studies of untreated and T6 treated Al2O3/Al7Si0.3Mg functional composite material

The microstructural, mechanical and unlubricated reciprocating wear characteristics of functionally graded 10 wt% Al2O3/Al7Si0.3Mg composite were analysed under untreated (UT) and heat-treated (HT) conditions. Microstructural analysis revealed Al2O3 particle gradation across the thickness and particle clusters in UT composite, whereas fine α-Si spheroids were observed in HT composite. Transmission electron microscopy studies on the HT composite revealed iron intermetallic and nano-sized β-Mg2Si precipitate phases, whilst electron backscatter diffraction studies show morphological changes in the α-Al grain structure after heat treatment. UT and HT composites underwent reciprocating wear trials under varying wear parameters (applied load and sliding distance) using a pin-on-flat plate linear reciprocating tribometer. Worn morphologies for both UT and HT composites were studied using a scanning electron microscope to investigate the wear mechanisms involved and atomic force microscopy to understand the difference in surface roughness. Response Surface Methodology is used to conduct statistical analysis and response optimisation on UT and HT composites. Due to Al2O3 particles and silicon spheroids, the HT composite outperformed the UT composite. According to the investigation, the wear resistance of both composites had increased (20–40%) with increasing reinforcement content but decreased with increasing wear parameters.

Quasi-in-situ EBSD Study of the Microstructure and Texture Evolution During Static Recrystallization in an Extruded Mg-Mn-Ce Alloy

A quasi-in-situ electron backscatter diffraction (EBSD) technique is used to study the microstructure and texture evolution in an extruded Mg-1Mn-0.2Ce (wt.%) alloy during annealing at 400°C. The as-extruded alloy has a bimodal and partially recrystallized microstructure with a strong [{10}bar{1}{text{0}}]//ED basal texture (ED represents extrusion direction). Upon annealing, the strong [{10}bar{1}{text{0}}]//ED texture is mitigated and gradually replaced by a major rare earth (RE)-texture and minor texture components lying within an arc between text{[10}bar{1}{text{0}}]//ED and text{[11}bar{2}text{0]}//ED. The RE-texture component observed from localized quasi-in-situ EBSD of a randomly selected area is text{[85}bar{13}text{6]}//ED, which is ~8.1° from the [{44}bar{8}{text{3}}]//ED RE-texture observed in the bulk sample. The texture change during quasi-in-situ annealing is associated with the preferential growth of the recrystallized (RX-ed) grains whose orientations are near text{[85}bar{13}text{6]}//ED and text{[32}bar{5}text{0]}//ED, at the expense of both RX-ed and deformed grains with [{10}bar{1}{text{0}}]//ED orientations. This grain growth process mainly occurs in the deformation bands, where there is an agglomeration of the basal <a> and/or pyramidal II <c+a> geometrically necessary dislocations (GNDs). The observed preferential grain growth could be due to the relatively low energy stored in these RX-ed grains that have specific orientations.

Scroll-like and platy molybdenite-3R from the Ufaley metamorphic block, South Urals: EBSD, XRD, SEM, EPMA and ICP-MS study

AbstractScroll-like crystals of molybdenite, 2–5 mm in size, were found in phengite rock from the outer contact of the granular quartz vein of the Kyshtym quartz deposit. Platy and partly scrolled molybdenite occur in the same phengite rock from the outer contact of the quartz–feldspar pegmatite of the Slyudyanogorsk mica deposit. Both occurrences are located in the Ufaley metamorphic block in the South Urals. Scroll-like molybdenite crystals can associate with platy and partly twisted crystals in the same samples. The chemical composition of molybdenite was studied by inductively coupled plasma mass spectrometry (ICP-MS) and electron probe microanalysis (EPMA). Polytypes of molybdenite were identified with electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). Both scroll-like and platy molybdenite crystals are only represented by the 3R polytype, are enriched in Re up to 1 wt.% and contain no other significant impurities. Scroll-like molybdenite is twisted mainly around the crystallographic axis X. Twinning with a rotation of 60 degrees around the Z crystallographic axis is fixed in the plane (ab). The most probable origin of scroll molybdenites is the consequent growth of molybdenite around nucleation centres, which are commonly represented by mica crystals. The formation of the 3R polytype is caused by the difference in dimension of the layers enriched and depleted in rhenium.

A quasi-in-situ EBSD study of the thermal stability and grain growth mechanisms of CoCrNi medium entropy alloy with gradient-nanograined structure

The thermal stability and mechanical properties of a gradient-nanograined structure (GNS) CoCrNi medium entropy alloy (MEA) processed by ultrasonic surface rolling were studied by using isothermal/isochronal annealing tests combined with quasi-in-situ electron backscatter diffraction (EBSD) characterization and Vickers micro-hardness (HV) measurements. A layer by layer high-throughput investigation method was used to quantitatively study the grain growth kinetics and grain boundary evolution with different initial grain sizes, which could effectively save specimen and time costs. The grain nucleation and growth, as well as shrink and disappearance process through Σ3 coincidence site lattice boundary migration with slightly lattice rotation during annealing were directly revealed. The layer by layer grain growth kinetics and calculated activation energy indicate that the thermal stability of nano-grained top surface layer is relatively higher than that of nano-twined subsurface layer for the gradient CoCrNi MEA processed by ultrasonic surface rolling. Further analysis show that the grain boundary relaxation and dynamic recrystallization of the topmost nano-grains led to the decrease of grain boundary energy, thus improving their thermal stability. The present work provided theoretical basis for the application of CoCrNi MEA at high temperatures. Moreover, the high-throughput method on the investigation of grain stability by using gradient structure can be easily extended to other materials and it is of great significance for understanding the microstructural evolution of gradient materials.

In-situ SEM and EBSD study on fretting fatigue crack initiation of a directionally solidified Ni-based superalloy

Fretting fatigue is an important cause of the failure of the turbine blade-disc dovetail joint in aero-engines. In this work in-situ scanning electron microscope (SEM) fretting fatigue experiments using dovetail shape specimens were conducted. The fretting fatigue damage process of Ni-based directionally solidified superalloys including slip trace evolution and crack initiation was captured. The misorientation and geometrically necessary dislocation (GND) density induced by fretting fatigue were quantified by electron back-scattered diffraction (EBSD). The significant correlation between crack path, slip trace, grain boundary microstructure and GND density was revealed. The EBSD analysis achieved good agreement with the in-situ SEM observation.

Evolution of microstructure and crystallographic texture during cold rolling of liquid phase sintered tungsten heavy alloy

In this study, the evolution of microstructure and crystallographic texture of two-phase tungsten heavy alloy (almost pure tungsten embedded in nickel‑tungsten‑iron matrix) during cold rolling was investigated systematically. Electron back scatter diffraction studies reflected that the matrix phase accommodates more strain in the early stages of deformation and that as deformation progresses, the matrix phase exhausts its work hardening ability, resulting in the onset of micro-shear band formation. The tungsten phase on the other hand showed the presence of large orientation gradients accompanied with significant flattening and elongation of grains. At higher rolling reductions (effective true strain of −2.66), extensive shear bands spanning across several tungsten particles and the matrix were observed in the microstructure, which in turn had implications on the evolution of the crystallographic texture. It was observed that weak αb. c. c. (<110>∥RD) and γ fiber (<111>∥ND) emerge in tungsten at low to intermediate rolling reductions, and that αb. c. c. fiber strengthens much more than γ fiber at higher rolling reductions with prominent intensity at rotated cube position. For the matrix phase, a weak beta fiber (fiber connecting the brass {011}<211>, copper {112}<111>, and S {123}<634> orientations in the Euler space) was observed at low to intermediate rolling reductions, followed by strengthening of Goss and Brass orientations at higher rolling reductions.

Electron Backscatter Diffraction Study of Ultrahigh-Pressure Tso Morari Eclogites (Trans-Himalayan Collisional Zone): Implications for Strain Regime Transition from Constrictional to Plane Strain during Exhumation

Abstract The Tso Morari Crystalline Complex (TMCC) of trans-Himalaya (eastern Ladakh, India) contains enclaves of ultrahigh-pressure eclogites that underwent deep burial (≥80 km) and subsequent rapid exhumation during continental subduction, collision, and final accretion of the Indian plate with the Eurasian plate. We present an electron backscatter diffraction (EBSD) study of eight eclogite samples to investigate the deformation mechanism and strain regimes active during peak (HP) metamorphism and subsequent postpeak rapid exhumation of the TMCC. Our study shows that the least retrogressed eclogite exhibits strong linear fabric (L tectonite) characterized by omphacite, having [001] axes parallel to and (110) poles perpendicular to lineation. These features concur with constrictional strain during peak (HP) metamorphism. A transitional planolinear fabric (LS tectonite) is shown by other eclogites that show petrographic evidence of omphacite alteration to amphibole and the presence of lower metamorphic grade minerals like actinolite and chlorite. Characteristics of lattice preferred orientation (LPO) of omphacite and quartz, indicated, respectively, by the LS and B indices, also suggest variation in strain regime from pristine eclogites to their altered counterparts. Based on these results, it is suggested that a constrictional strain regime prevailed during peak (HP) metamorphism in the TMCC due to the buoyant rise of TMCC in response to slab break-off and reverse slab pull during and after the deepest continental subduction. This buoyant rise was also facilitated by compression related to the ongoing India-Eurasia collision. This regime evolved later to plane strain that was superimposed on the UHP rocks at a shallower depth. It is plausibly associated with foliation-parallel extension during exhumation at midcrustal depths. A high-temperature prism c-slip in quartz shown by few samples is interpreted to have formed due to a subsequent granulite facies metamorphic overprint on the eclogite during collisional thickening.

Effect of grain size on the thermal stability of electrodeposited nanocrystalline nickel: X-ray diffraction studies

Nanocrystalline (NC) Ni coatings have widespread engineering applications, many of which are in high-temperature environments. Therefore, it is important to study the thermal stability of NC Ni. The present study compares the thermal stability of electrodeposited (ED) NC Ni of varying grain sizes: 20 nm, 50 nm, and 100 nm. In-situ high-temperature X-ray diffraction (XRD) investigations have been employed to follow the grain growth behavior of 〈111〉 and 〈200〉 grains under isochronal annealing up to 550 °C. Based on the calculated activation energies, the anisotropic growth mechanisms of 〈111〉 and 〈200〉 grains are evaluated. The studies revealed that the onset of grain growth occurred at progressively higher temperatures with increasing initial grain sizes. While near uniform grain size distribution is observed for the 20 nm grain size variant, bimodal distributions are observed for its counterparts. Electron Backscatter Diffraction studies of NC Ni samples in the final-processing temperature of XRD showed that <100>//ED texture is preserved during the annealing process. While high fractions of Σ3 coincidence site lattice (CSL) boundaries are observed in the 20 nm sample, reduced fractions with no particular trend is observed for the 50 nm and 100 nm grain-sized samples. It is shown here that the incomplete recrystallization arising from inhomogenous strain distribution is the reason for the observed bimodal distribution and deviation from an expected trend in the formation of Σ3 CSL as a function of initial grain size.

Magma mixing and exsolution phenomena in peralkaline rhyolites: insights from the Gold Flat Tuff, Nevada

The distribution and compositions of chevkinite-group minerals (CGMs) in the pantelleritic Gold Flat Tuff, Nevada, USA, are used to examine three aspects of the evolution of the tuff, which we feel are of general significance in peralkaline magmatism. First, both chevkinite-(Ce) and perrierite-(Ce) occur in certain facies, although normally these phases almost invariably occur in different igneous lithologies. Their co-occurrence in the tuff is due to the mixing of pantelleritic and intermediate magmas. Second, the tuff is the first recorded occurrence of a CGM in a pantellerite eruptive, with possible implications for the crystallization conditions. In particular, low values of aSiO 2 may have stabilized ilmenite + chevkinite rather than aenigmatite, although the unusually high LREE contents (∑La–Sm ≤ 1517 ppm) in the pantellerite may have played a role. Third, an unusual lamellar texture in the CGM is revealed by Atomic Force Microscopy to be formed by a rutile-like phase. The lamellae may have formed by exsolution from a rutile-like layer in the crystal structure. An electron back-scattered diffraction study of a single crystal showed a structural dislocation not apparent optically or by electron back-scattered imaging. This may have wider implications in mineralogical studies.

Chevkinite-group minerals in selected intrusions of the Mazury Complex, North-Eastern Poland: insights into the formation of a titanite-like phase by hydrothermal alteration

Chevkinite-group minerals forming large and common (up to 0.03 vol%) accessory phases in monzodiorites and granodiorites from the Mesoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite intrusions, Mazury Complex, north-eastern Poland, range from pristine magmatic types to hydrothermally altered varieties. The unaltered phase is perrierite-(Ce), with the uncommon feature of having Al dominant in the C site. Hydrothermal alteration of the perrierite-(Ce) followed two main trends: one shows depletion in Ca, Fe, Si, Al and Mg, and increasing Ti contents; the other shows increases in Si, Ti and Ca and decreases in light rare-earth elements (LREE), Y and Mg, at about constant Fe content. The second trend resulted in the formation of a phase compositionally similar to titanite. Result of chemical analyses show that the transition from perrierite-(Ce) to the titanite-like phase is sharp; an electron back-scatter diffraction (EBSD) study shows the titanite- like material to be amorphous. The hydrothermal alteration of a chevkinite-group mineral to titanite has commonly been reported in natural sequences but this is the first record of the identification of a titanite-like phase made on the basis of a structural analysis.

Tuning mechanical metastability in FeMnCo medium entropy alloys and a peek into deformable hexagonal close-packed martensite

We report here the compositional dependency of face-centered cubic (FCC) to hexagonal close-packed (HCP) martensitic transformation in FeMnCo medium entropy alloys (MEAs) and insights into the underlying transformation mechanisms. To this end, we designed MEAs with the same Fe-to-Mn ratio and explored the phase stability therein. Higher Co content was found to facilitate the FCC-HCP transformation kinetics. In situ electron backscatter diffraction studies underpinned an FCC-HCP-(new)FCC transformation chain and its underlying atomistic mechanisms were directly explored via aberration-corrected scanning transmission electron microscopy.

EBSD study of superplasticity: New insight into a well-known phenomenon

Electron backscatter diffraction (EBSD) was applied to investigate the superplastic behavior of a fine-grain Al-Mg-Li alloy. It was found that microstructural changes were noticeably influenced by the occurrence of continuous dynamic recrystallization. This mechanism involved a transverse subdivision of pre-elongated grains which eventually transformed into chains of nearly-equiaxed grains. A body of experimental observations, including extensive strain hardening, marked grain elongation, the formation of pronounced substructure in interior regions of grains, and the development of crystallographic texture, provided strong evidence of large amounts of intragranular slip operating during superplastic flow.

Ni-based alloy 713C manufactured by a selective laser melting method: characteristics of the microstructure

PurposeThe purpose of this paper is to obtain high-temperature-resistant material with high density and to conduct microstructural investigations of 3D-printed Ni-based alloy 713C specimens.Design/methodology/approachHigh-density specimens of Ni-based alloy 713C were obtained by the optimizing selective laser melting (SLM) process parameters and an X-ray diffraction (XRD) analysis confirmed the occurrence of γ and γ′ phases and the presence of carbides in the SLM-manufactured Ni-based alloy 713C. The analysis of electron backscatter diffraction (EBSD) studies suggested a preferred 〈100〉 direction orientation and low angle misorientation for the SLM specimens.FindingsThe high-density specimens of Ni-based alloy 713C were obtained by the optimized SLM process parameters. XRD analysis confirmed the presence of γ and γ′ phases and carbides in the SLM-manufactured Ni-based alloy 713C. Analysis of EBSD studies suggested a preferred 〈100〉 direction orientation and low angle misorientation for the SLM specimen.Originality/valueIn this study, 3D-printed Ni-based alloy 713C with a high density of 99% was obtained for the first time, to the best of the authors’ knowledge.

Processing of DP590 steel using single point incremental forming for automotive applications

ABSTRACT The demand for incremental sheet forming is increasing specifically in the automotive sector for forming complex shapes with high accuracy. The present work investigates the incremental forming behavior using different parameters namely, fracture forming limits, limiting wall angle, thickness variation, and form accuracy. The formability of the material has been evaluated using the varying wall angle conical (VWACF) and pyramidal (VWAPF) frustums. The limiting wall angles for conical and pyramidal frustums are found to be 68.28° ± 1.36° and 68.90° ± 1.37°. The strain distribution revealed that the pyramid faces and corners have undergone the plane strain and biaxial deformation respectively. The fracture limits and strain paths are identified experimentally and validated numerically using Finite Element (FE) simulations. The experimental and simulated thickness distributions have been compared and found in good agreement as the average absolute error was found to be less than 8.5 ± 0.02%. The error compensation method has been used for improving the accuracy of the formed components. The fracture in the specimens occurred without any hint of substantial necking. The electron backscatter diffraction (EBSD) study indicates the increase of local misorientations, and grain refinement, which has limited the formability of the material and ultimately led to the failure in the specimens.

EBSD study of advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn alloy subjected to equal-channel angular pressing

In this work, electron backscatter diffraction (EBSD) was applied for microstructural characterization of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn alloy subjected to equalchannel angular pressing (ECAP). It was found that the spheroidization process induced by ECAP was governed by the conventional boundary-splitting mechanism. The nearly-Burgers orientation relationship between the spheroidized a- and b-phases was revealed. This intriguing result can be attributed to the very high cooperation in slip activity between the phases.

An in-situ electron backscattering diffraction and viscoplastic self-consistent study of OFHC copper subjected to uniaxial tension

In-situ electron backscattering diffraction was used to track microstructure and texture development in polycrystalline copper during uniaxial tension. Characteristic of face-centred-cubic materials, copper develops a double fibre texture comprising a relatively strong 111 fibre and a weak 100 fibre parallel to the tensile axis. The observation of small stacking faults via transmission electron microscopy indicates that partial slip contributes to strain accommodation during uniaxial tension. The visco-plastic self-consistent model was applied to simulate the macroscopic stress-strain curve and crystallographic texture development by considering the effects of the grain-matrix interaction mode, latent hardening, perfect and partial slip. The simulations demonstrate that an intermediate grain-matrix interaction scheme coupled with weak latent hardening, dominant perfect slip and limited partial slip returns the best agreement between the experimental and simulated textures.

Neoproterozoic extension and decompression in the northern Eastern Ghats Province, India: Mid-crustal signature of Rodinia break-up?

The Eastern Ghats Province (EGP) of India is considered to have been a part of the supercontinents Rodinia and Gondwana at c. 1.0 Ga and 500 Ma, respectively. A range of ages spanning much of the Neoproterozoic have been periodically reported from parts of the EGP, indicating that the terrane remained tectonically active in the interval between Rodinia and Gondwana amalgamation, although the nature of the associated events remains uncertain. In this study conducted on the northern EGP, we constrain these enigmatic events from structural (field, microstructural and Electron Backscatter Diffraction studies), metamorphic (pseudosection modelling and geothermobarometry) and geochronological (monazite chemical dating) evidence. The area is multiply deformed, with the D1 and D2 shortening deformation accompanying granulite facies metamorphism that peaked at temperatures in excess of 900 °C, at ~955 ± 28 Ma. Following hydrous fluid infiltration at ~808 ± 10 Ma, the entire northern EGP was affected by an extensional deformation event D3 that reoriented all earlier fabrics into an E-W trending, northerly dipping orientation. Deformation microstructures and results of geothermobarometry indicate that D3 operated at around 600 °C at ~711 ± 18 Ma. Dextral strike-slip deformation (D4) along the Mahanadi Shear Zone operated under greenschist facies conditions and did not reset monazite isotope systematics in the region. The signature of mid-crustal extension during D3 is likely to be associated with the break-up of Rodinia. The lack of corresponding evidence for mid-Neoproterozoic extension in the adjacent Indian cratons suggests relative uplift of the EGP following Gondwana amalgamation.

Two key switches in regional stress field during multi-stage deformation in the Carboniferous–Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes

AbstractThe orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336–326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303–289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1–E3) separately occurred during D1–D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

Phase Transformation in 316L Austenitic Steel Induced by Fracture at Cryogenic Temperatures: Experiment and Modelling.

Investigations by electron backscatter diffraction (EBSD) and X-ray diffraction with the use of synchrotron radiation, as well as parallel extended finite element (XFEM) simulations, reveal the evolution of the 316L stainless steel microstructure in the vicinity of a macro-crack developing at the temperature of liquid helium (4.2 K). The fracture propagation induces a dynamic, highly localized phase transformation of face-centred cubic austenite into α’ martensite with a body-centred cubic structure. Synchrotron studies show that the texture of the primary phase controls the transition process. The austenite grains, tending to the stable Brass orientation, generate three mechanisms of the phase transformation. EBSD studies reveal that the secondary phase particles match the ordered austenitic matrix. Hence, interphase boundaries with the Pitsch disorientation are most often formed and α’ martensite undergoes intensive twinning. The XFEM simulations, based on the experimentally determined kinetics of the phase transformation and on the relevant constitutive relationships, reveal that the macro-crack propagates mainly in the martensitic phase. Synchrotron and EBSD studies confirm the almost 100% content of the secondary phase at the fracture surface. Moreover, they indicate that the boundaries formed then are largely random. As a result, the primary beneficial role of martensite as reinforcing particles is eliminated.