Electron Backscatter Diffraction Detector Research Articles

Fatigue crack initiation and propagation behavior of Inconel Alloy 690TT steam generator tube

Fatigue crack initiation and propagation behavior of Inconel Alloy 690TT steam generator (SG) tube under 0.2% strain amplitude were studied by scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) detector and extended finite element method (XFEM). The results showed that the main crack initiated at the discontinuous interface between the persistent slip bands (PSBs) and the matrix in the grain at the edge of the intrados surface. The metastable crack firstly transgranularly transited to the lateral surface, then penetrated steadily along the direction of maximum shear stress, and finally rapidly propagated perpendicularly to the loading axis, which was consistent with the numerical simulation results. Different fracture modes of specimen shape led to different fatigue lives. The fatigue life of tubular specimen was lower than that of bar specimen, the fatigue life of boat-shaped Alloy 690TT SG tube at 0.2% strain amplitude was 11,476 cycles.

Size effect of scratches on the degradation behavior of alloy 690TT in high temperature caustic solution

Size effect of scratches on the mechanical properties and degradation behavior of Alloy 690 T T were investigated in high temperature caustic solution using scanning electron microscopy (SEM) with energy dispersive X-ray (EDS) detector and electron back-scattered diffraction (EBSD) detector, and a quantitative dependent relationship of corrosion and stress corrosion cracking (SCC) behavior of scratched surface on the scratch size factor α (the ratio of scratch depth to scratch tip radius) was established. The results showed that the corrosion behavior of Alloy 690 T T was aggravated by the accelerated growth of inner oxide layer on scratched surface, which was due to the high strain zone formed by scratching process and tension stress. The thickness distribution of inner oxide layer on scratched surface was approximately described by the Gaussian function, while that of surface oxide layer followed a linear distribution. Additionally, the inner oxide layer thickness at scratch tip increased linearly with the increase of α, while that of surface oxide layer wasn’t related to α. The SCC at the scratch tip did not take place until α increased to a critical threshold value. The surface oxide particles near the crack mouth became sparse and the corresponding inner oxide layer became thinner, which was mainly affected by the low stress zone formed near the crack mouth.

Microstructure characteristics and mechanical properties of a laser cladded Fe-based martensitic stainless steel coating

In the present work, a Fe-based alloy (Fe60) coating was fabricated by laser cladding (LC) process. Heat treatment was conducted by heating the LC coating to 1050 °C by 30 °C/min, holding for 30 min and cooling in air. Microstructure characteristics of the coatings before and after heat treatment were studied using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and electron backscatter diffraction detector (EBSD). Micro-hardness, tensile strength of the coatings before and after heat treatment were also acquired. Before heat treatment, the LC coating was composed of martensite dendrite matrix with a small number of ferrite and retained austenite grains and a large number of fine carbides (Fe3C, M7C3 and M23C6) that are rich in Cr element in inter-dendritic area. After heat treatment, the martensite dendrite matrix was retained and a large number of new carbide particles precipitated in martensite dendrites, while the size and Cr content of inter-dendrite carbide particles increased. Micro-hardness of the coating decreased from 800 HV1 to 650 HV1 due to the release of residual stress and carbon atoms in the BCC structure lattice, elimination of high density defaults. However, ultimate tensile strength of the coating increased from 450 MPa to 550 MPa due to the precipitate hardening effect of new precipitated carbide particles in dendrites. The tear and cleavage appearance of the fractures proved that the fractures are quasi-cleavage fracture.

Effects of Ce Addition on Mechanical and Corrosion Properties of the As-Extruded Mg-Zn-Ca Alloy

The microstructure and corrosion properties of the as-extruded Mg-Zn-Ca alloy with and without Ce addition are investigated. The microstructure was characterized by optical microscopy, scanning electron microscopy coupled with electron backscatter diffraction detector. Ce addition retarded dynamic recrystallization during deformation, which resulted in the formation of bimodal microstructure with finely dynamically recrystallized (DRXed) grains and coarsely unDRXed grains. Texture of the DRXed region was weakened after small addition of Ce, mainly attributing to particle stimulated nucleation. The strength enhancement for the Ce containing Mg-Zn-Ca alloy was attributed to the fine microstructure and strong texture. Corrosion results indicated that Ce addition deteriorated corrosion resistance in 3.5 wt.% NaCl solution of the as-extruded Mg-Zn-Ca alloy, which was related to the dispersed second phases, refined microstructure and weak basal texture in DRXed region.

Research on dynamic compression properties and deformation mechanism of Ti6321 titanium alloy

This research reports detailed investigations on the dynamic compression properties and the deformation mechanism in Ti6321 titanium alloy subjected to high strain rate loading by using the split Hopkinson pressure bar (SHPB). Microstructures of deformed samples were analyzed by scanning electron microscopy (SEM) with an electron backscatter diffraction (EBSD) detector and transmission electron microscopy (TEM). The experimental results demonstrate that with the increase of strain rate, the strength of Ti6321 titanium alloy increases significantly, which indicates the phenomenon of strain rate hardening. Due to twinning, the initial plastic deformation mechanism is by twin shear, the twins' interface is straight, continuous, and symmetrically distributed. The majority of twins are found at low strain stage (the strain range of 0.03 ∼ 0.06), which justifies the early initiation and contribution of twins in plastic deformation of the material. It also indicates that during plastic deformation twinning dominates the dynamic deformation mechanism. As the strain (e) increases further (when the strain is greater than 0.06), the number of twins also increases up to ɛ = 0.20. After that, the dynamic deformation mechanism started shifting from twinning deformation to dislocation slip.

Characterisation of super duplex stainless steel by optimisation of EBSD parameters

Electron backscatter diffraction (EBSD) was used to characterise the microstructure of a super duplex stainless steel (SDSS) alloy Zeron 100 and the intermetallic phases sigma and chi in this material. The material was analysed in three conditions; as-received, heat-treated at 900 °C for 8 min and heat-treated at 750 °C for 4 h. Heat treatments were performed to introduce the intermetallic phases in the steel. It is difficult to get reliable indexing of the sigma and chi phases due to noisy and overlapping patterns. To get the best results, the Hough transformation parameters were optimised and an averaging technique was used. The optimisation was done by removing some of the reflectors in the sigma- and chi-phases in the original TSL material files used for pattern indexing. By changing Hough parameters, considerable improvements in the indexing of the patterns were observed along with the increase of average confidence index (CI) value for both intermetallic phases. The applied SEM, Zeiss Ultra 55 FESEM was equipped with a NORDIF UF-1100 EBSD detector to acquire and stream patterns to HD. Indexing and data processing were performed by TSL/OIM 7.3. In the present study, at the most four different phases are present in the SDSS.

EBSD characterization of the L-605 Co-based alloy welds processed by pulsed Nd:YAG laser welding

Herein, pulsed Nd:YAG laser welding of the L-605 Co-based alloy was investigated. The effect of the welding heat input (HI) on the penetration depth, microstructure, and mechanical properties of the weld metal was studied. A field emission scanning electron microscopy equipped with an electron backscatter diffraction (EBSD) detector was used to perform microstructural characterization. The results indicated that use of the HI value in the range of 48–80 J/mm could result in the formation of sound welds with full penetration depth at bead-on-plate configuration. EBSD studies revealed that when a low HI value was used to fabricate the double-welded sample, the {1 0 0} direction of austenite grains in the weld metal was parallel to the transvers and welding directions. Regarding the single-welded sample with a high HI value, the 〈1 0 0〉 direction was strongly oriented at an angle between 40° to 50° with respect to the welding direction. Improvement in the hardness of both single-welded and double-welded samples was observed, as compared to the based metal. The results of tensile tests showed that tensile strength of the weldments was higher or almost similar to that of the base metal. Overall, the changes in the HI values had no significant effect on mechanical behavior of the weldments.

A study of microstructure and mechanical property of a burn-resistant Ti alloy fabricated by HIPping

A burn-resistant Ti-25V-15Cr-2Al-0.2C alloy was fabricated by hot isostatic pressing (HIPping) from the prealloyed powders under a pressure of 200 MPa and at 900, 950, and 980 °C for 2 h. Microstructure was examined using scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD) detector and transmission electron microscope (TEM). Tensile tests were to evaluate mechanical behavior of the HIPped samples. The results show that HIPping temperature clearly affects the microstructure of the HIPped samples, thus the mechanical properties. For example, lower HIPping temperature produced more porosities at triple-junctions and more large grains resulted from the original powders, thus lower ductility was observed in the sample HIPped at 900 °C. However, the sample HIPped at 980 °C generates the best tensile properties with over 20% ductility, which is even better than those of as-extruded Ti-25V-15Cr-2Al-0.2C alloy.

A New Electron Backscatter Diffraction-Based Method to Study the Role of Crystallographic Orientation in Ductile Damage Initiation

The third generation of advanced high strength steels shows promising properties for automotive applications. The macroscopic mechanical response of this generation can be further improved by a better understanding of failure mechanisms on the microstructural level and micro-mechanical behavior under various loading conditions. In the current study, the microstructure of a multiphase low silicon bainitic steel is characterized with a scanning electron microscope (SEM) equipped with an electron backscatter diffraction detector. A uniaxial tensile test is carried out on the bainitic steel with martensite and carbides as second phase constituents. An extensive image processing on SEM micrographs is conducted in order to quantify the void evolution during plastic deformation. Later, a new post-mortem electron backscatter diffraction-based method is introduced to address the correlation between crystallographic orientation and damage initiation. In this multiphase steel, particular crystallographic orientation components were observed to be highly susceptible to micro-void formation. It is shown that stress concentration around voids is rather relaxed by void growth than local plasticity. Therefore, this post-mortem method can be used as a validation tool together with a crystal plasticity-based hardening model in order to predict the susceptible crystallographic orientations to damage nucleation.

Microstructural development and its effects on tensile properties of a high Ni TRIP steel produced by repetitive corrugation and straightening via rolling (RCSR)

Microstructural development and its effect on tensile properties of a Fe- 24Ni-0.3C Transformation Induced Plasticity (TRIP) steel subjected to repetitive corrugation and straightening via rolling (RCSR) process was investigated in this study. Microstructure developed during the application of one to 45 cycles of RCSR on TRIP steel sheets were analyzed by optical microscope and scanning electron microscope (SEM) equipped with electron backscatter diffraction detector and X-ray diffraction techniques. Results indicated that the volume fraction of martensite formed due to the deformation-induced by amplification of applied strain during RCSR process was about 75% accompanied with the formation of a large fraction of low angle boundaries. To study, tensile and hardness tests were carried out on several deformed samples their mechanical properties. The results also showed that after 40 cycles of the RCSR process, yield strength increased from 150 MPa in the starting material to 1157 MPa in the deformed state. As well, the uniform elongation reduced from 170% to 30% and the hardness value increased from 130 to 340 HV. This amount of improvement in tensile strength for this type of alloy by the application of RCSR has not been reported to date. Therefor the technique used in this research for the improvement of tensile properties can be very helpful for an alloy designer when very high tensile properties for a particular application is required.

Effects of alloying elements and annealing treatment on the microstructure and mechanical properties of Nb-Ta-Ti alloys fabricated by partial diffusion for biomedical applications.

Powder metallurgical (PM) Nb-25Ta-xTi alloys (x=5, 15, 25, 35at.%) were fabricated by the elemental powder sintering technology. Effects of alloying elements and annealing treatment on the microstructural evolution and mechanical properties were investigated by conducting various tests, including X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), electron back scattered diffraction detector (EBSD), transmission electron microscopy (TEM) and tensile tests. The results indicated that the alloys showed a unique Nb-rich and Ta-rich dual structure due to the insufficient diffusion between powders. With the increase of Ti content, the β phase was always retained and the alloys exhibited a relatively high density in the range of 82.4% to 90.5%. Furthermore, owing to a higher diffusion coefficient of Ti and the strengthening effect of solid solution, the volume shrinkage and tensile strength both increased along with the increase of Ti content. After the annealing treatment was introduced, the microstructure became more homogeneous and fine equiaxed grains appeared, which induced a decrease in modulus and better ductility. The Nb-25Ta-25Ti alloys exhibited a good in vitro biocompatibility due to the chemical components and the introduce of surface pores. The PM Nb-Ta-Ti alloys were promising for biomedical applications in tissue engineering after evaluated both mechanical properties and in vitro biocompatibility.

Interactions of Plasmonic Silver Nanoparticles with High Energy Sites on Multi‐Faceted Rutile TiO2 Photoanodes

AbstractThe plasmonic interactions between silver nanoparticles and various rutile TiO2 facets are studied by correlating Advanced Electron Microscopy and Electrochemical Impedance Spectroscopy (EIS) to help design a route towards an optimised polycrystalline film fabrication. By using an Electron Backscatter Diffraction (EBSD) detector, it was determined that using HF as directing agent during the hydrothermal growth of TiO2 promotes the formation of high‐angle grain boundaries. Silver photodeposition occurs preferentially at these boundaries, consistent with the presence of high energy sites on the (100)‐oriented rutile TiO2 nanorods. Further EIS study showed an increase in the photoelectrochemical activity in the visible range of the solar spectrum for the samples consisting of silver nanoparticles deposited on these grain boundaries.

Performance of Alloy 709 under creep-fatigue at various dwell times

A comprehensive experimental evaluation of the creep-fatigue behavior of Alloy 709 at 750 °C is reported in this study. Alloy 709 is a 20Cr–25Ni austenitic stainless steel, with high temperature creep strength and corrosion resistance, which can potentially be used in structural components of nuclear power plants. Creep-fatigue crack growth (CFCG) experiments were conducted using an in-situ heating-loading and Scanning Electron Microscope (SEM) equipped with Electron Backscatter Diffraction (EBSD) detector. To study the “real-time” CFCG behavior of Alloy 709 at 750 °C with varying dwell times in vacuum, flat dog bone samples were prepared. A starter notch was added, and a pre-crack was introduced by high frequency fatigue cycles at room temperature. Prior to loading and heating the entire area ahead of the crack tip was mapped using EBSD. These maps were utilized to generate a set of Coincident Site Lattice (CSL) boundary maps from the area ahead of the crack tip. Upon completion of the EBSD and CSL mapping, the heating and loading of samples took place in the SEM. During the experiment, crack growth was monitored on the surface of the sample using SEM imaging and data was transferred over to the CSL maps, to highlight the crack path with respect to the grain boundary and precipitations arrangement in the sample. Some samples went through EBSD-CSL mapping before heating and loading along with Transmission Electron Microscopy (TEM) imaging post heating and loading. Comparing the CSL maps before and after crack growth provided additional details about the dependence of crack path and crack growth mode on microstructure, primarily grain boundary character, and dwell time. TEM analysis of the microstructure after the crack growth was employed to validate the findings of the in-situ heating and loading SEM data. Real-time monitoring of microstructural phenomena, such as void nucleation, grain boundary cavitation, slip activation, and resistance of twin boundaries to cracking during CFCG tests, sheds a new light on the crack growth mechanism. The results indicated that at lower dwell times, the crack mainly propagates in a transgranular fashion, with the aid of slip lines. At higher dwell time, intergranular cavitation dominates the crack growth. However, as more than 50% of grain boundaries are coherent twin boundaries, which are low energy boundaries resistant to cavitation, crack growth is delayed when reaching such boundaries and hence twin boundaries impart some resistance to crack propagation in Alloy 709 at high temperatures.

Synthesis of a (ZrAl3+AlN)/Al composite and the influence of particles content and element Cu on the microstructure and mechanical properties

Al matrix composites reinforced by dual particles have attracted much attention recently. In this paper, utilizing liquid–solid reaction between ZrN powder and Al matrix, a (ZrAl3+AlN)/Al composite has been prepared. The in–situ synthesized ZrAl3 and AlN particles exhibit sub–micron and nano–sized, respectively. Based on the analysis of electron back–scattered diffraction detector (EBSD) and X–ray diffraction (XRD), the extruded Al–5ZrN, Al–10ZrN and Al–4Cu–10ZrN composites all prefer to form sheet texture in the longitudinal section and can be marked as {110}<111>. It was found that the increase of particles content leads to the increase of hardness and tensile strength at both room temperature (25 °C) and elevated temperature (350 °C), whereas the introduction of Cu element results in the increase of tensile strength at room temperature but decrease at elevated temperature. It is regarded that the formation of Al2Cu surrounding ZrAl3 and AlN particles may be responsible for the decreasing of tensile strength at 350 °C. This paper may be referred for designing dual–particles strengthened composites.

Microstructural analysis of Greenland ice using a cryogenic scanning electron microscope equipped with an electron backscatter diffraction detector

Mass loss from ice sheets contributes to global sea level rise, and accelerated ice flow to the oceans is one of the major causes of rapid ice sheet mass loss. To understand flow dynamics of polar ice sheets, we need to understand deformation mechanisms of the polycrystalline ice in ice sheets. Laboratory experiments have shown that deformation of polycrystalline ice occurs largely by dislocation glide, which mainly depends on crystal orientation distribution. Grain size and impurities are also important factors that determine ice deformation mechanisms. Compared with ice formed during interglacial periods, ice formed during glacial periods, especially ice that forms cloudy bands, exhibits finer grain sizes and higher impurity concentrations. A previous report suggests the deformation rate of ice containing cloudy bands is higher than that of ice without cloudy bands. To examine the microstructures and deformation histories of ice in cloudy bands, we applied the electron backscatter diffraction (EBSD) technique to samples from the Greenland Ice Sheet using an environmental scanning electron microscope (ESEM) equipped with cold stages. Prior to the EBSD analysis, we optimised our ESEM/EBSD system and performed angular error assessment using artificial ice. In terms of c- and a-axis orientation distributions and grain orientation spread, we found little difference between samples taken from a cloudy band and those taken from an adjacent layer of clear ice. However, subgrain boundary density and orientation gradients were higher in the cloudy band, suggesting that there are more dislocations in the cloudy band than in the clear ice layer.

Strain rate dependent dynamic mechanical response of bainitic multiphase steels

Bainitic steels, as a third generation of advanced high strength steels, are potential steel grades for automotive applications. Two grades of bainitic steels with low and high silicon content, with three different thermal treatments per grade and therefore different second phase constituents, are examined under quasi-static and high strain rate deformations. Microstructures are studied by advanced characterization techniques, including X-ray diffraction and scanning electron microscope equipped with an electron backscatter diffraction detector. Subsequently, the quasi-static and dynamic mechanical responses of the steels are correlated to the microstructures. A positive effect of the strain rate is observed for all the examined materials: when the strain rate is increased, both the tensile stress and deformation levels increase, thus also the energy absorption capacity. However, it is shown that the higher the fraction of second phase constituents, the lower the effect of strain rate becomes. In addition, the grain size directly correlates to the strain rate effect too. The phenomenological hardening model of Johnson-Cook is used to simulate the quasi-static and dynamic flow behaviors, allowing to quantify the strain rate sensitivity for each material. A comprehensive literature survey on the strain rate sensitivity of various steel grades reveals that steels with higher strength demonstrate a lower strain rate sensitivity factor. This trend can be approximated by a power law function which clearly is followed by the materials under consideration in this study.

Understanding Detrimental and Beneficial Grain Boundary Effects in Halide Perovskites.

Grain boundaries play a key role in the performance of thin-film optoelectronic devices and yet their effect in halide perovskite materials is still not understood. The biggest factor limiting progress is the inability to identify grain boundaries. Noncrystallographic techniques can misidentify grain boundaries, leading to conflicting literature reports about their influence; however, the gold standard - electron backscatter diffraction (EBSD) - destroys halide perovskite thin films. Here, this problem is solved by using a solid-state EBSD detector with 6000 times higher sensitivity than the traditional phosphor screen and camera. Correlating true grain size with photoluminescence lifetime, carrier diffusion length, and mobility shows that grain boundaries are not benign but have a recombination velocity of 1670 cm s-1 , comparable to that of crystalline silicon. Amorphous grain boundaries are also observed that give rise to locally brighter photoluminescence intensity and longer lifetimes. This anomalous grain boundary character offers a possible explanation for the mysteriously long lifetime and record efficiency achieved in small grain halide perovskite thin films. It also suggests a new approach for passivating grain boundaries, independent of surface passivation, to lead to even better performance in optoelectronic devices.

Imaging with a Commercial Electron Backscatter Diffraction (EBSD) Camera in a Scanning Electron Microscope: A Review

Scanning electron microscopy is widespread in field of material science and research, especially because of its high surface sensitivity due to the increased interactions of electrons with the target material’s atoms compared to X-ray-oriented methods. Among the available techniques in scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) is used to gather information regarding the crystallinity and the chemistry of crystalline and amorphous regions of a specimen. When post-processing the diffraction patterns or the image captured by the EBSD detector screen which was obtained in this manner, specific imaging contrasts are generated and can be used to understand some of the mechanisms involved in several imaging modes. In this manuscript, we reviewed the benefits of this procedure regarding topographic, compositional, diffraction, and magnetic domain contrasts. This work shows preliminary and encouraging results regarding the non-conventional use of the EBSD detector. The method is becoming viable with the advent of new EBSD camera technologies, allowing acquisition speed close to imaging rates. This method, named dark-field electron backscatter diffraction imaging, is described in detail, and several application examples are given in reflection as well as in transmission modes.

Nitrocarburising of annealed and severe plastically deformed 16MnCr5 steel

ABSTRACTThe microstructure resulting from a gaseous multistage nitrocarburising treatment applied to a 16MnCr5 steel has been investigated to study the microstructural evolution during the process and the effects of severe plastic deformation. The depth of the compound layer and the porous zone has been measured by optical microscopy. The microstructure has been investigated by means of a scanning electron microscope equipped with both an electron backscatter diffraction detector, to assess the amount and the distribution of nitrogen nitrides, and an energy-dispersive X-ray microanalysis to reveal the N diffusion depth. Finally, microhardness investigations have been carried out. The results indicate that severe plastic deformation influences the microstructure of the compound layer, the N concentration trends and the hardness profiles. The effects of severe plastic deformation lead to a greater initial diffusivity of nitrogen, a subsequent premature N saturation in the diffusion zone and an increased porous/compact-layer thickness ratio.

Space rocks and optimising scanning electron channelling contrast

Forescatter electron imaging is a popular microscopy technique, especially for scanning electron microscopes equipped with an electron backscatter diffraction detector. In principal, this method enables qualitative imaging of microstructure but quantitative assessment can be limited due to limited information about the contrast afforded. In this work, we explore forescatter electron imaging and demonstrate that imaging can be optimised for topographic, phase, and subtle orientation contrast imaging through appropriate sample and detector positioning. We demonstrate the relationship between imaging modes using systematic variation in detector positioning and compare this with pseudo-forescatter electron images, obtained from image analysis of diffraction patterns, to explore and confirm image contrast modes. We demonstrate these contrast mechanisms on a map obtained from a sample of the Gibeon meteorite.