Electron Backscatter Diffraction Analysis Research Articles

Effect of aging treatment on the microstructure, cracking type and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam

This study aimed to provide a comprehensive understanding of how aging treatments (namely, HT1 and HT2) affect the microstructure, cracking behavior, and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) method. Although both aged samples demonstrated similar grain structure and recrystallization behavior according to the electron backscatter diffraction (EBSD) analysis, as well as the precipitation of bimodal γ′ phase and MC- and M23C6-type carbides, notable differences were observed in the size and morphology, particularly the γ′ phase. The HT1 sample displayed coarsened primary γ′ phase, with sizes reaching up to 2 μm and exhibiting varied morphologies, including irregular and cuboidal shapes. Additionally, this treatment led to the formation of some γ′-γ eutectic regions and plate-like η phase, along with the decomposition of MC-type carbides into M23C6-type carbides. In contrast, the HT2 sample displayed uniformly distributed spherical primary γ′ phase with sizes ranging from 70 to 120 nm, accompanied by very fine secondary γ′ phase. Furthermore, it was found that changes in both aged sample microstructures could result in the formation of strain-age cracks due to the γ′ phase formation and liquation cracks due to the partial remelting of lower melting point phases. The findings also revealed that with the application of aging treatments, the hardness of the as-fabricated sample (339.8 ± 3.4 HV) increased to 440.2 ± 5.6 HV and 508.1 ± 4.8 HV for the heat treatment of HT1 and HT2, respectively.

An efficient synergistic double-sided friction stir spot welding method: A case study on process optimization, interfacial characteristics and mechanical properties of 2198-T8 aluminum‑lithium alloy joints

Friction stir spot welding has important applications in the joining of thin metallic plates. However, the asymmetric thermomechanical action inherent in the single-sided friction stir spot welding inevitably generates the hook defect at the joint interface, and the defect deteriorates with the improvement of the interfacial metallurgical bonding, which causes the irreconcilable contradiction and significantly restricts the breakthrough of the process stability and welding efficiency. The synergistic double-sided probeless friction stir spot welding (SDP-FSSW) technology proposed in this study adopts a dual-axis synergistic control system, which introduces intense plastic deformation from both sides of the interface to form a wavy hook by accurate axial motion during the welding process. This innovative process solves the problem of hook warpage while realizing rapid metallurgical bonding and mechanical interlocking at the interface, thus obtaining AA2198-T8 aluminum‑lithium alloy spot joints with a tensile/shear strength exceeding 9kN in a short dwell time (0–3 s). Through response surface methodology, the optimal process parameters are identified, i.e. rotation speed of 603 rpm, dwell time of 3 s, and plunge depth of 0.26 mm, at which condition the average joint strength is 13.0 ± 0.5kN, a 47 % increase compared to an optimized joint of single-sided probeless friction stir spot welding (8.9kN). The optical microscope examination shows that the wavy hook can be adjusted by the rotation speed and the higher rotation speeds will make the wave disappear and produce an approximately straight interface. The fractographic analysis shows that the wavy hook can inhibit crack propagation and has good mechanical interlocking effect, but the flat hook at high rotation speeds leads to crack propagation directly along the interface, and the failure mode is changed from plug-pull fracture to interfacial fracture. Therefore, the joint strength at 1000 rpm is only 7.0kN, which decreases by about 47 % compared with the optimal strength. The electron backscattering diffraction analysis shows that continuous dynamic recrystallization occurs in the hook region and good metallurgical bonding is formed, and there are also some discontinuous dynamic recrystallized grains distributed between the large grains due to the larger strain rates and lower temperature at the interface during the SDP-FSSW process. It has been found that the wavy hook with good metallurgical bonding and mechanical interlocking can be introduced in spot welded joints by controlling the interface forming, which is a viable method to create high quality, efficient and reliable spot joints.

Shape Anisotropy of Grains Formed by Laser Melting of (CoCuFeZr)17Sm2

For permanent magnetic materials, anisotropic microstructures are crucial for maximizing remanence Jr and maximum energy product (BH)max. This also applies to additive manufacturing processes such as laser powder bed fusion (PBF-LB). In PBF-LB processing, the solidification behavior is determined by the crystal structure of the material, the substrate, and the melt-pool morphology, resulting from the laser power PL and scanning speed vs. To study the impact of these parameters on the textured growth of grains in the melt-pool, experiments were conducted using single laser tracks on (CoCuFeZr)17Sm2 sintered magnets. A method was developed to quantify this grain shape anisotropy from electron backscatter diffraction (EBSD) analysis. For all grains in the melt-pool, the grain shape aspect ratio (GSAR) is calculated to distinguish columnar (GSAR < 0.5) and equiaxed (GSAR > 0.5) grains. For columnar grains, the grain shape orientation (GSO) is determined. The GSO represents the preferred growth direction of each grain. This method can also be used to reconstruct the temperature gradients present during solidification in the melt-pool. A dependence of the melt-pool aspect ratio (depth/width) on energy input was observed, where increasing energy input (increasing PL, decreasing vs) led to higher aspect ratios. For aspect ratios around 0.3, an optimum for directional columnar growth (93% area fraction) with predominantly vertical growth direction (mean angular deviation of 23.1° from vertical) was observed. The resulting crystallographic orientation is beyond the scope of this publication and will be investigated in future work.

Revealing the microstructural evolution and mechanical response of repaired Fe–Cr–Si based alloy by directed energy deposition

This study investigates the microstructure and mechanical properties of wear-resistant hardfacing structures fabricated on an AISI 1045 carbon steel substrate using a specially designed Fe–Cr based powder for directed energy deposition (DED). Electron backscatter diffraction (EBSD) analysis reveals that the texture predominantly consists of cube rotated {001}<110> and cube {001}<110> textures, in addition to weaker Brass {112}<111> texture components. These textures contribute to the random orientations of martensitic grains and facilitate the tracing of austenite reconstruction. Notably, the as-printed samples exhibited superior yield strength (999.4 ± 86.3 MPa) and ductility (9.6 ± 2.6%) along the build direction (BD), compared to conventional samples, which demonstrated a tensile strength of 790 MPa and ductility of 2%. This improvement is primarily attributed to the hardening effects associated with a low volume fraction of retained austenite and the precipitation of Cr carbides. Comprehensive mechanical response, nanoindentation hardness profile across the interface, and microstructural analyses were conducted to confirm the feasibility of using a Fe-based hardfacing alloy for DED. The findings underscore the outstanding balance of strength and ductility exhibited by as-printed hardfacing alloy, further enhanced by its high printability, highlighting its potential in producing wear-resistant structures for repair applications.

Additive manufacturing of novel aluminium matrix composites with enhanced strength and processability via boron nitride functionalization

The present work systematically investigates the effects of BN nanopowder functionalization on the processability, microstructure and tensile response of the custom Powder Bed Fusion Laser Beam (PBF-LB) Al alloy ‘AMALLOY3D’. The results show that a minor addition of BN (0.3% by weight) not only produces near fully dense parts (99.91%), but is also paired with improved flowability, enhancing the overall processability. Electron backscatter diffraction (EBSD) analysis revealed the transformation to a fully equiaxed grain structure in the BN-functionalized material, resulting in a 40% increase in yield strength. Energy dispersive spectroscopy using a scanning transmission electron microscope (STEM-EDS) was employed to reveal the intricate secondary phases’ arrangements. These observations coupled with the help of the CALPHAD approach led to the reconstruction of the solidification history of AMALLOY3D and the BN-functionalized material. The present study unravels the complex dynamics leading to the columnar-to-equiaxed transition in BN-reinforced AMCs, proving that such unique microstructures and exceptional tensile properties can be achieved without compromising PBF-LB processability.

Strain localisation and grain boundary-mediated deformation in pure titanium at low and high temperatures: In-situ optical microscopy and digital image correlation

Heterogeneous deformation occurs between grains in polycrystalline α-titanium. Understanding the role of temperature in local deformation is essential for its applications in extreme environments such as cryo- or high-temperature, but the underlying mechanism still remains elusive. Here we report a study of grain-scale deformation behaviour in CP-Ti plate at the temperature range from −60 °C to 280 °C. The full-field strain measurements were conducted on the tensile samples loaded parallel (RD) and transverse (TD) to the rolling direction, using in-situ optical microscopy and digital image correlation (OM-DIC). The DIC local strain maps were coupled with scanning electron microscopy and electron backscatter diffraction analysis. The grain boundary sliding and slip transfer occurred depending on the geometric relationship (i.e., deformation compatibility) between adjacent grains at 20 °C, and a micro-crack was observed at the {101‾1} twist boundary. The strain was recovered in the grains in the RD sample favourable for slip, whilst more accumulated in the grains in TD sample unfavourable for slip at 280 °C. The plasticity of grains differs with decreasing temperature to −40 °C, resulting in the presence of soft/hard grain pairs. The strong strain localisation between the soft and hard grains led to the cracking along the GBs (RD) and cross the grains (TD). Interestingly, the cracking was significantly reduced with decreasing temperature to −60 °C due probably to the temperature dependence of the plasticity of grains. The strain-hardening behaviour of α-Ti polycrystals was significantly affected by the temperature and crystal orientation dependence of grain-scale deformation mechanism.

Effect of laser shock peening on tribological properties of 55SiMoVA bearing steel

Wear is an important factor limiting the service life of 55SiMoVA bearing steel. In this work, laser shock peening (LSP) technology is used to improve the tribological properties of 55SiMoVA bearing steel, and the corresponding underlying mechanism is systematically discussed. After LSP, the kurtosis (Sku) of surface roughness asperities reduced from 10.355 to 5.488, and no new phase was generated. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis suggested LSP induced the generation of dislocation structures and deformation twins, leading to a decrease in the average grain size and an increase in the fraction of high-angle grain boundaries. Due to the work-hardening and fine-grain strengthening, the microhardness increased by 16.6 %, the maximum residual compressive stress amounted to −793.1 MPa, and the coefficient of friction (COF) and wear volume were significantly reduced. Scanning electron microscopy (SEM) results indicated that the wear mechanism of 55SiMoVA bearing steel before and after LSP was not transformed. However, the abrasive wear and delamination wear of the LSPed specimens were significantly improved, which was mainly attributed to grain refinement, increasing microhardness and constructing a residual compressive stress layer in the subsurface layer of 55SiMoVA bearing steel. During the sliding process, the increase in microhardness limits micro-plowing on the wear surface, and the residual compressive stress inhibits the crack formation and expansion, improving the wear resistance of 55SiMoVA bearing steel.

Revealing the anisotropic response of grain structures in additive manufactured Al-Mn-Sc alloys: Modeling based on experiments

The anisotropy of yield strength of additive manufactured (AM) Al-Mn-Sc alloy is attributed to the diverse distribution characteristics of grain size, aspect ratio and orientation. This work focus on controlling the yield strength and anisotropy of AM aluminum through microstructure design. In this work, microstructures information of laser powder-bed fusion (LPBF) processed Al-Mn-Sc alloys were obtained by electron back scatter diffraction (EBSD) analysis. The impact of grain size, aspect ratio and orientation on strength and anisotropy are quantitatively researched through modeling. Base on quantitative effect of orientation on strength and anisotropy, all microstructure partition schemes are calculated by MATLAB. Microstructure partition schemes of alloy with low anisotropy and high yield strength were predicted and simulation was enforced to certify the credibility of predication. Local stress in grain and orientation variation during deforming were obtained by simulation. It is concluded that the impact of orientation is more obvious than grain size and aspect ratio. Compared with strength and anisotropy obtained by simulation, the prediction of calculation shows fine precision. The impact of microstructures on mechanical properties and the reliability of modeling were verified.

Decoding ceramic fracture: Atomic defects studies in multiscale simulations

Microstructural atomic defects, including voids, cleavage, and inclusions, are commonly observed in alumina materials, and their impact on mechanical properties, such as fracture stress and toughness, is significant. In this paper, we introduce novel alumina models that incorporate experimentally observed void features. An atomic model is established to study the effects of micro-structural void features on fracture properties and atomic structure changes using molecular dynamics simulations. The electron backscatter diffraction and scanning electronic microscopy analysis of experimental samples are used to evaluate microstructural features that are used as inputs to the simulations (e.g., void aspect ratio, void angle). We apply an innovative Atomistic-to-Continuum (ATC) method based on Riemann sums to bridge atomic and continuum mechanics theories, evaluating the resistance of materials with atomic defects to crack propagation. The results show the greatest effects of pore angles on weakening mechanical properties such as peak strength and fracture energy density. The accuracy and efficiency of the ATC method in evaluating stress intensity factors are used to calculate the mechanical responses. Additionally, we establish a multiple layer perceptron neural network to evaluate the complex relationship between void features (aspect ratio, pore angle, relative distance) and typical fracture properties (fracture stress, critical stress intensity factor). A meta-analysis of these results from both machine learning methods and molecular dynamics simulations reveals the significant impact of each void feature on the sensitivity of typical fracture properties (peak strength, critical stress intensity factor at peak strength) and highlights the critical role of aspect ratio on fracture properties.

Microstructure and properties of Al-4.8Cu-0.45Mn-0.19Cd-0.18Ti-0.17Zr-0.14V aluminum alloy extrusion bar

The mechanical properties, texture transformation, and mechanism of Al–Cu–Mn alloy during annealing were studied using three-dimensional orientation distribution function (ODF), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results showed that the increase in yield strength after annealing at 200 °C is due to the decrease in the proportion of P and M textures and the increase in the proportion of Goss texture. The increase in the change rate of mechanical properties observed during annealing at 250 and 350 °C can be attributed to the higher proportion of M and P textures and the reduced proportion of Goss textures. Among them, the proportion of M texture increased significantly, and the Goss texture decreased significantly after annealing at 350 °C. This is because the structural energy density (Ev) value of the Goss texture is higher than that of the M texture at 250 °C and 350 °C. The Goss texture is in an unstable state of high energy order. The deformed Goss texture is unstable at high temperatures, leading to conversion into M and other textures. The EBSD and TEM analysis revealed that the hardness is mainly related to the change in dislocation density. When the annealing temperature is increased from 250 to 350 °C, the hardness is significantly reduced from 62 HV to 52 HV, and the dislocation density is reduced from 4.0 × 1014 ρ/m−2 to 2.4 × 1014 ρ/m−2.

Analysis of abrasive impact wear of the Mn8/SS400 bimetal composite using a newly designed wear testing rig

In this study, the abrasive impact wear behaviour of a bimetal composite made of medium manganese steels (MMSs) and low carbon steels (LCSs), i.e., the Mn8/SS400 bimetal composite, was investigated using a newly designed wear-testing rig. The need for a new rig arose from the difficulty in replicating real-world wear conditions. Our rig allows for precise control and measurement of wear, simulating harsh environments more accurately than other wear-testing rigs. The bimetal composite Mn8/SS400 demonstrated superior wear resistance, showing an improvement of up to 2.8 times compared to benchmark steels, attributed to its enhanced work hardening sensitivity. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD) analyses were employed to elucidate the wear mechanisms. After 300 h of abrasive impact wear, the subsurface microhardness of Mn8 reached 601.31 HV, significantly higher than that of the matrix hardness of 292.24 HV, indicating a substantial work hardening effect. The wear mechanism of the Mn8/SS400 bimetal composite was found to be a synergistic effect of grain refinement strengthening, dislocation strengthening, and twin strengthening. Initially, twin strengthening was the dominant mechanism up to 200 h of wear testing. However, after 300 h, contributions from all three mechanisms became increasingly significant, enhancing the overall wear resistance of the composite.

Insights into the microstructural evolution and strengthening mechanisms of friction stir spot welded advanced high strength ultrafine bainitic steel

Unlocking the full potential of advanced high-strength bainitic steels in spot-welding is a pivotal endeavor for harnessing their extraordinary mechanical properties in the automotive industry. This study suggests a shift in paradigm to address the inferior fusion weldability of this type of steel because of the formation of coarse martensite within the welded zone of weldments obtained by liquid-state welding, through the strategy of refining the martensite within the weld zone using the solid-state friction stir spot welding (FSSW) process. This paper delves into an in-depth investigation of the microstructural evolution and load-bearing capacity of a Fe-0.25C-3Cr-1.63Mn-1.5Si (wt%) ultrafine bainitic steel, having a remarkable tensile strength of 1.7 GPa, during the intriguing process of FSSW at rotational speeds of 600 to 2000 rpm. The research uncovers that the stir zone (SZ) undergoes dynamic recrystallization, resulting in a significantly refined microstructure. Regardless of the rotational speed employed, the high hardenability of the steel and rapid cooling during the process inevitably results in martensite formation within this region. However, a comprehensive microstructural characterization conducted by the electron backscatter diffraction (EBSD) analysis proves that the different thermal cycles induced by different rotational speeds lead into various prior austenite grain sizes, martensitic/bainitic packets and blocks attributes, and density of high-angle grain boundaries (HAGBs). Through the evaluation of strengthening mechanisms in different weld zones, the study sheds light on the key factors influencing strength. Block boundaries emerge as the primary contributor to SZ hardening, surpassing the role of geometrically necessary dislocations (GNDs) and solid solution strengthening. The load-bearing capacity observed during the tensile-shear test is governed by a delicate interplay between bonding width and crystallographic features (block size and HAGBs density) of the martensite formed within the SZ. The highest peak load was achieved under optimal welding conditions (rotational speed of 1000 rpm), which enabled the production of a sufficiently large bonding width, providing ample bonding area for load-bearing, along with an abundance of blocks and HAGBs to effectively impeding crack propagation.

Failure of a high-pressure flash gas pipeline from coal coke gasification to the cleaning section due to hydrogen-induced cracking

ABSTRACT The high-pressure flash pipeline of coal coke gasification leaked within one week after the operation. Further macroscopic observation showed that cracks appeared in the base material area near the weld. The medium transported by the pipe was low-concentration acid gas. Visual inspection, tensile testing, impact testing, chemical composition analysis, metallographic analysis, energy dispersive spectroscopy, X-ray diffraction analysis, and electron backscattering diffraction analysis were used to reveal the sources of cracks in the pipeline. It was found that the cracks were intergranular and filled with corrosion products. The chemical composition of the corrosion products is rich in Cr, S, and O. After the crack was opened, fracture features of ‘rock candy’ were observed, exhibiting brittle fracture characteristics. The cracks were caused by hydrogen-induced cracking along the grain boundary. On this basis, suggestions and countermeasures were put forward for the failure of the high-pressure flash gas pipeline.

Formation of orientation-dependent surface morphologies on tungsten after low energy helium plasma exposure: multiscale characterization and new insights

In ITER, the helium (He) impurity produced by the deuterium-tritium reaction will bombard the tungsten (W) divertor armor at the strike points. Consequently, strong interaction occurs therein that both impact the performance of the plasmas and the lifetime of the divertor. Despite an ever-increasing understanding of this interaction, some experimental phenomena remain mysterious, especially the formation of orientation-dependent surface morphologies. Here, we combine multiscale experimental characterization and theoretical models to shed new light on this problem. After low-energy He plasma exposure in a linear plasma generator, the polycrystalline W surface developed various morphologies. Through electron backscatter diffraction analysis, we found that the {111} grains developed cube-corner structures, the {110} grains developed ripple structures, whereas the {100} grains remained smooth. Then, electron-transparent lamellae were extracted from such grains to observe the subsurface He bubbles by transmission electron microscopy. The volume density, size distribution, and depth range of the He bubbles weakly depend on the crystallographic orientation, suggesting that the migration of W atoms causes the morphology variety. Accordingly, we proposed a two-stage formation mechanism. First, W atoms generated by over-pressurized He bubbles glide on the slip plane and in the slip direction to reach the surface, forming characteristic patterns that are enclosed by the slip traces. Second, morphological instability drives the evolution of the surface patterns, in which the initial surface structure and surface self-diffusion kinetics mediate. The proposed mechanism has been incorporated into a topographical instability model to enable asemi-quantitative analysis. The obtained new insights are valuable to the impurity control of the core plasmas and the lifetime analysis of the divertor for ITER.

In-plane biaxial low-cycle dwell fatigue behavior of CP-Ti based on DIC method

This study investigates the biaxial dwell fatigue behavior of commercial pure titanium (CP-Ti) under different load ratios and dwell times. The evolution of mean strain, ratcheting strain, and creep strain was systematically analyzed. The findings reveal that with the decrease of load ratio or the increase of dwell time, both ratcheting and creep strain exhibit an upward trend. The interaction between ratcheting strain and creep strain promotes crack initiation and propagation. The statistical analysis of crack paths by the digital image correlation (DIC) method indicates that crack initiation occurs between 0.7Nf and 0.8Nf, and fatigue failure is governed by the maximum principal strain. Moreover, the electron backscatter diffraction (EBSD) analysis results indicate that as the load ratio increases, the activity of prismatic slip systems decreases, while the activities of other slip systems and twinning modes increases. To enhance predictive accuracy, a modified SWT model by incorporating time-dependent creep damage and anisotropy is proposed for life prediction under biaxial dwell fatigue conditions.

Demonstration of an integrated-heating load frame for quantitatively assessing microscale tensile properties of copper and Zircaloy-2

Small-scale mechanical testing (SSMT) is of great interest in the nuclear materials community as it permits the use of surrogate irradiation techniques, such as ion beam irradiation when investigating the impact of irradiation damage on mechanical properties. The design of a micro-electro-mechanical-system (MEMS) micro-tensile stage is demonstrated to enable micron-sized specimen testing up to failure under ambient and reactor-relevant temperatures. Copper and Zircaloy-2 microscale specimens, having gauge lengths of 200 μm, gauge widths of 48 μm, and specimen-dependent constant gauge thicknesses of 10 μm to 26 μm, are fabricated using micro-wire electrical discharge machining and focused ion beam milling. From each gauge section, microstructure data is captured prior to testing using electron backscatter diffraction analysis, and an optimized digital image correlation speckle pattern is deposited on the specimen surface. The speckle pattern is tracked during deformation and post-processed to obtain strain-field evolution maps throughout deformation. Strain maps provide a means to account for and explain microstructure-dependent features observed in the captured stress-strain curves. The combination of using micro-wire electrical discharge machining, focused ion beam cleaning, and ion beam induced platinum deposition for micron-sized specimen preparation as well as utilizing microfabrication techniques to fabricate an integrated heating microtensile load frame reported herein serve as a demonstration of SSMT approaches that can be adopted to tackle challenging problems in nuclear materials research, including but not limited to the effects of ion beam irradiation on mechanical performance and providing experimental data to support small-scale modeling efforts of embrittling precipitates or radiation-induced segregation.

Effect of Lithiation and Delithiation on the Mechanical Properties of Electrodeposited LiCoO2 Cathode

Mechanical degradation of cathode active material, such as cracks result from volume changes and phase transitions, is one of the main causes of capacity fading in lithium-ion batteries. Understanding the active material’s deformation behavior during cycling and the impact of electrochemical charging on mechanical properties is crucial for understanding the mechanical degradation mechanism and extending battery lifetime.Herein, we investigate the mechanical properties of an electroplated LiCoO2 (LCO) cathode with crystallographic texture as a function of state of charge/discharge. Nanoindentation mapping is used to detect the differences in mechanical behavior between grain boundary and grain interior region. To determine the charged LCO crystals’ mechanical properties and avoid the effects from grain boundaries and air-exposure, in-situ nanoindentation experiments are conducted in a custom mechanical testing system within a scanning electron microscope. Considering the anisotropy of LCO, electron backscatter diffraction analysis is utilized to clarify the crystallographic orientation of the electrodeposited LCO cathode. Our result shows a decreasing tendency in elastic modulus and hardness with state of charge, which can be attributed to the expansion of LCO layered structure. The recovery of mechanical properties after discharge indicates that the changes in measured mechanical properties mainly come from Li deintercalation and intercalation rather than intergranular fracture during cycling. By releasing the relationship between mechanical properties and degree of delithiation, our study provides an insight into modeling studies of electro-chemo-mechanics for electrode materials. Figure 1

Microstructural stability and mechanical properties of the as-cast and heat-treated newly developed TiNbCrTa refractory complex concentrated alloy

In this study, a TiNbCrTa refractory complex concentrated alloy (RCCA) was prepared using vacuum arc remelting. The microstructural evolution and mechanical properties of both as-cast and heat-treated RCCA samples were analyzed. Heat treatment (HT) was performed at 800–1200 °C for 1 h in a vacuum-sealed environment. These samples exhibited a formation of Cr2Nb and Cr2Ti Laves phases. A variation in elemental distribution was observed, with interdendritic (ID) regions showing higher fractions of Ti and Cr, while the dendritic regions had a greater concentration of Ta and Nb. Micro-segregation at the IDs was confirmed through energy dispersive x-ray spectroscopy mapping, which inferred the formation of Cr- and Ti-rich phases during HT at 800–1200 °C. High-temperature HT at 1200 °C for 1 h led to the evolution of the hcp omega phase. Prolonged HT at 1200 °C for 96 h resulted in the evolution of a Cr-rich Laves phase (Cr2Ta), which was homogeneously distributed within the microstructure, indicating an unstable microstructure. Furthermore, despite prolonged HT, a variation in the elemental distribution persisted due to the presence of dendritic and ID regions. Electron backscattered diffraction analysis revealed the presence of bcc and hcp phases in the dendritic and ID regions, respectively, of the as-cast and HTed samples. The as-cast samples demonstrated a high compressive strength of approximately 2 GPa. Micro-hardness values increased with the HT temperature up to 1000 °C. Further increases under HT conditions did not significantly reduce the microhardness value, whereas prolonged HT at 1200 °C led to an increase in the microhardness value. Overall, the newly developed TiNbCrTa RCCA exhibited high-strength behavior even after the phase transformation.

Application of the EBSD Technique in the Study of Porosity and Permeability in Deformation Bands in Sandstone.

Deformation bands are common constituents of porous clastic fluid reservoirs. Various techniques have been used to study deformation band structure and the associated changes in porosity and permeability. However, the use of electron backscatter diffraction technique is limited. Thus, more information is needed regarding the crystallographic relationships between detrital crystals, which can significantly impact reservoir rock quality. We employ microscopic and microstructural investigation techniques to analyze the influence of cataclastic deformation bands on pore space. Porosity measurements of the Cretaceous Ilhas Group sandstone in NE Brazil, obtained through computerized microtomography, indicate that the undeformed domains exhibit a total porosity of up to 13%. In contrast, this porosity is slightly over 1% in the deformation bands. Scanning electron microscopy analyses revealed the presence of grain fragmentation and dissolution microstructures, along with cement-filling pre-existing pores. The electron backscatter diffraction analyses indicated extensive grain fragmentation and minimal contribution from intracrystalline plasticity as a deformation mechanism. However, the c axes of quartz crystals roughly align parallel to the orientation of the deformation band. In summary, we have confirmed and quantified the internal changes in a deformation band cluster, with grain size reduction and associated compaction as the main mechanism supported by quartz cementation.

Formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel S38815 weldment

This study aims to clarify the formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel (high-Si SS) S38815 weldment. A series of tests about microstructure and electrochemical characteristics were performed, including the electron backscatter diffraction (EBSD) analysis, Mott-Schottky tests, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic and potentiostatic polarization tests. The formation mechanism of heterogeneous microstructure related to high-silicon and its correlation on corrosion was discussed extensively. The results show that the significantly deformed and recrystallised grains were observed at the low temperature heat affected zone (LT-HAZ) and high temperature heat affected zone (HT-HAZ) respectively. The metastable pitting and low impedance values were formed in the above region, despite their low donor density. The deterioration in corrosion resistance of S38815 weldment as a result of high-angle grain boundaries (HAGBs) and carbides is more pronounced than the beneficial impact of Cr and Si oxidation. This study provides valuable references to the manufacturing and enhancing the anti-corrosion properties of this high-Si SS.