Electron Backscatter Diffraction Analysis Research Articles

The effect of pipeline root weld microstructure on crack growth behaviour

The girth weld is the weak link of high-pressure pipeline, which is easy to crack under the combined action of internal and external loads, defect and stress concentration. At present, the safety hazards of high-strength pipeline girth welds are prominent, and it is of great significance to study the failure law of girth welds to ensure the safe operation of pipelines. In this paper, the failure analysis of 6 welded joints with crack defects excavated on site in a gas transmission company was carried out. Through metallographic analysis, scanning electron microscope (SEM) observation and electron backscatter diffraction (EBSD) analysis, the relationship between root welding, weld microstructure and crack generation was analyzed in detail. The influence of grain boundary distribution behavior of weld microstructure on crack propagation path was studied, and the mechanism of welding inclusions on crack propagation and aggregation nucleation was revealed. The results show that the cracks in root welding, hot welding, filling welding and heat affected zone are all transgranular propagation types, and the deflection of crack propagation path may be related to the complex stress state at the welded joint. Local strain concentration often exists in the near crack surface, secondary crack and crack deflection position on the crack propagation path, which indicates that the formation and propagation of root cracks are likely to be related to the deterioration of weld metal properties caused by local strain concentration at the root. The research conclusions have certain reference value for the intrinsic safety design, construction, and integrity operation and maintenance of pipeline girth welds.

Microstructure and residual stress evolution during cyclic elastoplastic deformation of AISI316L fabricated via laser powder bed fusion

In metal additive manufacturing (MAM), microstructural properties such as texture, residual stresses, and dislocation density have emerged as key factors ruling the resulting mechanical performances. In this study, cylindrical AISI 316L specimens, fabricated with laser powder bed fusion (LPBF), were tested under cyclic elastoplastic (EP) deformation using a constant strain amplitude to highlight the evolution of residual stresses (RS), dislocation density and texture with increasing number of EP cycles, N, across the hardening-softening (H–S) transition stage, in the attempt to find correlations between relevant microstructural parameters and macroscopic properties. The structural and microstructural analysis is carried out through whole powder pattern modeling (WPPM) of neutron diffraction (ND) data and Electron Back-Scattering Diffraction (EBSD) analysis. The H–S transition is found to occur within 7–9 cycles, with RS fading out already after 5 cycles. Across the H–S transition, the trend of the maximum tensile stress correlates closely with the trend of WPPM-calculated total dislocation density, suggesting a major role of dislocations’ characteristics in the evolution of macroscopic mechanical properties. EBSD analysis reveals the rearrangement of geometrically necessary dislocations (GND) into cellular structures, and moderate grain refinement, which are deemed to be responsible for the quick fading of RS in the very early stage of EP loading. ND-based texture analysis reveals a (220) preferential orientation retained throughout the EP tests but with orientation density functions (ODFs) changing non-monotonically with N, suggesting preliminary partial randomization of grains around the deformation axis followed by the recovery of crystallographic anisotropy and more localized ODFs.

Investigation on microstructural evolution and local mechanical performance of friction stir lap welded AA6061-T6/ AA7075-T6 joints

The current study uses the friction stir lap welding (FSLW) technique to successfully fabricate two layered dissimilar AA6061/AA7075 joints. A defect-free joint with superior interfacial properties was obtained at the optimized process parameters (tool rotational speed / transverse speed) of 850 RPM/ 55 mm/min. The detailed investigations of microstructure evolution, crystallographic texture, and strength correlation were performed using the field emission scanning electron microscope (FE-SEM), optical microscope (OM), electron backscattered diffraction (EBSD), Vickers microhardness, nano-indentation, and miniature tensile tests. EBSD analysis reveals the presence of a significant grain refinement at the bottom (3.65 µm), middle (4.58 µm), and top region (6.34 µm) of stir zone (SZ) compared to AA6061 (42.56 µm) and AA7075 (34 µm) base metals. An increasing trend in the fraction of high angle grain boundary (FHAGBs) and recrystallization fraction was noticed from top to bottom of the build within the SZ. Continuous dynamic recrystallization (CDRX) with the gradient in strain, strain rate, and temperature leads to these microstructural variations within the SZ. The microhardness study shows a decrease in microhardness in the SZ due to thermal softening and precipitate dissolution at higher temperatures. Appreciable interfacial material mixing leads to remarkable strength, ductility, and strain-hardening behaviour within the SZ, especially at the interface section. Pole figures (PF) reveal the presence of major shear texture components (B/B̅, and C) with some minor presence of A1*/A2*and A/A̅ that confirms the presence of higher strains within the SZ. The dominant presence of recrystallization textures components (like cube {001} 〈110〉, Goss {011} 〈100〉, and P {011} 〈122〉 ) within the SZ confirms the presence of the CDRX mechanism.

How to characterise the anisotropy of laser powder bed fusion-processed parts? Towards a surrogate, non-destructive indentation-based approach

This work proposes a non-destructive indentation (NDI)-based surrogate mechanical testing framework for anisotropy and mechanical property evaluation of LPBF processed Inconel 718 superalloy. A Knoop-hardness tester was employed to develop the surrogate framework. Further post-heat treatments (PHTs) were performed at various cooling rates. The as-printed and PHT (SA, SB, SC, and SD) samples were characterized using X-ray diffraction (XRD) optical microscopy (OM), scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD) techniques. The yield locus plots show strong anisotropy for the as-printed sample. The IPF maps and pole figures for the as-printed samples showed elongated columnar grains with strong fiber texture along the (001) plane parallel to the build direction. They corroborated sufficiently with XRD, grain boundary map (GBM), and Kernel average misorientation (KAM) analysis. The yield locus shape of samples subjected to homogenization treatment becomes a nearly uniform ellipse with a reduction in the difference between σx and σy values, which can be attributed to the recrystallization of grains as observed by the transition from low-angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs). The PHT samples show a further increase in yield loci size due to the precipitation of γ’ and γ” strengthening phases due to aging treatment and corroborated with higher Taylor factor and dislocation density than the as-printed samples. The yield loci were sensitive to the PHT's cooling rates. Notably, among PHT ones, ‘SA’ samples exhibited a strong correlation (R2 ≈ 97.5 %) between the Taylor factor and yield locus. It was attributed to slower cooling rates (furnace cooled) with noticeably enhanced precipitation of strengthening phases, an increase in the volume fraction of recrystallized grains (from grain orientation spread (GOS) map), corroborating with higher dislocation density due to local strain as inferred from EBSD analysis. The proposed NDI surrogate approach was initially validated on an as-printed Inconel 718 stator blade. The yield locus showed a strong correlation between the stator blade and the as-printed sample, indicating the effectiveness of the proposed methodology.

Effects of forging deformation on variant selection and morphology of α in TiB/near α-Ti composites

The role of forging deformation on α-Ti in TiB/near α-Ti composites is still an unknown area. In the present work, the evolution of the variant selection and morphology of α-Ti was systematically investigated in as-sintered and as-forged TiB/near α-Ti composites through scanning electron microscope and electron back-scattering diffraction analysis. The results indicated that the α lamellae were refined, and their c-axes were either oriented at 45°or perpendicular to the Z-direction after hot forging. Six preferred orientation relationships (ORs) between TiB whiskers and α variants have been quantitatively identified using the misorientation axis-angle pair distribution maps. Compared to the as-sintered sample, the total length of the TiB/α phase boundary with six preferred ORs increased from 5.31% to 9.76% after hot forging. It was found that TiB contributed to the formation of the refined and equiaxed α variants that satisfied the preferred ORs with it. Moreover, an analysis of the reconstructed parent β grains revealed that the α variants heterogeneously nucleated from TiB, which did not satisfy the Burgers orientation relationship (BOR) with the parent β grains.

Study of Fatigue Crack Initiation and the Propagation Mechanism Induced by Pores in a Powder Metallurgy Nickel-Based FGH96 Superalloy.

Thermally induced pores (TIPs) are generally the source of fatigue crack initiation in the powder metallurgy (PM) Ni-based FGH96 superalloy. The effect of TIPs on fatigue crack initiation on the surface of the FGH96 superalloy was detected using scanning electron microscopy (SEM). The cause of fatigue crack deflection was studied using electron backscatter diffraction (EBSD) analysis. The results indicated that there are two states of TIPs including isolated TIPs and clustered TIPs located at the grain boundary. The investigation of crack initiation and propagation around TIPs was conducted in detail through the comprehensive integration of experimental findings and computational results. For cracks initiated by isolated TIPs, the maximum equivalent size and the ratio of the vertical-parallel axis to the loading direction of the TIPs reveal a linear relationship, and both of them determine crack initiation. Regarding clustered TIPs, the constituent pores of the clustered TIPs will compete to initiate cracks based on the experimental results, and the largest pore will be more likely to initiate cracking. Moreover, the results showed that fatigue crack propagation can be hindered by hard-orientation grains and twins with a low Schmid factor (SF). Large-angle crack deflection due to twins with a low SF can significantly increase crack length and resistance to crack propagation.

Electron backscatter diffraction analysis unveils foraminiferal calcite microstructure and processes of diagenetic alteration

Abstract. Electron backscatter diffraction (EBSD) analysis enables a unique perspective of the internal microstructure of foraminiferal calcite. Specifically, EBSD provides crystallographic data from within the test, highlighting the highly organised “mesocrystal” structure of crystallographically aligned domains throughout the test, formed by sequential deposits of microgranular calcite. We compared EBSD maps across the test walls of both poorly preserved and well-preserved specimens of the planktonic foraminifera species Globigerinoides ruber and Morozovella crater. The EBSD maps, paired with information about intra-test distributions of Mg/Ca ratios, allowed us to examine the effects of different diagenetic processes on the foraminifera test. In poorly preserved specimens EBSD data show extensive reorganisation of the biogenic crystal microstructure, indicating differing phases of dissolution, re-precipitation and overgrowth. The specimens with the greatest degree of microstructural reorganisation also show an absence of higher concentration magnesium bands, which are typical features of well-preserved specimens. These findings provide important insights into the extent of post-depositional changes, in both microstructure and geochemical signals that must be considered when utilising foraminifera to generate proxy archive data.

In-situ analysis of SCC initiation on Alloy 600 surface in primary water environment using digital image correlation with electron backscatter diffraction

This study examined the stress corrosion cracking (SCC) phenomenon of Alloy 600 in a high-temperature primary water environment. The investigation involved the observation of local plastic deformation and SCC initiation on the specimen surface using an observation apparatus, comprising a laser confocal microscope (LCM) and an autoclave equipped with a diamond window view-port. Prior to conducting the SCC initiation test, the crystalline structure of the specimen, including grain boundary (GB) characteristics, Schmid factor, and trace inclination angle, underwent examination using an electron backscatter diffraction (EBSD) technique. The local strain distribution was subsequently analyzed using a digital image correlation (DIC) method, employing LCM images obtained during the SCC experiments. The ex-situ EBSD analysis indicated that SCC mainly initiated at random high-angle grain boundaries (HAGB) with trace inclination angles close to 90° relative to the tensile axis. DIC analysis further revealed that most GBs in the vicinity of the highly strained area cracked among random HAGBs with a high trace inclination angle to the tensile axis. This confirms that the local strain gradient at GBs plays an important role in SCC initiation, serving as a more suitable indicator of an additional stress component to effective normal stress acting on GBs compared to the Schmid factor mismatch.

Novel role of thermomechanical grain boundary engineering in the microstructure evolution of austenitic stainless steel

The effect of special grain boundary development via the grain boundary engineering process (GBE) was explored in a bimodal microstructured 316L austenitic stainless steel with an average grain size of 1.92 μm. The GBE process was carried out by the rolling-annealing method via two routes of low and medium applied strain, followed by a short annealing period in a single-step and iterative manner. The grain boundary character distribution was obtained by Electron Backscatter Diffraction (EBSD) analysis, and the intergranular corrosion resistance and the tensile behavior of the samples were examined. Microstructural characterization showed that applying low strain repetitively increased the coincidence site lattice (CSL) and Σ3 boundaries percentage and created large twin-related domains (TRD). The reduced sensitization was attributed to a high proportion of CSLs and large-sized TRDs by applying a low-strain route. In the early stages of the low-strain route, the grain boundary character distribution showed a high number of primary twin nuclei in coarse grains and a continuous network of single twin nuclei in smaller grains, creating a high percentage of Σ3-grain boundaries. The low applied strain and the absence of the necessary driving force for the recrystallization and GBs migration led to the formation of twin nuclei, which would assist with the reduction of microstructure energy. A high percentage of Σ3 boundaries and an increase in the percentage of triple points consisting of low energy boundaries were found to be influential factors in increasing elongation.

Fatigue crack propagation characteristics of aluminum/steel laser-metal inert gas fusion-brazed joints in different micro-zones

Research on fatigue damage of aluminum/steel dissimilar joints is critical to ensure the reliability of multi-material lightweight structures. In this study, the fatigue crack propagation (FCP) characteristics of the interface, weld, and heat-affected zone (HAZ) of aluminum/steel laser-metal inert gas (MIG) fusion-brazed joints were investigated. Additionally, the influencing role of the microstructure of different micro-zones on the FCP behaviors was discussed. Single-edge notched tensile (SENT) specimens of the interface region exhibited a higher crack growth rate and crack threshold than SENT-weld and SENT- HAZ specimens due to the highly hard and brittle nature of the intermetallic compounds (IMC) at the aluminum/steel interface. Moreover, the fatigue fracture surface of SENT-interface specimens showed a brittle fracture pattern without fatigue striation characteristics, which was different from aluminum/steel solid-state and traditional aluminum alloy welded joints. Electron backscatter diffraction (EBSD) analysis results revealed that the synergistic effects of grain size, sub-grain boundaries, and micro-performance all contributed to the crack deflection of SENT-weld at a large angle to the HAZ, thereby resulting in more optimized crack resistance in the weld zone.

Near-room-temperature fabrication of dense BaZrO3 ceramic via acid–base chemical densification

A novel process to fabricate dense ceramic bulk of BaZrO3 perovskite oxide without firing was established. Although, BaZrO3 conventionally requires a sintering temperature of 1600 °C for densification, a relative density of 90% can be obtained via an acid-base chemical densification (ABCD) at 150 °C. In this process, a dense ceramic bulk body is fabricated through the acid–base reaction between the precursor compact and alkaline solution at temperatures ranging from room temperature to 150 °C. ABCD can reduce the energy consumption and CO2 emission comparing to traditional sintering processes due to its low process temperature. The microstructure of BaZrO3 prepared by this process is unique, consisting of aligned nanocrystals, as indicated by transmission electron microscopy and electron backscattered diffraction analysis. This novel process is a promising technique for fabricating next-generation ceramic devices.

Parametric Optimization of Selective Laser Melted 13Ni400 Maraging Steel by Taguchi Method

This study’s novel 13Ni400 maraging steel parts are additively manufactured through a selective laser melting process. The Taguchi approach is adopted to evaluate the combined influence of process variables (energy density), viz., laser power, layer thickness, hatch spacing, and scan speed, on responses like relative density, microhardness, surface roughness, and tensile strength. The powder and material characterization studies are conducted in terms of an optical microscope, scanning electron microscope (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and fractography analysis to explore the pre- and post-fabrication scenarios of the build parts. The consequences of energy density and process variables are studied through meticulous parametric studies. Finally, the optimum level of built parameters is identified and validated by a confirmative test predicting an average error of ~1.80%. This work is proficient in producing defect-free parts with maximum densification and improved mechanical properties for newly developed 13Ni-400 maraging steel by the selective laser melting (SLM) technique.

Effect of Mn addition in W-Ni-Cu heavy alloy processed through hot press sintering techniques on microstructure, microtexture and grain boundary character evolution

In this current study, the impact of manganese addition to 93 W-4.9Ni-2.1Cu-xMn (where x = 1, 2, 3, and 4 Wt%) on the microstructure, texture development, and grain boundary character distribution of tungsten heavy alloy (WHAs) was examined. The samples were produced through a vacuum hot press sintering, with parameters 50 MPa pressure, 10 °C/min heating rate, and 1450 °C sintering temperature for 20 min holding duration. To study the influence of manganese on the texture development and microstructure in conventional WHAs, electron backscatter diffraction (EBSD) was employed. The important findings from the EBSD analysis reveal that fibre texture (001) 〈111〉 and a higher fraction of low-angle grain boundaries in the Mn unalloyed compact resulted from extensive atomic jumps between the particles at elevated temperatures. Further texture analysis on the Mn-added compacts reveals that manganese oxide (MnO) formation during liquid phase sintering led to lower densification and randomized weak fibre texture development in manganese-alloyed compacts. In addition, the texture degradation in Mn-added compacts is mainly caused by recrystallization followed by sub-structural recovery during liquid phase sintering. This study indicates that increasing manganese content in WHAs stoichiometry led to a heterogeneous distribution of binder matrix (NiCu) in the sintered compact. As a result, W-4.9Ni-2.1Cu-4Mn alloy revealed decreased relative density (90.70%), microhardness (389.5 HV0.5), and electrical conductivity (15.74% of IACS).

Crystal plasticity approach for predicting mechanical responses in wire-arc directed energy deposition of NbZr1 refractory alloy

The refractory alloy, such as Niobium-1 wt% Zirconium (NbZr1) alloy, is a promising candidate for diverse applications in extreme environments. This study investigates an integrated experimental and computational methodology that can predict the mechanical properties of wire-arc directed energy deposited (DED) refractory NbZr1 alloy. The effect of large columnar grains with strong texture induced by the wire-DED process has been successfully incorporated into the representative volume element (RVE). Performing crystal plasticity (CP) simulation on RVE of NbZr1, deformation behavior and stress-strain relationship are predicted to explore the process-structure-property (PSP) relationship. The RVE has been created in synthetic microstructure generation software utilizing the grain statistics derived from electron backscatter diffraction (EBSD) analysis, capturing essential microstructural features. A phenomenological constitutive model and appropriate boundary conditions have been applied and solved, using the CP fast Fourier transform method. The CP model has been calibrated and validated utilizing the tensile test data along the build direction and deposition direction, respectively. The error in predicting yield strength and ultimate tensile strength is 0.91% and 0.67%, respectively, for the calibration simulation, whereas these values are 2.51% and 1.81% for the validation simulation. The results suggest strong agreement between the simulation and experimental observation. Even though global deformation behavior remains consistent across multiple RVEs with the same microstructural features, local stress-strain values vary, indicating structural anisotropy, which is also consistent with the digital image correlation (DIC) result. It is proven that this proposed CP method can effectively predict the mechanical responses of components with large grains and strong textures resulting from the wire-arc DED.

Mg–Zn–Cl-integrated functional interface for enhancing the cycle life of Mg electrodes

The instability of the Mg-electrolyte interface in nonaqueous electrolytes hinders the realization of rechargeable Mg batteries (RMBs). Herein, we adopted surface engineering to address this issue by alleviating the passivation characteristics of reductive Mg electrodes. Among a series of artificial interfaces derived from different elements, the Mg–Zn–Cl-integrated artificial interface imparted outstanding Mg deposition–dissolution cycling performance upon combination with a halide-free weakly coordinated anion-based electrolyte. The artificial interface allowed Mg deposition–dissolution reactions beneath the interface, as evidenced by systematic scanning electron microscopy observations combined with electron backscatter diffraction analyses, and such interfacial characteristics suppressed the intrusion of Mg deposits into microporous separators, leading to remarkably stable cycling even under exceptionally high utilization conditions (>30 %). The amorphous nature induced by Cl integration improved interfacial stability during the successive morphological changes of Mg electrodes owing to electrochemical deposition–dissolution cycling. In addition, the artificial interface enabled the employment of a thin PTFE-based separator, which was unattainable using unmodified Mg. The developed techniques can pave the way for assessing the interfacial behavior under harsh, lean electrolyte conditions, which is an extremely important but unexplored research area of RMB chemistry.

Cold deformation behavior and microstructure evolution of biomedical Cu-containing L605 alloy

The effect of copper (Cu) addition on the microstructure evolution and deformation mechanism of L605 (Co-20Cr-15 W-10Ni) alloy during cold deformation was investigated by using transmission electron microscopy (TEM), X-Ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis. The results indicated that the addition of Cu slightly decreased the yield strength and ultimate tensile strength, while it significantly increased the elongation. EBSD results revealed that hexagonal close-packed (HCP) martensite was generated during cold deformation and increased with increasing cold deformation level. The deformation microstructure of both alloys at different cold deformation levels shows that the stacking faulting was the primary deformation mechanism at early stage of cold deformation, in contrast, dislocation planar-slip and face-centered cubic (FCC) to HCP martensitic transformation were prevailed at both medium and late cold deformation level. Cu addition significantly suppressed the dislocation and stacking fault multiplication at early deformation stage and delayed the martensitic transformation at medium and late deformation stage, which could be ascribed to the relatively high stacking faulting energy by Cu addition, resulting in the low strain hardening behavior in the entire deformation process. These cumulative results and analyses could provide a solid foundation for the further development of this novel type of biomedical Cu-containing cobalt-based alloy.

Residual stresses of MAG-welded ultrahigh-strength steel rectangular hollow sections

Residual stresses are an important factor in the performance and stability of welded structures. This study investigates the characteristics and significance of residual stresses in MAG-welded ultrahigh-strength steel rectangular hollow sections. The research incorporates comprehensive X-ray diffraction residual stress measurements, electron backscatter diffraction analysis, statistical analyses, and finite element method simulations to provide valuable insights into the behaviour of welding residual stresses. The results reveal clear microstructural variations between the cold-formed corner and the flat side of the rectangular hollow section caused by welding heat input, emphasizing the need to consider these variations in residual stress assessments. Furthermore, the study examines the dependence of residual stresses on the steel grade, with higher strength steel exhibiting compressive stresses and lower strength materials experiencing tensile stresses in corner areas. Statistical analysis indicates that welding sequence and direction have negligible effects when applying the employed welding sequence. In any case, higher heat input leads to significantly larger residual stresses. Finally, the study presents a novel analytical model based on validated finite element simulations to predict the maximum variation of residual stresses depending on welding heat input. The findings provide valuable insights into the significance of welding residual stresses and their predictability. The comprehensive measurements, simulations and proposed models contributes to a better understanding of residual stress phenomena, facilitating the development of reliable design guidelines for welded structures in various engineering applications.

Scale-bridging phase-field approach for nucleation and microstructure evolution applied to the β to α phase transformation in pure titanium

Modeling concurrent nucleation and growth in the phase-field framework on experimentally relevant length scales remains a significant challenge due to spatial resolution and driving force limitations. This work proposes a modeling framework that overcomes these challenges by integrating the explicit nucleation method within the recently developed high-driving force phase-field model to investigate the influence of the cooling rate on solid-state nucleation and growth. The model accurately captures the growth behavior of individual nuclei across varying length scales, and allows efficient one grid point nucleation without modifying the high driving force equation. To accommodate nanoscale nucleation within a mesoscale phase-field framework, the model incorporates an analytical subscale step accounting for critical nucleus growth to one grid point. The model was applied to the β to α transformation in extra pure titanium, for which a material-specific input parameter study was performed. Simulation results were compared to experimental results on the cooling rate dependence of transformation temperatures and mean grain sizes obtained through an Electron Backscatter Diffraction analysis of furnace-, air-, and water-cooled samples. The model's significance lies in extending the phase-field method's applicability to simulate nucleation on much larger length-scales than previously achievable, bridging the gap between simulation and experimental length-scales.

EBSD investigation of microstructure and microtexture evolution on additively manufactured TiC-Fe based cermets—Influence of multiple laser scanning

Sustainable TiC-Fe-based cermets have been fabricated by adopting an Additive Manufacturing route based on laser powder bed fusion technology (L-PBF). The objective is to produce crack-free cermet components by employing novel multiple laser scanning techniques with variations in laser process parameters. Electron backscatter diffraction analysis (EBSD) was used to study the microstructure and microtexture evolution with variations in laser process parameters. The investigation revealed that adjusting the preheating scan speed (PHS) and melting scan speed (MS) influenced the growth and nucleation of TiC phases. Lowering these speeds resulted in grain coarsening, while higher scan speeds led to grain refinement with larger sub-grain boundaries. Moreover, a high scanning speed increases the degree of dislocation density and internal stress in the fabricated cermet parts. Notably, it is revealed that decreasing the laser scan speed enhanced the proportion of high-angle grain boundaries in the cermet components, signifying an increase in material ductility.

Investigation into hydrogen assisted fracture in Nickel oligocrystals

This study investigates the hydrogen embrittlement (HE) behavior of Nickel-201 alloy using the oligocrystal approach. To comprehend the influence of microstructure toward HE, various types of tensile oligocrystals (True-oligocrystals, Quasi-oligocrystals, Identical-oligocrystals, and Bi-crystal type oligocrystals) with diverse microstructure (in terms of Schmid factor distribution and grain boundary types) are generated using a combination of heat treatment and slicing method. The electron backscatter diffraction (EBSD) analysis is used to validate the development of the desired tensile oligocrystal samples. Identical oligocrystal samples established the transition in fracture mode from ductile transgranular (TG) to brittle intergranular (IG), solely driven by hydrogen uptake. Post-tensile deformation analysis validated the hydrogen-induced IG fracture initiation and propagation along the random high-angle grain boundaries (RHAGBs) only. Bi-crystal type oligocrystals with low angle grain boundaries (LAGBs) and coincident-site lattice (CSL) Σ3 grain boundaries exhibited resistance to hydrogen-induced intergranular fracture, thus establishing the ‘special’ nature of these grain boundaries against the HE under current testing conditions.