Electron Backscatter Diffraction Technique Research Articles

Construction of meta-dynamic recrystallization dynamic model of 316L stainless steel based on grain orientation spread during continuous variable rate thermal deformation

Because the deformation parameters (temperature, strain rate) in the actual manufacturing process are non-constant. We investigate meta-dynamic recrystallization behavior under the transient mutation state. First, based on a single-pass thermal deformation experiment and electron backscatter diffraction (EBSD) technique, this study establishes a quantitative calculation method for the volume fraction of meta-dynamic recrystallization under different deformation conditions, and find the GOS threshold basis for judging the occurrence of meta-dynamic recrystallization. Comparing the experimental results with the numerical simulation results, it is found that the MDRX behavior of the material could be accurately described. The meta-dynamic recrystallization evolution law of the material in the thermal deformation insulation stage under the variable strain rate state is investigated by continuous variable rate thermal deformation experiment and numerical simulation. It is observed that an increase of the average strain rate in the continuous variable strain rate state would promote the meta-dynamic recrystallization softening behavior of the material in comparison with the steady state deformation stage, and vice versa.

Influence of Grain Size and Film Formation Potential on the Diffusivity of Point Defects in the Passive Film of Pure Aluminum in NaCl Solution

The influence of grain size on the corrosion behavior of pure aluminum and the defect density and diffusion coefficient of surface passive films were investigated using electron backscatter diffraction (EBSD) and electrochemical testing techniques, based on the point defect model (PDM). Samples with three different grain sizes (23 ± 11, 134 ± 52, and 462 ± 203 μm) were obtained by annealing at different temperatures and times. The polarization curves and electrochemical impedance spectroscopy results for the pure aluminum in the 3.5% NaCl solution showed that with decreasing grain size, the corrosion current (icorr) decreased monotonously, giving rise to a noble corrosion potential and a large polarization resistance. The Motte–Schottky results showed that the passive films that formed on pure aluminum with fine grains of 23 ± 11 μm had a low density (3.82 × 1020 cm−3) of point defects, such as oxygen vacancies and/or metal interstitials, and a small diffusion coefficient (1.94 × 10−17 cm2/s). The influence of grain size on corrosion resistance was discussed. This work demonstrated that grain refinement could be an effective approach to achieving high corrosion resistance of passive metals.

Unveiling the formation of nanotwin-mediated metastable ζ-hydrides in fatigued Zr-1Nb-0.01Cu cladding tube

The impact of internal pressure fatigue treatment on the α-Zr matrix and hydride precipitates in Zr-1Nb-0.01Cu cladding tube has been systematically investigated using synchrotron-based high-energy X-ray diffraction, electron backscatter diffraction and transmission electron microscopy techniques. The evolution in d-spacings of the basal plane (0002), the pyramidal plane {101¯1} and the prismatic plane {101¯0} at azimuths from 0° to 360° indicates that the internal pressure fatigue treatment has imparted a degree of plastic deformation upon the α-Zr phase, which is further confirmed by the presence of {101¯2} deformation twins within the α-Zr phase. Concurrently, the prior internal pressure fatigue treatment at 400 °C significantly increased nucleation sites for zirconium hydrides during the subsequent furnace cooling process. High-density dislocations can be seen in both the δ-hydride precipitate ({111}<110> type) and the α-Zr matrix ({101¯0}<a> type) near the hydride-matrix interface. Additionally, δ-hydride {111}<112¯> nanotwins were observed within the micro-sized δ-hydrides in the fatigued cladding tube, resulting from the nucleation and growth of intra-granular δ-hydrides at different regions of the same parent α-Zr grain. Furthermore, the HCP-structured ζ-hydride phase was detected at the δ-hydride nanotwin forefront along the growth direction and at the curved δ-hydride nanotwin boundaries, providing direct experimental evidence to the notion that the metastable ζ-hydride serves as the precursor to the stable δ-hydride phase during the precipitation process. The current experimental findings contribute to the fundamental understanding of microscopic mechanisms underlying the delayed hydride cracking and the stress-induced hydride reorientation in Zr alloys.

An investigation to microstructural and texture evolution during the cold rolling of Al0.3CoCrFeNi high entropy alloy

In the present study, Al0.3CoCrFeNi high entropy alloy (HEA) was subjected to thickness reductions through cold rolling process in order to thoroughly investigate the evolution of microstructure and deformation texture. Important aspects of deformed microstructures such as the formation of twinning bundles and shear bands in the specimens were monitored. The evolution of texture during the cold rolling process was measured by X-Ray Diffraction (XRD) and Electron Back Scatter Diffraction (EBSD) technique which revealed the formation of Copper type texture at the initial stages of rolling due to slip deformation mechanism. Originated from twinning and followed by shear banding, the texture was subsequently developed toward predominantly Brass type. Microstructural features and texture evolution behavior of the investigated single phase FCC alloy was attributed to its low SFE level. Visco Plastic Self Consistent (VPSC) technique was coupled in the research to simulate the material behavior and to examine the contribution of slip and twinning systems. Benefiting VPSC justifications, the texture transition from Copper type to Brass type was related to lower CRSS value of slip in comparison to twinning at the small strains which was then grows faster at the later stages of rolling facilitating the onset of twinning and providing the texture transition basement.

Monitoring the phase evolution and fracture behavior of advanced multiphase QP steel using EBSD technique and digital image correlation

A novel multiphase 0.17C-5Mn-0.88Si-0.76Al-0.22Mo-0.06Nb steel was subjected to complex thermomechanical processing schedules to produce quenching and partitioning (Q&P) microstructures. The tests were performed in the Gleeble 3800 simulator applying multiple deformations in a plane state of strain and final deformation was applied at 850 °C. The samples were controlled cooled to 240 °C and 260 °C to produce some martensite fraction and subsequently partitioned at a temperature of 450 °C to enrich austenite in carbon from the supersaturated martensite. Different primary/secondary martensite microstructures containing retained austenite were produced, which were subjected to detailed microstructural and fracture studies using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The mechanical behaviour of the samples was investigated in static tensile tests using sub-sized flat samples. Digital image correlation (DIC) measurements were performed to monitor the strain distribution in a micro scale. Relationships between processing conditions and fracture behaviour were assessed in fractographic tests.

Quasi-in-situ observation of fatigue crack growth behavior of friction stir welded 2024-T4 joint

This study presents a quasi-in situ observation of the fatigue crack growth behavior in a friction stir welded 2024-T4 joint. The microstructure and fatigue properties of the joint were investigated using electron backscatter diffraction (EBSD) technique, scanning electron microscopy (SEM), and fatigue crack growth tests. The fatigue crack growth behavior of the joint was examined by conducting fatigue crack growth tests with different notch locations. The results show that the sample with the notch in the stir zone (SZ) exhibited the highest resistance to fatigue crack growth, followed by the notched samples of the Advancing side (AS) and Retreating side (RS) weldments. Microstructural observations showed a homogeneous microstructure with a fine grain size in SZ and it was observed that this fine-grained structure significantly enhanced the material’s resistance to fatigue crack growth. The experimental results were further analyzed using the Paris model to provide a quantitative understanding of the crack growth behavior. The study underlines the impact of microstructural characteristics and notch location on the fatigue performance of the weldment. Overall, the quasi-in situ observations and experimental findings contribute to a comprehensive understanding of the fatigue crack growth behavior in friction stir welded 2024-T4 joints.

Contrastive learning based on hierarchical graph of microstructures through directed energy deposition process to establish process-structure–property relationship via autoencoder

n this study, an innovative algorithm is developed to transform microstructures to hierarchical graphs without manual feature engineering. The hierarchical graph comprises two layers. Initially, pixel data, which includes Euler angles, phase, and position, forms the pixel-wise graphs within individual grains. Following this foundation, the grains serve as nodes, constituting the second layer. Importantly, the hierarchical graph preserves essential measurement data and structural details for training machine learning models. After that, a contrastive learning model based on hierarchical graph is designed to capture representations of microstructures obtained by the electron backscatter diffraction (EBSD) technique. This model can be directly extended for other microscopy techniques, such as Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), and Transmission Electron Microscopy (TEM). Using the learned microstructure representations, an autoencoder model for the directed energy deposition (DED) is developed to establish the relationship among process parameters, microstructures, and material properties, completing the process-structure–property cycle quantitatively. The performance of the present model is naturally benchmarked against two other models: a contrastive learning model based on pixel-wise graph (without manual feature engineering) and a contrastive learning model based on grain-wise graph (employing manual feature engineering). The results of the present model highlight the potential in decoding the process-structure–property relationships in the DED process.

Understanding the hot deformation behavior of Mo[sbnd]42Re alloy: Insights from strain rate sensitivity, microstructure, and misorientation

Mo42Re alloy, as a high-temperature structural and functional material, has broad application prospects in the nuclear industry. In this study, the hot deformation behavior of Mo42Re alloy was systematically investigated using hot compression tests and electron backscatter diffraction (EBSD) techniques in the temperature range of 1200–1500 °C and strain rate range of 0.001–1 s−1. The results showed that the flow stress of Mo42Re alloy exhibited a strong dependence on temperature and strain rate. The strain rate sensitivity index (m-value) was high under the conditions of 1350–1450 °C and 0.001 s−1. With increasing deformation temperature and decreasing strain rate, dynamic recrystallization (DRX) was significantly promoted, and the recrystallized volume fraction increased from 2.79% at 1200 °C/1 s−1 to 20.3% at 1500 °C/0.001 s−1. Meanwhile, the occurrence of and DRX effectively reduced the grain reference orientation deviation (GROD) gradients and kernel average misorientation (KAM) levels within the grains. This study revealed the mechanisms of microstructural evolution during hot deformation of Mo42Re alloy, providing important guidance for optimizing its thermomechanical processing parameters.

Twinning–Detwinning-Dominated Cyclic Deformation Behavior of a High-Strength Mg-Al-Sn-Zn Alloy during Loading Reversals: Experiment and Modeling

The deformation behavior of a high-strength Mg-Al-Sn-Zn alloy under loading reversals has been thoroughly examined through a combination of experimental measurements and crystal plasticity modeling. We focused on an age-treated alloy fortified by distributed Mg2Sn particles and Mg17Al12 precipitates, which underwent two distinct loading cycles: tension-compression-tension (TCT) and compression-tension-compression (CTC), aligned with the extrusion direction (ED). The initial and deformed microstructures of the alloy were analyzed using the electron backscattering diffraction (EBSD) technique. Notably, the alloy displays tensile and compressive yield strengths (YS) of 215 MPa and 160 MPa, respectively, with pronounced anelastic behavior observed during unloading and reverse loading phases. Utilizing the elasto-viscoplastic self-consistent model incorporating a twinning–detwinning scheme (EVPSC-TDT), the cyclic stress–strain responses and resultant textures of the alloy were accurately captured. The predicted alternation between various slip and twinning modes during plastic deformation was used to interpret the observed behaviors. It was found that prismatic &lt;a&gt; slip plays an important role during the plastic deformation of the studied alloy, and its relative activity in tensile loading processes accounts for up to ~66% and ~67% in the TCT and CTC cases, respectively. Moreover, it was discerned that detwinning and twinning behaviors are predominantly governed by stresses within the parent grain, and they can concurrently manifest during the reverse tensile loading phase in the TCT case. After cyclic deformation, the area fractions of residual twins were determined to be 7.51% and 0.93% in the TCT and CTC cases, respectively, which is a result of the varied twinning–detwinning behavior of the alloy in different loading paths.

Unveiling the self-annealing phenomena and its effect on microstructure and texture evolution in the room temperature rolled Cu-0.13Sn-0.04Mg alloy

ABSTRACT In this study, we investigated the microstructural evolution of a Cu-0.13Sn-0.04Mg alloy that underwent heat treatment followed by room temperature rolling (RTR). Initially heat-treated specimens were rolled at room temperature (RT) with reduction ratios (RR) of 40% and 75% to perform microstructural and crystallographic textural analyses. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were utilise to examine both initial and deformed microstructures. Both exhibited heterogeneous microstructural distributions. Shear bands (SBs) existed in the initial specimen and became main sites for the nucleation of new grains during heat treatment. A denser presence of SBs was noted in the RTR specimens. Remarkably, an unusual self-annealing phenomenon was observed in these specimens, culminating in the emergence of recrystallized grains at RT. A plethora of such grains was observed in the severely deformed specimens, with numerous nucleating grains appearing proximal to the SBs or deformed grain boundaries (GBs). Time dependent microstructure evolution was observed via ex-situ EBSD technique in the compressed specimens. Formation of new grains, increase in high angle grain boundaries (HAGBs), and dislocation annihilations were observed with the progress of time. The crystallographic texture evolution in the initial specimen was predominantly influenced by the S component. At lower strains, the fractions of Copper component increased, whereas at higher strains, a greater fraction of Brass and S components were induced. Following a 40% RR, a saturation in hardness value was observed, which could be potentially attributable to an accelerated rate of RT recrystallization in the case of 75% RR.

Substructure and texture evolution of a novel near-α titanium alloy with bimodal microstructure during hot compression in α+β phase region

Ti65 alloy has extensive potential applications in manufacturing high-temperature components in the aerospace industry. During thermomechanical processing in the α+β phase region, complicated microstructure and texture evolution occurs. In this work, isothermal hot compression experiments were conducted to comprehensively investigate the substructure and texture evolution of Ti65 alloy with bimodal microstructure via the electron backscatter diffraction (EBSD) technique, and the influence of processing parameters on the evolution of substructure and texture was systematically analyzed. The experimental results showed that the distribution of grain boundaries and the transformation of low-angle boundaries (LABs) to high-angle boundaries (HABs) exhibited sensitivity to temperature and strain rate. The fraction of sub-grain boundaries decreased, while the fraction of HABs increased with the increasing of strain rate or temperature due to the spheroidization of the lamellar α phase accompanied by the wedging of the β phase during deformation and the relative misorientation angle distribution between different α variants precipitated from β phase. Temperature rising at a high strain rate resulting from adiabatic heat promoted atomic activity, caused dislocations to be absorbed by sub-grain boundaries or HABs, and finally reduced the dislocation density in both αp and αs phases. Dynamic spheroidization was the main mechanism with increasing temperature, and coarsening of the lamellar α phase was the main mechanism with increasing strain rate. With the increase of temperature or decrease of strain rate, the texture of the αp phase became stronger and the basal and pyramidal slip could be activated. For the αs phase, spheroidization and variant selection together influence the orientation distribution. As a result, the texture evolution showed a complicated tendency.

Investigation on microstructural and mechanical integrity of GTAW dissimilar welded joint of IN 718/ASS 304L using Ni-based filler IN 625 using EBSD and DHD techniques

The current study investigates the relationship between the microstructural and structural characteristics of dissimilar gas tungsten arc welding (GTAW) between Inconel 718 (IN 718) and austenitic stainless steel 304L (ASS 304L) using Inconel 625 (IN 625) as a filler material. The microstructural characterization of the dissimilar weld includes the application of an optical microscope (OM), field emission scanning electron microscopy (FE-SEM) including energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). The optical and FESEM analysis of the base metals (BM) indicates the austenitic nature of the IN 718 BM matrix, which incorporates strengthening precipitates γ′ and γ'' distributed throughout the Nickel matrix. In contrast, the ASS 304L BM exhibits an austenitic microstructure along with twins. Moreover, IN 625 weld metal exhibits austenitic microstructure in the form of cellular, columnar, and equiaxed dendrites. Elemental segregation demonstrates the existence of Nb, and Mo-rich carbides, including the laves phases at the interdendritic regions of the IN 625 weld zone and IN 718 Heat-Affected Zone (HAZ). Ferrite stringers were noticed in the HAZ of ASS 304L. EBSD analysis shows the improved texture of the weld zone exhibiting fine equiaxed recrystallized microstructures. EBSD/Kernel average misorientation (KAM) micrographs reveal the existence of high strain at the weld metal grain boundaries. Vickers microhardness assessment of the dissimilar weld demonstrates the high hardness of 257.5 HV for the IN 625 weld zone because of the occurred NbC, laves phases, and Mo-rich carbides. Room temperature tensile characterization shows the failure of tensile specimens from ASS 304L BM reflecting the high strength of the IN 625 weld metal (662 MPa). Tensile tests at high temperatures were performed at 550 °C, 600 °C, and 650 °C. High-temperature tensile result exhibits a higher tensile strength of IN 625 weld zone than the ASS 304L BM, as the tensile specimens fails from 304L BM. The specimen exposed at 550 °C exhibits the highest tensile strength of 388 MPa. The Charpy impact toughness test was conducted, with notches at the HAZ of ASS 304L, HAZ of IN 718, and the weld center being evaluated. The toughness value of the weld metal decreases (99 J) due to occurrence of the secondary precipitates. To analyze residual stress, the deep hole drilling (DHD) technique was used, which revealed that the peak residual stress (230 MPa) is induced at 6 mm from the weld surface and falls into the tensile stress category.

Fatigue cracking behavior and life assessment of TC11 titanium alloy in very high cycle regime at two working temperatures

Axial loading fatigue tests were conducted with two stress ratios to investigate fracture surface behavior and associated failure analysis governing crack nucleation of TC11 titanium alloy at two working temperatures, spanning high-cycle and very high-cycle fatigue regimes. Furthermore, scanning electron microscopy, optical microscopy, and electron-backscattered diffraction techniques were employed to analyze the cracking mechanism. The interior failure is attributed to the cleavage of the large equiaxed αp-grains and facet-facet cluster area-fisheye formation. Moreover, the crack growth threshold values and the transition sizes from small to long cracks decrease with temperature rise. In addition, small cracks follow the path that requires minimum energy for propagation as per the microstructural orientation and are governed by maximum shear stress, resulting in the formation of crystallographic facets. Based on the analysis above, the interior fracture mechanism was summarized as related to the microstructure characteristics. Considering the fatigue cracking behavior and microstructural features, a model for predicting crack nucleation life is developed, exhibiting a better consistency between predicted and experimental fatigue lives.

Revealing the inhomogeneous nature of microstructure and texture evolution in the cold-rolled CoCrFeMnNi alloy during static recrystallization

In the present investigation, equiatomic CoCrFeMnNi high entropy alloy (HEA) was subjected to 80% cold rolling (as-rolled) followed by isothermal annealing treatment at 700 °C for different time periods. Microstructural characterization was performed using electron back-scattered diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques on the as-rolled and annealed samples. The as-rolled microstructure consisted of elongated grains mainly composed of strong α-fiber and weak γ-fiber textures. The as-rolled sample showed the formation of ingrain SBs in the γ-fiber grains, which served as preferential sites for grain nucleation. The annealing treatment of as-rolled samples at 700 °C cause static recovery (SRV) before 5 minutes of heat-treatment, whereas static recrystallization (SRX) was observed after 5 minutes of heat-treatment in the CoCrFeMnNi alloy samples. A faster rate of recrystallization kinetics was observed after 15 minutes of heat-treatment. The annealing treatment reduced the intensity of α-fiber and enhanced the Copper, Cube and P ({011}<122>) texture components. Copper components originated from coarse recrystallized grains, which were the results of localized grain growth phenomena. Unusual behavior of banded featured α-fiber grains was observed during the annealing process. These banded grains in the partially annealed samples consisted of subgrain-boundaries and showed a delayed response to recrystallization as compared to grains with other orientations. Stored energy (SE) and Taylor factor (M) calculations were also used to understand the delayed recrystallization response of the banded featured/retained deformed grains. The microhardness value of the as-rolled sample was approximately 450 Hv, which decreased to around 230 Hv for the fully recrystallized grains.

A hardness-based constitutive model for numerical simulation of blind rivet with gradient hardness distribution

A286 superalloy blind rivets find extensive applications in the structural connections of aerospace equipment owing to their exceptional strength and heat resistance. However, the gradient hardness distribution within the rivet sleeves complicates achieving precise numerical simulation results with traditional constitutive models. This study aims to establish a constitutive model suitable for materials exhibiting gradient hardness to support the development of A286 superalloy blind rivets. Initially, quasi-static compression experiments were conducted on A286 superalloy samples at different hardness levels (160–324 HV), strain rates (0.01–10 s⁻¹), and temperatures (25–600°C). Subsequently, the influence of material microstructural evolution on flow stress during compression was investigated using electron backscatter diffraction technique. Furthermore, a hardness-based Johnson-Cook (J-C) constitutive model was developed by introducing hardness and offset compensation onto the original J-C model and compared with its counterpart. Finally, the hardness-based model was employed to simulate the bulge compression forming of A286 blind rivets and validated through experimental trials. The findings reveal that dislocation strengthening predominantly contributes to the increased material flow stress with escalating strain rates and sample hardness. Compared to the original J-C model, the stress prediction error of the hardness-based model reduced from 26.8 % to 2.9 %, effectively depicting the variation in material flow stress under different hardness values. The simulated values of bulge morphology, dimensions, and load closely align with experimental data, affirming the efficacy of the hardness-based model in numerically simulating blind rivets with gradient hardness distribution.

Experimental characterization and crystal plasticity finite element simulation of the microstructural evolution in CVD tungsten during multi-step rolling

Atmospheric pressure chemical vapor deposition (CVD) is a promising technique for the preparation of tungsten products with high purity, high density and almost unlimited thickness. The tungsten prepared by using the CVD method (CVD-W) usually has a columnar coarse grain microstructure with strong preferred orientations. Multi-step rolling at gradually decreased operating temperatures is an effective method to lower the ductile-to-brittle transition temperature in pure tungsten. So far, the microstructural evolutions of CVD-W during the multi-step rolling processing is still unclear. In this study, the microstructure evolution and texture development of CVD-W during multi-step rolling are investigated by the coupling of electron backscattering diffraction technique and full-field crystal plasticity finite element simulations. After multi-step rolling, the sample exhibits through-thickness texture gradient. A layered structure with elongated 〈100〉 // ND and 〈111〉 // ND grains is observed in the central region and Goss orientation mainly appears in the surface region. Crystal plasticity finite element simulations show that {001}〈110〉 is a stable orientation under the plane strain compression, which is realized by the rotation of {100} grains around ND. Meanwhile, the shear flow promotes the rotation of {100} grains around TD, leading to the formation of 〈111〉 // ND orientation. 〈110〉 // ND orientation is observed near the shear bands, which is generated through the rotation of {100} grains around <100> // RD axis. The rolled CVD-W exhibits crystallographic orientation dependent recrystallization behavior, which is related to the orientation dependent distortion energy generated in the rolling processing. Our studies provide fundamental insights into the microstructure evolution and texture development of CVD-W under the multi-step rolling processing.

Crystal Plasticity Finite Element Analyses on the Formability of AA6061 Aluminum Alloy with Different Ageing Treatments

Different ageing treatments have been developed to achieve targeted properties in aluminum alloys through altering microstructures. However, there is a lack of understanding regarding the effect of ageing treatments on the formability of these alloys. In this study, we employed crystal plasticity finite element (CPFE) modeling, in conjunction with the Marciniak-Kuczynski (M-K) approach, to investigate the effects of ageing treatments on the mechanical properties and formability of AA6061 aluminum alloy. The as-received sheet was in the T6 heat treatment state, which was subjected to artificial ageing and pre-ageing, respectively, to achieve two age-hardened alloys with modified precipitation states. The microstructures and crystallographic textures of the three alloys were measured using the electron backscattering diffraction (EBSD) technique, and uniaxial tensile tests were performed along the rolling direction (RD), transverse direction (TD), and diagonal direction (DD, 45° to the RD) for each alloy. The forming limit curve (FLC) of the as-received alloy was determined using the Nakazima test. The dependence of mechanical strength, tensile ductility, and work-hardening behavior on the ageing treatments was clarified. Then, the tensile test results were utilized to calibrate the modeling parameters used in the CPFE model, whereas the FLC predictability of the developed model was validated with the experimental one. In the formability analysis, the effects of the ageing treatment on the FLC exhibit a notable dependency on loading paths, and the pre-aged alloy exhibits better formability than the other two at the plane strain tension state, thanks to its high work-hardening levels. In addition, the deformed textures along the different loading paths and the effects of the initial texture on the FLC are also discussed.

Effect of annealing temperature on the evolution of microstructure, texture, and mechanical properties of hot-rolled 12Cr-ODS steel

To achieve high thermal efficiency, today's nuclear reactor structures are exposed to higher temperatures and pressures, which requires the use of high-strength steels with specific properties, such as ODS steels. There is a need to clarify the evolution of the microstructure and properties of steels at elevated temperatures. This study systematically investigates the evolution of microstructure, texture, and mechanical property variations of 12Cr-ODS steels after hot-rolling and subsequent annealing at 1000 °C and 1200 °C. The investigation utilizes optical microscopy, electron backscatter diffraction technique, and mechanical property measurements. The microstructure of hot-rolled samples shows a layered alternating distribution, which is distinguished by a notable presence of the α-fiber texture. Following annealing at 1000 °C, the martensite grains are smaller with a reduced hardness, while maintaining a strong α-fiber texture. After annealing at 1200 °C, there is a rapid increase in the growth of martensite grains, a significant rise in hardness, a reduction in the α-fiber texture characteristics, and an improvement in the γ-fiber texture characteristics. Moreover, the maximum intensity of the α-fiber texture diminishes as the annealing temperature increases. The mechanical properties of the samples deteriorated after annealing at 1200 °C, which can be attributed to the coarse martensite grains and the texture components containing the {001} cleavage plane dominating the occurrence of brittle cleavage fracture. The 0.1Y sample after annealing at 1000 °C exhibits an excellent combination of strength (1458 MPa) and ductility (20.3%), which is owing to the unique heterogeneous grain structure and the evolution of favorable texture.

The mechanical properties of Al3Sc single crystal investigated by nanoindentation using Hertzian elasticity theory method and Oliver-Pharr method

The crystal structure, orientation, reduced modulus, and hardness of Al3Sc single crystal were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and nanoindentation techniques, combined with Hertzian elastic theory method (Hertz) and Oliver-Pharr method (O&P). Millimeter-sized Al3Sc single crystals were prepared using quasi-equilibrium solidification of hypereutectic Al-15(wt %) Sc alloy. The XRD results showed that the samples were composed of L12-Al3Sc and Al phases. The EBSD and nanoindentation results showed that for five Al3Sc single crystals with different orientations, the reduced moduli measured by Hertz method were 146.6 ± 0.4–148.3 ± 0.2 GPa; while measured by O&P method they were 147 ± 2–150 ± 3 GPa. The corresponding hardnesses were varied between 3.8 ± 0.1 and 3.9 ± 0.1 GPa. The Poisson's ratio and elastic constants were determined through iterative calculation based on the relationship between the reduced modulus and Young’s modulus at various orientations. The polycrystal elastic properties, bulk modulus, shear modulus and Young's modulus, were determined. The elastic constants c11, c12, and c44 were 179.2 ± 0.4, 44.1 ± 0.1, and 68.3 ± 0.3 GPa, respectively; the Poisson's ratio was 0.196 ± 0.001. The Young's modulus of five Al3Sc single crystals oriented in different directions was in the narrow range 161–164 GPa. The anisotropy factor of Al3Sc crystal was 1.011 ± 0.002, confirming that it is elastically isotropic. These results provide fundamental information for the research and development of the Al3Sc intermetallic compound and related alloys in future.

Change in Hydrogen Trapping Characteristics and Influence on Hydrogen Embrittlement Sensitivity in a Medium-Carbon, High-Strength Steel: The Effects of Heat Treatments.

Medium-carbon, high-strength steels are widely used in the field of hydrogen energy because of their good mechanical properties, and they can be readily tailored by heat treatment processes such as the normalizing-tempering (N&T) and quenching-tempering (Q&T) methods. The hydrogen embrittlement (HE) susceptibility of a medium-carbon, high-strength steel was investigated utilizing microstructural characterization with scanning electron microscopy (SEM), the electron backscatter diffraction (EBSD) technique, and transmission electron microscopy (TEM). A study was also conducted on the steel's hydrogen transport behavior as affected by the N&T and Q&T treatments. The steel contained more hydrogen traps, such as dislocations, grain boundaries, lath boundaries, and carbide interfaces, after the Q&T process, which was associated with a lower HE sensitivity when comparing the two treatments. In comparison, the N&T process produced larger-size and lesser-density carbides distributed along the grain boundaries, and this resulted in a relatively higher HE susceptibility, as revealed by the slow-strain-rate tensile (SSRT) tests of the hydrogen-charged steels and by the fractographic study of the fracture surface.