Twinning-induced Plasticity Research Articles

Microstructures and mechanical properties of additively manufactured Fe–30Mn–3Al–3Si TWIP steel using laser powder bed fusion

Twinning induced plasticity (TWIP) high manganese steel demonstrates high ultimate tensile strength (UTS) and ductility, but its low yield strength limits its applications. This study presents the additive manufacturing of Fe–30Mn–3Al–3Si TWIP steel using laser powder bed fusion (LPBF) with enhanced mechanical properties. The average grain size of the LPBF-fabricated Fe–30Mn–3Al–3Si was 5.4 ± 1.3 μm, which was only one-tenth of that of a wrought one. In-situ formed Al-rich oxide nanoparticles were observed to be uniformly distributed in the matrix. The size of the oxide nanoparticles was about 30 nm with a volume fraction of about 0.9 %. The tensile yield strength was 554 ± 3 MPa and the UTS was 837 ± 7 MPa with an elongation of 41.5 ± 2.6 % for horizontal direction. Low anisotropy was observed for LPBF-fabricated Fe–30Mn–3Al–3Si. Compared with the wrought Fe–30Mn–3Al–3Si, the yield strength was increased by 140 %. This work provides a benchmark for the additive manufacturing of high manganese steel.

Enhancing plasticity in laser additive manufactured high-entropy alloys: The combined effect of thermal cycle induced dissolution and twinning

Breaking the trade-off between strength and ductility and pursuing stronger and more ductile metal materials has been a long-standing dream for scientists. Interestingly, even for the same material, different manufacturing methods can lead to significantly different performance. In this study, we utilized different laser additive manufacturing techniques (laser direct energy deposition (LDED), and laser powder bed fusion (LPBF)) to fabricate FeCoCrNiMo0.5 high-entropy alloy (HEA). Through microstructural analysis, we discovered a novel thermal cycling-induced dissolution (TCID) mechanism. By controlling the cooling rate post thermal cycling, we achieved the dissolution of precipitate phases and increased the Mo content within the matrix. Based on this phenomenon and supported by theoretical calculations, we revealed a reduction in stacking fault energy (SFE), which gave rise to a twinning-induced plasticity (TWIP) mechanism. This led to a dramatical increase in plasticity (LDED: 1.6 %, LPBF: 17.7 %) in the LPBF alloy, while maintaining similar strength (LDED: 784.9 MPa, LPBF: 840.89 MPa). This study provides guidance for designing metals structures with balanced strength and plasticity.

Improving strength-ductility synergy of twinning-induced plasticity steel by introducing a sandwich structure via submerged double-face friction stir processing

Twinning-induced plasticity steels typically exhibit remarkable plasticity and ultimate tensile strength, but the inferior yield strength has become a bottleneck limiting their application. In this work, a unique gradient sandwich structure that aims to break the bottleneck was successfully fabricated using a submerged double-face friction stir processing technique. The sandwich structure is composed of a coarse-grained zone in the core and two ultrafine-grained zones on the surfaces. An ultrahigh yield strength (1215 MPa) which is 2.2 times that of the as-received base material (543 MPa) is achieved for the sandwich structure. Additionally, significant elongation (19 %) and corrosion resistance are retained simultaneously. The coordinated deformation and effective strain transfer between the ultrafine-grained zones and coarse-grained zone facilitate the dispersion of stress and uneven deformation, which contributes to the excellent strength-ductility of the sandwich structure. This work provides a feasible method for fabricating high-performance steels.

Superior combination of strength and ductility in Fe-20Mn-0.6C steel processed by asymmetrical rolling

A Ce-alloyed twining-induced plasticity steel with the gradient structure was prepared through asymmetrical rolling. The primary role of Ce addition was to refine grains, and the asymmetrical rolling also effectively reduced grain sizes, and increased dislocation density. Under the combined effects of asymmetrical rolling and Ce addition, the steel exhibited superior combination of strength and ductility, with the yield strength of 1320 ± 5 MPa, ultimate tensile strength of 1775 ± 10 MPa and good elongation of 27 ± 1 %. Dislocation strengthening was the key factor of the increasing yield strength. As grain size decreased, the thicknesses of twins were significantly refined to several nanometers, accompanied with the activation of secondary twins. The promoted TWIP effect effectively enhanced the strain hardening ability of the steel.

Achieving high ductility in Fe45Mn35Co10Cr10 metastable high entropy alloy by constructing chemical boundary with stacking fault energy heterogeneity

Additively-manufactured metastable high entropy alloys are emerging as promising alternatives for energy absorption in protective equipment due to their exceptional ductility. In this study, an elongation of over 50 % was achieved in a directed energy deposition fabricated Fe45Mn35Co10Cr10 metastable high entropy alloys (MHEAs). The inherent high cooling rate and repeated heat treatment in the directed energy deposition process were harnessed to deliberately induce an uneven distribution of Mn elements, forming a cellular structure with chemical boundary. The unique heterogeneity stacking fault energy results in a synergistic interplay of multiple deformation mechanisms such as, dislocation slip, transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). In the initial stage of deformation, dislocation slip and TRIP contribute to the main plasticity. Stacking faults/martensite are confined within the cellular structure with low stacking fault energy (SFE). As strain increases, TWIP and TRIP are activated in the high SFE regions. Twins and martensite across the cell wall were observed. As strains exceed 40 %, primary martensite variant and twinning with a particular intersection angle take place to further enhance the deformation ability. The chemical boundary with stacking fault energy heterogeneity not only simultaneously activates both TRIP and TWIP, but also maintains the martensite and twins at the nanoscale.

Role of carbon on the enhanced strength-ductility synergy in a high-entropy alloy by multiple synergistic strategies

A new Fe47Mn31Co10Cr10C2 high-entropy alloy (HEA) was developed to investigate the role of carbon in enhancing the strength-ductility synergy by utilizing multiple synergistic strengthening strategies with mitigating the adverse effect of carbon. Compared with the Fe40Mn40Co10Cr10 twinning-induced plasticity (TWIP) HEA, the carbon-doped Fe47Mn31Co10Cr10C2 HEA after annealing at 1173 K for 10 min exhibited a higher strain-hardening rate, and significantly improved yield strength (YS) and ultimate tensile strength (UTS), with maintaining high elongation. The remarkable improvements in YS were mainly attributed to the multiple synergistic strengthening mechanisms, including enhanced grain boundary strengthening, hetero-deformation-induced (HDI) strengthening, and Cr23C6 precipitation strengthening. The higher strain-hardening rate could be ascribed to the enhanced TWIP effect and HDI strain-hardening. The effective stacking fault energy (SFE) of the Fe40Mn40Co10Cr10 and Fe47Mn31Co10Cr10C2 HEAs were calculated by thermodynamics to be 23.4 mJ/m2 and 22.1 mJ/m2, respectively. This revealed that reducing the Mn content effectively counteracted the increasing effect of carbon on the SFE for the carbon-doped HEA. The promotion of deformation twinning in the Fe47Mn31Co10Cr10C2 HEA could be ascribed to the comprehensive effect of the SFE and the stress levels of the alloys. On one hand, compared with the Fe40Mn40Co10Cr10 TWIP HEA, the lower SFE in the Fe47Mn31Co10Cr10C2 HEA led to a drop in the critical stress for deformation twinning. On the other hand, due to the strong multiple synergistic strengthening with carbon doping, the stress levels of the alloys were significantly enhanced, thus making the activation stress of twinning much easier to achieve. This study contributes to the alloy design guidance of properly utilizing carbon to achieve high strength-ductility synergy in alloys by multiple synergistic strategies.

Two-stage rolling and partial annealing enables heterogeneous structure and strength-ductility enhancement for austenitic stainless steel

Austenitic stainless steels are widely used in civil and defense industries. However, its low yield strength severely limits its fields of application. Under conventional processing routes, uniform grain refinement improves strength but unfortunately sacrifices ductility. In order to achieve the balance of strength and ductility, a new processing route of cold rolling and cryogenic rolling combined with partial annealing was proposed in this work. The results showed that the two-stage rolling and annealing produced dual-phase heterogeneous microstructure containing micron-sized grains (>1 μm), submicron-sized grains (500–1000 nm), and ultra-fine grains (100–500 nm) arranged in lamellar structures. Compared with the single-stage cold rolled and annealed steel, the tensile strength increased to 1.1 GPa, which was slightly higher than the single-stage cryogenic rolled and annealed steel. Furthermore, the elongation was improved to 25 %. The improvement of tensile properties was mainly due to the contribution of persistent hetero-deformation induced (HDI) hardening and twining induced plasticity (TWIP) effect to work hardening. This study not only proposed a simple and effective way to improve the mechanical properties of austenitic stainless steels, but also provided guidance for the design and development of high performance heterostructured materials.

Role of {332} twinning on adiabatic shear behavior during dynamic loading in β-type Ti–15Mo alloy

The microstructural evolution and formation mechanism of the adiabatic shear band (ASB) in {332}<113> twinning-induced plasticity (TWIP) Ti–15Mo alloy were investigated by applying stopper rings in a split Hopkinson pressure bar apparatus. Accompanied by activation of numerous {332}<113> twins, ASB consisting of elongated fine-grains initiated in the dynamically compressed sample with 0.28 true strain. Multiple twins adjacent to the ASB region were severely distorted and refined along the shear direction. Further deformation led to refinement of elongated twins into elongated subgrains, then some of them were subdivided into equiaxed fine-grains. The morphology of the fine-grains within the ASB underwent a complete transition from elongated to equiaxed as the strain increased to 0.33. The equiaxed fine-grains exhibited a random distribution of orientation, which was regarded as the result of dynamic recrystallization. The formation of equiaxed fine-grains was found to obey rotational dynamic recrystallization mechanism through the thermodynamic and kinetic calculations.

Effect of friction stir welding with different heat input on microstructure evolution, mechanical properties and deformation behavior of twin-induced plasticity steel

The effect of friction stir welding (FSW) with different heat input on microstructure evolution, mechanical properties and deformation behavior of twin-induced plasticity steel was investigated in this paper. The results show that compared to the basal material (BM), the grain size in the stir zone (SZ) of FSW joint with low heat input was refined, and a large amount of deformation twins was formed. The grain was refined and numerous dislocations were formed in the stir zone-heat affected zone (SZ-HAZ) interface. In the FSW joint with high heat input, the grain size in SZ increased, while no deformation twins were observed. A large number of fine equiaxed grains were formed in the SZ-HAZ interface, while the grains in HAZ coarsened. Compared to the BM, the tensile strength and yield strength of low heat input joint increased to 1108 MPa and 597 MPa, respectively, while the elongation decreased to 50.4%, resulting in a strength-elongation product of 92% of BM. The joint with high heat input experienced a decrease in tensile strength, yield strength, and elongation to 806 MPa, 465 MPa, and 22.8%, respectively, with a strength-elongation product of only 30% of BM. During the tensile deformation process, the plastic deformation in the low heat input joint was mainly concentrated in BM, followed by HAZ, while SZ exhibited minimum plastic deformation, and the tensile fracture occurred at zone between SZ and HAZ. In the high heat input joint, the maximum plastic deformation occurred in the SZ, with lower plastic deformation in BM and HAZ, and finally fractured at the SZ. The constrain effect of different micro-zones and hindrance effect of dislocations and fine grains were main responsible for the deformation behavior of low and high heat input joints.

Microstructure evolution and twinning-induced plasticity (TWIP) in hcp rare-earth high- and medium-entropy alloys (HEAs and MEAs) due to tensile deformation

The microstructure evolution due to the tensile deformation of the equiatomic quinary high-entropy alloy Ho-Dy-Y-Gd-Tb (HEA-Fb) is assessed. HEA-Fb has extraordinarily similar alloying elements. It is one of the few hexagonal-close-packed single-phase representatives of HEA. HEA-Fb is compared to the equiatomic quaternary medium-entropy alloy (MEA) Ho-Dy-Gd-Tb with no Y (4-Y). For a hexagonal HEA, in contrast to the cubic HEA, little information on plastic deformation and underlying mechanisms is available. A detailed study using electron microscopy-based multi-scale characterization (SEM, S/TEM, and STEM-EDS) explains significant differences between the ductile behavior of the quaternary MEA 4-Y and the brittle behavior of the quinary HEA-Fb at room temperature. Twinning during plastic deformation is decisive for ductility, which challenges the widely discussed high-entropy effect on the mechanical behavior of the HEA. For the quaternary MEA 4-Y, a twinning-induced plasticity effect is found. In the latter, oxidized twins are present in the undeformed state. In both alloys, the twin orientations are indexed as [2¯201], while the matrices have the perpendicular [112¯0] orientation. Additionally, the analysis of twin structures confirms the importance of twin boundaries as obstacles for dislocations and stacking fault mobilities. The results are discussed in the context of the existing knowledge gaps in the field of hexagonal MEAs and HEAs.

Effect of post-weld heat treatment on microstructure and mechanical properties of twinning-induced plasticity (TWIP) steel joints

The effect of post-weld heat treatment on microstructure and mechanical properties of twinning-induced plasticity (TWIP) steel joints obtained by melting electrode inert gas-shielded welding (MIG welding) was systematic studied. A total of two post-weld heat treatment processes are proposed, i.e., post-weld annealing treatment (PWAT) with temperature/time of 1100 ℃/1 h and subsequent furnace cooling and post-weld solution treatment (PWST) with temperature/time of 1100 ℃/1 h and subsequent water quenching, which were compared with the case of post-weld non-treatment (PWNT). Following annealing treatment at 1100°C, the joint tensile strength dropped by 6.6 % (from 845.46 MPa to 789.85 MPa), while its elongation at break increased by 40.87 % (from 29.80 % to 41.98 %). The significant increase in plasticity was due to the significant elimination of weld stresses in the joints after annealing. Moreover, the stresses in the weld metal of the PWST joints were instead significantly elevated and the carbides were solidified, which resulted in the lower strength. When post-weld heat treatment was applied, the impact toughness of the joints was lower than when untreated. This was primarily due to the greater percentage of the low-angle grain boundaries and the precipitation of MC-type carbides. Consequently, post-weld annealing treatment was an effective method to further enhance the strong plasticity of new twinning-induced plastic steel joints.

TiZrHfNb refractory high-entropy alloys with twinning-induced plasticity

The twinning-induced plasticity (TWIP) effect has been widely utilized in austenite steels, β-Ti alloys, and recently developed face-centered-cubic (FCC) high-entropy alloys (HEAs) to simultaneously enhance the tensile strength and ductility. In this study, for the first time, the TWIP effect through hierarchical {332<113> mechanical twinning has been successfully engineered into the TiZrHfNb refractory HEAs by decreasing temperature and tailoring the content of Nb to destabilize the BCC phase. At cryogenic temperature, the comprehensive hierarchical {332}<113> mechanical twins are activated in TiZrHfNb0.5 alloy from micro- to nanoscale and progressively segment the BCC grains into nano-scale islands during deformation, ensuring sustainable strain hardening capability and eventually achieving a substantial 35% uniform tensile elongation. In addition, at 77 K, the tensile strength and uniform elongation of TiZrHfNbx alloys can further be adjusted by a moderate increase of Nb. The results above shed new light on the development of high-performance refractory HEAs with a high and adjustable strength and ductility combination down to the cryogenic temperature.

ω-Strengthened Ti-23Nb alloy with twinning-induced plasticity developed via reverse martensitic transformation

The twinning-induced plasticity (TWIP) effect contributes to high strength and ductility synergy in metastable β Ti alloys. Moreover, stress-induced α″ martensites (SIMs) are usually concurrent with TWIP, resulting in low yield strength. As a new pathway, the production of ω-strengthened metastable β Ti alloys from full α″ Ti alloys can be accomplished via reverse martensitic transformation. However, the deformation mechanisms of the metastable β Ti alloys acquired by this pathway have not been adequately reported. Accordingly, in this study, the full α″-type solution-treated (ST) samples of Ti-23Nb at.% alloy were annealed at 573 K followed by slow cooling to acquire the air-cooled (AC) and furnace-cooled (FC) samples with β phase and ω precipitates. Mechanical properties and deformation behaviors of these samples were systematically investigated. The AC and FC samples exhibited higher yield strengths than the ST samples. Although SIMs still existed in the AC samples, they were completely suppressed in the FC samples. The annealed samples demonstrated high ductility due to the TWIP effects stemming from {332}<113>β twins. Furthermore, a distorted α″ phase exhibiting the abnormal orientation relationships (ORs) <11¯0>β//<001>α″, {332}β//{100}α″, and {110}β//{110}α″ with both β matrix and twin was revealed by high-resolution transmission electron microscopy and crystallographic analyses. These ORs were governed by the lattice distortion associated with a unique β matrix → distorted α″ → {332}β twin pathway. This study suggests that metastable β Ti alloys with enhanced mechanical properties can be achieved via the α″ → β reverse martensitic transformation and ω precipitation.

Research on deformation behaviors at different temperatures of lean duplex stainless steel S32101 produced by direct cold rolling process

In this paper, the mechanical properties, work hardening characteristics and deformation mechanism of lean duplex stainless steel (LDSS) S32101 produced by direct cold rolling were studied under different temperature conditions. The yield strength (YS) and tensile strength (TS) of S32101 decreased with the increase of deformation temperature, while the elongation increased first and then decreased. The TS of S32101 at −70 °C was 1052.6 MPa, the elongation remained 57.2%, and the product of strength and elongation (PSE) was as high as 60.2 GPa·%, which was mainly due to the synergistic strengthening of transformation induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects in austenite at cryogenic temperatures. The efficiency of grain refinement at cryogenic temperature was improved by TRIP effect and deformation twins (DTs), indicating that it had the potential to be applied at low temperature (−70 ∼ −30°C). Moreover, the high density nanotwins and the strong interaction between the dislocation and nanotwin bundles also contributed to strain hardening at low temperatures and thus better comprehensive mechanical properties could be achieved.

Manipulating TWIP/TRIP via oxygen-doping to synergistically enhance strength and ductility of metastable beta titanium alloys

Metastable β-Ti alloys exhibiting twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) generally have excellent ductility, but typically at the expense of relatively low yield strengths which has restricted their widespread use. Our work shows that interstitial oxygen can be employed to regulate β phase stability to significantly enhance both strength and ductility of TWIP/TRIP alloys. For a Ti-32Nb wt.% base alloy, inclusion of 0.3 wt.% O enhanced ductility by more than 140 %, reaching up to 54 % strain, and improved the tensile yield strength by over 95 % to 632 MPa. Compared to other common engineering alloys such as Ti-45Nb, elongation was increased by 29 %, and the yield strength increased by 182 MPa, respectively. Here, we elucidate on impacts of oxygen doping on TWIP/TRIP behaviors in the Ti-32Nb alloy. We reveal that oxygen regulates the critical stress for martensitic transformation, twinning, and dislocation slip. At lower oxygen doping concentrations (≤0.3 wt.% O), multi-stage martensitic transformation and martensitic twinning resulted in high ductility. In higher oxygen content alloys (≥0.5 wt.% O), deformation occurred initially via twinning, while strain induced martensite was subsequently induced in retained β phase regions. Oxygen concentrations control the deformation mechanisms, providing a flexible means to synergistically balance an alloy's strength and ductility. The use of oxygen to enhance stability of the β phase and regulate deformation behaviors is a promising new approach for creating high-performance TWIP/TRIP metastable β-Ti alloys with outstanding mechanical properties.

Effect of rolling on the microstructure and mechanical properties of (FeCrNi)94Ti3Al3 medium entropy alloy fabricated via selective laser melting

The microstructure evolution and mechanical properties of the (FeCrNi)94Ti3Al3 medium entropy alloy, fabricated through selective laser melting, were investigated after warm-rolling. The as-built (FeCrNi)94Ti3Al3 alloy exhibited a heterogeneous microstructure with alternating coarse face-centered cubic (FCC) phase grains (∼20 μm) and fine body-centered cubic (BCC) phase grains (∼1 μm). However, after warm-rolling and subsequent recrystallization, the alloy transformed into a dual-phase equiaxed grains structure consisting of FCC and BCC phases with an average grain size of approximately 2.8 μm. Additionally, the previously banded distribution of the BCC phase changed to a random distribution. Notably, during the deformation process, a twinning-induced plasticity (TWIP) effect was observed in the warm-rolled and recrystallized (FeCrNi)94Ti3Al3 alloy, resulting in excellent ductility and a wide work-hardening platform.

Mechanical behavior of twinning-induced plasticity (TWIP) steel fibre reinforced cementitious composite under impact loading

Twinning-induced plasticity (TWIP) steel fibre is a supermaterial known for its outstanding impact resistance. This paper, for the first time, applied TWIP steel fibre to increase the impact resistance of cementitious composites. The mechanical properties behaviours of TWIP steel fibre-reinforced cementitious composites (T-SFRCC) were investigated and compared with conventional SFRCC with normal steel fiber. The fractal theory was utilized to analyze the deterioration of damage in various SFRCCs subjected to impact loads, displaying TWIP steel fiber could prevent the cracks propagation and fewer fractal dimension compared with others. Results demonstrate that T-SFRCC has comparable compressive strength to SFRCC while exhibiting higher flexural strength. When subjected to impact loading, T-SFRCC demonstrates markedly improved energy absorption and impact toughness, such as better impact force and displacement. Specifically, the energy absorption capacity of T-SFRCC can exceed five times that of SFRCC with corrugated steel fiber, particularly evident when the drop height reaches 1200 mm. The influences of different fiber types and hammer drop methods on the impact resistance of SFRCCs were also discussed, which can provide reference for TWIP steel fiber in the field of cementitious composite materials.

Microstructures and mechanical properties of additively manufactured Fe–21Mn-0.6C TWIP steel using laser powder bed fusion

Twinning induced plasticity (TWIP) high manganese steel exhibits high ultimate tensile strength (UTS) and ductility, but its low yield strength restricts its applications. This research presents a Fe–21Mn-0.6C TWIP steel with enhanced mechanical properties additively manufactured using laser powder bed fusion (LPBF). The average grain size of the LPBF-fabricated Fe–21Mn-0.6C was 17.1 μm in the vertical direction, which was a quarter of that of a wrought one. The tensile yield strength was 657 MPa and the UTS was 1089 MPa with an elongation of 47.9% for the vertical direction. Compared to the wrought Fe–21Mn-0.6C, the yield strength increased by 110%. The high strength of LPBF-fabricated Fe–21Mn-0.6C is primarily attributed to solution, grain boundary and dislocation strengthening. Serrations were observed in the stress-strain curves at the initial stage of deformation, showing large stress drops. In the annealed sample, serrations appeared at a later stage of deformation with little stress drops. This difference in serration phenomenon is attributed to the varying dislocation density in the two samples.

Effect of stacking-fault energy on dynamic recrystallization, textural evolution, and strengthening mechanism of Fe−Mn based twinning-induced plasticity (TWIP) steels during friction-stir welding

This study aims to elucidate the effect of stacking fault energy (SFE) on the microstructural evolution and related hardening mechanisms of Fe−18Mn−0.6C−(0 and 1.5)Al and Fe−30Mn−3Al−3Si (wt.%) twinning−induced plasticity (TWIP) steels during friction stir welding (FSW) using a high−resolution electron backscattered diffractometer. With increasing SFE, the intensities of the Goss, CuT, and Brass components increased via active dynamic recrystallization (DRX) accompanied by twinning. The 30Mn weld, which had the highest SFE, exhibited the highest recrystallization fraction (94.8 %) and an increasing rate of hardness (40.9 %). This is because a higher SFE can enhance dislocation mobility, leading to an active rate of continuous DRX as well as discontinuous DRX. Consequently, the refinement of the recrystallized grains effectively assisted the hardening of the 30Mn weld after FSW. Hence, we concluded that SFE should be considered to improve the properties of TWIP steels after FSW.

Comparative study on mechanism of hydrogen embrittlement of Fe–18Mn-0.6C twinning-induced plasticity (TWIP) steel subjected to friction-stir welding (FSW) and tungsten inert-gas (TIG) welding

In present study, we investigated the effect of welding technique on resistance of hydrogen (H) embrittlement in Fe–18Mn-0.6C (wt.%) twinning-induced plasticity (TWIP) steel by using an electrochemical H-charging, thermal desorption spectroscope, and electron microscope. The friction-stir welding (FSW) specimen was less sensitive to H embrittlement relative to base metal and tungsten inert-gas (TIG) welding specimens by differences in microstructure and deformation mechanism. During H-charging of the FSW specimen, numerous dislocations/Σ3 boundaries reduced H diffusion into specimen interior, causing shallowest depth of brittle fracture. In contrast, the depth of brittle fracture in the H-charged TIG specimen was much larger due to rapid H diffusion by decreased grain boundaries including Σ3 annealing twin boundaries. During tensile deformation, the H-charged FSW specimen underwent the reduction in stress concentration by inactive TWIP as well as strong resistance of boundary decohesion. It was because of alleviation of H-enhanced localized plasticity (HELP) mechanism, leading to suppression of H-induced crack growth. Conversely, the H-charged base metal and TIG specimens revealed large stress concentration by active TWIP and weak boundaries owing to strong effects of HELP + H-enhanced decohesion (HEDE) mechanisms, exhibiting rapid H-induced crack propagation.