Grain Boundary Cohesion Research Articles

Grain boundary crystallography and segregation in Ni-based superalloy INC738 manufactured by electron-beam powder bed fusion in as-built and annealed conditions

The excellent high-temperature properties of Ni-based superalloy INC738 are due to its hierarchical microstructure, making it an ideal engineering material for high-temperature applications. Engineering parts are now increasingly made via electron beam powder bed fusion (EPBF), an additive manufacturing technique suitable for such hard-to-weld Ni-based superalloys, due to lower thermal gradients and unmatched scan path control. The thermal cycles induced by EPBF impact characteristics of the γ-matrix, γ’ precipitates, secondary phases such as carbides, grain boundary (GB) solute segregation and, in turn, properties including GB cohesion and strength. However, a more thorough understanding of the GB microstructure evolution with focus on GB chemistry and character is required to optimise properties. We systematically investigate texture, grain structure, GB habit planes, and GB segregation in INC738 fabricated with linear versus random EPBF scanning strategies. We show that random scanning is a suitable strategy to inhibit cracking, refine grains, and decrease segregation of Cr, Mo, C, and B at GBs. For both scanning strategies, γ/γ GBs predominantly terminate on {100} planes and are decorated with C, B, Mo, and W. Upon 2 h annealing at 1180 °C and 1250 °C, the GB character and texture are shown to remain stable despite a reduction in GB interfacial excess. After 24 h annealing at 1250 °C, GB segregation and depletion are nearly eradicated, while static recrystallisation is observed with a predominant formation of annealing twins and GBs terminating on {111} planes. These findings are critical for defect-free additive manufacturing of INC738 and similar grades for superior high-temperature performance.

Concurrent dramatic enhancement of high-temperature strength and ductility in a high-entropy alloy via chain-like dual-carbides at grain boundaries

Grain boundaries (GBs) are often known as intergranular cracking sources in alloys at high temperatures, resulting in limited high-temperature strength and ductility. Here, we propose a GB-dual-carbide (denoted as GB-DC) strengthening strategy and have developed a high-performance (NiCoFeCr)99Nb0.5C0.5 high-entropy alloy (HEA) with exceptional strength-ductility synergy at 1073 K. Chain-like coherent M23C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic (FCC) matrix during deformation. Nano-scale NbC particles are distributed alternatively between M23C6 carbides and inhibit their coarsening. Both strength and ductility of the GB-DC HEA increase dramatically at strain rates ranging from 10−4 to 10−2 s−1 at 1073 K, compared with those of the single-phase NiCoFeCr HEA. Specifically, yield strength of 142 MPa, ultimate tensile strength of 283 MPa, and elongation of 34 % were obtained, which are twice that of the reference NiCoFeCr HEA (82 MPa, 172 MPa, and 18 %, respectively). EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature, and TEM analysis revealed that dislocations can go through the coherent phase boundaries (CPBs) and activate dipoles inner M23C6 carbides, which weakened the stress concentration in GBs. This substantially reduces the critical stress for dislocation generation and transmission to a stress level lower than that required for intergranular fracture. Theoretical estimation suggests that carbides result in a much higher activation energy (∼510 kJ/mol) for GB sliding and a rather low interface energy (∼101 mJ/m2) compared with the GB energy (1000 mJ/m2), which rationalizes the enhanced GB cohesion by carbides.

The microcrack inhibition and mechanical properties of an in-situ synthesized refractory high-entropy alloy fabricated by additive manufacturing

A crack-free refractory high-entropy alloy (RHEA), composed of (Cr25Mo25Nb25V25)99C1 was synthesized in-situ from blended elemental powders using laser directed energy deposition (DED). This study revealed that a minor addition of carbon effectively enhances the grain-boundary cohesion of the DEDed RHEA, thereby mitigating microcrack propagation along the grain boundaries during the additive manufacturing process. Notably, the DEDed RHEA exhibited exceptional high-temperature mechanical properties, highlighted by a yield strength of 787 MPa at 1000 °C along with sustained strain-hardening capacity, surpassing other additively manufactured high-entropy alloys reported to date. The remarkable high-temperature strength of the DEDed RHEA can be attributed to the potent pinning effect exerted on dislocations within both dendritic and interdendritic regions at elevated temperature. This effect stems from severe lattice distortion, local chemical fluctuations (LCFs), solute atom pinning, and dislocation interactions. The method employed to inhibit microcrack formation, along with the elucidation of the high-temperature strengthening mechanism, opens avenues for the fabrication of RHEAs tailored for high-temperature structural applications.

Ultrafine-grained refractory high-entropy alloy with oxygen control and high mechanical performance

Grain boundary engineering plays a significant role in the improvement of strength and plasticity of alloys. However, in refractory high-entropy alloys, the susceptibility of grain boundaries to oxygen presents a bottleneck in achieving high mechanical performance. Creating a large number of clean grain boundaries in refractory high-entropy alloys is a challenge. In this study, an ultrafine-grained (UFG) NbMoTaW alloy with high grain-boundary cohesion was prepared by powder metallurgy, taking advantages of rapid hot-pressing sintering and full-process inert atmosphere protection from powder synthesis to sintering. By oxygen control and an increase in the proportion of grain boundaries, the segregation of oxygen and formation of oxides at grain boundaries were strongly mitigated, thus the intrinsic high cohesion of the interfaces was preserved. Compared to the coarse-grained alloys prepared by arc-melting and those sintered by traditional powder metallurgy methods, the UFG NbMoTaW alloy demonstrated simultaneously increased strength and plasticity at ambient temperature. The highly cohesive grain boundaries not only reduce brittle fractures effectively but also promote intragranular deformation. Consequently, the UFG NbMoTaW alloy achieved a high yield strength even at elevated temperatures, with a remarkable performance of 1117 MPa at 1200 °C. This work provides a feasible solution for producing refractory high-entropy alloys with low impurity content, refined microstructure, and excellent mechanical performance.

Enhanced grain boundary cohesion mediated by solute segregation in a dilute Mg alloy with improved crack tolerance and strength

Effects of solute segregation at grain boundaries (GBs) on the deformation mechanism and fracture behavior remain obscure for magnesium (Mg) alloys. Here, by introducing Zn segregation at GBs, we obtained an Mg-0.5Al-0.4Mn-0.2Ce-0.4Zn (wt.%) alloy achieving fracture elongation (FEL) of ∼33.6 %, with a remarkable FEL improvement by 100 % in comparison to Zn-free counterpart. Meanwhile, the tensile yield strength (TYS, 195.5 MPa) is increased by ∼27.5 MPa after trace Zn addition. Although trace Zn addition improves the fraction of GBs with high misorientation, it reconciles crack tolerance with enhanced strength. The introduction of Zn not only promotes pyramidal 〈c + a〉 slips and inhibits twinning nucleation, but also enhances the GB cohesion by Zn segregation. Based on in-situ microstructure observation, we found that the enhanced GB cohesion enables the segregation-inspired hierarchical crack buffering, as well as deflecting and branching. Enhanced GBs can also facilitate the continuous emission of 〈c + a〉 dislocations in neighboring grains irrespective of the onset of microcracks, forming a plastic zone to retard local strain concentration, thus avoiding microcrack percolation and attaining a crack-mediated elongation reserve of above 15 %. Besides, the higher TYS in the Zn-containing alloy mainly stems from the enhanced solid-solution strengthening of Zn solutes, thus achieving strength and crack tolerance synergy.

Evading the intermediate-temperature embrittlement of L12-strengthened high entropy alloys by alleviating intergranular oxidation

L12-strengthened high entropy alloys (HEAs) usually suffer from severe intermediate-temperature embrittlement. In this study, we revealed that the intermediate-temperature embrittlement of a (Ni2Co2FeCr)92Nb4Al4 L12-strengthened HEA originates from the severe oxidation of intergranular D019 precipitates which weakens the grain-boundary cohesion. With the minor addition of 1.5 at% Si, we successfully achieved a brittle-to-ductile transition in the alloy via alleviating intergranular oxidation. The alloyed Si preferentially partitioned into the intergranular precipitates, significantly improved their oxidation resistance and pinning effects on the grain boundaries, which effectively mitigated environmentally assisted grain-boundary damage and thus suppressed the crack propagation upon deformation.

First-principles study of oxygen segregation and its effect on the embrittlement of molybdenum symmetrical tilt grain boundaries

Elemental segregation can pronouncedly affect the cohesion of grain boundary (GB), which shows tremendous potential in altering the thermal stability and mechanical properties of metals. In this work, we systematically investigate the segregation behavior of oxygen (O) atoms at a series of GBs in molybdenum (Mo), using first principles calculations, to reveal the effect of O segregation on the embrittlement of Mo GBs. It is found that O atoms energetically prefer to segregate at sites in both the GB core and the vicinity of the GB plane. The strengthening energy is strongly associated with the GB structure, and it linearly decreases with the continuous deformation of the GB. O segregation can lead to an increase in the volume of polyhedron sites and a decrease in the charge density among adjacent Mo atoms across the GB plane. The weakened Mo-Mo bonds are believed to disrupt the GB cohesion, thereby increasing the intergranular cleavage tendency of Mo. Interestingly, O segregation does not always trigger GB embrittlement. The Σ5(310)[001] symmetric tilt grain boundary (STGB) with an O atom doped at the cap trigonal prism (CTP) site possesses a strength as strong as the clean GB. O segregation promotes the generation of Mo-O bonds across the GB plane, which counteracts the adverse effect of weakened Mo-Mo bonds. This work deepens the understanding of the possible effect of O segregation on GB cohesion of Mo from the atomic and electronic scales, providing guidance for enhancing the mechanical properties of Mo via GB structure optimization.

Grain boundary microstructure-property relationships in the cast & wrought Ni-based superalloy René 41 with boron and carbon additions

Cast & wrought Ni-based superalloys are required for manufacturing high-performance components in gas turbine engines. Their excellent high-temperature properties and corrosion resistance are brought about by their complex microstructure of a γ-matrix, intra- and intergranular γ' precipitates, carbides, and borides. The most highly-alloyed superalloy grades provide the high-temperature strength required for the design of next generation gas turbine engines but their processability remains challenging due to grain boundary (GB) cracking. A common mitigation approach is the addition of B and C to improve GB cohesion and strength. However, their detailed roles in GB segregation and precipitation and the link to GB properties during processing remains largely unexplored.We provide a systematic study on decorated GBs in the cast & wrought Ni-based superalloy René 41 with B and C additions. Tensile testing reveals that B additions reduce its ductility due to GB cracking but slow down grain growth during heat treatments more effectively, than C additions. GB-M2B, M6C, M23C6, and GB-γ' precipitates decorating GBs are sequentially precipitated. Their structures and compositions are shown to be unaffected by B and C additions. However, significant differences in the interfacial segregation of solutes are revealed. B is captured by GB-M2B and therefore unavailable to improve GB cohesion. C depletion and enrichment of solutes at interphase boundaries are identified as origin for the reduced ductility and thus, GB cracking. The findings are summarized as microstructural model and advance the detailed understanding of the processing – microstructure – properties relationships of cast & wrought Ni-based superalloys.

Effect of boron addition on the microstructure and cryogenic mechanical properties of N50 stainless steel after aging treatment

The effect of boron on the microstructure and cryogenic mechanical properties in N50 austenitic stainless steel after aging treatment was revealed by a comparative investigation of 0B and 25B (25 ppm) N50 steels. The results showed there is a large amount of irregular block and rod-like Cr2N precipitated along grain boundaries with intra-granular precipitation of lamellar Cr2N in 0B steel; nevertheless, the nucleation and growth of Cr2N were significantly suppressed in 25B steel. It is related to the retarded diffusion of Cr, Mo, and V atoms caused by the pre-occupied B atoms during the precipitation of nitride. Theoretical calculations verify that the high B segregation at grain boundaries is caused by both equilibrium and non-equilibrium segregation. The weakened precipitation of nitride and the enhanced cohesion of grain boundaries by segregated B synergistically suppress the initiation and extension of intergranular cracks. The impact toughness of 25B–N50 steel at both 77 K and 4.2 K can reach 200 J, which is about 2.5 times higher than that of 0B–N50 steel.

Nonmetallic trace elements induced rhenium co-segregation in nickel Σ5 [001](210) symmetrical tilt grain boundary

The thermally/mechanically-driven structural instability of nano- and coarse-grained polycrystalline metals originates from the unstable grain boundaries (GBs). GB segregation of solute elements could not only stabilize but also embrittle GBs. To improve GB stability and cohesion in parallel via solute segregations, in this work the segregation behavior of six non-metallic impurities X at the Σ5 [001](210) GB of nickel-based alloys, their co-segregations with Re element that has no GB segregation tendency, and segregation-induced changes in GB properties were investigated comprehensively from first-principles calculations. We discovered that these nonmetallic elements can segregate to the Ni GB and thus stabilize it, but they are GB embrittlers except B. Annealing temperature and bulk concentration have no effect on the S segregation. With the X pre-segregations, induced GB segregations of Re were observed, which lowers the excess energy and enhances the cohesive strength of all X-segregated GBs. The attractive interactions between C/N/B and Re atoms promote the Re segregation. The stabilizing and strengthening mechanisms of Re segregation were mainly attributed to the changes in Fermi level location and the increased interplanar bonding, respectively. Our findings may gain more insights into the atomic-scale GB co-segregations and stabilization of polycrystalline Ni-based alloys.

Interstitial Segregation has the Potential to Mitigate Liquid Metal Embrittlement in Iron.

The embrittlement of metallic alloys by liquid metals leads to catastrophic material failure and severely impacts their structural integrity. The weakening of grain boundaries (GBs) by the ingress of liquid metal and preceding segregation in the solid are thought to promote early fracture. However, the potential of balancing between the segregation of cohesion-enhancing interstitial solutes and embrittling elements inducing GB de-cohesion is not understood. Here, the mechanisms of how boron segregation mitigates the detrimental effects of the prime embrittler, zinc, in a Σ5 [001] tilt GB in α-Fe (4 at.% Al) is unveiled. Zinc forms nanoscale segregation patterns inducing structurally and compositionally complex GB states. Ab initio simulations reveal that boron hinders zinc segregation and compensates for the zinc-induced loss in GB cohesion. The work sheds new light on how interstitial solutes intimately modify GBs, thereby opening pathways to use them as dopants for preventing disastrous material failure.

Atomic-scale understanding of solute interaction effects on grain boundary segregation, precipitation, and fracture of ultrahigh-strength maraging steels

Understanding the fundamental mechanisms of embrittlement and de-embrittlement is crucial for the development of strategies toward advanced steels with improved performance. In this study, the solute interaction effects on grain boundary (GB) segregation, precipitation, and fracture of Fe–Ni–Ti–(Mo) maraging steels were systematically investigated through a combination of experimental and theoretical techniques, including scanning transmission electron microscopy, atom probe tomography, and first-principles calculations. Our results reveal that the Fe–Ni–Ti maraging steel suffers from serious intergranular embrittlement and the mechanism is related to the formation of coarse Ni3Ti precipitates and associated precipitate-free zones (PFZs) at GBs, which facilitate the crack initiation and growth along the GBs. Interestingly, adding Mo to the maraging steel effectively suppresses the intergranular embrittlement, thereby substantially improving the ductility. Atomistic analyses reveal that Mo de-embrittles the GBs by reducing the segregation of Ni and Ti, which substantially inhibits the formation of coarse Ni3Ti precipitates and PFZs at the GBs, thereby alleviating their harmful impact on the GB cracking. In addition, the Mo segregation enhances the GB cohesion, which may play a minor role in suppressing the GB fracture.

Synergistic effects of Nb and Mo on hydrogen-induced cracking of pipeline steels: A combined experimental and numerical study

The synergistic effects of Nb and Mo on hydrogen-induced cracking (HIC) of pipeline steels were studied experimentally and numerically. The results showed that Mo was primarily segregated at grain-boundaries (GBs) or solid-dissolved in the matrix, while most Nb and a small amount of Mo formed dispersed (Nb,Mo)C nano-precipitates and refined the microstructure. Compared with Nb alloying, the multiple additions of Nb-Mo played dual roles in affecting H diffusion: primarily, the H-traps densities such as GBs, precipitates, and solute Mo atoms increased, providing an advantage; however, Mo slightly reduced the H-trapping capacity of precipitates, playing an adverse role. Nonetheless, the beneficial effects far outweighed the adverse effects, thereby reducing H diffusivity and inhibiting crack initiation. Additionally, Nb and Mo hindered crack propagation synergistically as follows: (i) Mo enhanced GB cohesion by repelling H, impeding intergranular cracking and hydrogen-enhanced decohesion (HEDE); (ii) Nb reduced the proportion of Σ3/high-angle grain boundaries, increasing cracking resistance; (iii) (Nb,Mo)C precipitates impeded H-dislocation interactions, reducing the hydrogen-enhanced localized plasticity (HELP).

Effect of anisotropy and slip transfer on hydrogen-assisted cracking of a 2205 duplex stainless steel: A critical analysis

Duplex Stainless Steels (DSSs) for engineering applications usually show dual-phase microstructure with directional phase distribution and considerable crystallographic texture. Here, we investigate the effect of anisotropy on the Hydrogen Embrittlement (HE) susceptibility of a 2205 DSS. Moreover, slip transfer across Grain Boundary (GB) is experimentally and theoretically analyzed. The specimen sampling along 45° Rolling Direction (RD) showed remarkable HE resistance owing to the delayed initiation and slow evolution of microcracks. Hydrogen-Assisted Cracks (HACs) frequently initiated at the austenite GBs, because the synergistic interactions between hydrogen-enhanced planar slip and slip transfer across GB promote stress/hydrogen accumulation and reduce the GB cohesion.

Trace Ce addition for inhibiting Bi segregation induced embrittlement in ultrahigh-purity copper

Bismuth (Bi), as an impurity element in copper and copper-based alloys, usually leads to the catastrophic intergranular fracture even with a ppm concentration. However, the intrinsic mechanisms of the embrittlement remain largely unclear and the control of such a brittleness has been rarely reported. Here, we investigate the influence of trace amounts of Bi on the ductility of ultrahigh-purity copper (99.99999%) at temperatures between room temperature (RT) and 900 °C. On this basis, the ductility improvement of CuBi alloy by adding different concentration of Ce is also systematically studied. Compared to the ultrahigh-purity copper, the Bi-containing alloy exhibits a remarkable decrease in ductility, with the severe reduction occurs at 450–900 °C. This is caused by the grain boundary (GB) segregation of Bi layers, which reduces the GB cohesion because of the weak BiBi bonds. However, after trace Ce are added, the ductility of CuBi alloy in the temperature range of 450–900 °C is significantly increased. The obvious enhancement is due to the reaction behavior of Ce and Bi to form the precipitated phases, as well as the preferential segregation of Ce to GBs and phase boundaries, which change the existing form of Bi in copper. Our findings provide a comprehensive understanding on the microstructural origin of Bi-induced GB embrittlement and an effective way for inhibiting such an embrittlement.

First-principles study of the effect of N on the ∑5 (210) [001] grain boundary of γ-Fe

High-nitrogen austenitic steels possess excellent properties owing to the solid solution strengthening of nitrogen, which is widely used in many fields. So it’s significant to investigate the effect of nitrogen on the properties of high austenitic nitrogen steels. In order to get atomic scale understanding of the influence of nitrogen, the first principles method was used to investigate the energetics, site preference, and segregation of nitrogen at γ-Fe ∑5 (210) [001] grain boundary (GB) and different atomic layers near GB plane. It is found that the nitrogen atom prefers to occupy the octahedral site. As nitrogen locates at different atomic layers away from the GB plane, the segregation energy presents increase first and then decrease. The mechanical properties were analyzed by Rice-Wang theory and theoretical tensile stress test, which shows that nitrogen at ∑5 (210) [001] GB has an embrittling effect on GB cohesion, while nitrogen located away from the GB plane presents a strengthening effect. The underlying mechanism was analyzed by bond length, charge density, and density of states (DOS). The segregation of nitrogen at ∑5(210) [001] grain boundary has negative effect on grain boundary cohesion, while nitrogen locating away from grain boundary plane presents strengthening effect on grain boundary.

Enhancement of ballistic performance enabled by boron-doping in subzero-treated (ferrite+austenite+martensite) triplex lightweight steel

Investigations of dynamic deformation and ballistic performance of ultra-high-strength lightweight steels for steel armor applications have not been conducted to date. In this study, effects of boron(B)-doping on ballistic performance were explored in subzero-treated Fe-0.3C-9Mn-5Al and Fe-0.3C-9Mn-5Al-0.005B (wt%) lightweight steels in relation to band structures and B segregation. The dynamic deformation and adiabatic shear band (ASB) formation behaviors were examined by a Hopkinson pressure bar (SHPB). The band structure is critical in inhibiting ASB propagation, as it is continuously blocked at tempered-martensite/ferrite boundaries. The crack propagates along the embrittled ASB and penetrates into tempered-martensite/ferrite boundaries, producing delamination of elongated grains in the undoped steel. On the other hand, the delamination does not occur in the B-doped steel because the segregation of solute B at prior austenite grain boundaries enhances the grain-boundary cohesion. Thus, the B-doped steel outperforms conventional rolled homogeneous armor steels and the undoped steel as well, providing a significant deal of potential for developing excellent ballistic-performance lightweight steel armors.

Corrosion mechanism of lead-bismuth eutectic at grain boundary in ferritic steels and the effect of alloying elements: A first-principles study

In this study first-principles calculations are used to investigate the corrosion mechanism of liquid metal embrittlement (LME) by lead-bismuth eutectic (LBE) at grain boundary (GB) in ferritic steels using BCC Fe Σ5 (013) GB. The effects of two important alloying elements (Nb and V) on the LBE corrosion are also considered. Our results show that Pb and Bi are prone to permeation along the GB. Pb and Bi in Fe GB will induce GB expansion and form weak bonds, and thus weaken the GB cohesion, inducing a significant decrease in work of separation and maximum GB strength. Our studies also show that the LME sensitivity of Bi is greater than that of Pb, which is consistent with the experimental results. Furthermore, Nb and V are found to have a hindering effect on the crack generation caused by Pb and Bi, and can somehow improve the ability against the LBE corrosion. Our theoretical study provides a fundamental understanding of LBE corrosion mechanism in ferritic steels and can serve as the foundation for improving ferritic steels through alloying elements.

Influence mechanism of boron segregation on the microstructure evolution and hot ductility of super austenitic stainless steel S32654

• B improves hot ductility of S32654 at 850–1150 °C but worsens that at 1200–1250 °C. • B segregation at GB detected by APT was the main reason affecting hot ductility. • B segregation inhibits Mo segregation and then σ phase precipitation at 900–950 °C. • B segregation promotes nucleation and inhibits growth of DRX grain at 1100–1150 °C. • B segregation enhances the liquefaction cracking tendency at 1200–1250 °C. Influence mechanism of B segregation on the microstructure evolution and hot ductility of S32654 at 850–1250 °C was systematically investigated through experimental research and theoretical calculation. The results demonstrated that the segregation of B at grain boundary (GB) played different roles in the microstructure evolution and hot ductility at various temperatures. At 850 °C, B segregation inhibited Mo segregation at the GB and enhanced the GB cohesion. At 900–950 °C, B segregation restricted the diffusion and segregation of Mo to the GB, inhibiting the precipitation of σ phase. At 1000–1050 °C, B segregation accelerated the dislocation accumulation and limited the GB migration, promoting the nucleation and inhibiting the growth of DRX grains. At 1100–1150 °C, B has little effect on the DRX due to sufficient energy supply by higher temperature. Under the above beneficial effects of B, the hot ductility of S32654 was improved to varying degrees at 850–1150 °C. However, as the temperature increased to 1200–1250 °C, B segregation decreased the solidus temperature and enhanced the liquefaction cracking tendency, resulting in a deterioration of the hot ductility.

Hydrogen assisted intergranular cracking of alloy 725: The effect of boron and copper alloying

To overcome the Hydrogen embrittlement (HE) susceptibility of the standard Alloy 725 (Mod A), two alloys with minor alloying modifications with B (Mod B) and B+Cu (Mod C) were produced. Then, the intergranular cracking susceptibility was investigated on bi-crystal beams by electrochemical in situ micro-cantilever bending test. The atom probe tomography and first principles calculations were employed to capture and calculate the grain boundary (GB) segregation and its effect on the GB cohesion. Cross-sectional view of the bent beams showed the superior resistance of Mod B against HE by facilitating the GB dislocation transfer/generation. While bending Mod A sample in hydrogen environment leads to form a sharp intergranular cracking, Mod B showed some nano-voids/cracks mostly in dislocation slip bands and rarely in GB path. However, a reduction of strength was observed in load-displacement (L-D) curves of Mod B. The addition of Cu, although not participated in GB segregation, compromised the lost strength of Mod B. In Mod C, after bending in H-charged condition, the nano-voids were formed in GB, but no load drop in L-D curves nor crack propagation in post-deformation observations was detected. The micro-alloying proposed in this study could be an important contribution to the future developing of H resistant alloys via GB segregation engineering.