Fraction Of Grain Boundaries Research Articles

Plastically heterogeneity-driven fracture in additive manufactured steels

Tuning the fracture evolution to resist crack propagation by engineering microstructures is effective for enhancing the toughness of metals. However, many microstructures produced through existing traditional technologies cannot overcome the dilemma known as the strength-toughness trade-off in metals. Here, we report a plastically heterogeneity-driven fracture manner affected by the unique microstructures in additive manufactured (AM) 316L stainless steels that endows a superior combination of strength and toughness, surpassing the conventional 316L steels. The good toughness is due to the natural heterogeneous microstructural arrangement of coarse-grain (CG) and fine-grain (FG) zones in the AM steel. Plasticity is typically initiated within FG zones with a larger fraction of high-angle grain boundaries (HAGBs). In contrast, the CG zones are less susceptible to plasticity localization before the full strain hardening capacity of the FG zones is exploited. It results in strong strain/stress partitioning and regional hardening processes, providing mesoscale soft-hard barriers to crack propagation. In addition, the low-angle grain boundaries (LAGBs) and dislocation cells at the microscale are demonstrated to strengthen the matrix uniformly without introducing stress concentration and damage incidents detrimentalto toughness. This work demonstrates the extensive engineering application prospect of AM steels and the potential of the line-by-line or layer-by-layer build strategies for developing more fracture tolerate AM steels.

An experimental and numerical study on strain controlled fatigue response of TRIP steel under influence of hydrogen

The present work aims to study the influence of hydrogen charging on the transformation induced plasticity steel under strain-controlled low cycle fatigue (LCF). Hydrogen charging had detrimental effect on strain-controlled LCF lives. Cyclic hardening in un-charged specimen due to strain-induced martensitic transformation (SIMT) dominated over cyclic softening. In contrast, generation of large fraction of low angle grain boundaries in hydrogen charged specimen leads to cyclic softening and supresses cyclic hardening due to SIMT. Additionally, Cyclic plasticity modelling using Ohno-Wang kinematic hardening model is validated by simulating cyclic stress–strain hysteresis loop and cyclic softening curve of uncharged and hydrogen charged specimens.

Accelerated phase growth kinetics during interdiffusion of ultrafine-grained Ni and Sn

The phase growth is investigated during the interdiffusion of an ultra-fine grained Ni (UFG) (grain size, d ∼ 320 nm) and coarse-grained Sn diffusion couple in the temperature range of 175–215 °C. The UFG Ni was produced through spark plasma sintering (SPS) of ball-milled Ni powder. Formation of only Ni3Sn4 intermetallic phase is observed, as confirmed by electron probe microanalysis (EPMA), micro-x-ray diffraction (XRD), and Transmission Kikuchi Diffraction (TKD) measurements. Using the CALPHAD approach, the driving forces for the formation of possible intermetallic phases in the Ni-Sn system were estimated and the highest value was found for Ni3Sn4, which matches the experimental observations. Time-dependent measurements at 200 °C revealed an acceleration in the growth (∼2 orders of magnitude) of Ni3Sn4 compared to the scenario prevalent in the coarse-grained (CG) Ni/Sn diffusion couple. This is reflected in the calculated integrated diffusivities for the UFG-Ni/Sn diffusion couple. The accelerated phase growth kinetics are attributed to the increased fraction of grain boundaries (GBs) in the UFG-Ni, which leads to an increased contribution of GB diffusion to the overall diffusion flux. The formation of Ni3Sn4 at GB was further ascertained using correlative microscopy strategy including transmission electron microscopy, transmission Kikuchi diffraction and scanning transmission electron microscopy.

Elucidating the deformation behavior of as-cast B2 CoTi intermetallic using in-situ tensile testing

This study deals with microstructural aspects of the deformation behavior of as-cast homogenized CoTi intermetallic by using in-situ tensile testing coupled with EBSD analysis. CoTi exhibits excellent wear resistance and noticeable room temperature ductility. Therefore, it is commonly used as coating material or a reinforcing phase in superalloys. In-situ study of this intermetallic is pertinent as it will provide information about the microstructural evolution during deformation under tensile loading. During the initial stage of deformation, the plastic strain localization was observed to occur at softer grains due to the activation of {011}⟨100⟩ slip systems, which resulted in the accumulation of GNDs and increase in fLAGBs (fraction of low angle grain boundaries). However, fLAGBs did not increase significantly at higher strains. In addition, the contribution of texture towards deformation behavior was found to be weak. The intermetallic exhibited a mixed-mode failure, where both transgranular and intergranular features were observed on the fracture surface. A slightly higher strain to failure in the intermetallic has been attributed to both the increase in the GNDs density at the initial stage of deformation and increase in SSDs at the later stage of deformation, leading to strain hardening.

A two-scale thermo-mechanically coupled constitutive model for grain size- and rate-dependent deformation of nano-crystalline NiTi shape memory alloy

In this paper, a two-scale thermo-mechanically coupled constitutive model is established to predict the grain size (GS)- and rate-dependent deformation of nano-crystalline super-elastic NiTi shape memory alloy (SMA). At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains. Owing to the relatively large volume fraction (VF) of grain boundary in nano-crystalline NiTi SMA, an individual grain is further considered as a composite containing the grain interior (GI) and grain boundary (GB) phases. For the GI phase, a crystal plasticity-based model accounting for the internal heat generation is developed through the fundamental laws of irreversible thermodynamics. The constraint of GB phase on the martensite transformation in the GI phase is considered by introducing a scaling law between the transformation hardening modulus (THM) and GS. Owing to its un-transformable nature and relatively high yielding stress, the GB phase is assumed to behavior constitutively linear thermo-elasticity. To evaluate the thermo-mechanical interactions among the grains, GI phase and GB phase, and obtain the overall response of the polycrystalline RVE, a double inclusion self-consistent homogenization scheme involving the material nonlinearity and thermo-mechanical coupling effect is developed in an incremental form. At the macroscopic scale, the overall thermo-mechanical responses for the specimen of nano-crystalline NiTi SMA are obtained by solving the equations of force balance, deformation compatibility, and thermodynamic equilibrium through an approximation method. Finally, considering the specific texture measured in experiments, the proposed model is validated by predicting the GS- and rate-dependent deformation of nano-crystalline NiTi SMA sheet. Furthermore, the anisotropic thermo-mechanical responses of the sheet caused by the texture are predicted and discussed.

Chemical inhomogeneity inhibits grain boundary fracture: A comparative study in CrCoNi medium entropy alloy

Grain boundary (GB) fracture is arguably one of the most important reasons for the catastrophic failure of ductile polycrystalline materials. It is of interest to explore the role of chemical distribution on GB deformation and fracture, as GB segregation becomes a key strategy for tailoring GB properties. Here we report that the inhomogeneous chemical distribution effectively inhibits GB fracture in a model CoCrNi medium entropy alloy compared to a so-called ‘average-atom’ sample. Atomic deformation kinematics combined with electronic behavior analysis reveals that the strong charge redistribution ability in chemical disordered CrCoNi GBs enhances shear deformation and thus prevents GB crack formation and propagation. Inspects on the GBs with different chemical components and chemical distributions suggest that not only disordered chemical distribution but also sufficient “harmonic elements” with large electronic flexibility contribute to improving the GB fracture resistance. This study provides new insight into the influence mechanism of GB chemistry on fracture behavior, and yields a systematic strategy and criterion, from the atoms and electrons level, forward in the design of high-performance materials with enhanced GB fracture resistance.

An Attempt to Understand Stainless 316 Powders for Cold-Spray Deposition

Cold gas dynamic spray (CS) is a unique technique for depositing material using high-strain-rate solid-state deformation. A major challenge for this technique is its dependence on the powder’s properties, and another is the lack of standards for assessing them between lots and manufacturers. The motivation of this research was to understand the variability in powder atomization techniques for stainless steel powders and their subsequent properties for their corresponding impacts on CS. A drastic difference (~30%) was observed in the deposition efficiencies (DEs) of unaltered, spherical and similar sized stainless steel (316) powders produced using centrifugal (C.A) and traditional gas atomization (G.A) techniques. The study highlights more the differences on a precursor level. Using recent advancements in large scale statistical measurements, such as laser diffraction shape analysis and µCT scanning; and traditional methods, such as EBSD and nanoindentation, an attempt was made to understand the powder’s properties. Insights on powder size and shape were documented. Significant differences were observed between C.A and G.A powders in terms of grain size, fraction of high-angle grain boundaries (HAGBs) and nanohardness. The outcomes of this study should be helpful for understanding the commercialization of the cold-spray process for bulk manufacturing of powder precursors.

Effect of deformation degree on microstructure and mechanical properties evolution of TiBw/Ti60 composites during isothermal forging

AbstractIn order to investigate the influence of deformation degree on microstructure and mechanical properties during hot compression, TiB whiskers reinforced Ti60 composites were subjected to isothermal forging at 1030 °C and strain rate of 1×10−2 s−1 under 30%, 50%, and 70% deformation degrees. The results showed that with strain increasing, the fraction of high angle grain boundaries (HAGBs) significantly increased to 71.47% at 70% deformation degree, and the texture components of αs colonies gradually became dominant due to the enhanced recrystallization efficiency. TiB can promote nucleation of recrystallized grains and impede grain growth. After isothermal forging, the mechanical properties of composites at both RT and 600 °C were improved, and the specimen compressed at 50% deformation degree showed the best tensile strength and elongation. During tensile tests, the TiB whiskers can bear the load transmitted from surrounding matrix, showing strengthening effect on the material.

Compressive properties of a severely deformed fine-grained Mg−6Gd−3Y alloy

An extruded Mg−6Gd−3Y alloy was processed by 6 passes of simple shear extrusion (SSE) at 553 K to refine the microstructure. The microstructural studies were performed through electron back-scattered diffraction (EBSD) and also transmission electron microscopy (TEM) to investigate the microstructural features which emerged after SSE. It was revealed the SSE-processed alloy had a duplex microstructure containing both fine dynamically recrystallized (DRX) grains and some large deformed grains. A relatively high fraction of low angle grain boundaries (LAGBs), induced within the un-DRXed deformed grains, was identified by EBSD results. TEM studies revealed the formation of round Mg5Gd-type nano-particles through dynamic precipitation only in the DRXed regions of microstructure in the SSE-processed alloy. Compressive mechanical properties and strain hardening behavior of the alloys were assessed by compression testing of both alloys at room temperature. SSE processing resulted in enhanced yield stress and reduced ductility. Both the extruded and SSE-processed alloys exhibited a three-stage strain hardening behavior with a much more pronounced stage II of hardening in the latter one. According to the mechanical properties results, there was a noticeable difference in the strain hardening rate and also dislocation storage rate of the extruded and SSE-processed alloys. This discernible strain hardening behavior of the two alloys was attributed to the formation of fine DRXed grains, dynamic precipitation of nano-sized Mg5Gd particles, and induction of LAGBs, which emerged after SSE.

Effect of molybdenum partitioning on the evolution of microstructure, grain boundary constitution and corrosion behaviour of electrodeposited zinc-molybdenum coatings

Effect of compositional partitioning on microstructural evolution and corrosion behaviour of Zn-Mo coatings (Mo: 2.8 – 6.5 wt%) electrodeposited on mild steel substrate has been explored. Corrosion resistance of Zn coating increased with Mo addition until an optimum addition (Zn-4.2 wt% Mo) beyond which it decreased for higher Mo content (Zn-6.5 wt% Mo). The corrosion current density (icorr) values for pure Zn, Zn-2.8 wt% Mo, Zn-4.2 wt% Mo, Zn-6.5 wt% Mo coating was 17 μA/cm2, 12.25 μA/cm2, 7.5 μA/cm2, 14.2 μA/cm2 respectively. Incorporation of Mo resulted in the formation of Zn-Mo solid solution and Zn3Mo2 compound phases along with segregation of Mo at Zn grain boundaries. High corrosion resistance of Zn-4.2 wt% Mo coating was due segregation of Mo at Zn grain boundaries, higher fraction of low angle grain boundaries and coincidence site lattices when compared to the pristine Zn coating. Lower corrosion resistance of Zn-6.5 wt% Mo coating was primarily due to higher coating strain because of the solid solution of Mo in Zn and formation of Zn3Mo2 particles in the coating matrix.

Grain size effects on high cycle fatigue behaviors of pure aluminum

Friction stir processing (FSP) was used to prepare coarse-grained (CG), fine-grained (FG), and ultrafine-grained (UFG) materials to investigate the grain size effects on high cycle fatigue properties. A linear relationship similar to the Hall-Petch relationship was acquired between the fatigue strength and grain size. Excellent grain boundaries stability in FSP UFG material inhibited the formation of large-scale shear bands and grain growth, which contributed to higher fatigue strength exponent and fatigue damage resistance. Compared with other UFG materials, increasing the fraction of high angle grain boundaries can significantly improve the fatigue strength.

The effect of build orientations on mechanical and thermal properties on CuCrZr alloys fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) is a kind of popular additive manufacturing process to fabricate sophisticated components in recent years. However, it is still challenging to fabricate copper alloys due to excellent thermal properties and high reflective to laser beams during LPBF process. As such, green laser beam has been employed in present work to fabricate copper-chromium-zirconium (CuCrZr) alloys in present work. To enhance performance, post-heat-treatment was employed on the alloys. The mechanical properties in present work are superior to most of LPBF-built CuCrZr alloys using conventional infrared laser. So far, most of studies about additive manufactured (AM-ed) CuCrZr alloys only focus properties of alloys perpendicular to build directions. Hence, the mechanical properties and thermal properties of LPBF-built alloys along different build orientations were investigated. The slender columnar grains were observed. Nevertheless, heat-treated samples along transverse directions own better mechanical properties (yield strength (YS): 505 MPa, ultimate tensile strength (UTS): 585 MPa, Elongation (EL): 14.4%) and better thermal properties (307 W/mK). While the heat-treated samples along build directions own lower strength (YS: 472 MPa, UTS: 495 MPa) with better ductility (EL: 17.8%) and poor thermal conductivity (255 W/mK). The mechanical and thermal anisotropy attributes the stronger {110} grain orientation and lower fraction of low angle grain boundaries (LAGBs) along build directions due to the columnar structure with fine equiaxed grains.

Densification, Microstructure and Anisotropic Corrosion Behavior of Al-Mg-Mn-Sc-Er-Zr Alloy Processed by Selective Laser Melting

High-performance additives manufactured by Al alloys provide significant potential for lightweight applications and have attracted much attention nowadays. However, there is no research on Sc, Er and Zr microalloyed Al alloys, especially concerning corrosion behavior. Herein, crack-free and dense Al-Mg-Mn-Sc-Er-Zr alloys were processed by selective laser melting (SLM). After optimizing the process parameters of SLM, the anisotropic corrosion behavior of the sample (volume energy density of 127.95 J·mm−3) was investigated by intergranular corrosion (IGC) and electrochemical measurements. The results showed that the XY plane of the as-built sample is less prone to IGC, and it also has a higher open circuit potential value of −901.54 mV, a higher polarization resistance of 2.999 × 104 Ω·cm2, a lower corrosion current of 2.512 μA·cm−2 as well as passive film with superior corrosion resistance compared to the XZ plane. According to our findings, the XY plane has superior corrosion resistance compared to the XZ plane because it has fewer primary phases of Al3(Sc, Er, Zr) and Al2MgO4, which can induce localized corrosion. Additionally, a higher fraction of low-angle grain boundaries (LAGBs) and a stronger (001) texture index along the building direction are also associated with better corrosion resistance of the XY plane.

Additive manufacturing of pure niobium by laser powder bed fusion: Microstructure, mechanical behavior and oxygen assisted embrittlement

In this study, pure niobium (Nb) was additive manufactured by laser powder bed fusion (LPBF). The effect of energy density and oxygen content on the densification behavior, microstructure and mechanical properties of the LPBF-built Nb were investigated. It was demonstrated that the density steadily increased and the pores were gradually eliminated with the increase of energy density. A maximum density of 99.7% was achieved at the energy density of 146 J/mm3. Further increase of energy density led to an intense Marangoni convection and a slightly decrease of density. The average grain size of the LPBF-built Nb was 70 μm approximately. A large fraction of low-angle grain boundaries and a high density of dislocations were observed in the LPBF-built Nb. The ultimate tensile strength (UTS) of the LPBF-built Nb increased steadily with the increase of energy density due to the increment of density. The fine grains and high-density dislocations resulted in high strength of the LPBF-built Nb. The maximum yield strength and UTS were as high as 550 MPa and 630 MPa respectively with a considerable elongation of 26%. Oxygen deteriorated the mechanical properties of the LPBF-built Nb significantly. The increase of oxygen enhanced the tensile strength of Nb and reduced its plasticity significantly. The LPBF-built Nb became brittle when the oxygen content increased from 0.05 wt % to 0.23 wt %. The elongation to fracture of the LPBF-built Nb decreased to less than 2% regardless of the input energy density. It was proposed that the interstitial oxygen atoms exert a repulsive force on the dislocation and block its movement, leading to a sharp decrease in the plasticity of LPBF-built Nb.

Influence of Aging Temperature on Mechanical Properties and Structure of M300 Maraging Steel Produced by Selective Laser Melting.

This paper deals with the study of high-strength M300 maraging steel produced using the selective laser melting method. Heat treatment consists of solution annealing and subsequent aging; the influence of the selected aging temperatures on the final mechanical properties-microhardness and compressive yield strength-and the structure of the maraging steel are described in detail. The microstructure of the samples is examined using optical and electron microscopy. The compressive test results show that the compressive yield strength increased after heat treatment up to a treatment temperature of 480 °C and then gradually decreased. The sample aged at 480 °C also exhibited the highest observed microhardness of 562 HV. The structure of this sample changed from the original melt pools to a relatively fine-grained structure with a high fraction of high-angle grain boundaries (72%).

Enhancing mechanical properties of ultrafine-grained tungsten for fusion applications

Tungsten, while showing many favorable properties, faces challenges in high-performance applications due to its brittle nature. One strategy to improve strength and toughness in tungsten is to refine the grain size down to the ultra-fine grained (ufg) regime. However, as the grain size is reduced, the fraction of grain boundaries that provide easy paths for crack growth increases, thereby limiting the gain in ductility. Therefore, strengthening the grain boundaries is of great importance if one wants to tap the full potential of this material. Using ab-initio calculations, potential grain boundary cohesion enhancing doping elements were identified, and doped ultra-fine grained tungsten samples were fabricated from powders and characterized extensively using small-scale testing techniques. We found that additions of boron and hafnium improve the mechanical properties of tungsten remarkably. Furthermore, an additional low-temperature heat treatment of the boron-doped sample promotes grain boundary segregation, enhancing the properties even further. Thus, in this work we provide an effective pathway of improving mechanical properties in ultra-fine grained tungsten using grain boundary segregation engineering. This opens the door for many challenging applications of ufg W in harsh environments. To further underline the potential employment of ufg W in nuclear fusion reactors, a favorable swelling behavior and mechanical property response after irradiation with helium is presented within this work.

Twin-Related Grain Boundary Engineering and Its Influence on Mechanical Properties of Face-Centered Cubic Metals: A Review

On the basis of reiterating the concept of grain boundary engineering (GBE), the recent progress in the theoretical models and mechanisms of twin-related GBE optimization and its effect on the mechanical properties is systematically summarized in this review. First, several important GBE-quantifying parameters are introduced, e.g., the fraction of special grain boundaries (GBs), the distribution of triple-junctions, and the ratio of twin-related domain size to grain size. Subsequently, some theoretical models for the GBE optimization in face-centered cubic (FCC) metals are sketched, with a focus on the model of “twin cluster growth” by summarizing the in-situ and quasi-in-situ observations on the evolution of grain boundary character distribution during the thermal-mechanical process. Finally, some case studies are presented on the applications of twin-related GBE in improving the various mechanical properties of FCC metals, involving room-temperature tensile ductility, high-temperature strength-ductility match, creep resistance, and fatigue properties. It has been well recognized that the mechanical properties of FCC materials could be obviously improved by a GBE treatment, especially at high temperatures or under high cyclic loads; under these circumstances, the materials are prone to intergranular cracking. In short, GBE has tremendous potential for improving the mechanical properties of FCC metallic materials, and it is a feasible method for designing high-performance metallic materials.

The microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy during the reciprocating extrusion process (REP)

In this paper, the microstructure and texture evolution of Mg-5Sn-1Si-0.8Y alloy fabricated by reciprocating extrusion process (REP) at 340 ℃ for 2–8 passes is characterized by optical microscopy (OM), Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD).The results show that the microstructure was refined significantly, dynamic recrystallization (DRX), fragmentation of the second Mg2Si phase and precipitation of the Mg2Sn phase occurred during REP. With the increase of the REP passes, the fraction of low angle grain boundaries (LAGBs) showed a decreasing trend and the secondary phases distribution became more and more homogeneous and the degree of DRX was increased. At the same time, the initial extruded fiber basal texture was gradually weakened and became random as the REP passes increases. The hardness of the alloy also shown an increasing trend with the increase of REP passes. The grain refinement mechanism, texture evolution and increase of hardness were mainly related to the dynamic recrystallization and the particle stimulation nucleation (PSN) effect of the second phases.

Detail characterization on the microstructure evolution of nickel-base alloy 600MA via surface mechanical attrition treatment

Microstructure evolution of alloy 600MA was explored after surface mechanical attrition treatment (SMAT) with different durations via scanning electronic microscopy, electron backscattered diffraction, transmission electron microscopy and transmission Kikuchi diffraction. The grain refinement and coarsening occurred gradually as strain accumulated with increasing SMAT time. During grain refinement, the initiation and development of dislocation walls or cells came up at early stage. A strip of dislocation wall led to straight element concentration just prior to the formation of ultrafine-laminated (UFL) structures containing abundant twin boundaries (TB) and low angle grain boundaries (LAGB). The UFL structures with a texture orientation were subdivided by the development of dislocation arrays into ultrafine-grained (UFG) structures with random orientations. Meanwhile, the elements were dispersedly concentrated in a few grains. During grain coarsening, the dispersed element concentration still existed. The fraction of LAGB, TB and dislocation density was significantly reduced while the fraction of high angle grain boundary (HAGB) increased along with grain growth. • The grain refinement and coarsening occurred gradually as strain accumulated with increasing SMAT time. • During grain refinement, the initiation and development of dislocation walls or cells came up at early stage. • A strip of dislocation wall led to straight element concentration just prior to the formation of ultrafine-laminated (UFL) structures containing abundant twin boundaries (TB) and low angle grain boundaries (LAGB). • The UFL structures with a texture orientation were subdivided by the development of dislocation arrays into ultrafine-grained (UFG) structures with random orientations. • During grain coarsening, the fraction of LAGB, TB and dislocation density was significantly reduced while the fraction of high angle grain boundary increased along with grain growth.

An extraordinary-performance gradient nanostructured Hadfield manganese steel containing multi-phase nanocrystalline-amorphous core-shell surface layer by laser surface processing

• Gradient nanostructured layer on austenitic Hadfield manganese steel was fabricated by laser surface remelting technique. • Gradient refinement transits from dislocations activities and twinning in sub-region to three kinds of martensitic transformations, and finally a multi-phase nanocrystalline-amorphous core-shell structural surface. • The multi-phase nanocrystalline-amorphous core-shell structural surface with average grain size of ∼ 8 nm is obtained. • The core-shell structural surface exhibits tensile strength of ∼ 1.6 GPa, micro-pillar compressive strength of ∼ 4 GPa at a strain of ∼ 8% and nanoindentation hardness of ∼ 7.7 GPa. • Dislocation activities are kept inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface. Reducing grain size (i.e. increasing fraction of grain boundaries) could effectively strengthen nanograined metals but inevitably sacrifices the ductility and possibly causes strengthening-softening transition below a critical grain size. In this work, a facile laser surface remelting-based technique was employed and optimized to fabricate a ∼600 μm-thick heterogeneous gradient nanostructured layer on austenitic Hadfield manganese steel, in which the average grain size is gradually decreased from ∼200 μm in the matrix to only ∼8 nm in the nanocrystalline-amorphous core-shell topmost surface. Atomic-scale microstructural characterizations dissected the gradient refinement processes along the gradient direction, i.e. transiting from the dislocations activities and twinning in sub-region to three kinds of martensitic transformations, and finally a multi-phase nanocrystalline-amorphous core-shell structural surface. Mechanical tests (e.g. nanoindentation, bulk-specimen tensile, and micro-pillar compression) were conducted along the gradient direction. It confirms a tensile strength of ∼1055 MPa and ductility of ∼10.5% in the laser-processed specimen. Particularly, the core-shell structural surface maintains ultra-strong (tensile strength of ∼1.6 GPa, micro-pillar compressive strength of ∼4 GPa at a strain of ∼8% and nanoindentation hardness of ∼7.7 GPa) to overcome the potential strengthening-softening transition. Such significant strengthening effects are ascribed to the strength-ductility synergetic effects-induced extra work hardening ability in gradient nanostructure and the well-maintained dislocation activities inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface, which are evidenced by atomic-scale observations and theoretical analysis. This study provides a unique hetero-nanostructure through a facile laser-related technique for extraordinary mechanical performance.