Simultaneous Improvement Of Strength Research Articles

Hydrogen embrittlement and failure mechanisms of multi-principal element alloys: A review

• Hydrogen embrittlement (HE) of multi-principal element alloys is reviewed. • HE behavior between traditional alloys and high-entropy alloys is compared. • Further research directions on HE of high-entropy alloys are identified. • Strategy for the improvement of strength and HE-resistance are suggested. Multi-principal element alloys exhibit excellent physical, chemical and mechanical properties, and they are used as novel structural materials for potential applications in nuclear energy, hydrogen energy, and petrochemical fields. However, exposing components made of the alloys to service conditions related to the mentioned applications may induce hydrogen embrittlement (HE) as one of the typical failure mechanisms. In this review, we report and summarize the progress in understanding HE in multi-principal element alloys, with a particular focus on high-entropy alloys (HEAs). The review focuses on four aspects: (1) hydrogen migration behavior (hydrogen dissolution, hydrogen diffusion, and hydrogen traps); (2) factors affecting HE (hydrogen concentration, alloy elements and microstructure); (3) tensile mechanical properties in the presence of hydrogen and micro-damage HE mechanisms; (4) the design concept for preventing hydrogen-induced mechanical degradation. The differences in the HE behavior and failure mechanisms between HEAs and traditional alloys are compared and discussed. Moreover, specific research directions for further investigation of fundamental HE issues and a strategy for a simultaneous improvement in strength and HE resistance are identified.

Simultaneous improvement in strength and ductility of extruded Mg alloy via novel closed forging extrusion

A novel continuous plastic process employed on AZ31 Mg alloy called closed forging extrusion (CFE) was presented. The optical microscopy, scanning electron microscopy, electron back-scatter diffraction and tensile and compressive tests were employed to investigate the microstructure evolution and strengthening mechanism. The results indicated that the CFE-process can promote dynamic recrystallization (DRX), eliminate the coarsen unDRXed grain regions, refine the grains effectively, and improve the strength, plasticity and anisotropy of the alloy. The grain refinement was mainly attributed to the stress, which facilitated the nucleation of recrystallization and refined the microstructure via the CFE. The fully DRXed ultrafine grained structure improved the strength and plasticity simultaneously. After 60 s closed forging and continuous extrusion, the alloy exhibits relatively high TYS, UTS, CYS, elongation and yield asymmetry of 305 MPa, 337 MPa, 295 MPa, 27% and 0.97, respectively.

Mechanical properties of (HfCo)100−x(NbMo)x refractory high-entropy alloys with a dual-phase bcc-B2 structure

The common concept for the development of the high-performance metallic materials is associated with the combination of a soft disordered matrix and hard ordered reinforcements. However, unusual combinations of a hard disordered phase and a soft(er) ordered phase are also possible. In this work, we explored structure and mechanical properties of (HfCo)100−x(NbMo)x (x = 0; 10; 25; 60; 75; 100 at%) refractory high-entropy alloys. The binary HfCo and NbMo alloys had ordered B2 and disordered bcc structures, respectively. The (HfCo)100−x(NbMo)x (10 ≤ x ≤ 75) alloys had mostly a dual-phase structure of disordered (Nb, Mo)-rich bcc and ordered (Hf, Co)-rich B2 phase. Almost fully a eutectic-like structure was found in the (HfCo)75(NbMo)25 alloy. "Cube-on-cube" orientation relationships between the bcc and B2 phases ((110)bcc||(110)B2, [001]bcc||[001]B2) were detected. In addition, a small amount of Nb-rich bcc and/or Hf-rich fcc oxide phases were detected in some alloys. The B2 HfСo alloy was ductile but extremely soft, while, the NbMo alloy was hard and brittle. Simultaneous improvement of strength and ductility in the dual-phase (HfCo)100−x(NbMo)x (10 ≤ x ≤ 75) was revealed. The (HfCo)90(NbMo)10 alloy with a close to single-phase B2 structure exhibited a yield stress anomaly (YSA) at 500 °C. The YSA was associated with a change of dominant slip mode from a<100>to a<110>. Relationships between the chemical composition, microstructure, and the mechanical properties of the (HfCo)100−x(NbMo)x alloys were discussed.

Simultaneous improvement of strength and damping capacities of Mg-8Li-6Y–2Zn alloy by heat treatment and hot rolling

Mg-8Li-6Y–2Zn alloy with high damping capacity and adequate strength was prepared by heat treatment and hot rolling. Combined with density of states (DOS) calculation and microstructure characterization, the mechanical properties and damping capacities of Mg-8Li-6Y–2Zn alloy in different states were systematically investigated. The as-cast alloy is mainly composed of coarse dendritic and granular (Mg, Zn)24Y5 phase. 18R-type long-period stacking ordered (18R-LPSO) phase, is introduced into the alloy after heat treatment at 500 °C for 6 h, which can effectively improve the strength and elongation of the Mg-8Li-6Y–2Zn alloy. After hot rolling, the dynamic precipitation of the nanoscale (Mg, Zn)24Y5 phase consumes many solute atoms. The decrease in the number of solute atoms leads to an increase in the distance of dislocation movement, thereby increasing the damping capacity. Compared with the as-cast alloy, the tensile strength of the heat-treated + rolled alloy increased from 140 MPa to 210 MPa, and the damping capacity increased from 0.006 to 0.018.

Design of Cu–Cr Alloys with High Strength and High Ductility Based on First-Principles Calculations

Designing a material to realize the simultaneous improvement in strength and ductility is very meaningful to its industrial application. Here, the first-principles calculations based on density functional theory (DFT) were adopted to investigate the stability, elastic properties and Debye temperature of binary Cu–Cr alloys; and the effect of micro-alloying elements on their mechanical properties, including the bulk modulus B, shear modulus G, Yong’s modulus E and Poisson’s ratio σ, was discussed. The elastic constants show that all the studied binary Cu–Cr alloys are mechanically stable, and the Cu–0.7Cr alloy has a combination of good strength and ductility. Moreover, the addition of Ag, Sn, Nb, Ti and Zr can improve the basic properties of Cu–0.7Cr alloy, and the Cu–0.7Cr–1.1Sn possess a large strength combined with improved ductility and strong covalent bonds due to the large Debye temperature. Additionally, the introduction of Y and In further improves the mechanical properties (strength and ductility) of the excellent Cu–0.7Cr–1.1Sn alloy. Our studied results can provide guidance for the theoretical design and experimental improvement of Cu-based alloys.

Simultaneous improvements in strength and ductility of as-extruded Mg-1.0Sn-0.5Zn alloy via Ce addition in combination with pre-twining deformation

In the present study, the comprehensive effects of Ce addition and pre-twining deformation on the microstructure evolution and mechanical properties of Mg-1.0Sn-0.5Zn alloys were systematically investigated. After Ce addition, two phases (CeMgSn and CeMgZn2) were newly emerged, which eventually hampered grain growth and postponed {10−12} tensile twin extinction during annealing subsequent to pre-compression. Besides, due to prominent grain refinement, the addition of Ce into as-extruded Mg-Sn-Zn alloy gave rise to a noticeable improvement in strength. As for the application of pre-twining deformation, it could induce a significant increase in the tensile ductility via texture tailoring, and the relative Visco-Plastic Self-Consistent (VPSC) simulation confirmed that the main reason was attributed to the vigorous activation of {10−12} tensile twins. As a result, both the strength and ductility of the as-extruded Mg-Sn-Zn alloy were substantially improved via the combination of Ce addition (obvious grain refinement) and pre-twining deformation (effective texture regulation).

A feasible route to produce 1.1 GPa ferritic-based low-Mn lightweight steels with ductility of 47%

High- and medium-Mn (H/M-Mn) base lightweight steels are a class of ultrastrong structural materials with high ductility compared to their low-Mn counterparts with low strength and poor ductility. However, producing these H/M-Mn materials requires the advanced or high-tech manufacturing techniques, which can unavoidably provoke labor and cost concerns. Herein, we have developed a facile strategy that circumvents the strength–ductility trade-off in low-Mn ferritic lightweight steels, by employing low-temperature tempering-induced partitioning (LTP). This LTP treatment affords a typical Fe-2.8Mn-5.7Al-0.3C (wt.%) steel with a heterogeneous size-distribution of metastable austenite embedded in a ferrite matrix for partitioning more carbon into smaller austenite grains than into the larger austenite ones. This size-dependent partitioning results in slip plane spacing modification and lattice strain, which act through dislocation engineering. We ascribe the simultaneous improvement in strength and total elongation to both the size-dependent dislocation movement in austenite grains and the controlled deformation-induced martensitic transformation. The low-carbon-partitioned large austenite grains increase the strength and ductility as a consequence of the combined martensitic transformation and high dislocation density-induced hardening and by interface strengthening. Additionally, high-carbon-partitioned small austenite grains enhance the strength and ductility by planar dislocation glide (in the low strain regime) and by cross-slipping and delayed martensitic transformation (in the high strain regime). The concept of size-dependent dislocation engineering may provide different pathways for developing a wide range of heterogeneous-structured low-Mn lightweight steels, suggesting that LTP may be desirable for broad industrial applications at an economic cost.

Simultaneous improvement of strength and elongation of laser melting deposited Ti-6Al-4V titanium alloy through three-stage heat treatment

This study reported a strategy of three-stage heat treatment to simultaneously improve yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of laser melting deposited (LMDed) Ti-6Al-4V titanium alloy . After the three-stage heat treatment, the basketweave microstructure consisting of acicular α laths in the as-built sample was transformed to a multiscale-α microstructure consisting of the coarse-plate α, fine-plate α and ultrafine α in the heat-treated sample. The effect of microstructure on the tensile properties was revealed via in-situ tensile test combined with the analysis of the deformation and fracture mechanism . Although the coarse-plate α in heat-treated sample is larger than the acicular α in as-built sample, the combination of multiscale α grains with a certain relative content aroused an increment of the YS from 879 ± 28 MPa in as-built sample to 973 ± 9 MPa in heat-treated sample. The good deformation compatibility among the multiscale α grains impeded the crack propagation effectively, which resulted in the improvement of the EL from 14 ± 2% to 16 ± 1%. Furthermore, the improvement of the EL enhanced the dislocation multiplication and strain hardening in the multiscale α microstructure to induce the increment of the UTS from 945 ± 40 MPa to 1092 ± 20 MPa. The results could provide a guidance for tailoring microstructure and improving the strength and ductility of additive manufacturing titanium alloy.

Microstructure, mechanical properties and wear resistance of Ti particles reinforced AZ31 magnesium matrix composites

The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites (MMCs). In this work, the Ti particles reinforced AZ31 magnesium (Mg) matrix composites achieved simultaneous improvement in strength, elongation and wear resistance. The Ti particles reinforced AZ31 composites were fabricated by ultrasonic-assisted stir casting with hot extrusion. The results showed that a strong interfacial bonding was obtained at Ti/Mg interface because of the formation of semi-coherent orientation relationship of TiAl/Mg, TiAl/Al 2 Ti and Al 2 Ti/Mg interfaces. The as-extruded 6 wt.%Ti/AZ31 composite presented the best compressive mechanical properties and wear resistance with ultimate tensile strength, elongation and wear rate of 327 MPa, 20.4% and 9.026 × 10 −3 mm 3 /m, obviously higher than those of AZ31 alloys. The enhanced mechanical properties were attributed to the grain refinement and strong interfacial bonding. The improved wear resistance was closely related to the increased hardness of composites and the formation of protective oxidation films. • Ti particles refine the grain size of Ti/AZ31 composites. • A strong interfacial bonding forms at Ti/Mg interface. • Ti/AZ31 composites get an increase in strength, elongation and wear resistance.

Effects of carbon addition on microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy prepared by powder metallurgy

To improve the mechanical properties of Fe50Mn30Co10Cr10 high entropy alloy (HEA), a series of carbon-containing HEAs based on Fe50Mn30Co10Cr10 were successfully prepared by powder metallurgy. The effects of carbon content on microstructural evolution and mechanical properties of the as-sintered HEAs were investigated. The improved FCC phase stability and the decreased Σ3 twin grain boundary proportion as the increase of carbon content are mainly due to the increased stacking fault energy. As the carbon content increases, the phase structure of the as-sintered HEAs changes from FCC + HCP phases to FCC phase and then to FCC + M23C6 phases, and the deformation-induced martensitic transformation from FCC to HCP weaken gradually. The solid solubility of carbon in the as-sintered Fe50Mn30Co10Cr10 HEAs is below 2 at.%. A large number of carbides can be observed in the microstructure of the alloys at higher carbon content. The yield strength of the alloys increases approximately linearly with carbon content, while the uniform elongation first increases and then decreases. The (Fe50Mn30Co10Cr10)98C2 HEAs with nano-carbides and ultrafine manganese oxide exhibited a yield strength of 362 MPa, an ultimate tensile strength of 792 MPa, and uniform elongation of 36.7%, showing simultaneous improvement in strength and ductility compared with the carbon-free alloy. This is due to the joint contribution of multiple strengthening mechanisms in the carbon-containing HEA. Interstitial solid solution strengthening and grain boundary strengthening act as the dominant strengthening mechanism. Alloying with carbon element is a feasible method to enhance the mechanical properties of HEAs prepared by powder metallurgy.

Effect of Oxide Metallurgy on Inclusions in 125 ksi Grade OCTG Steel with Sulfide Stress Corrosion Resistance.

The effects of Al deoxidation and Zr deoxidation on the microstructure and properties of sulfide stress corrosion resistant high-strength steel have been investigated. The feasibility of the Zr deoxidation instead of Al deoxidation was confirmed by the thermodynamic analysis of the deoxidation of various elements. The experimental results indicate that the average diameters of the inclusions in Al-Steel and Zr-Steel were 2.45 μm and 1.65 μm, respectively. The Al-Steel and Zr-Steel contained 22.38% and 68.77% inclusions per unit area, respectively, and the fraction of inclusions in the Al-Steel and Zr-Steel with diameters less than 2 μm was about 73.46% and 89.63%, respectively, indicating that the Zr deoxidation process could effectively refine inclusions and promote dispersion. The average diameters of austenite grain for the Al-Steel and Zr-Steel were about 9.1 μm and 8 μm, respectively. The fine particles in Zr-Steel could pin the austenite grain boundaries and clearly refine the grains. The average grain size of tempered martensite was 8.2 μm and 3.8 μm, respectively. The yield strength of the Al-Steel and Zr-Steel was 922 MPa and 939 MPa, respectively; the impact energy was 60 ± 6 J and 132 ± 6 J, respectively. Moreover, the fracture time of the NACE-A was from 28 h (Al-Steel) to 720 h (Zr-Steel) without fracture. The experimental steel deoxidized by Zr achieved a simultaneous improvement in strength, toughness and sulfide stress corrosion resistance, and the effect of inclusions on the fracture of the sulfide stress corrosion resistant high-strength steel can be explained by the Griffith theory.

Superior strength–ductility synergy of (TiC + Ti5Si3)/Ti composites with nacre-inspired architecture

Inspired by the ultrastrong and tough nacre structure, in this study, we prepared in-situ titanium (Ti) matrix composites (TMCs) containing laminated Ti, planarly aligned TiC and vertically distributed Ti5Si3 phases, which is close to the unique “brick-and-mortar” architecture of nacre. This concept was realized via electrophoretic depositing Si powders and graphene oxides (GOs) on pure Ti foils followed by spark plasma sintering. Results showed that dramatically higher yield strength (YS) of 829 MPa could be achieved in the composite, which is 178% higher than that of pure Ti counterpart while maintaining good plasticity of 8.1% in elongation. Compared with the laminated TiC/Ti composite with higher strength and moderate plasticity, simultaneous improvement in strength (19%) and ductility (33%) was attained in the nacre-like composites, leading to superior strength–ductility synergy. The strengthening and toughening mechanism were discussed based on microstructures and fractographs. Our study offers a facile approach to fabricating large-sized nacre-like artificial composites with outstanding properties.

Investigation of Microstructures and Mechanical Properties of SiC/AA2024 Nanocomposites Processed by Powder Metallurgy and T6 Heat Treatment

SiC/AA2024 nanocomposites with 1 and 5 vol.% SiC nanoparticles have been prepared by a powder metallurgy route involving high-energy ball-milling (HEBM), spark plasma sintering (SPS), and hot extrusion. The microstructures and mechanical properties of the nanocomposite samples before and after T6 heat treatment were investigated. The samples exhibited a bimodal microstructure with SiC nanoparticles being dispersed in it. With increasing the SiC nanoparticle content from 1 to 5 vol.%, the yield strength (YS) and ultimate tensile strength (UTS) increased and the elongation to fracture (El) slightly decreased. After T6 heat treatment, a simultaneous improvement of the strength and ductility was observed, with the YS, UTS, and El increasing from 413 MPa, 501 MPa, and 5.4% to 496 MPa, 572 MPa, and 6.7%, respectively, in the 1 vol.%SiC/AA2024 nanocomposite sample. Analysis of the deformation behavior shows that this improvement is likely caused by the increased density of geometrically necessary dislocations (GNDs) resulting from the bimodal microstructure. The dispersed intragranular Sʹ precipitates generated by the T6 heat treatment also make a contribution to the increase of strength and ductility by accumulating dislocations. It is feasible to realize simultaneous improvement of strength and ductility in the SiC/AA2024 nanocomposites via powder metallurgy and subsequent heat treatment.

Simultaneous improvement of strength and ductility by Mn addition in extruded Mg–Gd–Zn alloy

The influence of Mn content on the microstructure, tensile properties and strain-hardening behaviors of extruded Mg−1Gd−0.5Zn−xMn (x=0, 0.3 and 1, wt.%) alloy sheets was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The results show that the completely recrystallized grain structure and the extrusion direction (ED)-titling texture are observed in all the extruded sheets. The mean grain size and weakened ED-titling texture of the extruded sheets are gradually reduced with increasing Mn content. This is primarily associated with the formation of new fine α-Mn particles by Mn addition. Tensile properties show that the addition of Mn also leads to the improvement of yield strengths, ultimate tensile strengths and elongations of the extruded Mg−1Gd−0.5Zn−xMn sheets, which is mainly due to the fine grains and α-Mn particles. In addition, the Mg−1Gd−0.5Zn−1Mn sheet has the lowest strain-hardening exponent and the best hardening capacity among all prepared Mg−1Gd−0.5Zn−xMn sheets.

Effect of warm-rolling on the strength and ductility of multilayered composite steel

Making composite steel is an effective method to improve the strength and ductility of steel, but it often follows the mixture rule. Further increasing the strength and ductility simultaneously of composite steel is challenging. In this study, warm-rolling was introduced into a multilayered martensite/austenite composite steel after the compositing process. Results revealed that some C atoms diffused from the martensite layer into the neighbouring austenite layer, resulting in a reduced hardness in the martensite layer of common composite steel. Introducing warm-rolling deformation not only hardened each layer effectively, but also clearly improved the ductility of the austenite layer. This facilitated the coordination deformability of the austenite layer and resulted in simultaneous improvements in strength and ductility for warm-rolled composite samples. Better mechanical properties (tensile strength of 1546 MPa and a uniform elongation of 14.9%) were obtained for a sample with a lower degree of reduction (10%). The mechanism leading to improved mechanical properties is analysed in detail in this paper.

Effects of Zn Addition on the Microstructure and Mechanical Properties of As-Extruded Mg-2Al-0.5Ca Alloy

The effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-2Al-0.5Ca-xZn (x = 0, 0.3, 0.6, 0.9 wt.%) alloys were investigated in this work. The results showed that the extruded sheets exhibited a completely dynamically recrystallized microstructure, the grain size was refined, and texture weakening was achieved with Zn addition because of the segregation of Zn atoms on grain boundaries, which suppresses the growth of dynamic recrystallized grains. The addition of 0.6 wt.% Zn improved both the tensile strength and ductility of the as-extruded Mg-2Al-0.5Ca alloy. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed a 0.2% proof stress of 145 MPa, an ultimate tensile strength of 317 MPa, and an elongation of 30.0% along the extruded direction. The simultaneous improvement of strength and ductility was mainly due to the fine and homogeneous grain microstructure and the weakened extrude direction (ED)-tilted texture. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed little in-plane anisotropic tensile properties, with a 0.2% proof stress, ultimate tensile strength, and elongation in the 45° direction of 148 MPa, 299 MPa, and 25.0%, and those in the transverse direction of 148 MPa, 269 MPa, and 16.8%, respectively.

Microstructure and tensile properties of chemically heterogeneous steel consisting of martensite and austenite

We made the chemical heterogeneity in steel consisting of mostly martensite with retained austenite by applying intercritical annealing prior to full austenitization. It enables simultaneous improvement in strength and ductility, which have been regarded as mutually exclusive properties. Contribution from two types of chemical heterogeneity could be identified; micro-scale and nano-scale heterogeneity inheriting the chemistry of intercritical austenite and Mn-enriched cementite respectively. The micro-scale chemical heterogeneity creates soft and hard domains in the martensitic microstructure by dissimilar solid solution strengthening, generating strain partition and back stress which contribute to the improvement of strength. On the other hand, the nano-scale chemical heterogeneity from highly Mn-enriched cementite evolved into Mn-enriched austenite in the final microstructure. The exceptional stability of nano-scale Mn-enriched austenite renders persistent strain hardening, contributing the enhanced ductility.

On impact of cryogenic temperature rolled 6082 Al alloy by dome- and conical-nosed projectiles

The simultaneous improvement in strength and toughness through cryogenic temperature rolling observed in recent studies is of profound interest for designers in defence, automobile and aerospace domains. The present work discusses the effects of different projectile nose shapes – dome and conical – on the ballistic impact behaviour of the 1 mm thick AA 6082 alloy targets, rolled to different cryogenic strains, using the experimental data for impact velocities ranging from 50 to 250 m/s reported in our earlier work. The cryogenic rolling strains were imparted by providing different thickness reductions, namely, 50%, 66.66%, 75% and 80%. The target performance was also analysed using velocity drop approach. The projectile nose shape influenced the ballistic limit strongly for 50% and 75% thickness reductions. Conical-nosed projectiles were found to be better penetrators than the dome-nosed projectiles within the overall tested velocity range of 50–250 m/s. The observations confirmed the dominance of the samples with 66.66% thickness reduction impacted with both dome and conical-nosed projectiles in the average and maximum velocity drops after the ballistic limits, indicating superior performance.

Simultaneously enhanced strength-plasticity of graphene/metal nanocomposites via interfacial microstructure regulation

Interfacial microstructure characteristics (e.g., volume fraction, thickness, moduli) are crucial to the overall mechanical properties of graphene/metal nanocomposites. Herein, we investigate the effects of different interfacial characteristics on simultaneous improvement of strength and plasticity of nanocomposites. Graphene nanoplatelets (GNPs) reinforced Ti6Al4V composites with appropriate interfacial effects are first fabricated based on powder metallurgy. Combining the interphase model, the field fluctuation method, the second-order stress moment and continuous damage theory, the multiscale theoretical framework for predicting the entire stress-strain relations is developed, and its accuracy is verified by the tensile test results of GNP/Ti6Al4V nanocomposites. The effects of the micromechanical variables including volume fraction and stiffness of interphase, as well as geometrical size factor (ratio of interphase thickness to the GNP equivalent diameter) and aspect ratio of GNPs on the maximum strength and failure strain are quantitatively analyzed to demonstrate how the strength and plasticity of nanocomposites are enhanced concurrently. This work provides a new perspective for graphene/metal nanocomposites with excellent tensile properties by optimizing interfacial characteristics.

Development of 1.2 GPa Ferrite-based Lightweight Steels via Low-temperature Tempering

Previously reported low-Mn ferritic-based lightweight steels are potential candidates for industrial applications, however, they typically exhibit lower strength, with &lt; 1 GPa and lower strength-ductility balance, than medium- and high-Mn austenitic lightweight steels. Herein, we introduce a low-temperature tempering-induced partitioning (LTP) treatment that avoids the strength-ductility dilemma of low-Mn ferriticbased steels. When the LTP process was performed at 330 oC for 665 s, the strength of typical ferritic base Fe-2.8Mn5.7Al0.3C (wt%) steel with heterogeneously sized metastable austenite grains embedded in a ferrite matrix, exceeded 1.1 GPa. Notably, the increased strength-ductility balance of the LTP-processed ferritic steel was comparable to that of the high-Mn based austenitic lightweight steel series. Using microscale to nearatomic scale characterization we found that the simultaneous improvement in strength and total elongation could be attributed to size-dependent dislocation movement, and controlled deformation-induced martensitic transformation.