Strength-ductility Trade-off Research Articles

Manipulation of Microstructure and Mechanical Properties in N-Doped CoCrFeMnNi High-Entropy Alloys

Herein, we carefully investigate the effect of nitrogen doping in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) on the microstructure evolution and mechanical properties. After homogenization (1100 °C for 20 h), cold-rolling (reduction ratio of 60%) and subsequent annealing (800 °C for 1 h), a unique complex heterogeneous microstructure consisting of fine recrystallized grains, large non-recrystallized grains, and nanoscale Cr2N precipitates, were obtained in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA. The yield strength and ultimate tensile strength can be significantly improved in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA with a complex heterogeneous microstructure, which shows more than two times higher than those compared to CoCrFeMnNi HEA under the identical process condition. It is achieved by the simultaneous operation of various strengthening mechanisms from the complex heterogeneous microstructure. Although it still has not solved the problem of ductility reduction, as the strength increases because the microstructure optimization is not yet complete, it is expected that precise control of the unique complex heterogeneous structure in nitrogen-doped CoCrFeMnNi HEA can open a new era in overcoming the strength–ductility trade-off, one of the oldest dilemmas of structural materials.

Microstructure and Mechanical Properties of Spark Plasma Sintered and Severely Deformed AA7075 Alloy

In this paper, the microstructure and mechanical properties of AA7075 with a coarse-fine-grained laminated microstructure produced by spark plasma sintering (SPS) and the cyclic extrusion severe deformation (KOBO) technique were investigated. It was found that an inhomogeneous grain microstructure was formed from coarse and fine grains by the SPS process and then was transformed into a coarse-fine-grained laminated microstructure by means of KOBO extrusion at room temperature. The grain refinement during KOBO extrusion resulted in a fine grained laminated microstructure created due to the formation of low-angle grain boundaries (LAGBs), followed by dynamic recrystallization, leading to high-angle grain boundaries (HAGBs). The EBSD analysis results reveal the formation of a deformed and partially recrystallized ultrafine grain microstructure owing to the generation and development of shear bands during KOBO extrusion. The ultimate tensile strength (UTS) of the AA7075 alloy rose after SPS-KOBO severe deformation up to 422 MPa, with high strains of about 33%. The obtained results clearly show that the SPS-KOBO extrusion technique allows a bimodal laminated fine gradient grain microstructure to be obtained due to deformation and dynamic recrystallization, which result in both high strength and good ductility. The new heterogeneous AA7075 alloys obtained by the SPS-KOBO combined techniques demonstrate that microstructural heterogeneities can assist in overcoming the strength–ductility trade-off.

Static recrystallized annealing treatment-induced strength-ductility trade-off in cold-rolled Co36Fe36Cr18Ni10 multi-principal alloy

Multi-component alloys are recrystallized with various heterogeneous microstructures to regulate their main properties. However, the production of conventionally structured alloys with high strength and superior ductility is exigent because ductility is typically deteriorated by strength enhancement. The microstructure features of alloys determine their mechanical properties. In this work, a new multi-component Co 36 Fe 36 Cr 18 Ni 10 alloy is developed. The alloy was prepared by arc melting and solidified in a Cu mold with a single face-centered cubic phase that provides an outstanding ductile matrix. The mechanical properties and microstructures were systematically investigated through tensile tests, electron backscatter diffraction, and transmission electron microscopy. The as-cast alloy was cold-rolled at 90% reduction and subsequently annealed at 700, 800, and 900 °C. The texture evolution formed numerous fine grains with stacking faults, dislocations, and nanoscale annealed twins in their interior, effectively improving the mechanical properties of the alloy. In single-phase alloys, the twins dominated the matrix and the efficiency of grain refinement achieved by annealing at 700 °C afforded strength improvement. The strength and ductility trade-off is attributed to a microstructure that combines incompletely recrystallized and recrystallized grain regions, forming a heterogeneous microstructure whose performance dimensions span from the submicron to the nanoscale. The microstructure of the fabricated multicomponent alloy was created by large-deformation cold rolling followed by low-temperature annealing treatment. The results show that heterogeneous designs can be effectively achieved by implementing simple low-temperature annealing processes with reduced energy consumption. This strategy provides a means for developing new generation structural materials with high strength and ductility. • The Co 36 Fe 36 Cr 18 Ni 10 alloy exhibits a beneficial combination of strength and ductility when annealed at 700°C. • Stacking faults, dislocation entanglement and nanotwins interactions are effective way to strengthen FCC structure alloys. • Low SFE promotes annealed twins formation and LAGB is the nucleation site for strain-induced martensitic phase transitions.

Offsetting strength-ductility tradeoff in Mg-Sn-Zn-Zr alloy by a novel differential-thermal ECAP process

Equal-channel angular pressing (ECAP) technique is a promising method to enhance the properties of Mg alloys. Herein, a novel differential-thermal ECAP process (DTECAP) with pre-aging treatment (T6) was developed to simultaneously improve strength and ductility of Mg-Sn-Zn-Zr (TZK) alloys. After T6-DTECAP, the TZK alloy exhibited high ultimate tensile strength (UTS) of ~323 MPa and excellent elongation (El.) of ~28.7%, showing superior balance of strength and ductility. Examination microstructures of TZK alloys revealed that the excellent comprehensive properties were mainly associated with the activation of {10–12} tension twin variants and non-basal slips. Moreover, the grain refinement, fine second phases, and transition of strong ED texture to fiber (10–10) < 11–20 > texture along TD were also beneficial for the enhanced properties. This work aims to provide a novel insight for the development of high-performance Mg alloys using T6-DTECAP processing.

Yield strength-ductility trade-off breakthrough in Co-free Fe40Mn10Cr25Ni25 high-entropy alloys with partial recrystallization

High performance materials with low cost have been the goal of the pursuit of engineering materials. In this study, an economic cost-effective Co-free Fe40Mn10Cr25Ni25 (at%) high-entropy alloy (HEA) was developed. According to the concept of heterogeneous microstructure design, a partially recrystallized microstructure was developed by cold-rolling, followed by subsequent annealing. Surprisingly, the current alloy displays a yield strength of 710 MPa, an ultimate tensile strength of 880 MPa, and a uniform elongation of 18%. The overcome of yield strength-ductility trade-off is achieved by the heterogeneous microstructure composed of coarse non-fully recrystallized grains and fine recrystallized grains. The reinforcement of strength stems from the hindering effect on the dislocation movement caused by the deformation inhomogeneity. A resultful strategy is presented to constitute a cost-effective HEA with a good combination of high strength and ductility in this study.

A Novel Cu-Containing Al0.5CrCuFeV High-Entropy Alloy with a Balanced Strength-Ductility Trade-Off

A Novel Cu-Containing Al0.5CrCuFeV High-Entropy Alloy with a Balanced Strength-Ductility Trade-Off

Achieving super-high strength and acceptable plasticity for a near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy through manipulating hierarchical microstructure

In the present study, a hierarchical microstructure, which was significantly different from the traditional microstructure of titanium alloys, was prepared by specially designing the solution and aging treatment parameters of a near β-type hot-rolled Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy: (1) Firstly, in the process of solution-treatment (920 °C/1 h/WQ), a hierarchical microstructure in equiaxed primary α grains (αp) composed of nano-scale equiaxed α grains (αps) and β phase embedded between αps was formed by controlling the diffusion rate of β stable elements in αp regions. (2) Then, in the process of aging-treatment (550 °C/6 h/AC), a hierarchical microstructure composed of acicular secondary α phase (αs) with a thickness of dozens of nanometers, smaller acicular α phase (αss) with a thickness of 10 nm, distributed in the space of two αs, and whisker β phase (βwhisker), was observed in transformed β (βt) regions. Comparing to the solution-treatment of 900 °C/1 h/WQ followed by the same aging-treatment, smaller αp, a large number of nano-scale equiaxed αps, and denser and finer acicular α phases were found in the titanium alloy. Due to the combined strengthening effect of equiaxed αp refinement, nano-scale equiaxed αps and acicular α phases, the hierarchical microstructure exhibited super-high yield strength of 1255 MPa and ultimate tensile strength of 1420 MPa. Meanwhile, the refined equiaxed αp and the nano-scale equiaxed αps could offset the negative effect of acicular α phases on plasticity, hence to maintain the plasticity at an acceptable level (elongation: 6%). Such hierarchical microstructure in the titanium alloy overcame the limitation of the strength-ductility trade-off to a certain extent.

Microstructural characteristics and mechanical properties of Fe44-XMn30Co10Cr10Al3Si3CX (X = 0, 1) multi-component complex steel

The microstructural characteristics of Fe44-xMn30Co10Cr10Al3Si3CX (X = 0, 1) multi-component complex steel with Fe holding the highest atomic fraction is investigated. Results show Fe43Mn30Co10Cr10Al3Si3C1 overcomes strength-ductility trade-off through the heterogeneous lamellar structure, which is ascribed to the evolution of elongated grains during rolling process and particles precipitation with pinning effect during annealing process. The back-stress strengthening mechanism in the current alloy, with heterogeneous lamellar structure, is verified through electron backscatter diffraction based geometrically necessary dislocation density analysis.

Plasma spheroidized MoNbTaTiZr high entropy alloy showing improved plasticity

Refinement of the harder phase in two-phase MoNbTaTiZr high-entropy alloys (HEA) prepared by a powder metallurgy route has enhanced strength and plasticity of the alloy. The MoNbTaTiZr HEA powder used in this study was prepared by hydrogenation–dehydrogenation followed by plasma spheroidization, having an inherent dual-phase structure (bcc1 and bcc2) similar to the arc melted alloy of the same composition but with much finer morphology of the bcc2 phase. The homogenous and fine distribution of the harder Zr-rich phase (bcc2) with ~10% volume fraction embedded inside the Ta-rich phase (bcc1) evaded the strength–ductility trade-off. The shear-band delocalization in the bcc1 matrix phase improved the strength as well as the plasticity of the alloy. The alloy has potential in biomedical implants because it shows excellent corrosion resistance and lower magnetic susceptibility, making it an MRI (magnetic resonance imaging)-friendly alloy.

Investigation of phase-transformation path in TiZrHf(VNbTa)x refractory high-entropy alloys and its effect on mechanical property

Refractory high-entropy alloys (RHEAs) show a great potential as structural materials due to their remarkable properties, such as high strength and thermal stability. Despite these advantages, the RHEAs still suffer from the limited ductility at room temperature. To overcome the strength-ductility trade-off, the new RHEA design strategy, transformation-induced plasticity (TRIP) HEAs, have been developed by applying metastability-engineering approach. With the newly developed RHEAs design strategy, we designed metastable RHEAs, TiZrHfVxNbxTax (x = 1.0, 0.5 and 0.1) with decrease of the β-stabilizing elements (V, Nb, and Ta) to promote the transformation-induced ductility and work-hardening capability. The proper addition of the β-stabilizing elements (V, Nb, and Ta) into the ternary equi-molar TiZrHf alloy (TiZrHfV0.1Nb0.1Ta0.1) leads to stress/strain-induced phase transformation from the body-centered cubic (BCC) to hexagonal-close-packed (HCP) α′ and/or orthorhombic α″ phases. Detailed studies on the phase transformation sequence during the deformation were carried out using X-ray diffraction (XRD), electron back-scattered diffraction (EBSD), and transmission-electron microscope (TEM), which revealed the stepwise phase transformation that is responsible for the strong strain hardening behavior. Furthermore, we further suggested the new transformation-induced-plasticity (TRIP) HEA design strategy, applying the Bo-Md approach.

Tuning process parameters to optimize microstructure and mechanical properties of novel maraging steel fabricated by selective laser melting

Maraging steel is a promising material for additive manufacturing due to its ultrahigh yield strength, reasonable ductility and good weldability. However, the ductility of the fabricated part will be degraded after aging treatment. In this regard, we firstly designed a new composition of maraging steel Fe-18.3Ni-9Co-4.84Mo-0.92Ti-0.27Al-0.13Cr-0.01C (wt.%), whose strength and ductility can be simultaneously improved by selective laser melting. The relationship between laser process parameters and forming defects has been studied. Using single-track and single-layer experiments, fully dense parts were fabricated with a certain range of process parameters, corresponding to the 30–50% lap rate in the X–Y plane and 70% remelted rate along Z-axis. Besides, we found film-like reverted austenite along the martensite lath boundaries in the as-fabricated part. The effects of heat treatment processes on the reverted austenite and mechanical properties of the fabricated parts were also studied; the strength-ductility trade-off of maraging steel after heat treatment can be alleviated. The tensile strength and elongation of printed samples after direct aging treatment can respectively reach 2037 MPa and 6.4%, and 2182 MPa, 4.8% after solution and aging treatment.

Investigation of the strengthening mechanism in 316L stainless steel produced with laser powder bed fusion

Of the many benefits of the additive manufacturing process, laser powder bed fusion (L-PBF) has specifically been shown to produce hierarchical microstructures that circumvent the common strength-ductility trade-off. Typically, high strength materials have limited ductility, and vice versa. The L-PBF microstructure, consisting of fine cells, is formed during the rapid solidification of the laser powder bed fusion process. The cell boundaries are often characterized by the segregation of alloying elements and a dislocation network. While there are a number of works describing the strengthening mechanisms in L-PBF-produced 316L, there are still some gaps in understanding the effect of stress-relief and annealing at various annealing temperatures (400, 800 and 1200 °C) on the plastic strain accumulation during deformation. In this study, the authors evaluated strain partitioning using electron backscatter diffraction and kernel average misorientation maps. The results show strain partitioning to be dependent on both the annealing temperature and the pre-straining of samples. Further, the results indicated that the dislocation structure was stable until 400 °C, whereas at 800 °C strain was no longer detected at the cell boundaries. Similarly, after the heat treatment at 800 °C, elemental segregation at the cell walls was no longer detectable. Upon straining, the boundaries of as-built and annealed samples at 400 and 800 °C registered accumulation of additional strain as compared to the unstrained states. The results demonstrate that even a weak array of dislocations along the cell walls can successfully pin dislocations, albeit at a reduced capability relative to the co-existent dislocation and segregate structures found in microstructures of the as-built and annealed samples at 400 °C.

Precipitation and micromechanical behavior of the coherent ordered nanoprecipitation strengthened Al-Cr-Fe-Ni-V high entropy alloy

Coherent ordered nanoprecipitation (CON) hardening is an efficient strategy for breaking the strength-ductility trade-off. Revealing the precipitation mechanism and its influence on mechanical property is significant for further optimization of CON-strengthened alloys. In this work, we investigated the precipitation and mechanical behavior of the coherent FCC/L12 spinodal nanostructure and nano-lamellar BCC phase in a newly developed CON-strengthened Al0.5Cr0.9FeNi2.5V0.2 high entropy alloy (HEA). We found that high-density defects induced by pre-deformation promoted the segregation of Cr, resulting in composition redistribution. The thermodynamics state of the matrix shifted into a spinodal regime and the ordering energy of L12 phase increased, facilitating the formation of coherent FCC/L12 spinodal nanostructure. Meanwhile, the Cr segregation promoted the precipitation of Cr-enriched nano-lamellar BCC phase. During tensile deformation, the FCC phase yielded first, followed by L12 and BCC phases in sequence. The L12 and BCC strengthening phases contributed to an ultrahigh macroscopic yield strength. Due to the low-misfit interconnected spinodal nanostructure, the differences in phase stress between FCC and L12 phases was insignificant, which could avoid the stress concentration and retain ductility. The nano-lamellar feature of the stiff BCC phase delayed the crack initiation and propagation. Our research revealed not only the significant effect of pre-deformation on CONs formation and refinement, but also the deformation mechanism of CONs, which shed new light on the microstructural optimization and mechanical property improvement of CON-strengthened alloys.

Ultrastrong medium entropy alloy with simultaneous strength-ductility improvement via heterogeneous nanocrystalline structures

Medium Entropy Alloy (MEA) has been of great research interests in materials science. However, the strength and ductility, like most metals, cannot be obtained in MEAs simultaneously so far, without changing their chemical compositions. Here, we present a new way to fabricate gradient heterogenous nanograined structure for overcoming strength-ductility trade-off of the equiatomic Medium Entropy Alloy (MEA) at multiple length scales. Ultrasonic assisted cyclic thermal dynamic solid-state physical process was developed to fabricate ultrastrong gradient heterogenous nanograined FeCoNi MEA structures with heterogenous nanocrystalline (NC). The microstructure and mechanical behaviors of the gradient heterogenous nanograined MEA are investigated. We studied the mechanical responses of the FeCoNi MEAs with designed crystalline structures. The yield strength of the heterogenous nanograined FeCoNi MEA (1.45 GPa) was increased by 8 times compared to that of coarse-grained FeCoNi MEA, while ductility was increased from 33% to 45% after the processing. The strengthening mechanism in the NC FeCoNi MEA is found to be dominated by grain refinement and heterogenous grain structure. We also found an identical strain rate sensitivity exponent for the FeCoNi medium entropy alloy at multiple length scales, implying that dislocation mediated deformation mechanism dominates in the heterogenous FeCoNi MEA. This study provides a new way to fabricate novel gradient heterogenous nanograined structures to achieve both high strength and ductility in MEAs and provide fundamental understanding of the mechanical strengthening and deformation mechanisms of the nanograined MEAs.

What really governs the upper bound of uniform ductility in gradient or layered materials?

Gradient metallic materials, which can be made by surface mechanical attrition, non-equilibrium growth, or other thermomechanical means, have been deemed as an effective way to overcome the strength-ductility tradeoff as commonly seen in traditional metallic alloys. Although a large number of research works have been devoted to the unique strengthening mechanisms as resulting from the enhanced plastic-strain gradients and back stresses in these novel materials, the disproportionally fewer studies on ductility are rather restricted to the delay of the Considère necking limit due to the elevated work hardening. This view is incomplete, because the onset of necking (i.e., the uniform ductility) depends critically on both the amplitude and wavelength of initial perturbations. Even with a mere simplification of gradient materials by a film-on-substrate or a sandwich structure, this work shows that with random surface perturbations, the upper bound of uniform ductility is dictated by an extremely short-wavelength perturbation at the surface of the outer hard layer (thus denoted as Rayleigh mode). On the other hand, a pre-patterned surface with perturbations of varying periods is practicably unable to evolve into the Rayleigh asymptote and thus can achieve even higher uniform ductility. A revisit of literature experiments is suggested to be undertaken with a particular focus on the spectral growth kinetics of surface morphology and its connection to uniform ductility in these gradient materials.

Mechanical property enhancement of high-plasticity powder metallurgy titanium with a high oxygen concentration

High-plasticity titanium materials with high oxygen content were prepared by powder metallurgy (PM) and hot rolling, using pure Ti and ZrO2 powder as raw materials. Completely dissolved oxygen and zirconium atoms resulted in the lattice constant change, thereby increasing the strength. Although the oxygen content was up to 0.56 wt% (much higher than the oxygen threshold of 0.33 wt%), PM Ti still exhibited high plasticity. The Ti-0.5 wt% ZrO2 sample (0.43 wt% O) had UTS of 737 MPa and EL. of 28%, while the Ti-1.0 wt% ZrO2 sample (0.56 wt% O) had UTS of 824 MPa and EL. of 15%. Compared to pure Ti, the addition of 0.5 wt% ZrO2 resulted in a noticeable increase in UTS (increased by 9%) and EL. (increased by 19%). The strength-ductility trade-off dilemma of PM Ti alloy was broken. The formation of fine and equiaxed dynamic recrystallized grains may be one of the reasons that increased the ductility. The reinforcement effect of ZrO2 was calculated as 146.7 MPa/wt% ZrO2.

Effect of oxygen content on the mechanical properties and plastic deformation mechanisms in the TWIP/TRIP Ti–12Mo alloy

In the last decades, biomaterials have improved the life and its quality for millions around the Globe. Titanium-based biomaterials have rapidly become the gold standard for bone contact applications. Despite their successful performance, their low strength-ductility trade-offs and work-hardening rates limit their use for example for the manufacture of vascular stents. Although a high strength-ductility trade-off and a high work-hardening rate were reported for the TWIP/TRIP Ti–12Mo alloy, strengthening strategies are required to approach its strength to the ones of Co–Cr alloys, main metallic materials used to produce stents. In this study, the investigated strengthening strategy was the increase of oxygen content from 0.04 to 0.18 wt% in the Ti–12Mo alloy. The effect of this increase on its microstructure, mechanical properties and plastic deformation mechanisms was studied. Athermal ω precipitates were observed throughout with the β matrix of both solution-treated alloys. X-Ray diffraction and transmission electron microscopy suggested that the quantity of ω phase was larger in the alloy with a higher oxygen content, contrasting with the common knowledge that O suppresses ω phase precipitation. Independently of oxygen content, {332}<113> twins and stress-induced martensite (SIM) α" occurred in the deformed microstructures. Based on the electron backscatter diffraction analyses, the area fraction of SIM α" decreased by increasing oxygen content. Although elongation decreased with this oxygen content increase, Ti–12Mo-0.18O exhibited a high true uniform elongation of 25% and a true ultimate tensile strength higher than the Ti–12Mo-0.04O alloy. Hardness and yield strength also increased by increasing oxygen content, while elastic modulus did not change.

Property enhancement of CoCrNi medium-entropy alloy by introducing nano-scale features

CoCrNi -medium-entropy alloy (MEA) has been widely investigated due to its superior mechanical properties that overcome strength-ductility tradeoff. Here we show further property enhancement of CoCrNi MEA by introducing nano-scale features. Both CoCrNi and oxide dispersion strengthened (ODS) CoCrNi are fabricated by mechanical alloying and spark plasma sintering. Microstructural characterization and mechanical testing of these nanostructured MEAs revealed that the nano-scale features significantly improves the strength of the alloys. In ODS-CoCrNi MEA, Y 2 Ti 2 O 7 oxides with an average diameter of 7.3 ± 3.2 nm are incoherent with the matrix, and a specific orientation relationship exists between Y 2 Ti 2 O 7 and the matrix, which is [011] Y2Ti2O7 //[011] Matrix , (400) Y2Ti2O7 //(200) Matrix and (22 2 ‾ ) Y2Ti2O7 //(11 1 ‾ ) Matrix . The recrystallization and grain growth processes are effectively suppressed by the introduction of Y 2 Ti 2 O 7 nanoparticles. Strengthening mechanism analyses indicate that the strength improvement of ODS-CoCrNi is mainly ascribed to the precipitation strengthening of Y 2 Ti 2 O 7

Nano dual-phase CuNiTiNbCr high entropy alloy films produced by high-power pulsed magnetron sputtering

Dual-phase high entropy alloys have been proved to have the ability to overcome the strength-ductility trade-off. However, high-entropy alloy films are difficult to obtain a dual-phase structure due to the extremely high cooling rate during the preparation process and the high-entropy effect of the film itself. In this paper, the dual-phase CuNiTiNbCr high-entropy alloy films were prepared by high-power pulsed magnetron sputtering at different working pressures. The composition, microstructures, mechanical properties and electrochemical corrosion performance were tested by energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), nano-indentation, Vickers indentation and electrochemical polarization. The CuNiTiNbCr films exhibited a dual-phase structure composed of FCC matrix phase and Cu-rich BCC precipitated phase. The film presented a two-layer structure, the single FCC phase structure near the substrate and the FCC + BCC structure above. Comparing with FCC phase, the dual-phase structure exhibited higher hardness. With the increase of deposition pressure, the structure of the film became looser, and the hardness, toughness and corrosion resistance were all decreased due to the influence of the structure. It is proved that high-power pulsed magnetron sputtering is a feasible way for the phase structure regulation and performance improvement of high-entropy alloy films.

A micromechanical model for heterogeneous nanograined metals with shape effect of inclusions and geometrically necessary dislocation pileups at the domain boundary

Heterogeneous nanostructured materials, including metals, alloys, and composites, have attracted significant scientific interest because of their outstanding performance in overcoming the strength-ductility trade-off, enhancing fatigue strength, and reducing friction and wear damage. In this study, we developed a new micromechanical model to predict the overall mechanical response of heterogeneous nanograined metals that consist of plastically deformable soft and hard domains. This dual-domain heterogeneous structure was modeled as a matrix-inclusion system, and the problem was solved through a secant-moduli approach that considered the existence of geometrically necessary dislocation (GND) pileups at the domain boundaries. We assumed that the inclusions are aligned along one direction according to experimental observations. A significant improvement in this development from previous micro-mechanical models was that the hetero-deformation induced extra strengthening inside the plastically deformable inclusions of different shapes due to the GND pileups was taken into account. In this process, the stress-strain responses of the constituent phases of various grain sizes that spanned over four orders of magnitude are also established by the dislocation density-based model. In accordance with Eshelby's equivalent-inclusion principle, the inclusions are taken to be of spheroidal shape, with an aspect ratio (i.e., length-to-diameter ratio, denoted by β) that could be much larger or smaller than unity. We considered in details the condition that the overall uniaxial tension is applied along the direction of the aligned inclusions, and examined the consequences if the extra strengthening is not considered and if it is considered. It is found that, if extra strengthening was not considered, the inclusion shape had a significant influence on the strain-hardening capability of the heterogeneous metals. The strain-hardening rate increased with increasing β if β≥1, whereas it decreased with increasing β if β<1, which resulted in a maximum strain-hardening rate at β=100 and a minimum one at β=0.5 among all the aspect ratios considered. Interestingly, the strength-ductility trade-off could be overcome by modulating only the shape of the inclusions. In contrast, if extra strengthening was incorporated, the variation of the strain-hardening rate was reversed because larger β (as β≥1) provided less strain partitioning, lower GND density, and reduced back stress, whereas bigger β (as β<1) yielded higher ones. When the overall uniaxial stress was applied normal to the direction of the aligned inclusions, the β dependence of the strain-hardening rate was different. Our findings showed that the tuning of inclusions shape, extra strengthening, grain sizes, and volume fractions of the inclusions circumvented the strength-ductility trade-off and achieved outstanding strength-ductility synergy as demonstrated by the strength-ductility map.