Excellent Strength-ductility Synergy Research Articles

Developing Ultrafine Twinned Microstructure Enabled Excellent Strength–Ductility Synergy in Mg–Al–Zn Alloy by Submerged Friction Stir Processing

Developing Ultrafine Twinned Microstructure Enabled Excellent Strength–Ductility Synergy in Mg–Al–Zn Alloy by Submerged Friction Stir Processing

Strength-ductility synergy through tailoring heterostructures of hot-rolled ferritic-martensitic steels containing varying Si contents

By utilizing the feature that adding Si is able to effectively increase Ac1 and Ac3 temperatures of ferritic-martensitic (FM) steels, four FM steel sheets with different Si additions (0–1.0 wt%) were prepared by hot rolling at the same intercritical temperature to obtain various heterostructures. Their mechanical properties were evaluated and well correlated with detailed microstructural characteristics revealed by multiple characterization methods. Results show that the 0 Si specimen has a nearly complete martensitic structure; the 0.4 Si specimen consists of ∼23.5 vol% island-like ferrites embedded in martensites exhibiting a typical bi-modal structure (BMS); the 0.7 Si specimen consists of ∼46.8 vol% lamellar ferrites alternating with lamellar martensitic structures corresponding to a typical heterogeneous lamella structure (HLS); the 1.0 Si specimen is mostly comprised of ferrites no longer belonging to typical heterostructures. With increasing Si content, sizes of martensitic laths gradually decrease while the ferritic grains are coarsened. The 0.4 Si and 0.7 Si specimens exhibit high values (∼17 GPa%) of the product of ultimate tensile strength (UTS) and total elongation (TE), demonstrating a good strength-ductility synergy. Comprehensive analyses reveal that the 0.4 Si specimen with BMS exhibits a considerable hetero-deformation induced (HDI) strengthening effect, facilitating the production of the highest UTS (1476.3 MPa), while the 0.7 Si specimen with HLS shows a stronger HDI strain hardening effect leading to a higher TE (12.5%). This study could offer an important reference for designing and processing of FM steels with excellent strength-ductility synergy.

The cobalt-free Fe35Mn15Cr15Ni25Al10 high-entropy alloy with multiscale particles for excellent strength-ductility synergy

The evolution of microstructure and tensile properties of a newly designed cobalt-free high entropy alloy, Fe35Mn15Cr15Ni25Al10 (at.%), has been investigated during the annealing and aging processes. A dual-phase alloy with a face-centered cubic (FCC) and body-centered cubic (BCC) or ordered B2 structure, along with multiscale heterogeneous precipitates, has been formed. The precipitated phases consist of bulk primary B2–NiAl and secondary BCC/B2 particles that range in size from the nanometer to micrometer scale. By prolonging the aging time, the yield strength is strongly enhanced, increasing from 250 MPa to 860 MPa at the peak aging stage. The primary sources of strengthening are precipitation hardening and hetero-deformation-induced strengthening from the BCC or ordered B2 phase. Furthermore, the incorporation of various strengthening mechanisms and high-strain hardening capability at cryogenic temperatures (77 K) results in improved strength and ductility simultaneously. A highly cost-effective high-entropy alloy, doped with a high concentration of aluminum, has been developed.

Effect of sintering parameters on phase evolution, microstructural development and mechanical behavior of Ni46Al12Co18Cr8Fe12Mo4 high entropy alloy synthesized via mechanical alloying and spark plasma sintering

The aim of this research work was to study phase evolution, microstructural development and resulting mechanical properties in Ni46Al12Co18Cr8Fe12Mo4, at. % high entropy alloys (HEAs) synthesized via spark plasma sintering (SPS) of 50 hr mechanically alloyed (MAed) powder with varied sintering parameters. Detailed microstructural analysis of the consolidated samples revealed that sintering at 1100 °C resulted in improved densification, i.e. up to 99% and enhanced grain growth compared to the samples sintered at lower temperatures. Phase analysis of the sintered HEAs envisaged formation of face centered cubic (FCC) structured single-phase solid solution with minor amount of brittle sigma (σ) phases. Phase diagram generated from Thermo-Calc shows that volume fraction of the σ phases decreases continuously with temperature and further they dissolve at 1180 °C, which is in close agreement with experimental results of differential thermal analysis (DTA) performed on the sintered samples. Moreover, microhardness of the consolidated HEAs decreased gradually with increase in sintering temperature, ascribed to lower volume fraction of the brittle σ phases at higher temperature. Further, nanoindentation test was conducted to estimate the hardness of the individual phases and it was found that nanohardness of σ phase is approximately 1.7 times higher than that of the solid solution phase. The HEA sintered at 1100 °C showed an excellent strength-ductility synergy, with a compressive yield strength of 1121 ± 21 MPa and the elongation to failure up to 20 ± 1%, attributed to the presence of ductile FCC phase with minor amount of brittle σ phase. The present study demonstrates the potential of SPS technique to synthesize Ni base HEA with excellent thermal stability and superior mechanical properties for structural applications.

Simultaneously enhancing the strength and strain hardenability by Si substitution in metastable high-entropy alloys

We have demonstrated the potential to simultaneously enhance the strength and strain hardenability of metastable dual-phase high-entropy alloys (HEAs) by substituting the constituent transition metal element with Si. This leads to the development of a face-centered cubic single-phase Fe50Mn30Cr10Si10 HEA with excellent strength-ductility synergy, low density and low alloying costs. The substantial solid-solution hardening effect achieved through Si-alloying leads to a higher yield stress for this HEA compared to its dual-phase counterpart when their grain sizes are comparable. In addition, the Si-alloying imparts a low stacking fault energy (∼12.8 mJ/m2) to this HEA, facilitating the progressive formation of hexagonal close-packed martensite plates during plastic deformation. Furthermore, the Si-alloying increases the volume fraction of the deformation-induced martensite plates (up to 75.5%) and renders their thickness ultra-thin (<20 nm), thereby leading to remarkable strain hardenability.

Towards excellent strength-ductility synergy via high temperature short time annealing in low-carbon ultrafine grain steel

A new ar-chitecture of ultrafine grain (UFG) steel with coarsen bimodal size distribution was realized by high-temperature short time annealing process. Abundant comparisons on ferrite size, precipitates, and dislocation were performed with previous works. In the present study, the synthetical mechanical properties showing a tensile strength of 974.9 ± 27.1 MPa and 18.5 ± 1.66% elongation in UFG steel with grain size of 374 nm was enhanced without much strength sacrifice. High-temperature short time annealing process promoted the intragranular Nb(C, N) particles formation and the recrystallization ferrite coarsening. However, the better work hardening ability confirmed by the increased intragranular Nb(C, N) particles dominated the synthetical mechanical properties in UFG steel. The intragranular Nb(C, N) particles advocated the stimulation and accumulation of geometrically necessary dislocations (GNDs), thus the strength increment by work hardening counteracted the decreased strength resulted from coarsen ferrite grains.

Breaking through the strength-ductility trade-off in graphene nanoplatelets reinforced titanium matrix composites via two-scale laminated architecture design

In this study, we report a novel approach to enhance strength and stiffness in titanium alloys while maintaining ductility. We prepared a two-scale laminated structured titanium matrix composite (TMC) using graphene nanoplatelets (GNPs) introduced into a Ti6Al4V matrix. The intrinsic structure of the GNPs was preserved, and an appropriate interface reaction facilitated strong bonding. Strengthening and toughening effects were achieved through uniform distribution, diverse interface designs, firm interface bonding, and laminated architecture. Our results demonstrate that the laminated GNPs/Ti6Al4V composite exhibits excellent strength-ductility synergy, with an enhanced yield strength (+163.35 MPa compared to pure Ti6Al4V) while maintaining a good ductility of 17.39%. This study presents a practical approach to achieving a balance between strength and ductility in titanium matrix composites.

Optimization in strength-ductility of Mg-Gd-Y-Zn-Zr alloy processed by upsetting-extrusion combined with intermediate thermo-mechanical treatment (ITMT)

In this work, the effects of intermediate annealing and intermediate annealing subsequent aging treatment on the second phase precipitation, dynamic recrystallization (DRX) behavior, and mechanical properties of Mg-9Gd-4Y–2Zn-0.5Zr (wt.%) alloy were comparatively studied. The results showed that the one-pass upsetting-extrusion (UE) deformation intermediate annealing treatment sample (UAE) exhibited the highest dynamic recrystallized (DRXed) grains number fraction and the largest average DRXed grain size, which was mainly attributed to the precipitation of a large number of β-Mg5RE phases (>1 μm) at the grain boundaries (GBs) and within unDRXed grains after annealing treatment. These β-Mg5RE phases promoted DRX through particle-stimulated nucleation (PSN) mechanism during subsequent extrusion process. However, the lack of the pinning effect of the fine second phase precipitations led to the growth of DRXed grains. The DRXed grains of the deformation intermediate annealing subsequent peak-aging treatment sample (UAAE) were significantly smaller than the UAE sample. This is mainly due to the fact that the densely distributed prismatic β′ phases precipitated by the peak-aging treatment were rapidly transformed into nano-scale β-Mg5RE phases and pinned at the DRXed grain boundaries to inhibit the growth of the DRXed grains during the subsequent extrusion process. The ultimate tensile strength (UTS) and failure elongation (EL) of the UAAE sample were 274 MPa and 14.3%, respectively, 4.2% and 85.7% higher than those of the UE sample, showing excellent strength-ductility synergy. The randomly oriented fine DRXed grains, coarse unDRXed grains with high-density dislocations and substructures, and nano-scale β-Mg5RE particles were co-contribute to the strength-ductility synergy.

Selective laser melting of AlCoCrFeMnNi high entropy alloy: Effect of heat treatment

The dilemma concerning the trade-off between the strength and ductility of alloys has persistently been a significant problem in engineering applications. Conventional techniques such as grain refinement, severe plastic deformation, and precipitation strengthening usually increase strength at the expense of ductility. High entropy alloys with dual-phase structures, on the other hand, generally display excellent strength-ductility synergy. In this study, we attempted to mix pre-alloyed powders of two distinct phases (body-centered cubic - bcc and face-centered cubic - fcc) to fabricate AlCoCrFeMnNi HEAs with a dual-phase structure by selective laser melting. Furthermore, we investigate the impact of varying heat treatment temperatures (900 °C, 1000 °C, and 1100 °C) on its phase composition, microstructure, and mechanical properties. The results show that with an increase in the heat treatment temperature, the volume of the fcc phase increases gradually and the volume of the bcc phase decreases. The columnar structure in the fcc phase transforms into a cellular structure, and a spinodal decomposition is observed with the bcc phase. As the heat treatment temperature increases, the yield strength decreases while the elongation substantially increases, with the samples heat-treated at 1100 °C showing the best comprehensive properties (yield strength ∼700 MPa, tensile strength ∼950 MPa, and ∼15% ductility).

On the excellent strength-ductility synergy of wire-arc directed energy deposited Mg-Gd-Y-Zn-Zr alloy via manipulating precipitates

On the excellent strength-ductility synergy of wire-arc directed energy deposited Mg-Gd-Y-Zn-Zr alloy via manipulating precipitates

Enhanced strength-ductility synergy of laser additive manufactured stainless steel/Ni-based superalloy dissimilar materials characterized by bionic mechanical interlocking structures

The unique mechanism of toughness enhancement found in natural materials has served as inspiration for the development of a new generation of dissimilar metal materials (DMMs). Here we present a bionic mechanical interlocking structure strategy that stainless steel 316L and Inconel 625 DMMs with an enhanced strength-conductivity trade-off processed by laser additive manufacturing (AM), possessing an ultimate tensile strength of 675.64 MPa, and a uniform elongation of 33.6%. The incompatible deformation between SS316L (plastic deformation) and IN625 (non-deformation) contributes to overcoming the strength-ductility trade-off. The integration of alternating soft and hard non-uniform structures plays a pivotal role in effectively absorbing and dissipating the energy introduced by external loads during crack propagation. This geometric arrangement and multilevel structure at the interface notably reduces the effective stress intensity factor along the crack path, leading to added resistance against loading. The multi-strengthening mechanism coupled with the heterogeneous deformability gives the material excellent strength-ductility synergy, especially the bionic mechanical interlocking structure extending the crack expansion path, which helps to avoid premature failure of weak interface layers. These findings will provide new insights into the controlled design of high-performance DMMs, which highlights the potential to inherit merits from constitutive materials for better strength-ductility combinations.

Realizing excellent strength-ductility synergy in ultrafine-grained medium W content composites reinforced with multiple strengthening mechanisms

In this article, ultrafine-grained W–Ni–Fe composite with medium W content was successfully fabricated via methods composed of spray-drying, two-stage reduction and low-temperature sintering. It is noticed that the variation of matrix phase fractional volume was effective to tailor the microstructure, mechanical performance and deformation behavior. The microstructure of the medium heavy alloy (MHA) underwent the obvious change from traditional coarsen W grains (>40 μm) to those with sizes of only 3.5 μm, accompanied by a large number of nanosized W precipitate. The two main fracture types of MHA are the W cleavage fracture and matrix phase ductile rupture. The additions of Mo and La2O3 revealed three kinds of strengthening effects, including fine-grained, solid-solution and dispersion strengthening. Experimental results showed that a significant enhancement in tensile properties (∼972.5 MPa and 26.5%) were benefitted from the cooperation of multiple strengthening and plasticized mechanisms, and the detailed effects of deformed twinning and precipitation strengthening were analyzed. The current findings demonstrated that MHA possessed an outstanding combination of strength and ductility and was a promising alternative to conventional tungsten heavy alloys (WHAs) for a more extensive range of applications.

Designing ultrastrong and thermally stable FeCrAl alloys with the fine-grained structure

Designing microstructurally stable FeCrAl alloys with excellent strength-ductility synergy is highly desirable for their engineering applications. However, due to the preference nucleation of precipitates at grain boundaries (GBs), the improved precipitation strengthening of these alloys is usually accompanied by intergranular embrittlement. Here, we propose a novel thermomechanical processing route coupled with the Si alloying strategy via precipitation of coherent deformable Laves precipitates inside equiaxed fine-grains to achieve FeCrAl alloys with ultrahigh yield strength over ∼992 MPa, excellent uniform elongation of ∼7.6% at room temperature, and superior thermal stability at temperature ∼1200 °C. The Si alloying not only decreases the stacking fault energy of Laves precipitates favorable for their stacking-fault-mediated deformation but also hinders grain coarsening at 1200 °C due to the Si-enrichment favorable for GB pinning effects. Our results prove the possibility of achieving the collaborative enhancement of mutually exclusive properties in alloys, such as strength-ductility-thermal stability via nanoprecipitation engineering, and offer a promising route to prepare dispersion-strengthened materials.

A scheme for achieving strength-ductility trade-off in metallic glasses

The strength-ductility paradox in structural materials remains a long-standing dilemma in advanced materials synthesis. Metallic glasses (MGs) that are structural materials of remarkably high-strengths are not exclusive in structural applications due to their inherently poor plasticity. This study addresses this conundrum by presenting a scheme for achieving excellent strength-ductility synergy in MGs from structural and energetic standpoints. By applying a two-step pathway of mechanical rejuvenation and cyclic stress loadings upon a Zr2Cu as-constructed MG model, deformation behavior was analyzed by molecular dynamics simulations. As higher energy states of the MG characterized by enhanced compressive plasticity was found by mechanical rejuvenation due to internal stress accumulation accompanied with an unusual increase in free volume and atomic energy, cyclic stress loading upon rejuvenation annihilated loosely-packed regions to advance a more stable state with less energy to enhance structural stability with an improvement in elastic strain limit and strength. By theoretical modelling, strength-ductility trade-off was demonstrated by the delay in shear transformation zone activities that orchestrated the generation and intersection of multiple shear bands. As a result, a two-step scheme in which soft regions are aggregated to a concentered mass intensified to higher potential energy followed by dissipating the consolidated mass into randomly dispersed soft regions is the key to achieve the strength-ductility trade-off in MG materials. The outcome of this study will further advance structure-property characterization in amorphous solids.

Achieving excellent strength-ductility synergy via high density dislocation and nano-twinning in cryo-rolled FeCoCrNiMo0.2 high-entropy alloy

High-density dislocations and nano-twinning are known to significantly influence the work hardening ability of materials, presenting a potent approach for enhancing their overall strength. Here, a superior tensile strength-ductility synergy in a FeCoCrNiMo0.2 high entropy alloy (HEA) with high density dislocation and nano-twinning was achieved by employing cryo-rolling followed by subsequent annealing. Through electron microscope observation, the effects of geometrically necessary dislocation density and nano-twinning on tensile strength and plasticity are elucidated. The microstructure analysis reveals a substantial presence of dislocations and nano-twinning within the deformed grains following short-time annealing at 600 °C and 800 °C. The strategic presence of nano-twins serves as effective impediments to dislocation slip, resulting in the storage of dislocations within the grains, which contributes to the alloy's superior strength-ductility synergy and remarkable work hardening ability. Impressively, the obtained tensile strength-ductility matching exhibits yield strength and ductility values of 992.1 MPa/0.19 and 719 MPa/0.39, respectively. Upon increasing the annealing temperature to 1000 °C, high-density annealing twins emerge in the recrystallized grains, accompanied by a concomitant reduction in the geometrically necessary dislocation density due to dislocation rearrangement and annihilation. Furthermore, a small amount of topological close-packed (TCP) phase and L12 phase precipitation during annealing are observed, contributing to increased work hardening ability of the alloy. The findings underscore the importance of microstructural engineering as a valuable strategy for optimizing the mechanical properties of HEAs with a face-centered cubic structure.

Development of a Ti30Hf20Nb20Ta10V10Mo7W3 refractory high entropy alloy with excellent mechanical properties and wear resistance

Refractory high entropy alloys (RHEAs) have attracted a great deal of attention for the competitive properties at elevated temperatures, whereas the ambient-temperature brittleness has been still a bottleneck for practical applications. Herein, we report on a newly-designed Ti30Hf20Nb20Ta10V10Mo7W3 RHEA which exhibits an excellent combination of mechanical properties and wear resistance in a wide temperature range. The present RHEA possesses a yield strength of 1225 ± 17 MPa together with a fracture strain of > 45 % at room temperature, showing an excellent strength-ductility synergy. The alloy also maintains considerable yield strength and ductility at elevated temperatures, outperforming numerous ductile RHEAs. In addition, the coefficient of friction and wear rate decrease with increasing temperature from room temperature to 800 ℃. Interestingly, the alloy exhibits a wear rate as low as (5.50 ± 0.11) × 10−6 mm3 N−1 m−1 at 800 ℃, which is related to the formation of continues and dense oxide layer.

Achieving excellent strength-ductility synergy of Ti6Al4V alloy produced by powder metallurgy and thermo-mechanical treatment

This study aimed to enhance the mechanical properties of Ti6Al4V alloy through powder metallurgy and thermo-mechanical treatment (TMT). By engineering a fine primary α phase (αp) and heterogeneous martensite (α′) microstructure, comprising fine martensite laths (FMLs) and coarse martensite laths (CMLs), we achieved an exceptional combination of strength σb∼1148.15 MPa and ductility ϵf∼24.32%. Detailed TEM analysis revealed variations in nanohardness between αp and α′ regions, strain partitioning between the two constituents, and a strain gradient from the αp/α′ interface to the grain interior of αp and α’. This activated a large number of geometrically necessary dislocations (GNDs) near the interface, mostly with <c+a> components, contributing significantly to the alloy's extraordinary work-hardening abilities. Strengthening of Ti6Al4V alloy was mainly attributed to the formation of hierarchical nanotwins and solid solution of Al elements in αp and α′, effectively impeding dislocation motion. These results open up possibilities for obtaining Ti6Al4V with high strength and ductility synergistically, with potential applicability to other materials.

Excellent strength-ductility synergy in a novel medium manganese steel containing 2.4Al-2.9Mn-4.1Ni realized through limited thermo-mechanical processing steps

In this study, the effect of microstructural and micro-textural evolution on tensile properties in hot forged (HF) and hot rolled (HR) medium-Mn steel containing ∼4 wt% Ni is systematically investigated. The microstructures of HF and HR specimens comprise of martensite (α′), nanosized NiAl (B2) precipitates and retained austenite (RA). The excellent tensile properties in HF and HR specimens have been achieved through minimal thermomechanical processing routes. The HR specimen exhibits better strength (∼1868 ± 69 MPa), and ductility (∼16.5 ± 1%) as compared to the HF specimen (∼1765 ± 32 MPa, and ∼12 ± 2%). The prior austenite grain (PAG) size of HR specimen is lower than HF, leading to lower width of lath martensite which contributes to achieving higher strength in the former specimen. Apart from the lath width, the presence of twin martensite along with RA, higher fraction of high angle grain boundaries (HAGBs), and ∑3 boundaries improve the strength-ductility synergy in HR specimen as compared to HF condition. The development of higher intensity γ-fiber <111>//ND during hot rolling has resulted in better ductility in HR specimen, whereas the presence of high intensity Cube texture {001}<100> has deteriorated the tensile properties of HF specimen. Further, visco-plastic self-consistent (VPSC) simulation has been carried out to understand the influence of primary {110}<111> and secondary {112}<111> slip systems activation on strain hardening response of the specimens. It has been observed that the higher activation of primary slip system {110}<111> in HR specimen leads to better strain hardening response at stage IV as compared to HF specimen.

Simultaneously increasing mechanical and corrosion properties in CoCrFeNiCu high entropy alloy via friction stir processing with an improved hemispherical convex tool

It generally shows the trade-off for the mechanical properties and corrosion resistance of high entropy alloys (HEAs). In this study, friction stir processing (FSP) with an improved hemispherical convex tool was applied to process the as-cast CoCrFeNiCu HEA, which simultaneously increased the mechanical properties and corrosion resistance of the HEA by a large degree. After FSP, the grains were significantly refined from 6 μm to ∼300 nm, with 91% of high angle grain boundaries and 18% of nanometer twins, leading to a remarkable increase in the yield strength from ∼194 MPa to ∼935 MPa. More importantly, the FSP HEA showed an excellent strength-ductility synergy with yield strength of ∼695 MPa and a uniform tensile elongation of ∼17.5% after annealing, which was mainly attributed to the comprehensive role of equiaxed ultrafine microstructure, second phase and the high fraction of annealing twins (27%). In addition, the FSP HEA showed higher corrosion resistance than the base material by electrochemical test, which was mainly attributed to the improvement of the self-corrosion potential and the stability of the passivation film caused by the mitigation of Cu segregation and grain refinement. This study provides a new way to simultaneously increase the mechanical properties and corrosion resistance in HEAs.

Strength-ductility synergy and grain refinement mechanisms in a Co-Cr-Ni medium-entropy alloy with novel analogous harmonic structure

A novel strategy is implemented to enhance the strength-ductility synergy in the Co-Cr-Ni-based medium-entropy alloy (MEA) by designing analogous harmonic structures (AHS), where the soft face-centered cubic (FCC) matrix is surrounded by hard multiphase constitutes. The high yield strength of 1028 MPa and ultimate tensile strength of 1558 MPa coupled with considerable uniform elongation of 20% are achieved for the AHS-MEA. Upon uniaxial tension, a large number of the nanograins appear in the core near the interface meanwhile the hard σ precipitates are penetrated by the mobile dislocations in the shell. A finite-element based model is developed to elucidate the intrinsic mechanisms underlying microstructure evolution during plastic deformation. Similar to the equal channel angular pressing/extrusion and high pressure torsion, the coexistence of large tensile hydrostatic stresses and shear stresses plays a crucial role in the grain refinement. The study provides new insights into the nanocrystalline formation mechanism and excellent strength-ductility synergy.