Simultaneous Enhancement Of Strength Research Articles

Computer Alloy Design of Ti Modified Al-Si-Mg-Sr Casting Alloys for Achieving Simultaneous Enhancement in Strength and Ductility.

In this paper, an efficient design of a Ti-modified Al-Si-Mg-Sr casting alloy with simultaneously enhanced strength and ductility was achieved by integrating computational thermodynamics, machine learning, and key experiments within the Bayesian optimization framework. Firstly, a self-consistent Al-Si-Mg-Sr-Ti quinary thermodynamic database was established by the calculation of phase diagram method and verified by key experiments. Based on the established thermodynamic database, a high-throughput Scheil-Gulliver solidification simulation of the A356-0.005Sr alloy with different Ti contents was carried out to establish the "composition-microstructure" quantitative relationship of the alloy. Then, by combining the computational thermodynamic, machine learning, and experimental data within the Bayesian optimization framework, the relationship "composition/processing-microstructure-properties" of A356-0.005Sr with different Ti contents was constructed and validated by the key experiments. Furthermore, the optimum alloy composition of the Ti-modified A356-0.005Sr casting alloy was designed based on this integration method with the Bayesian optimization framework and verified by the experiments. It is anticipated that the present integration method may serve as a general one for the efficient design of casting alloys, especially in the high-dimensional composition space.

Simultaneous enhancement of strength and toughness of ultrafine-grained dual-phase steel with a bimodal lamellar microstructure

A novel heterogeneous lamellar microstructure with ultrafine grains was successfully introduced into a DP590 steel plate using a simple two-step controlled rolling process (TCR) described in this work. The ferrite and martensite are laminated, with an average size of 1.7 μm and 1.2 μm, respectively. The ferrite shows a bimodal grain size distribution and intensified α-fiber and rotated cubic texture. Compared to conventional controlled-roll (CCR) steel, TCR steel demonstrated 46.6 % higher tensile strength with a considerably higher work hardening rate while maintaining a reasonably high uniform elongation of 12.1 %. Furthermore, the impact energy at –60 °C was increased by almost 100 %. The ultrafine-grained lamellar microstructure in TCR steel was believed to be responsible for the synergistic deformation and delamination fracture toughening that resulted in the simultaneous improvement in tensile and impact properties.

Amorphization activated by semicoherent interfaces of FCC/BCC HEA multilayers during deformation

Eutectic high entropy alloys (EHEAs) are widely advocated materials for overcoming the strength-ductility trade-off due to their abundant heterogeneous interfaces. However, the lack of a full understanding of the plastic carrier-interface interaction mechanism obscures the essential role of the interface in the simultaneous enhancement of strength and ductility. To elucidate the underlying mechanisms from an interface perspective, FCC/BCC multilayers with semicoherent and coherent interfaces were prepared by a magnetron sputtering system. The mechanical properties and microstructure evolution of multilayers were investigated by using nanoindentation, X-ray diffractometer and transmission electron microscopy, respectively. Moreover, the dislocation motion behavior and stress distribution during plastic deformation were analyzed by MD simulation. It is found that the plastic deformation behavior and mechanical properties of EHEAs are sensitive to the heterogeneous interfacial structure. During plastic deformation, the coherent interface facilitates the continuous slip of dislocations, whereas the semicoherent interface promotes amorphization by dislocations pileup. The results are important for understanding the plastic carrier-interface interaction mechanism, and the findings provide new insights for the development of high strength-ductility HEA materials.

Simultaneous enhancement of strength and ductility for AZ31 magnesium alloy by pre-twinning induced heterostructure

Pre-twinning was used to tailor the strength and ductility of AZ31 magnesium alloy. Simultaneous enhancements in both ductility and strength were achieved in the AZ31 after the introducing of a high fraction of twin-matrix pairs. The slip trace analysis indicated that although the area-weighted average global Schmid factors (SFs) were not significantly changed, much more non-basal slip was activated in the pre-twinned sample compared with that in the as-received sample, which was beneficial to achieving higher work hardening and obtaining higher uniform elongation. The high-resolution digital image correlation (DIC) combined with ex-situ electron backscatter diffraction (EBSD) characterization revealed that the uniformity of the grain-size scale strain distribution was improved and the local strain concentration at the boundary was reduced during the loading as result of the extra activated non-basal slip, which delayed intergranular crack initiation and increased ductility. The activation of much non-basal slip with high critical resolved shear stress, the hetero-deformation, and the fine equivalent grain size caused the strengthening of the AZ31 sample with a high fraction of twin-matrix pair interfaces. These results imply that tailoring the twin-matrix interface density is an effective strategy to achieve excellent strength-ductility combinations in HCP metals.

Circumventing strength-ductility paradox in high entropy alloys through deformation processing

Engineering materials are known to show trade-off between high tensile strength and ductility. The simultaneous enhancement of strength and ductility can make them more appealing for various structural applications. In this study, we demonstrate a facile technique to address the conflicting strength-ductility trade-off in crystalline materials. AlCoCrFeNi high entropy alloy (HEA), one of the most popular multi-principal alloy system, was considered for the investigation. The as-cast AlCoCrFeNi alloy showed a coarse grain microstructure with BCC/B2 phase. The as-cast alloy was subjected to severe plastic deformation using a facile technique known as stationary friction processing (SFP). The SFP for only 15 min resulted in an order of magnitude reduction in the grain size along with BCC to FCC phase transformation. The processed sample demonstrated more than 2 times higher ultimate tensile strength (∼650 MPa) compared to as-cast HEA (∼310 MPa). Further, the ductility of the processed HEA was enhanced from 11 % to 18 %. The combination of fine grain structure along with BCC to FCC transition through SFP enabled exceptional mechanical properties in the HEA. This approach can easily be extended to other alloy systems for designing high tensile strength and superior ductility.

Simultaneously enhanced strength and ductility in heterogeneous grain structured Ni26Co26Fe25Cu17Ti6 high entropy alloy by introducing an appropriate amount of Y2O3 nanoparticles

The strength and ductility trade-off is a long-standing issue of single face-center-cubic (FCC) high entropy alloys (HEAs). In the present work, the in-situ formation of heterogeneous grain structure coupled with the introduction of Y2O3 nanoparticles in FCC structure Ni26Co26Fe25Cu17Ti6 HEA is proposed as a strategy to enhance the strength and ductility synergy. The oxide dispersion strengthened (ODS) Ni26Co26Fe25Cu17Ti6 HEAs were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) methods and the influences of different Y2O3 additions on the evolutions of oxide precipitates, heterogeneous microstructure and mechanical properties of ODS-HEAs were systematically investigated. The results show that the introduction of Y2O3 facilitates the new precipitation of finer and semi-coherent Y2Ti2O7 oxide nanoparticles, in addition to the protogenous TiO in the Ti-containing HEA matrix. All the studied ODS-HEAs display the bimodal grain microstructure, in which numerous oxide dispersoids are distributed exclusively in the fine-grained (FG) region. With the increase of Y2O3 addition, the average grain size of FG region first decreases and then increases in ODS-HEA, while the proportion of FG region shows the opposite trend. When the content of Y2O3 is 1.05 wt%, the yield strength, ultimate tensile strength and elongation to fracture of ODS-HEA at room temperature are 21%, 27% and 157%, respectively, higher than those of Ni26Co26Fe25Cu17Ti6 base alloy. The simultaneous enhancement of strength and ductility in ODS-HEA by introducing a proper amount of Y2O3 is mainly attributed to the additional precipitation strengthening contribution of generated Y2Ti2O7 oxide nanoparticles having semi-coherent interfaces with the FCC matrix.

High strength and high ductility of Mg-10Gd-3Y alloy achieved by a novel extrusion-shearing process

To simultaneously improve the strength and ductility of the Mg-10Gd-3Y alloy, we propose a new processing route: conventional extrusion (EX), followed by an equal channel angular pressing (ECAP) deformation, without stopping. The new process is called: extrusion-shearing (ES). By employing ES at 400 °C, the tensile yield strength of the Mg-10Gd-3Y alloy was increased to 289 MPa, together with a high ultimate tensile strength of 361 MPa, and a good tensile elongation to failure of 27.4 %, at room temperature. The underlying mechanisms for the simultaneous enhancement in strength and ductility were investigated. The extra shearing deformation by the ECAP-stage of the ES testing led to the formation of a fully recrystallized homogenous microstructure with an average grain size of 4.3 µm, with dynamic precipitation of Mg5(Gd,Y) particles at/near grain boundaries. Both macro and micro texture characterizations indicated a strong decrease in the intensity of the crystallographic texture during the ECAP part of the ES process, and a new type of texture. The multicomponent nature of the obtained texture and the microstructural modifications together with a dispersive distribution of precipitates contributed to an excellent combination of high strength and ductility of the Mg-10Gd-3Y alloy processed by ES.

Influence of Co content on the simultaneous enhancement of strength and ductility in severely drawn textured Ni-Co microwires

ABSTRACT This study examines the deformation behaviour of Ni-Co microwires exhibiting high strengths and ductility, where the addition of Co is intended to decrease the stacking fault energy. A reduction in stacking fault energy is likely to retard the recovery processes, refine grain size and enhance strain hardening by dislocation interactions at twin boundaries. Microwires were drawn to a strain of 5.88, from annealed Ni-Co alloys with Co content varying from 30 to 60 wt%. Subsequent tensile testing revealed a simultaneous increase in strength and ductility with an increase in Co content. The enhanced strength is a consequence of the finer grain size with an increase in Co, and the larger ductility is related to a combination of greater strain hardening and a higher strain rate sensitivity with an increase in Co. The textured drawn Ni-Co wires exhibited higher strengths than those obtained by severe plastic deformation with comparable grain sizes.

Infrared-light-driven self-healing MoS2/polyvinyl alcohol hydrogel with simultaneous enhancement of strength and ductility

Self-healing hydrogels exhibit special self-healing or self-recovery function like human skin after injuring, thereafter, draw lots of attention in biomedical applications. However, self-healing hydrogels with strong mechanical and rapid self-healing properties are not fully realized. MoS 2 /polyvinyl alcohol (PVA) hydrogels are developed to achieve rapid self-healing function by utilizing the excellent photothermal conversion effect of MoS 2 under near-infrared (NIR) light. Effects of microstructure and content of MoS 2 on self-healing and mechanical properties of MoS 2 /PVA hydrogels are investigated, including flower-like MoS 2 spheres by bottom-up hydrothermal reaction and MoS 2 sheets by liquid-phase stripping method. The MoS 2 /PVA hydrogels embodied with the two types of MoS 2 were produced by simple freezing/thawing method, and exhibited rapid self-healing function, together with simultaneous enhancement of strength and ductility. The MoS 2 /PVA hydrogel modified by flower-like MoS 2 spheres with a content of 0.5 wt% presents a significant self-healing function with a healing efficiency up to 90.0% within 5 min, and an enhancement of tensile strength of 9.1 MPa (190% to blank PVA) and a ductility of 162.5% (290% to blank PVA). Furthermore, the MoS 2 /PVA gel with flower-like MoS 2 spheres into the PVA networks produces a significant enhancement of fracture strength (58.4 MPa) after fully curing, characterized by an increases of 612% compared with the pure PVA. The photo-induced self-healing and strengthening effects of the MoS 2 /PVA hydrogels are discussed. • A rapid self-healing MoS 2 /PVA hydrogels is developed under near-infrared light. • Photo-thermal conversion effect of MoS 2 produces the self-healing property. • Flower-like MoS 2 spheres exhibit better healing efficiency than MoS 2 sheets. • MoS 2 /PVA hydrogels present a simultaneous increase of strength and plasticity. • 2D and 3D strengthening effects of the MoS 2 /PVA composites are discussed.

Investigations on the interface-dominated deformation mechanisms of two-dimensional MAX-phase Ti3Al(Cu)C2 nanoflakes reinforced copper matrix composites

Two-dimensional (2D) materials showing the giant advantage over their bulk counterparts are believed to be the ideal reinforcement for metal matrix composites, whereas the deformation mechanism of which is currently unknown. Herein, we investigated the interface effect of 2D MAX phase Ti3Al(Cu)C2 nanoflakes (MAX NFs) obtained by a Cu-atoms-diffusion assisted exfoliation method on the plastic deformation process of Cu matrix. Tensile tests demonstrated a simultaneous enhancement in strength and fracture elongation with the increase of MAX NFs content. The composites exhibited a four-stage deformation process involving an extended “yield plateau” before obvious strain hardening stage. Microstructural examination revealed that the 2D nature of MAX NFs and the coherent interface structure facilitated the nucleation of partial dislocations, which coordinated the initial plastic deformation by gliding and interacting to form Lommer-Cottrel (LC) locks. At high strain levels, both LC locks and MAX NFs served as obstacles for dislocation cross-slip and thus achieved significant forest hardening (or latent hardening) effect, validated by EBSD texture from the in-situ tensile tests and visco-plastic self-consistent simulation. This sort of interface-induced microstructure evolution promoted tortuous micro-cracks along discontinuous slip bands and significant crack bridging and deflection extrinsic toughening mechanisms. The current findings provide a possible strategy of simultaneously enhancing strength and ductility through tailoring 2D geometric shape of reinforcements and their interface with the metal matrix.

Cooperative enhancement of strength and ductility in metallic materials: The role of local stress/strain evolution on the plastic flow behavior

Simultaneous enhancement of strength and ductility is one of the eternal topics for the community of metallic materials. The heterostructure architecture, e. g. layered structure, is one of the potential methods to evade the strength-ductility trade-off dilemma in recent years. However, there is still a lack of a deeper understanding to excellent strength-ductility combinations. In the present study, we focused on the local stress, which drives local plastic deformation. The local represents the affected scale of the stress. The evolution processes of local stress/strain upon loading of typical model materials of Ti/Ti, Ti/Al, and Al/Al layered metals (LMs) were quantitatively characterized by in situ electron microscope, synchrotron X-ray diffraction, and neutron diffraction. We found that the deformation characteristics were closely associated with the local stress/strain evolution process, and highlighted the key role of local stress/strain in revealing the deformation mechanisms. This work therefore may open a new route to design new metallic materials through the tailoring of local stress/strain evolution.

Simultaneous enhancement of strength and ductility via microband formation and nanotwinning in an L12-strengthened alloy

Metallic alloys with high strength and large ductility are required for extreme structural applications. However, the achievement of ultrahigh strength often results in a substantially decreased ductility. Here, we report a strategy to achieve the strength-ductility synergy by tailoring the alloy composition to control the local stacking fault energy (SFE) of the face-centered-cubic (fcc) matrix in an L12-strengthened superlattice alloy. As a proof of concept, based on the thermodynamic calculations, we developed a non-equiatomic CoCrNi2(Al0.2Nb0.2) alloy using phase separation to create a near-equiatomic low SFE disordered CoCrNi medium-entropy alloy matrix with in situ formed high-content coherent Ni3(Al, Nb)-type ordered nanoprecipitates (∼ 12 nm). The alloy achieves a high tensile strength up to 1.6 GPa and a uniform ductility of 33%. The low SFE of the fcc matrix promotes the formation of nanotwins and parallel microbands during plastic deformation which could remarkably enhance the strain hardening capacity. This work provides a strategy for developing ultrahigh-strength alloys with large uniform ductility.

All‐Organic Filler with Fractal Structure for Reinforcement and Toughening of Aromatic Polyamide Film

AbstractThe simultaneous enhancement in strength and toughness seems to be an intrinsic contradiction in multiple material designs, including the structural regulation of polymer composites. In this study, benzimidazole‐containing aromatic‐polyamide thin films are used as typical rigid polymers with high strength and modulus to study their strength–toughness collaboration via a multi‐scaled stress distribution mechanism. A fully organic deformable filler with a fractal structure is designed. Utilizing the large‐scale deformability of the filler to absorb the energy and dislocation node structure of the filler to disperse the stress, the composite thin film is significantly toughened, which is reflected in the elongation at break increased by 144.9% and energy at break increased by 154.2%. In addition, the specific fractal structure of the filler provided a larger interaction area, which enhanced the interfacial bonding force and improved the strength of the film. Moreover, owing to the larger interaction area provided by the fractal structure, the interface bonding force between the filler and matrix due to the similar chemical structures is further improved and the tensile strength of the composite thin film is increased from 389.2 ± 11.98 to 426.2 ± 4.41 MPa.

Simultaneous Enhancement of Strength and Toughness in a Medium-Carbon Martensitic Steel by Ti-Mo Addition

Simultaneous Enhancement of Strength and Toughness in a Medium-Carbon Martensitic Steel by Ti-Mo Addition

Simultaneous enhancement of strength and ductility in friction stir processed 2205 duplex stainless steel with a bimodal structure: experiments and crystal plasticity modeling

Simultaneous enhancement of strength and ductility in friction stir processed 2205 duplex stainless steel with a bimodal structure: experiments and crystal plasticity modeling

Simultaneous enhancement of strength and ductility in selective laser melting manufactured 316L alloy by employing Y2O3 coated spherical powder as precursor

In this work, the 316L spherical powders coated with homogeneous Y2O3 layer have been prepared by in-situ chemical method. Then the influence of Y2O3 on the microstructure and mechanical properties of 316L specimens prepared by selective laser melting was studied. It was found that the grain morphology and crystallographic texture of the SLMed 316L specimens with different Y2O3 contents show the same anisotropy along the vertical direction and horizontal direction, which is independent of the doping content of Y2O3. The formation of twins in specimens doped with Y2O3 can be attributed to the combined effects of large residual stress, low stacking fault energy and in-situ heat treatment. Compared with the strength (707 ± 3 MPa) and ductility (42.5 ± 0.3%) of the undoped 316L specimen, the strength (732 ± 5 MPa) and ductility (49.5 ± 0.8%) of the 316L specimen doped with 0.25 wt% Y2O3 is improved simultaneously. The increase of strength is mainly attributed to the formation of twins, the strengthening mechanism caused by the precipitated particles and the refinement of cellular structures. The high ductility is attributed to the influence of the refinement of cellular structures and the formed twins.

Intermediate stacking fault and twinning induced cooperative strain evolution of dual phase in lean duplex stainless steels with excellent cryogenic strength-ductility combinations

The effects of intermediate substructures on the strain evolution in dual phase and the correlated mechanical properties at different temperatures were investigated in two lean duplex stainless steels (LDSSs) with different stacking fault energy (SFE). At room temperature (RT), the 1#-LDSS shows a lower yield strength (YS) but high tensile elongation (TEL) values than those of the 2#-LDSS due to a more significant TRIP effect, resulting from a lower SFE and mechanical stability of austenite (γ). Meanwhile, the plasticity of the ferrite (α) strip is also accommodated by the grain rotation process and texture transformation from component ⟨123‾⟩{111} to ⟨112‾⟩{111}, preventing a drastic dislocation generation in the α/γ interfaces. However at liquid nitrogen temperature (LNT), although a strong dislocation hardening of dual phase accompanied with a two-stage γ→ε→α’ transformation sequence occurs at low strains of 1#-LDSS, the severe dislocation accumulation in ferrite becomes the potential site of crack nucleation, leading to a high ductility loss compared to the RT. In contrast, a simultaneous enhancement of strength and ductility can be obtained in the 2#-LDSS at LNT. The introduction of intermediate stacking faults (SFs) and twins due to a lower critical resolved shear stress (CRSS) can not only provide additional work hardening capacity in the early deformation stage, but also lead to a gentle dislocation increment in ferrite. The cooperative co-deformation contributes to a sustainable high strain hardening until large strains. Therefore, a high YS over 1.3 GPa and a large TEL of about 50% can be obtained in the 2#-LDSS

Evolution of strength properties and defect sub-structure of the hypoeutectic A319.0 alloy irradiated by a pulsed electron beam and fractured under tensile stress

The paper intends to investigate strength and plasticity properties and defect sub-structure of the hypoeutectic А319.0 alloy irradiated by a pulsed electron beam. The study has established and the revealed extinction contours point out that the irradiation of the А319.0 alloy by a pulsed electron beam brings about the formation of an up to 100 µm thick surface layer in the elastic-stressed state. The structure of the modified layer comprises nano-dimensional non-equiaxed cells. The reason for the non-equiaxity in a cellular structure is suggested to be the irregular heat removal from the surface of modification. X-ray microspectroscopy has found out that high-speed crystallization cells are formed by an aluminum-based solid solution and separated with thin layers, which are enriched mainly by silicon atoms and, to a smaller degree, by atoms of magnesium, iron and copper.The data obtained in the mechanical testing suggest that the irradiation was carried out in the following conditions: 50 J/cm2 and 50 µs results in the simultaneous enhancement of strength (by 22%) and plasticity (by 44%) properties of the А319.0 alloy – these are the best positive values in the set of conducted experiments. The study on А319.0 alloy samples irradiated and fractured under the tensile stress has highlighted that their fracture is dominated by the mechanism of intercrystalline quasi-brittle rupture caused by forming lengthy thin layers of the second phase along the boundaries of high-speed crystallization cells.

Simultaneous enhancement of strength and ductility by aging treatment in fine-grained Mg-13Gd alloy

Ideal structural materials should have both high strength and good ductility. Aging treatment is an effective way to increase the strength of Mg alloys, but usually sacrifices their ductility. Here we have successfully achieved the synergetic enhancement of strength and ductility of the extruded Mg-13Gd alloy via aging treatment, and obtained a Mg alloy with a tensile yield strength of 400 MPa and an elongation of 15%. The synergetic improvement of strength and ductility is mainly attributed to the formation of high-density nanoscale β′ precipitates and a certain proportion of precipitation free zone in the microstructure dominated by dynamically recrystallized fine grains. The yield drop phenomenon in the tensile curves is sensitive to the existence of movable pinned-dislocations within grains. It is expected that the discussion in this study will be helpful to developing Mg alloys with high strength and ductility via aging treatment.

Extra Strengthening and Work Hardening in Novel Precipitation‐Hardened FeCrNiSix Medium‐Entropy Alloys

Precipitation strengthening is believed as an important strengthening method that optimizes the strength of alloys. Herein, the possibility of precipitation strengthening is demonstrated by introducing the intermetallic (Cr, Si)‐rich σ phase in the novel FeCrNiSix MEAs system. It is found that simultaneous enhancement in strength and work hardening can be attained by adding Si element in the FeCrNi MEA. Specifically, the FeCrNiSi0.2 alloy realizes a good balance of strength and ductility due to the precipitation of ultrafine‐ or even nanoscale‐sized σ phase. Moreover, quantitative analyses are conducted to assess the underlying strengthening mechanisms.