Ductility Of Alloy Research Articles

On the fracture of aluminum plates perforated by rigid flat-nosed projectiles

We present a series of 2D numerical simulations for the perforation process of aluminum plates impacted by rigid steel cylinders. The simulations accounted for the residual velocities of these projectiles as a function of their impact velocities, as obtained recently by several workers. The aluminum plates in these works were made of the quasi-brittle 2024-T351 and 7075-T651 alloys, and the more ductile 6061-T651 alloy. The material properties of these alloys, for their strength and failure parameters, were taken from published works. We find that the ductility/brittleness property of these alloys is related to the different values of their corresponding strains to failure at shear states. Our simulations for the two quasi-brittle alloys resulted in good agreement with the measured data. On the other hand, the simulations for the 6061-T651 alloy agreed with the corresponding data only when we used a relatively low value of the Taylor-Quinney coefficient for this alloy. We also highlight various problems with the issue of mesh sensitivity in simulating the perforation of metallic plates by rigid cylinders. Particularly, we found that these simulations do not converge to definite values for the residual velocities even when the mesh size is reduced to 0.025 mm. Moreover, we found that the experimental data for the residual velocities can be accounted for by different failure curves, depending on the mesh size of the simulation. Thus, a given failure criterion cannot be validated by such simulations.

Influence of the manufacturing strategy on the microstructure and mechanical properties of Invar 36 alloy parts manufactured by CMT-WAAM

AbstractThe influence of the manufacturing strategy of Invar 36 alloy parts manufactured by Directed Energy Deposition by Arc (DED-Arc) also known as wire and arc additive manufacturing (WAAM) using cold metal transfer (CMT) technology has been investigated. This study focuses on the influence of applying different deposition strategies on the resulting microstructure and mechanical properties. As manufacturing costs and time are critical issues which determine the business case in WAAM applications, it is important to use the smallest possible amount of feedstock material. Therefore, different manufacturing strategies are used to obtain the variable wall thicknesses required for each part preform using WAAM as a manufacturing route. Differences in manufacturing temperature and thermal history due to different deposition strategies have been recorded. Deep microstructural analysis in as-built condition revealed that granular alignment and the crystallographic texture obtained differ between deposition strategies studied. This is the reason why there are differences in the mechanical properties, such as yield strength, ultimate tensile strength, elongation, and hardness, of the different strategies analyzed. The results revealed that the higher strength is obtained in three overlapped weld beads for the walls (514 and 581 MPa in building direction and perpendicular direction, respectively), compared to single weld bead wall (481 and 489 MPa), circular single weld bead wall (460 and 484 MPa), and meandering weld bead wall (467 and 439 MPa). The opposite is true for elongation, which is a typical correlation between strength and ductility in Fe-based alloys, having the highest elongation in the meandering weld bead wall (26 and 30%) and circular single weld bead (30 and 27%) compared to single weld bead wall (27 and 23%) and three overlapped weld bead wall (23 and 20%). It can therefore be concluded that an Invar 36 alloy part manufactured by CMT-WAAM with different strategies will have different mechanical properties, having a difference in ultimate tensile strength of 54 MPa and 142 MPa, and in elongation of 7% and 10% in building direction and perpendicular direction, respectively, between the most and the least resistant zone.

Integrated design of aluminum-enriched high-entropy refractory B2 alloys with synergy of high strength and ductility.

Refractory high-entropy alloys (RHEAs) are promising high-temperature structural materials. Their large compositional space poses great design challenges for phase control and high strength-ductility synergy. The present research pioneers using integrated high-throughput machine learning with Monte Carlo simulations supplemented by ab initio calculations to effectively navigate phase selection and mechanical property predictions, developing single-phase ordered B2 aluminum-enriched RHEAs (Al-RHEAs) demonstrating high strength and ductility. These Al-RHEAs achieve remarkable mechanical properties, including compressive yield strengths up to 1.7 gigapascals, fracture strains exceeding 50%, and notable high-temperature strength retention. They also demonstrate a tensile yield strength of 1.0 gigapascals with a ductility of 9%, albeit with B2 ordering. Furthermore, we identify valence electron count domains for alloy ductility and brittleness with the explanation from density functional theory and provide crucial insights into elemental influence on atomic ordering and mechanical performance. The work sets forth a strategic blueprint for high-throughput alloy design and reveals fundamental principles governing the mechanical properties of advanced structural alloys.

Achieving excellent ductility with increased Schmid Factor but decreased direct strain contribution of basal slip in an intergranular misorientation tailored magnesium alloy

Weakening the basal texture was a commonly used method to improve the ductility and formability of magnesium alloys. The easier activation of basal slip was often considered to be an important reason for the improved ductility of the weak basal textured magnesium alloys. However, basal slip alone cannot well satisfy the Von Mises criterion and its activation was nearly saturated in strong basal textured magnesium alloys. The deformation mechanisms of weak basal textured magnesium alloys are still open to debate. In this work, the Schmid Factor (SF) of the basal slip is obviously increased and a high fracture elongation of ∼35% is achieved in AZ31 alloy by careful tailoring of grain orientation and rational selection of loading direction. Grain size scale strain distribution by high-resolution digital image correlation (DIC) and slip activation based on the slip trace method were used to in-depth analyze the deformation mechanisms. Although the basal slip’ average SF increases, the strain statistics show that the direct strain contribution of the basal slip to the deformation gets decrease, contrary to conventional expectation. This is mainly attributed to the coupling effect of the increased basal slip’ SF with the large intergranular misorientation, which significantly promotes the activation of non-basal slip and increases its contribution to the deformation, thus leading to a lower direct strain contribution of the basal slip. The results of the study may help to further reveal the plastic deformation mechanism of magnesium alloys and improve the plasticity of magnesium alloys.

Exceptional tensile ductility and strength of a BCC structure CLAM steel with lamellar grains at 77 kelvin

The low-temperature tensile brittleness of body-centered cubic (BCC) metals and alloys can seriously compromise their service applications. In this study, we prepared a BCC structured China low activation martensitic steel (CLAM) steel with lamellar grains by regulating the rolling and heat-treatment processes, successfully reversing the decreasing trend of ductility in the steel with decrease in temperature. Compared with current face-centered cubic (FCC) structural steels and high-entropy alloys, the lamellar grained CLAM steel exhibits an excellent synergy of strength and ductility at 77K, but with lower raw material costs. The superior low temperature ductility of the lamellar grained steel can be attributed to an increase in grain strength at low temperatures which promotes the propagation of layered tearing cracks; this in turn leads to a significant increase in the necking area of the steel, thereby compensating for the decrease in ductility. We conclude that our lamellar grain structures can be utilized to significantly enhance the low-temperature tensile ductility of BCC metals and alloys, thereby expanding their service range to cryogenic temperatures.

Achieving ultrahigh strength and ductility in biodegradable Zn-xCu alloys via hot-rolling and tailoring Cu concentration

In this present paper, a biodegradable Zn-xCu alloys with an ultrahigh strength and ductility can be achieved via hot-rolling and tailoring Cu concentration, and the role of Cu concentration on the microstructure and texture evolution in the Zn-xCu alloys during hot-rolling were investigated by XRD, EBSD and TEM analysis. The results show that the microstructure of as-cast Zn-xCu alloys consisted of large sized CuZn5 phase and Zn matrix grains before hot-rolling, and numerous submicron CuZn5 phase can dynamically precipitate during hot-rolling of Zn-xCu alloys. The existence of CuZn5 phase can result in the particle stimulated nucleation of recrystallization (PSN), and then result in the formation of fine recrystallized grains. Moreover, three texture components including 0001<112¯0>, 101¯1<1¯012> and 112¯0<0001> textures can form in the Zn-xCu alloys after hot-rolling. With boosting Cu concentration, the intensity of 112¯0<0001> texture gradually reduced, while the intensity of 0001<112¯0> and 101¯1<1¯012> texture components firstly raised with the augment of Cu concentration, and then reduced. For the Zn-xCu alloys with 8 wt%Cu concentration, a combination of high yield strength, ultimate tensile strength and elongation (269.7 MPa, 322.9 MPa and 26.3 %) can be achieved, which can meet the high-performance demands of biodegradable metal vascular stents.

Ductilization of single-phase refractory high-entropy alloys via activation of edge dislocation

Refractory high entropy alloys (RHEAs) are of particular interest for their superior high-temperature strength. However, most of RHEAs are suffered from the brittleness especially at room temperature which hindered their applications. Here, we choose TiZrHfNbx (x=0.4, 0.6, 0.8, 1) as a model alloy system in which all the alloys exhibited a single-phase BCC structure. With the increasing Nb content, the fracture strain significantly increased from 8.76% to 33.21% without sacrificing the overall yield strength. The dislocation interactions were systematically investigated through extensive experimental and theoretical approaches. The limited tensile ductility of TiZrHfNb0.4 was attributed to the long straight screw dislocations confined in a few slip planes. In sharp contrast, the dislocations in TiZrHfNb alloy are rather homogeneously distributed and the superior tensile ductility of TiZrHfNb alloy is due to the activation of edge dislocations which is rare in ordinary BCC structured alloys. The atomic scale physical origin of different dislocation configuration and behaviors can be attributed to the higher misfit volume and elastic asymmetry of TiZrHfNb alloy. The outcome of this research not only reveal a new ductilization mechanism but also provide a new pathway to design ductile RHEAs through regulation the atomic scale environment.

Achieving synergy between strength and ductility in metastable β-titanium alloy through a novel multi-morphological microstructure

In order to overcome the trade-off of strength and ductility in traditional homogeneous microstructure, a novel multi-morphological microstructure in metastable β-titanium alloy Ti55531 was prepared by thermomechanical processing and post heat treatment. The multi-morphological microstructure consists of two shapes of equiaxed and lamellar, three scales of micro, submicron and nanometer α phase, and nanometer residual β phase. Micrometer-sized lamellar α phase and equiaxed α phase are obtained through the (α+β) phase region rolling, and nanometer-sized lamellar α phase is derived from aging treatment, with two step aging treatment leading to submicron-sized and nanometer-sized lamellar α phase. Meanwhile, the micrometer-sized α phase effectively prevents grain boundary migration, resulting in small β grains (less than 10 μm). This new multi-morphological microstructure results in a simultaneous enhancement in both strength (1175MPa) and ductility (20%) of the Ti55531 alloy. The synergistic improvement mechanism of strength and ductility was qualitatively analyzed in this research. The relationship between the yield strength and microstructure of the alloy was calculated, and the predicted strength was in agreement with the experimental values. It is concluded that precipitation strengthening is the primary strengthening method for multi-morphological Ti55531 alloy, and the strengthening of grain boundary increases sevenfold when the β grain size is smaller than 10 μm.

Effect of trace Bi addition on the microstructure and mechanical properties of hypoeutectic Al-Mg-Si-Mn alloy

The effects of Bi on the eutectic structure and mechanical properties of AlMg5Si2Mn alloy were investigated. The results show that when trace Bi is added to the alloy, the eutectic Mg2Si phase in the alloy is successfully refined from long plate-like to fine fiber rod-like and coral-like structure. It is mainly attributed to the precipitation of Bi atomic clusters on the front of the solid-liquid interface and form a component supercooling, in which part of Bi atoms react with Mg atoms to form nanosized Mg3Bi2 particles, which effectively inhibits the rapid growth of eutectic Mg2Si and promotes the branching and refining of eutectic Mg2Si. The strength and ductility of AlMg5Si2Mn alloy containing Bi are significantly improved simultaneously. Compared to the unmodified alloy, the largest tensile strength, yield strength and elongation to failure of the 0.3wt % Bi-modified alloy are increased to 28.04%, 12.3% and 129.1%, respectively. The fracture mode of the alloy changes from brittle fracture to ductile fracture.

Microstructure evolution and strain rate sensitivity of ductile Hf20Nb10Ti35Zr35 medium-entropy alloy after thermal cycling

The medium-entropy alloy Hf20Nb10Ti35Zr35 has a ductile BCC structure in the as-solution-treated state and could be age-hardening with fine precipitates. In this study, the thermal stress produced by thermal cycling was found to accelerate the precipitation of the α" and the evolution of ω → α phase of Hf20Nb10Ti35Zr35. The α''-martensite phase of Hf20Nb10Ti35Zr35 tended to grow in the (001)β plane, with the misorientation angle being concentrated around 52° after 10 thermal cycles. Moreover, the misorientation angle tended to have a bimodal distribution after 50 thermal cycles. Nanomechanical testing was performed to measure the strain rate sensitivity (SRS) at room temperature. The result shows that SRS of Hf20Nb10Ti35Zr35 changed from a small positive value of 0.09247 to a small negative one of either −0.02125 or −0.0445. This was mainly attributable to the decrease in the volume of the β phase or the increase of the α" + α composite phase. This demonstrates that thermal cycling treatment of the present alloy could induce more precipitation of the second phase for hardening and enhance uniform deformation behavior.

The silicide precipitation mechanism and spheroidization behavior of αp phase in a novel near-β titanium alloy during isothermal multi-directional forging process

The tread-off between the strength and ductility of near-β titanium alloys has significantly limited their applications. In this study, a novel near-β titanium alloy containing Si element was designed, and the influence of α-phase spheroidization and silicide precipitation on the mechanical properties was investigated during isothermal multi-directional forging (IMDF) process. The results showed that the β grain is easy to deform and elongate, and the deformed alloy mainly undergoes dynamic recovery (DRV) rather than dynamic recrystallization (DRX). Some silicides are dissolved due to the temperature rise caused by IMDF and the diffusion of atoms on the top of the irregularly shaped silicides. Zr and Si elements are redistributed and segregated at the dislocation, resulting in the formation of submicron-scale and nano-scale silicides. Lath-like αp phase will precipitate from the prior β grain after heat treatment in the dual-phase region, and the volume fraction of αp phase increases with the decrease of heat treatment temperature. In addition, rotation deformation and spheroidization of the lath-like αp phase occur during multi-pass IMDF in the dual-phase region. When multi-pass IMDF temperature is 770 ℃, the silicide distribution is uniform, and the αp phases are equiaxed, which is conducive to the improvement of ductility. The obtained results provide a new way to prepare the Si-containing near-β titanium alloys with excellent mechanical properties.

Rhenium alloying strengthens a ductile refractory high entropy alloy

Strengthening alloys at both ambient and elevated temperatures without compromising room temperature ductility remains a significant challenge in the structural materials field. Recently, we reported a ductile NbTaTi-based refractory high-entropy alloy (RHEA) capable of maintaining high strength up to 1200°C. In this study, we demonstrate that adding 1 at. % Re to this alloy provides further strengthening while preserving excellent cold machinability. Additionally, microstructure optimization was achieved through partial recrystallization, resulting in a heterogeneous lamella structure with alternating coarse and fine grain layers. This optimized structure further enhances the alloy's room temperature tensile strength, exceeding 1 GPa with uniform elongation above 10%. The designed alloy also retains a high strength of nearly 150 MPa at 1300°C. Our findings demonstrate that Re alloying is an effective strategy for improving the mechanical properties of NbTaTi-based RHEAs.

Materials Design by Constructing Phase Diagrams for Defects

AbstractPhase transformations and crystallographic defects are two essential tools to drive innovations in materials. Bulk materials design via tuning chemical compositions is systematized using phase diagrams. It is shown here that the same thermodynamic concept can be applied to manipulate the chemistry at defects. Grain boundaries in Mg–Ga system are chosen as a model system, because Ga segregates to the boundaries, while simultaneously improving the strength and ductility of Mg alloys. To reveal the role of grain boundaries, correlated atomic‐scale characterization and simulation to scope and build phase diagrams for defects are presented. The discovery is enabled by triggering phase transformations of individual grain boundaries through local alloying, and sequentially imaging the structural and chemical changes using atomic‐resolution scanning transmission electron microscopy. Ab initio simulations determined the thermodynamic stability of grain boundary phases, and found out that increasing Ga content enhances grain boundary cohesion, relating to improved ductility. The methodology to trigger, trace, and simulate defect transformation at atomic resolution enables a systematic development of defect phase diagrams, providing a valuable tool to utilize chemical complexity and phase transformations at defects.

Tailoring strength and ductility in novel Ni50Cr20Co15Al10V5 high entropy alloys by cold-rolling followed by aging treatment

In this work, novel Ni50Cr20Co15Al10V5 high entropy alloys were designed and subjected to aging treatment to achieve excellent strength-ductility synergy. The microstructures of the alloys were characterized using X-ray diffraction, electron backscattered diffraction, electron channeling contrast imaging, and transmission electron microscopy methods. The tensile properties and strengthening mechanism were studied and compared to the recrystallized sample. The results indicated that after aging treatment, L12 and BCC precipitates formed at the grain boundaries, enhancing both the yield strength and ultimate tensile strength while maintaining an acceptable elongation of 24.8 %. Dislocation slip dominated the deformation process, and precipitation strengthening contributed significantly to the enhanced yield strength. Molecular dynamics simulations indicated that Ni-Al, Cr-Cr, Cr-V, and Co-V elemental pairs formed the chemical short-range order (SRO) structures, which improved the yield strength of the alloys.

On the work-hardening behaviour of the additively manufactured Al-Si-Mg alloys: Composite-like versus networked microstructure

Al-Si-Mg alloys are widely used for manufacturing components via laser powder bed fusion in various industrial applications where ductility and the capacity to accommodate the strain hardening are key criteria. The ductility of the laser powder bed-fused Al alloys has become a crucial property due to their fine cellular microstructure. Post-processing heat treatments improve ductility, but resultant microstructural changes affect the work-hardening behaviour, deformability, and uniform elongation values. This study aims to investigate the work-hardening capability, uniform elongation and deformability of AlSi7Mg and AlSi10Mg samples after different post-processing heat treatments by using tensile tests, optical and scanning electron microscopies. At aging temperatures below 200 °C, the fully cellular structure of eutectic Si governs both the work-hardening behaviour and the strengthening mechanisms, despite the precipitation phenomenon. When direct-aging temperatures exceed 200 °C, the coarsening of the Si-eutectic network modifies work-hardening behavior (Stages 1–3), accentuating the effects induced by the precipitates. Artificial aging highlights the role of precipitates in controlling both work-hardening properties and deformability.

Architecture of nano-lamellar structure in Fe-B alloys via laser remelting treatment to achieve simultaneous strength-ductility enhancement

Fe-B alloys are of interest due to their promising anticorrosion performance in Al melt, but new forms that are also ductile are needed for their widespread use. The challenge in developing Fe-B alloys that are both corrosion-resistant and ductile lies in the intrinsic tradeoff between B concentration and brittle-to-ductile transition temperature. Here, we show a new strategy for the achievement of room temperature ductility in Fe-B alloys by architecting nano-lamellar structure under the laser remelting treatment. The test results indicate that the microhardness, yield strength and tensile strength of the nano-lamellae structural remelting layer are as high as 877 HV0.2, 1012 MPa and 1123 MPa, respectively, and the uniform elongation is also enhanced to 4.51 % simultaneously. This work paves a new avenue for simultaneously improving the strength and ductility of eutectic alloys with brittle phase and widens the application scope for Fe-B alloys (B≥3.0 wt percentage, wt%).

Study on Low-Temperature Deposition of Diamond-like Carbon Film on the Surface of Bionic Joint Thread and Its Properties

The double-connection structure of bionic joints of mining drill pipes has solved the problem of drill drop caused by fatigue cracks. However, with low-melting-point elastic–ductile alloy filling in the bionic joint, the thread on the joint cannot be hardened by high-temperature surface hardening treatments such as quenching and nitriding, making it prone to thread gluing or excessive wear. In this paper, the feasibility of diamond-like film deposition on the surface of a bionic drill pipe thread was studied. A tungsten transition film was used to improve the thickness of the film and the interfacial bond strength between the film and the substrate. The test results show that the total thickness of the DLC film is about 3~5 μm, the roughness is less than 2 μm, the hardness of the film reaches 24.4 GPa, the friction coefficient is 0.04, and the critical load is 56 N. SEM and EDS analyses show that the tungsten film and the bionic joint thread form a metallurgical structure. The morphology of the diamond-like carbon film is uniform and dense, and there is no obvious stratification between the substrate material. The joint with a diamond-like coating treatment has a longer service life than joints receiving conventional high-temperature nitriding treatment.

Exceptional strength-ductility synergy in the novel metastable FeCoCrNiVSi high-entropy alloys via tuning the grain size dependency of the transformation-induced plasticity effect

In-depth knowledge of the coupling between grain refinement and the transformation-induced plasticity (TRIP) effect in metastable alloys is a viable approach for the improvement of strength-ductility synergy, which needs systematic research with consideration of commercial austenitic stainless steels and novel high-entropy alloys (HEAs). Accordingly, in the present work, two Si-containing metastable HEAs in the Fe47Co30Cr10Ni5V8-xSix system (x = 3 and 6 at.%) were designed, and the TRIP-assisted AISI 304L stainless steel was also considered for comparison. The alloys were processed by cold rolling and annealing to obtain different grain sizes. Reducing the stacking fault energy (SFE) through adjusting chemical composition contributes to minimizing the detrimental effect of grain refinement on the ductility of TRIP alloys, while extremely low SFE must be avoided owing to the fast kinetics of deformation-induced martensitic phase transformation, which leads to the deterioration of ductility. In contrast to AISI 304L stainless steel, a strong TRIP effect was maintained upon grain refinement in the Fe47Co30Cr10Ni5V2Si6 HEA due to the remaining apparent SFE in the appropriate TRIP range. The tuned kinetics of martensitic transformation was found to be responsible for the exceptional ductility (∼65%) of Fe47Co30Cr10Ni5V2Si6 HEA at an ultrahigh tensile strength of 1250 MPa. Therefore, considering the identical trend of SFE with grain size, an appropriate initial SFE value is important for tuning the grain size dependency of the TRIP effect. Moreover, the ultrahigh strength was attributed to the high volume fraction of α΄-martensite as well as the high strength of the martensite phase due to the high Si content. Accordingly, for achieving strong-yet-ductile HEAs, a high Si content is recommended to benefit from solid solution strengthening in the martensite phase, a specially-designed chemical composition is needed for attaining a high volume fraction of α΄-martensite, and SFE should be in a desirable range to tune the kinetics of martensitic phase transformation.

Grain size hardening versus texture softening: Mechanical anisotropy of an AZ31B magnesium alloy processed by equal-channel angular pressing

Microstructural evolution of hexagonally close-packed (hcp) alloys subjected to severe plastic deformation differs from that of alloys with cubic crystal structure. While grain refinement is the main objective in conventional ECAP texture changes in hcp materials can result in lower strength but improved ductility depending on the deformation direction. This paper addresses the question of how the processes of grain size hardening and texture softening contribute to the highly anisotropic mechanical behavior of a severely deformed AZ31B magnesium alloy. ECAP is performed at different temperatures starting at 250 °C for the first 4 passes and subsequently reduced to 200 °C (C5, C6) and 150 °C (C7, C8). The mechanical properties of the resulting material conditions are investigated with tensile tests in four different deformation directions. While the yield strength increases up to 280 MPa in the transverse direction (TD), an opposite trend of low strength and good ductility can be observed for deformation in the extrusion (ED) and normal directions (ND). Additional microstructural investigations using EBSD show that the grain size is reduced by 95% during ECAP. Moreover, texture measurements using XRD reveal a strong fiber texture, with a high number of basal planes parallel to the shear plane of ECAP deformation, which results in a significantly improved ductility and lower strength in ED and ND. The results are discussed in the light of the competition between grain size hardening and texture softening. They highlight the potential of ECAP for the improvement of strength and ductility for magnesium alloys.

Tailoring Strength and Ductility in Dual-Phase High-Entropy Alloys: Insights from Deep Learning Molecular Dynamics Simulation on FCC/BCC Thickness Ratios

This study investigates the influence of FCC/BCC thickness ratios on the mechanical properties of AlCoCrFeNi dual-phase high-entropy alloys (DP-HEAs) using deep learning-enhanced molecular dynamics simulations. The results demonstrate that varying the thickness ratio significantly affects the stress-strain behavior, dislocation density evolution, and local structural transformations during tensile deformation. DP_0.5, with a thinner BCC phase, exhibits higher dislocation densities and enhanced strain hardening, resulting in increased strength but reduced ductility. In contrast, DP_3.0, with a thicker BCC phase, shows lower dislocation densities, leading to improved ductility but lower strength. The phase transformation from BCC to HCP structures is a key mechanism contributing to plastic deformation, with the BCC/FCC interface playing a critical role in dislocation nucleation and propagation. These findings provide valuable insights into optimizing the microstructural design of DP-HEAs to achieve a tailored balance of strength and ductility, offering the potential for advanced structural applications.