Improvement In Ductility Research Articles

Microstructural evolution and mechanical property of friction stir welded joints in AlSi10Mg alloys fabricated by laser powder bed fusion

Friction stir welding (FSW) was introduced to join laser powder bed fusion (LPBF) AlSi10Mg alloys in this study. Microstructure and texture evolution, microhardness distribution and tensile properties of the FSW joints were investigated. The evolution of grain size, grain boundary and misorientation angles distribution, dynamic recrystallization and crystallographic texture in various regions of the FSW joint concerning base metal (BM), thermo-mechanically affected zone (TMAZ), upper part of nugget zone (UPNZ) and low part of nugget zone (LPNZ) was characterized by using electron back-scattered diffraction (EBSD). The analysis reveals a strong texture evolution of shear components on the TMAZ, UPNZ and LPNZ as well as a fully recrystallized grain structure on the UPNZ and LPNZ. Additionally, a gradual evolution in Si-rich eutectic from continuous cellular networks in the BM to totally globularized particles in the UPNZ and LPNZ occurs in the FSW joint. The microhardness rapidly decreases to the TMAZ from the BM through heat affected zone (HAZ) reaching the lowest value of ∼65.0 HV at the TMAZ/NZ boundary. The FSW joint in LPBF AlSi10Mg alloys exhibits an ultimate tensile strength (UTS) of 247 MPa and an elongation-to-failure (EI) of 8.8%. The UTS of FSW joints is reduced compared to the BM, but the EI has been increased by 160%, implying an improvement in tensile ductility.

Heterogeneous distribution of isothermal ω precipitates prevents brittle fracture in aged β-Ti alloys

Isothermal ω (ωiso) precipitates in β Ti-alloys can increase the yield strength of the material, but unfortunately at a dramatic cost of the ductility. The embrittlement is mainly attributed to the suppression of twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects, as well as the formation of dislocation channels associated with localized deformation. To address this issue, we propose a heterogenous microstructure in Ti-15Mo-3Al alloy using conventional rolling method, in which the heterogeneous distributions of both Mo element and ωisoprecipitates are realized after aging. Both the nano-hardness and elastic modulus of ωisorich (Mo-lean) regions are larger than that of ωisodepleted (Mo-rich) regions. A four-time increase in tensile ductility is achieved in the heterogeneous microstructure without a loss of tensile strength, compared with the homogeneous counterpart. The ductility improvement can be ascribed to the blocking effect of ωisodepleted regions against the propagation of dislocation channels which later evolve into micro-cracks.

Core-shell magnetic particles reinforced magnesium matrix composites with an excellent combination of mechanical and electromagnetic interference shielding properties

Structural and functional integration of metal matrix composites is both a goal pursued by researchers and a challenging issue. In this study, a series of Al3Fe@Fe core-shell structured micro-sized particle reinforced magnesium matrix composites were prepared by using AZ31 alloy and Fe powders. The Al3Fe@Fe core-shell structure induces the “back-stress” strengthening in the composite due to the difference in deformation ability of matrix, Al3Fe “shell” and Fe “core” during the deformation process. This also improves the strain hardening ability of the composite, resulting in synchronous improvement of both strength and ductility. In addition, the reinforcing particles with “core-shell” structure endow the composite with certain magnetism, achieving a synergistic contribution of dielectric and magnetic losses, significantly enhancing the electromagnetic shielding effectiveness of the composite. Compared with the matrix alloy, the addition of 15 wt% Fe in the composite increased the SET by 70 %, and the SEA/SET increased from 0.46 to 0.73.

STUDY ON THE INFLUENCE OF TREATMENT PARAMETERS ON THE HARDNESS OF 6XXX SERIES ALUMINIUM ALLOYS

The appropriate application of heat treatments results in structural changes in alloys, and such changes enable the improvement of strength, hardness, ductility and other mechanical characteristics. This paper is mainly aimed at studying and analysing the influence of the quenching temperature and of the ageing holding time on the hardness of 6xxx series aluminium alloys. The thermal processes and parameters involved in the heat treatment of this alloy are studied, such as quenching and ageing, and the manner in which these treatments influence the properties of the resulting materials will be investigated.

Surface-Modified Electrospun Glass Nanofibers from Silane Treatment and Their Use for High-Performance Epoxy-Based Nanocomposite Materials.

As a new and promising reinforcing filler, electrospun glass nanofibers (EGNFs) have attracted attention in the field of polymer composite materials. However, the reinforcing effectiveness of surface-modified EGNFs using different silane coupling agents in epoxy resin is still not quite clear. In this research, a series of silane coupling agents with increasing chain lengths in the order of methyl trimethoxysilane (MTMS), (3-aminopropyl) triethoxysilane (APTES), (3-glycidyloxypropyl) trimethoxysilane (GPTMS), and dual silane coupling agent APTES-GPTMS were employed to carry out surface treatment on the EGNFs. The pristine and silane functionalized EGNFs were then incorporated into epoxy resin as reinforcing fillers at low loading levels, i.e., 0.25 wt.%, 0.5 wt.%, and 1 wt.%, and the mechanical properties of the resultant epoxy nanocomposites, including strength, stiffness, ductility, and toughness, were evaluated. A commercial product of glass nanoparticles (GNPs) was used as a control to compare the reinforcing effectiveness of the EGNFs and the GNPs. This study revealed that the EGNFs could provide significant reinforcing and toughening effects at ultra-low loading (0.25 wt.%) in epoxy nanocomposite materials. Furthermore, surface modification of the EGNFs with silane coupling agents with long chain lengths, e.g., by using dual silane coupling agents, APTES-GPTMS, could enhance the interfacial bonding between the EGNFs and the epoxy matrix and further increase the mechanical performance of the EGNF-reinforced epoxy nanocomposite materials. Through this research, we realized epoxy nanocomposite materials with much-improved mechanical properties, i.e., 37%, 24%, 18%, 57% improvement in strength, stiffness, ductility, and toughness, respectively, with respect to those of the cured neat epoxy material with an ultra-low loading (0.25 wt.%) of APTES-GPTMS-EGNFs. Our research paves the road for developing lighter and stronger epoxy nanocomposite materials with EGNFs.

Achieving excellent strength-ductility in Al–Si–Cu–Mg cast alloy via effective work hardening

The synergistic improvement of strength and ductility in Al–Si–Cu–Mg cast alloys is an important issue for their engineering applications. Aging treatment can effectively improve the strength of the alloy, but inevitably sacrifice the ductility of the alloy. In this paper, work hardening caused by multiple solute-atoms is designed to achieve the high strength-ductility of the alloy. The multiple Cu, Mg and Si solute-atoms results in the high proportions of low angle grain boundaries, the dislocation tangles with high density and fine dislocation cells in solution-treated Al–7%Si-2/3%Cu-0.5%Mg alloys after plastic deformation. The higher Cu level can promote work hardening effect, resulting in the improvement of ultimate tensile strength. The solution-treated Al–7%Si–3%Cu-0.5%Mg alloy shows the ultimate tensile strength of 440 MPa with an excellent elongation of 16.58% by effective work hardening. The in-situ EBSD tensile results show that dislocation accumulation extends from high angle grain boundaries and Si particles to intragranular areas, which weakens excessive stress accumulation on high angle grain boundaries and effectively promotes the synergistic improvement of strength and ductility. The contribution of dislocation strengthening at various strain levels was estimated, which implies that dislocation accumulation is dominated to working hardening during plastic deformation stage. This study proposed a new design idea for the synergistic improvement of strength and ductility in Al–Si–Cu–Mg cast alloys.

Simultaneous improvement in strength and ductility of CT20 titanium alloy at cryogenic temperature

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of the CT20 alloy with a <-12-11>//ND texture were investigated. The CT20 alloy with equiaxed microstructure exhibits excellent mechanical properties with simultaneous increase in strength and elongation at cryogenic temperature. In current study, the initial <-12-11>//ND texture promotes basal slip actuation effectively and continuously increases Schmid factor (SF) of other slip systems to promote multiple slip. Cryogenic temperature weakens the deformation texture due to the promotion of multiple slip. Since the decrease of the stacking fault energy (SFE), more twins in number and variety nucleate at 77 K and promote multiple slip. It causes strong cryogenic twinning-induced plasticity (TWIP) effect. Grain refinement induces strong cryogenic dynamic Hall-Petch effect resulting in high strain-hardening rate (SHR) and strength. The yield strength (YS, ∼1052.67 MPa), ultimate tensile strength (UTS, ∼1102.51 MPa) and elongation (EL, ∼21.1 %) of the 77 K specimen are about 84.1 %, 69.1 % and 38.8 % higher than its counterpart at RT, respectively. In addition, cryogenic temperature changes the initiation location of cracks and promotes cracks initiation at grain boundaries homogeneously.

Bimodal structured chromium-tungsten composite as plasma-facing materials: Sinterability, mechanical properties, and deuterium retention assessment

Even though tungsten (W) is considered to be the most favored plasma-facing material (PFM) for nuclear fusion reactors thanks to its beneficial physical properties, its advantage for those plasma-facing components to be subjected to medium heat flux and high neutron irradiation dose is compromised by unfavorable nuclear behavior such as intermediate-level radioactive waste activation and embrittlement caused by lattice damage and transmutation. Chromium (Cr) or Cr-based materials may have the potential to mitigate these shortcomings while maintaining acceptable thermal and physical performances required for PFM. They could offer attractive design options, particularly for those parts where the particle fluxes are relatively low and the heat flux is not too high (≤ 5 MW/m²) while nuclear loads are high (≥ 5 dpa). In this article, we report the first results of a preliminary technology feasibility study for an engineered Cr-based material fabricated based on a powder-metallurgical route. To explore an optimal metallurgical condition ensuring reasonable mechanical properties and low deuterium retention, a novel two-phase Cr-W composite was developed via current-assisted rapid sintering at low sintering temperature. The composite showed a cell-like bimodal microstructure consisting of a coarse-grained Cr phase surrounded by a 3D interconnected network of an ultrafine-grained W phase. The composite exhibited substantial improvements in ductility as well as high-temperature strength compared to pure W and Cr. After undergoing W heavy ion irradiation, the damaged Cr-W composite with a two-phase bimodal microstructure showed a comparable deuterium retention capacity to pure W. Finally, the potential applicability as PFM is discussed.

Simultaneously enhancing strength and ductility of high-Nb-containing TiAl alloy via extrusion-assisted microstructure tailoring

In most metallic materials, the strength-ductility trade-off serves as an inevitable scenario. Therefore, improving the room/high-temperature strength/ductility of high Nb-TiAl alloys based on a lamellar microstructure is important for practical applications. In this work, a novel microstructure with fine lamellar colonies and a certain number of residual γ grains was developed through hot extrusion in the near α phase region. The results indicated that the lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. The as-extruded Ti-45Al-8Nb-(W, B, Y) alloy demonstrated a good combination of high strength and ductility. The tensile strength and ductility were 1129 MPa and 2.04% at room temperature (RT), respectively, and 744 MPa and 51.20%, respectively, at 850 °C. A simultaneous improvement in strength and ductility below ductile-brittle transition temperature (DBTT) could be attributed to the abundant deformation twins and their intersections, as well as prominent strain working caused by high-density dislocations in the γ phase. Due to dynamic recrystallization, the ductility was significantly enhanced when stretched over DBTT. This extrusion-assisted microstructure tailoring strategy could be extended to other TiAl systems and may serve as a useful solution for addressing the significant engineering constraints posed by the low RT ductility and poor hot-working capabilities of high Nb-TiAl alloys.

Boron microalloying for high-temperature eutectic high-entropy alloys

The eutectic high-entropy alloys have shown promising mechanical behaviors while their softening at elevated temperatures is still a challenge. Generally, the boundaries are the weak parts to be strengthened with increased temperatures in eutectic high-entropy alloys. Here, we found that the minor addition of boron in Ni30Co30Cr10Fe10Al18W2 eutectic high-entropy alloy can significantly strengthen the FCC grain boundaries and the FCC/B2 phase boundaries at elevated temperatures. A remarkable tensile yield strength over 581 MPa with elongation of 71 % at 800 °C is achieved with minor boron addition, corresponding to a 45 % increase in yield strength and 129 % improvement in ductility compared with the boron-free counterpart. Accompanied by the boron-strengthened phase boundary, sustainable dynamic recovery occurs in the FCC and B2 phases during high-temperature tensile testing, ensuring excellent ductility. Moreover, the benchmark test indicates that the strengthening effect of boron and borides on the boundaries contributes up to 166 MPa to the yield strength of eutectic high-entropy alloy at 800 °C. These findings shed light on the development of high-temperature eutectic high-entropy alloys with a microalloying strategy.

Microstructure and mechanical properties of hybrid nano-titanium carbide-carbon nanotubes (nano-TiC-CNT) reinforced aluminium matrix composite

To use Al composites in structural applications, we need to improve strength and ductility at the same time. In this article, we explore three main concepts to solve this problem: improving the dispersion uniformity of CNTs in Al powder without damaging its structure by solution coating technique, fabricating a hybrid composite by reinforcing Al with nano-TiC-CNT, comparing the properties of nano-TiC-CNT and micron-TiC-CNT hybrid composites. Microstructure observation by SEM, TEM, and XRD revealed well-dispersed and preserved CNTs without the formation of a second phase. The Al-0.5CNT composite showed good tensile strength and elongation at break of 278 MPa and 14%, respectively. Further improvements in tensile strength and ductility of 285 MPa and 23%, respectively, were measured after the addition of 2.5 wt%; (1.4 vol%) TiC nanoparticles to Al-0.5CNT composite. However, the introduction of 2.5 wt-% TiC macroparticles only improved the tensile strength by 48% but elongation at break was up to 32%. The improved strength and ductility are attributed to the introduction of geometrical necessary dislocation and Orowan looping of dislocations leading to back stress strengthening. The new Al composite is expected to find application in automotive and aerospace component manufacture and thermal management.

Ductility improvement of GFRP-RC beams using precast confined concrete block in compression zone

Ductility improvement of GFRP-RC beams using precast confined concrete block in compression zone

Collaborative improvement of strength and ductility over Mo composites enabled by WC and La2O3

The low ductility of refractory Mo-based materials limits their further processing and wide applications. To address this challenge, a composite strengthening and toughening strategy was proposed by the simultaneous addition of WC and La2O3. And a collaborative improvement of strength and ductility is achieved over the as-sintered Mo-WC-La2O3, exhibiting a total elongation (TE) of 33.63% and an ultimate tensile strength (UTS) of 611.33 MPa, about 50.27% and 24.76% larger than those of pure Mo, respectively. Furthermore, the corresponding microstructural features and tensile fracture behavior were also discussed to explore the improvement mechanism. And it is found that the enhancement should be attributed to the high relative density, grain refinement, generated substructures and secondary phase particle refinement. Moreover, the additional toughening mechanisms of crack deflection, particles pull-out and crack halt can also prevent crack extension, which helps to give full play to the potential ductility of Mo composites. This work provides a new pathway for manufacturing advanced Mo-based products with excellent strength-ductility balance.

Comparisons of the Performance of Novel Lightweight Three-Dimensional Hybrid Composites against GLARE Fiber–Metal Laminate

The objective of the work presented in this paper is to overcome several major shortcomings of the recently introduced 3D composites (3DCs) and their fiber–metal-laminate renditions (3DFMLs). A new class of lightweight, stiff, and resilient three-dimensional hybrid composites (3DHCs) is introduced in this study, referred to as “inserts enhanced 3D hybrid composites” (IE3DHCs). The performances of all configurations were characterised by conducting three-point flexural tests using a span-to-thickness ratio of 32:1. The flexural performance of 3DFMLs with different core thicknesses was first compared using GLARE-3/2-0.4 as a baseline, revealing the superior performance of 3DFMLs; the optimal performance was exhibited by 3DFML with a 3DC core. However, the lower ductility of 3DFMLs, as well as their poorly controlled and time-consuming fabrication process were recognized. The newly developed materials (IE3DHCs) had a comparatively simpler fabrication processes with significantly higher quality control. More importantly, IE3DHCs exhibited an approximately improvement in ductility and as much as a 250% improved design strength compared to 3DFMLs. These findings showcase the promising potential of IE3DHCs for future research and real-world applications. Additionally, robust finite element models were developed to simulate flexural tests and optimize future renditions of the IE3DHCs.

Physical property characterizations of natural rubber nanocomposites through experimental techniques, models and CRR concept

AbstractIn this research, the combinations of silica (SiO2), with either graphite (GR) or graphene oxide (GO), are studied as hybrid reinforcements of natural rubber (NR). Whereas individual improvements of rigidity, strength or ductility can be obtained depending on the composition, a synergistic reinforcement is specifically evidenced after addition of GO/SiO2 with a 3:1 ratio. For this formulation, both strength and modulus drastically increase while keeping the strain at break at a decent level. From the confrontation of all tensile tests results with theoretical reinforcement models, a good correlation between the experimental data and the Guth Gold model is observed, which reveals that the mechanical properties should essentially be governed by the filler/matrix interactions. This assumption has been discussed through the cooperative rearranging region (CRR) concept, by analyzing the calorimetric response of the nanocomposites at the glass transition. Not only the 3:1 GO/SiO2 composition is the only one for which the glass transition clearly shifts to higher temperatures, its CRR average size is also the lowest in comparison with reference NR. This result, interpreted as the signature of the most efficient intercalation of the fillers, matches well with the steep strain hardening recorded for this nanocomposite.

Improving the strength and ductility of magnesium alloys by Sc alloying: An experimental and first-principles study

Mg–Sc alloys have great application potential due to the positive effect of Sc on improving corrosion resistance and mechanical properties. In this work, the effects of Sc content on the strength and ductility of Mg-xSc (x=0, 1, 2, 3 at.%) alloys were investigated by experiments and first-principles calculations. The results indicate that, with the increase of Sc content, the hardness, strength, and ductility of the alloys increase significantly. The improvement of strength is attributed to the solid solution strengthening and grain size refinement effect. The addition of Sc reduces the prismatic unstable stacking fault energy of the alloys, thereby promoting the activation of stacking faults and <c+a> dislocations, resulting in the significant improvement of ductility. The mechanism of the enhanced ductility of Mg-xSc solid solution alloys is revealed, which provides guidance for designing high-performance Mg alloys.

Functionally graded IWP reinforced cementitious composites: Design, fabrication, and the enhanced ductility

The Schoen I-graph-wrapped package (IWP) structures have many promising applications for their high specific mechanical properties. In this work, functionally graded IWP (FG-IWP) architectures were developed and constructed to enhance the ductility of the produced cementitious composites. The FG-IWP architectures were designed using two grading strategies: relative-density-based and cell-size-based. The flexural test was used to investigate the mechanical behavior of the proposed composites, including flexural strength and deflections. The failure patterns and strain distributions of the specimens were measured using the Digital image correlation (DIC) approach. The results reveal that the designed IWP architectures noticeably improve the flexural strength and ductility of the composites. Comparing the FG-IWP to the uniformly configured IWP architectures, the grading strategies exhibit an increased ductility. Furthermore, the two grading strategies have different effects on ductility improvement. Cell size gradient strategy yields greater enhancement in flexural strength, whereas relative density strategy leads to better enhancement in ductility. The variations of cell size and relative density parameter ranges also result in distinct improvement on mechanical properties. Overall, the outcomes of this study present an FG-IWP-based novel approach for improving the ductility of cementitious materials.

Towards reducing tension-compression yield and cyclic asymmetry in pure magnesium and magnesium-aluminum alloy with cerium addition

In this study, we report the effect of cerium (Ce) addition on the tension-compression yield and cyclic asymmetry in commercially pure magnesium (Cp-Mg) and Mg–Al alloy at room temperature (RT). The investigated materials Cp-Mg, Mg-0.5Ce, and Mg–3Al-0.5Ce were extruded at 400 °C, followed by annealing at the same temperature for 1 h. Incorporating 0.5 wt% Ce in pure Mg results in the weakening of its basal texture, uniform distribution of Mg12Ce precipitates, and grain size refinement. Consequently, the tensile yield strength and ductility of pure Mg increased, and tension-compression yield asymmetry was eliminated. However, the presence of 3 wt% Al in Mg suppresses the beneficial effects of Ce addition. The formation of non-uniformly distributed complex precipitates, such as Mg–Al–Ce and Al11Ce3, limits the weakening of the basal texture, reduction in grain size, improvement in ductility, and elimination of tension-compression yield asymmetry observed in Mg-0.5Ce. Nevertheless, Al contributes to the solid solution strengthening in Mg and possibly lowers the critical stress required for twinning in Mg, resulting in the highest tensile strength of Mg–3Al-0.5Ce. Finally, the addition of 0.5 wt% Ce enhances the cyclic strength, stabilizes cyclic stress response, reduces inelastic strain, and minimizes cyclic asymmetry in both pure Mg and Mg–Al alloy while maintaining a comparable fatigue life. Overall, Ce addition positively impacts the microstructure and mechanical behavior of pure Mg and its investigated alloy. The reasons for these improvements are discussed in detail.

Enhanced strength-ductility synergy of laser powder bed fused Inconel 718 via tailoring grain structure and precipitates

Inconel 718 fabricated by laser-powder bed fusion (L-PBF) exhibits a hierarchical microstructure, rendering traditional standard heat treatment processes not entirely suitable. To enhance the tensile properties, a novel heat treatment strategy to simultaneously tailor the grain structure and precipitates of L-PBFed Inconel 718 is proposed. This study aims to investigate the effects of homogenization time, coupled with water cooling, on grain structure, precipitation, and room-temperature tensile properties. The results demonstrate that increasing the homogenization time from 1 h to 4 h results in a significant improvement of tensile ductility by 33.7%, while maintaining higher tensile strength compared to the wrought counterparts. The utilization of water cooling following homogenization effectively suppresses the formation of undesirable δ phases and promotes the precipitation of γ′′ phases during subsequent aging treatment, leading to exceptional tensile strength. Furthermore, the prolonged homogenization time facilitates recrystallization and promotes uniform deformation between adjacent grains, thereby enhancing the material's ductility. This study provides theoretical guidance for the development of customized heat treatment processes to achieve superior mechanical properties in additive-manufactured metallic materials.

Effect of grain boundary engineering on grain boundary character distribution and deformation behavior of a TRIP-assisted high-entropy alloy

This study carried out two-step thermo-mechanical processing (TMP) in grain boundary engineering (GBE) to optimize the grain boundary character distribution (GBCD) and tensile properties of a transformation-induced plasticity-assisted high-entropy alloy (TRIP-HEA). The evolution and mechanism of GBCD in the HEA were characterized and discussed using electron backscatter diffraction (EBSD). The tensile properties of the HEA after undergoing different TMPs were evaluated through room-temperature uniaxial tensile tests, and the influence of GBE on the deformation mechanisms was investigated using techniques such as EBSD and transmission electron microscopy (TEM). The results indicated that the fraction of low Σ coincident site lattice (CSL, Σ ≤ 29) boundaries exhibited a decreasing trend followed by an increasing trend with an increase of second-step cold rolling strain during TMPs, and the overall fraction of Ʃ9 + Ʃ27 boundaries showed an increasing trend. When the reduction ratio was 10%, the low-ƩCSL boundaries fraction reached ~66.35%. In terms of tensile properties, all GBE specimens showed improvement in strength and ductility. When the reduction ratio of second-step cold rolling was 20%, the yield strength was 506.7 MPa, which was ~59% higher than base material (BM) sample. The ultimate tensile strength was 885.6 MPa, ~26% greater than BM sample. In addition, when the reduction ratio of second-step cold rolling was 3%, the total elongation was 52.6%. The main deformation mechanisms of the HEA were dislocation slip, stacking fault (SF), nano-twining, and phase transformation. The optimization of GBCD had multiple effects on the deformation mechanisms. It manifests in several ways, such as the enhancement of strain uniformity through ΣCSL grain boundaries, improving the ability of dislocation multiplication and stress-induced cracking resistance, as well as the strengthening due to the combined effects of phase transformation and grain refinement.