Ductility Enhancement Research Articles

Co50Cr20Ni20Fe5Mn5 high entropy alloy: Overcoming the strength-ductility trade-off of Cantor alloy

In this study, we aimed to design and investigate a non-equiatomic high strength and ductile high entropy alloy (HEA) by controlling the FCC phase stability. A new Co-rich Co50Cr20Ni20Fe5Mn5 HEA was synthesized by vacuum arc remelting and processed through homogenization, cold rolling, and recrystallization. The alloy’s phase composition, mechanical properties, and plastic deformation behavior were characterized using X-ray diffraction (XRD), tensile testing, and Transmission Electron Microscopy (TEM) analysis. The tensile properties of the alloy were compared with those of the conventional Co20Cr20Ni20Fe20Mn20 HEA produced and processed using the same technique and route. The results showed that reducing the Fe and Mn concentrations while increasing the Co concentration reduced the FCC phase’s stability, leading to the occurrence of partial FCC to HCP phase transformation upon cooling from high temperature and TWIP-TRIP effects during tensile deformation. The Co50Cr20Ni20Fe5Mn5 HEA exhibited improved mechanical properties, including higher yield strength (502 MPa), ultimate tensile strength (1002 MPa), and total elongation (50%) compared to the reference Cantor HEA (405 MPa, 766 MPa, and 40%, respectively). The principal strengthening mechanisms contributing to the increased yield strength with higher Co concentration were identified as initial HCP phase strengthening and grain boundary strengthening. The enhancement in ultimate tensile strength and ductility is attributed to the TWIP-TRIP effects during the tensile deformation of the Co50Cr20Ni20Fe5Mn5 HEA.

Effect of high-temperature hydrogenation on mechanical properties of a Mg-B4C composite

This study aims to understand the influence of high-temperature hydrogenation treatment on the mechanical properties and microstructure evolution of an as-forged Mg-B4C composite containing rare earth elements. During the hydrogenation treatment, a considerable number of (Gd,Y)H2 hydrides with the FCC parameter of a = 0.52 nm were formed in the consumption of Gd and Y solute atoms in the matrix and eutectic Mg24(Gd,Y)5 particles. After hydrogenation treatment, the Mg-B4C composite shows a dramatic decrease in yield strength (from 140 MPa to 94 MPa) and tensile strength (from 220 MPa to 160 MPa), respectively. However, there is a notable increase in elongation (from 4.3 % to 6.6 %). The deterioration of strength in the Mg-B4C composite after hydrogenation treatment can be attributed to grain coarsening, solid solution weakening and a reduction of dislocation density. Meanwhile, the enhancement of ductility in the Mg-B4C composite after hydrogenation treatment can be attributed to the activation of more non-basal dislocations, the presence of smaller dimples, and a decrease in tearing ridges observed after fracture.

Understanding extra strengthening in gradient nanotwinned Cu using crystal plasticity model considering dislocation types and strain gradient effect

Gradient nanotwinned (GNT) Cu, composed of various homogeneous nanotwinned (HNT) components, successfully achieves the synergistic enhancement of strength and ductility due to the combined advantages of gradient and nanotwinned structures. However, the complicated dislocation-twin boundary (TB) interactions in each HNT component and extra strengthening mechanism in GNT Cu remain elusive. In this study, a crystal plasticity model, which takes into account the reaction characteristics of various dislocation types at the TB and the extra size dependent geometrically necessary dislocations (GNDs) induced by plastic strain gradients, is developed for understanding both HNT and GNT Cu. The developed model successfully captures the mechanical behavior and microstructure evolution of HNT Cu with different TB orientations and grain sizes (and twin thicknesses). The simulation results emphasize the importance of incorporating dislocation types when describing dislocation-TB interactions. Furthermore, the intrinsic mechanism for the extra strengthening in the GNT Cu is revealed through the analysis of deformation contours and microstructural evolutions. The results show that the HNT components with the lower original strength have the higher extra back stress increment with the increase of structural gradient. This study provides valuable insights into predicting and further optimizing the strength of the GNT Cu through manipulating the gradient microstructure.

Ultrahigh deformability of Ti-6Al-4V assisted by high-density pulsed electric current treatment

In this study, the mechanical properties and microstructural evolution of the pre-strained titanium alloy Ti‐6Al‐4V under high-density pulsed electric current (HDPEC) treatment were investigated. The results showed that the HDPEC treatment successfully restored the plastic deformation or strain hardening of the pre-strained Ti‐6Al‐4V without deteriorating its strength. In addition, multi-HDPEC treatments were conducted to examine the cumulative effect on plastic recovery, and ultrahigh deformability with an increasing rate of 287% was achieved at a current density of 250 A/mm2 for 20 ms. Microstructural characterization indicated that dislocations and the associated sub-grain boundaries were remarkably reduced after the HDPEC treatment, contributing to ductility enhancement. Additionally, the rapidly heat-treated sample with a thermal history curve similar to that of the HDPEC-treated samples did not show obvious microstructural changes, indicating that the athermal effect of the HDPEC treatment plays an important role in modifying the microstructure of the material. The α'/α'' martensite phases were formed in the β phase after the HDPEC treatment, which is possibly related to the high cooling rate and diffusion of the V element (β phase stabilizer element). Specifically, at the current condition of 250 A/mm2 for 20 ms, some tiny martensite phases precipitated in the β phase without heavily deteriorating the microstructure and mechanical properties. Therefore, owing to its low cost and high efficiency, the HDPEC treatment can be applied to Ti-alloy components with internal plastic deformation to realize rapid restoration or achieve long service periods without significantly altering the microstructure.

Phase transformation in additively manufactured Co-Cr-Mo alloy after solution and aging heat treatment

The unique structure and solute distribution of CoCrMo alloys produced using Laser Powder Bed Fusion (L-PBF) technique require custom heat-treating processes to achieve the targeted phase distribution and mechanical properties. The rise of multi-material additively manufactured structures also prompts further study at temperatures beyond standard aging and solution treatment conditions. In the present study, the phase transformation behavior, precipitate distribution, and γ-ε phase boundary orientation relationships of as-printed and solution heat-treated CoCrMo samples after aging heat treatment at 940 °C were investigated. The results show a higher ε-phase fraction of 71.2% in directly aged samples compared to 49.2% in solution heat-treated samples. This discrepancy is attributed to band-like isothermal transformation, coherent grain face massive transformation, and recrystallization. Carbide nucleation sites shifted from disintegrated cellular structures in directly aged samples to grain boundaries and twin interfaces in solution-treated samples. The presence of transgranular ε-phase bands and adjacent grains with analogous orientations observed after direct aging were linked to the weak 〈110〉 // BD and 〈111〉 // BD texture after printing. Tensile tests demonstrated an increase in tensile strength from 1162 MPa to 1261 MPa after direct aging, while significant enhancement in ductility from 16.4% to 26.1% was attained after solution heat treatment. While direct aging is more suitable for applications requiring high strength and wear resistance, solution heat treatment is advantageous when a consistent morphology and stress-free isotropic structures are desired.

Enhancement of ductility characteristics of fiber-reinforced ternary geopolymer mortar

There is a need for ambient-cured geopolymer as a potential replacement for conventional ordinary Portland cement (OPC) based concrete. But geopolymers, that belong to the ceramic family, behave in a brittle manner and hence this research focusses on the enhancement of ductility using fibers. Thus, this experimental work was conducted to investigate the performance of polypropylene (PP) and micro steel fiber (MS) of fiber-reinforced geopolymer mortar (FRGM) on the hardened properties. The volume fractions of fiber used were 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisted of fly ash (FA), ground granular blast furnace slag (GGBS), and palm oil fuel ash (POFA). The hardened properties investigated are compressive strength, splitting tensile strength, modulus of elasticity (MoE), and ultrasonic pulse velocity (UPV). Furthermore, the load-deflection response was investigated in terms of deflection, load, flexural, and toughening mechanisms. The morphology of matrix mortar with the bonding of the fibers was examined through field emission scanning electron microscope (FESEM). The results revealed that the splitting tensile strength was enhanced with the inclusion of 0.5% of PP fibers and up to 1.5% of MS fibers by 27% and 177%, respectively. The enhancements in the ultimate flexural strength with 1.5% fiber were found 173% and 33% higher for MS and PP fibers, respectively compared to the control mixes. The inclusion of both MS and PP fibers showed a significant enhancement in the post-cracking flexural and toughness energy measured at L/150 mm. Furthermore, the addition of fiber volume of 0.5–1.5% enhanced the toughness by 33% (T600), 62% (T150), and 28% (T600), 46% (T150) for MS and PP mixes, respectively.

Overcoming strength-ductility trade-off by building a micro-nano laminated structure based on an ultralow amount of single-dispersed carbon nanotubes

CNTs/Ti composites (Carbon nanotube reinforced titanium matrix composites) with a novel micro-nano laminated structure consisting of alternating CNTs nanolayers and Ti microlayers were successfully prepared by electrophoretic deposition combined with spark plasma sintering and temperature-controlled rolling. The CNTs/Ti composites exhibited a simultaneous enhancement in both strength and ductility compared to pure Ti fabricated by the same methods, despite the addition of CNTs being an ultra-low 0.02 weight percent (wt.%). The improvement in strength was attributed to (i) the high strengthening efficiency of individually dispersed, structurally intact CNTs and (ii) Heterogeneous deformation-induced (HDI) strengthening resulting from the heterogeneous deformation between soft Ti microlayers and hard CNTs nanolayers. Furthermore, the HDI hardening induced by the micro-nano laminated structure led to extra work hardening, enhancing the uniform deformability of CNTs/Ti composites. Consequently, strain localization was suppressed, as observed by in-situ tensile experiments, thereby preventing the initiation of interfacial. Additionally, interfacial crack propagation was significantly delayed due to CNTs bridging and crack tip blunting by ductile Ti microlayers, thereby promoting the total elongation to failure. Moreover, a progressive fracture process consisting of three stages was proposed, based on three-dimensional visualization and quantitative analysis of crack volumes. This provided a new strategy for overcoming the strength-ductility trade-off of traditional metal (Ti, Al, Fe, Ni, etc.) matrix composites through the reasonable design of a hierarchical architecture based on an ultra-low amount of high-quality nanoscaled reinforcements.

Enhanced strength-ductility synergy of an AlCoCrFeNi2.1 eutectic high entropy alloy by ultrasonic vibration

The mechanical properties of eutectic high entropy alloys (EHEAs) can be significantly improved by adjusting its microstructure; however, the conventional adjustment approaches are inefficient and trapped in a strength-ductility tradeoff. In this study, we applied a compressive stress of 350 MPa (about 60 % yield strength) with ultrasonic vibration of 20 kHz frequency and 20 μm amplitude on an AlCoCrFeNi2.1 EHEA for different processing time. The ultimate tensile strength and total elongation of the EHEA were prominently enhanced to 1050 MPa and 27.4 % after 20 min ultrasonic processing, representing an increment of 17 % and 54 % from the initial state (900 MPa and 17.8 %), realizing the synergistic enhancement of both strength and ductility. The structural analysis of the ultrasonically processed AlCoCrFeNi2.1 EHEA shows that the strengthening effect induced by BCC(B2) precipitates with a typical size of 1 μm provoked by ultrasonic vibration was the primary reason for the enhanced strength. The synchronous deformation of alternating soft FCC(L12) phase and hard BCC(B2) phase as well as the motivated multiple slip systems intensified the strain hardening effect, resulting in the improvement of strength-ductility synergy. This study provided a new and efficient way to overcome the strength-ductility tradeoff and prepare a EHEAs with high mechanical properties.

Role of Zn addition on the microstructure and tensile property in Mg–Mn–Nd alloys

The role of Zn addition (1, 2 wt%) on the microstructural characteristics and tensile properties of the extruded Mg–1Mn–1Nd (MN11) alloy is discussed. The addition of Zn negligibly influences the particle type; however, Zn addition causes un–homogeneous distribution structure firstly and then develops homogeneous structure because of the change of size and distribution of Mg12Nd particles. The MZN111 sheet shows higher yield strength (YS) along the extrusion direction (ED), and lower YS along the transverse direction (TD), compared to the MN11 sheet. This improvement is attributed to the Zn solute atoms via solid-solution strengthening effect, while the reduction is ascribed to the formation of TD–orientation texture and coalescence of dynamic recrystallized (DRXed) grains. As the Zn content increases to 2 wt%, The MZN121 sheet with highest strength can be ascribed to the homogeneous distribution of finest grains via the grain–boundary strengthening effect and more Zn solute atoms via solid–solution strengthening effect. The increased size of Mg12Nd particles with 1 wt% Zn content and coalescence of DRXed grains, which can significantly reduce the ductility of MZN111 sheet. Further, the ductility enhancement of the MZN121 sheet is mainly due to the homogeneous distribution of fine grains and homogeneous alignment of Mg12Nd particles.

Tailoring crack width control of LC3-based engineered cementitious composites (ECC) via fiber hybridization: From micromechanics design to macro investigation

As a class of strain-hardening cement-based material, Engineered Cementitious Composites (ECC) feature high tensile ductility and multiple cracking. However, ECCs reinforced with hydrophobic fibers attain high ductility but also exhibit larger crack widths caused by the weak bonding of the fiber/matrix interface, attenuating the durability potential of resulting infrastructures. This research aims at tailoring the crack width control ability of ECC through hybridizing hydrophilic PVA and hydrophobic PP fiber. A systematic design procedure was proposed based on the micromechanical analysis with a multi-scale investigation. Experimental results verified the hypothesized composite ductility enhancement by PP fiber and strength enhancement and crack width reduction by PVA fiber. Tight crack width of 50 μm at 2 % tensile strain can be achieved by a fiber hybridization ratio of 1:1 to ensure extreme durability. Changes in the microstructure of the matrix, associated with fresh property alteration due to fiber hybridization, were captured by micro CT scanning. Finally, the trade-off between mechanical performance, durability, and material sustainability was investigated for optimal material design. This research demonstrates that hybridizing PVA fiber with PP fiber holds promise to enhance material sustainability while maintaining the advantageous characteristics of ductile ECC and tight crack width for extreme durability.

Influence of Isothermal Aging on Microstructure and Shear Property of Novel Epoxy Composite SAC305 Solder Joints.

With the rapid iteration of microsystem integrated technology, the miniaturization of electronic devices requires packaging materials with higher reliability. In this work, the microstructure evolution and mechanical properties of novel epoxy composite SAC305 solder joints were studied after isothermal aging to evaluate the enhanced effect of epoxy addition. The thickness variation and morphological evolution of the interfacial layer were analyzed. The results showed that, as the aging time was prolonged, the Cu6Sn5 interfacial layer remarkably coarsened and Cu3Sn compounds formed between the Cu6Sn5 layer and Cu pad due to the continuous atomic diffusion. Compared with the monolithic joint, the epoxy composite SAC305 joints had a lower overall IMC growth rate during aging, closely related to the initial morphologies of the interfacial layers. The shear test results showed an apparent decrease in the shear forces of all the solder joints as the aging time increased. Nevertheless, because of the extra mechanical support provided by the epoxy layer, the epoxy composite joints demonstrated notably enhanced mechanical properties. After 1000 h aging treatment, the shear force of SAC305 joints containing 8 wt.% epoxy was 26.28 N, showing a 24.08% increase over the monolithic joint. Cu-Sn IMCs were detected on the shear fracture of the monolithic joint after 1000 h aging, indicating the fracture occurred near the interface and displayed a ductile/brittle mixed fracture. Concerning the epoxy composite joints, cracks were still initiated and extended within the solder bulk, demonstrating a noticeable enhancement in ductility due to the addition of epoxy.

Enhance cryogenic ductility and strength of body-centered tetragonal Sn by pre-twinning and recrystallization

Previous researches on high-symmetric metallic materials demonstrate that the introduction of twins can overcome the strength-ductility trade-off. However, it is uncertain if such a pathway is valid for metals with a low-symmetry crystal structure. Here, the low-symmetry body-centered tetragonal Sn achieved a simultaneous enhancement in tensile ductility from 6 % to 14 % elongation and strength from 36 MPa to 60 MPa at 77 K through pre-twinning combined with room-temperature self-recrystallization. The in-situ tensile experiments reveal that the pre-existing and new deformation twins, as well as dynamic recrystallization and multiple dislocation planar slip contribute to the enhancement of cryogenic mechanical properties.

Mitigating the strength-ductility inversion in B4C/Al composites by constructing heterogeneous structure

Heterogeneous B4C/Al composites with soft and hard zones (SZs and HZs) were fabricated through a new approach combining segmented ball milling with pressure infiltration. The segmented ball milling was implemented in two steps, which included high-speed ball milling in the first step (step Ⅰ) and low-speed ball milling in the second step (step Ⅱ). It indicated that with the increase of step Ⅰ ball milling time, the width of SZs reduced. The heterogeneous composite with an SZ width of ∼2.71 μm (Hetero-2μm) exhibited a 161% increase in elongation compared to the homogeneous composite, with almost no decrease in ultimate tensile strength. Due to the mechanical incompatibility between the SZs and HZs, geometrically necessary dislocations (GND) accumulated near the interface. However, the length of GND pile-ups was finite, resulting in the presence of non-interface-affacted zones (NIAZ), which was harmful to the strength. The high strength of Hetero-2μm was attributed to the reduction of NIAZ width. Furthermore, the uniform distribution of plastic strain and some external toughening mechanisms, such as crack proliferation and deflection, were believed to be the reason for the ductility enhancement.

Influence of Gd and Li additions on the microstructural evolution and mechanical properties of hot-rolled AZ31 alloy

Thermomechanical processing and alloying are two common approaches to enhance the mechanical properties of Mg. Thus, the effects of Gd and Li elements, as two elements with various properties, on the microstructure and mechanical properties of a hot-rolled and consequently annealed AZ31 alloy were analyzed. The microstructure and texture was analyzed by scanning electron microscopy and electron back scattered diffraction. Accordingly, the mean grain size of 46 μm in the AZ31 alloy was reduced to 41 and 26 μm in the AZ31–2.9Gd and AZ31–2.3Li alloys, respectively. Grain refinement occurred due to continuous dynamic recrystallization and twinning-induced recrystallization in all of the alloys. Textural evolution showed that neither Gd nor Li could inhibit the occurrence of basal texture. Room temperature mechanical properties were assessed by using the shear punch test (SPT) method. The results exhibited that the strength of the AZ31 alloy was improved from 116 MPa to 139 MPa and 141 MPa by respective additions of Gd and Li. Strength enhancement was mainly attributed to the grain boundary strengthening and second-phase particles hardening. One promising observation was the simultaneous enhancement of shear strength and ductility by the addition of Gd and Li. This observation was ascribed to the more uniform distribution of second-phase particles and lower volume fraction of twins as potential sites for crack initiation. As long as mechanical strength is concerned, results favor the use of Li as alloying element in Mg, especially due to the more noticeable lightweighting potential compared to Gd.

Experimental testing of post-tensioned steel-timber hybrid frames equipped with energy-dissipating braces

The weak properties of wood in perpendicular-to-grain direction have imposed significant design challenges for post-tensioned (PT) timber frame structures. To resolve the challenges, the authors of this study have introduced a novel solution, the steel-timber hybrid PT frame. To further enhance its lateral performance, additional damping and stiffness (ADAS) braces were integrated into the hybrid frame. In this study, the feasibility of the combination was experimentally examined at the system level. Cyclic tests were conducted to evaluate the performance of two 2/3 scaled frame specimens: a conventional PT timber frame and a PT steel-timber hybrid frame with ADAS braces. The combination of a hybrid frame with ADAS braces showed substantial enhancements in lateral strength, initial stiffness, system ductility, and energy dissipation compared to the conventional PT timber frame. The experimental results highlighted the significant role of ADAS braces in enhancing energy dissipation, while their contribution to stiffness was less dominant. Analytical analysis further revealed an inverse relationship between the increase in ADAS contribution to lateral stiffness and the self-centering competence of the frame. A design equation was proposed to assist practitioners in achieving an optimal balance between the self-centering capacity of the PT hybrid frame and the stiffness enhancement provided by ADAS braces.

Strengthening mechanisms of semi-coherent boundaries between Al8Mn4Y and the Mg matrix in magnesium alloys

Cracking at phase or grain boundaries has been demonstrated as the dominant failure mode in Mg alloys, emphasizing the necessity for boundary enhancement to improve both the strength and ductility of the alloy. However, producing strongly bonded twin boundaries in Mg alloys is challenging. Therefore, a novel method to enhance the bonding between intermetallics and the matrix was proposed in this work by forming semi-coherent boundaries. Utilizing transmission electron microscopy (TEM), a previously unexplored intermetallic compound (IMC), Al8Mn4Y, has been identified and systematically investigated. The orientation relationship between lattices of Al8Mn4Y and Mg matrix revealed that the angle between {0 1‾ 0}Al8Mn4Y and {000 1‾}α-Mg planes is only 3.9°. Furthermore, typical lattice mismatches were observed in every four Al8Mn4Y lattices along the <010>Al8Mn4Y direction at the bonding interface, demonstrating their semi-coherent relationship. Subsequently, the mechanical properties of Al8Mn4Y were measured using nanoindentation, and the corresponding impact of Y-containing intermetallics on the mechanical properties of the alloy was also evaluated through tensile tests and fracture analyses. The results revealed that the refinement of conventional intermetallics originally present in the alloy, in conjunction with the newly generated Y-containing particles and the resulting semi-coherent boundaries following the addition of Y, effectively alleviated the stress concentrations and reduced cracking at phase and grain boundaries, contributing to the simultaneous enhancement of both strength and ductility in Mg alloys. Ultimately, the effects of Y on the elastic and plastic deformation of Mg alloys were quantified using four individual contributions, and the mechanisms responsible for the concurrent augmentation of strength and ductility were elucidated, offering valuable insights into the design strategies for future Mg alloys.

Achieving remarkable enhancement of yield strength and high ductility in a fine-grained Mg-6Zn-0.2Ca alloy via rotated hard-plate rolling

Developing Mg alloys with high strength-ductility synergy presents a major challenge. In this work, a novel Mg-6Zn-0.2Ca alloy prepared via rotated hard-plate rolling (RHPR) exhibits a simultaneous high yield strength (YS) of ∼268 MPa and ductility of ∼22%. The RHPRed alloy features a fine-grained structure containing high-density low angle boundaries (LAGBs) and densely distributed nano-coherent precipitates, contributing to a remarkable improvement of YS (∼82 MPa) in comparison to the conventional rolling counterpart, while homogenizing tensile deformation. In the RHPRed alloy, the presence of ellipse-shape texture and grain-boundary disclinations adjacent to LAGBs promotes the activity of pyramidal <a> and <c + a> slip that governs the high ductility. The current work demonstrates the essential role played by high-density LAGBs and nano-coherent precipitates to the high strength-ductility synergy, which may provide insights into microstructural control strategy towards superior performance of Mg-Zn-Ca alloys.

Simultaneous strength and ductility enhancement of wire-arc directed energy deposited Al–Cu alloy by interlayer laser shock peening

Wire-arc directed energy deposition (wire-arc DED), recognized for its ability to produce large-scale parts, has gained considerable attention. However, a critical issue with this method is the high prevalence of internal porosity defects found in the manufactured aluminum components, adversely impacting their mechanical properties. For the first time, this study introduces in-situ interlayer Laser Shock Peening (LSP) during wire-arc DED of 2319 aluminum alloy. The thickness of each deposited layer was meticulously regulated within the 0.7–1.3 mm range utilizing a spiral-path oscillation mode. Following this process, LSP was applied to the top surface of each layer. Compared to the as-deposited samples, interlayer LSP-treated samples showed a significant decrease in pore numbers by 73.9% and a reduction in the total area by 87.4%.Furthermore, the LSP-treated samples displayed improved mechanical properties with increases in ultimate tensile strength, yield strength, and elongation by 20.1%, 19.1%, and 27.3%, respectively. The primary impact of LSP on the microstructure is the generation of high-density dislocations, providing a driving force for grain refinement during subsequent layer heat input. With the combined effects of heat input and dislocation density, samples treated with LSP form a tight metallurgical bound around the closed pores. This process of effective defect elimination and an increased dislocation density between the layers results in a simultaneous improvement in strength and plasticity.

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.

Defect-healing of a laser-powder bed fusion Ti6Al4V alloy via electro-assisted micro-forging

In recent years, the concept of hybrid manufacturing has been proposed to heal the defects in additive manufactured (AM) materials, taking advantage of both the AM technique and additional secondary processes such as hot forging. However, the healing mechanism of defects, as well as the relationship between defects elimination and microstructure evolution need to be further studied. In this work, we designed laser-powder bed fusion (L-PBF) Ti6Al4V samples with high initial porosity, making it easier to trace the pores during the quasi in-situ X-ray tomography (XRT) observation. The samples were conducted hot forging by Gleeble-3800 system, which is named as electro-assisted micro-forging (EAMF) treatment, considering the characteristic of this process is to directly electrify the specimen to generate Joule heat. The results show that the porosity was effectively reduced by combining effects of electric current, heat energy and compressive stress during EAMF. Simultaneous enhancement of strength and ductility was realized. The defect-healing mechanism that comprising various stages was comprehensively disclosed. The competitive relationship between defect-healing and microstructure coarsening was revealed, which has a guiding effect on the subsequent optimization of process parameters.