Tensile Fracture Surfaces Research Articles

Thermo‐mechanical performance of oil palm/bamboo fiber reinforced bio epoxy hybrid composites

AbstractThe aim of this work to fabricate bamboo (B)/oil palm (O) fibers based biocomposites to assess mechanical, thermal and morphological properties. Flexural strength and modulus of hybrid biocomposite (7B:3O) exhibited a higher value (71.18 MPa and 5.24GPa) respectively among all biocomposite samples. On the other hand, pure biocomposite (B) showed a higher impact strength value (6977.8 J/m2) compared to other biocomposites. The results of TGA showed that thermal stability was observed significantly for hybrid biocomposites compared to other samples. In addition, the maximum decomposition temperature values were displayed in the hybrid biocomposite (5B5O), which was 377.82°C. Through DMA, it was likely to find the storage modulus curves (E′), loss modulus (E″) and damping factor (tan δ) for the biocomposites. The E′ showed an increase in the (3736.84 MPa) contrasted to other corresponding samples which were 3121.81 MPa, and 3209.67 MPa for 3B7O MPa and 5B5O samples, respectively. Overall, the results of DMA displayed an enhancement in the storage modulus (E′) in terms of the hybrid biocomposites representing greater stiffness and lower damping factor. SEM micrographs were utilized to understand the fiber bonding and fiber adhesion with the epoxy matrix. Furthermore, it confirmed SEM results that hybrid natural fibers enhance the complete characterisations of bio‐epoxy materials. Additionally, SEM images of the tensile fracture surfaces discovered voids and cracks. Finally, it can be concluded that the selection for the developed hybrid biocomposites provides excellent and economical lightweight biomaterials for automotive, aerospace, contractions and building components.Highlights Green hybrid biocomposites by oil palm/bamboo fiber/bioepoxy resin. Mechanical, thermal, DMA of hybrid composites carried out. Hybrid biocomposite(7B:3O) exhibited higher flexural strength value (71.18 MPa). TGA showed that the biocomposites are thermally further stable. DMA displayed an enhancement in the storage modulus (E′).

Size Selection of Crack Front Defects: Multiple Fracture-Plane Interactions and Intrinsic Length Scales.

Material failure is mediated by the propagation of cracks which, in realistic 3D materials, typically involves multiple coexisting fracture planes. Multiple fracture-plane interactions create poorly understood out-of-plane crack structures, such as step defects on tensile fracture surfaces. Steps form once a slowly moving, distorted crack front segments into disconnected overlapping fracture planes separated by a stabilizing distance h_{max}. Our experiments on numerous brittle hydrogels reveal that h_{max} varies linearly with both a nonlinear elastic length Γ(v)/μ and a dissipation length ξ. Here, Γ(v) is the measured crack velocity v-dependent fracture energy, and μ is the shear modulus. These intrinsic length scales point the way to a fundamental understanding of multiple-crack interactions in 3D that lead to the formation of stable out-of-plane fracture structures.

Taguchi-based grey relational analysis for multi-response optimization of the characteristics of HRAMMCs reinforced with agro-waste and SiC produced by ultrasonic-assisted bottom pour two-stage stir casting

Abstract This study aims to examine the impact of agricultural waste materials—specifically silicon carbide (SiC) and palm sprout shell ash (PSSA)—on the mechanical properties, including density, porosity, tensile strength, compression strength, impact strength, and hardness, as well as the tribological behavior of Al-Cu-Mg alloy-based HRAMMCs. Parametric optimization was conducted on HRAMMCs to predict the effect of input constraints on the performance of the composite, considering the weight percentage of SiC, PSSA, and ultrasonic-assisted stirring time. Taguchi’s L9 orthogonal array was used for the design of experiments (DOE), and the composites were fabricated accordingly. Their physical, mechanical, and tribological properties were determined experimentally. Taguchi-based Grey Relational Analysis for multi-optimization highlighted the potential of the HRAMMCs, with a density of 2.545 g cm−3, porosity of 5.810%, ultimate tensile strength of 341 MPa, flexural strength of 321 MPa, compressive strength of 394.016 MPa, Vickers hardness of 136.883 HV, wear rate of 6.88E-12 m3 m−1, and a coefficient of friction of 0.397. ANOVA shows that the developed mathematical model is a better fit for examining the impact of various factors on the GRG of and corresponding properties of developed HRAMMCs, Indicating the R2 value of the developed model is 99.33% (0.9933). The 2 wt% SiC, 2 wt% PSSA, and a stirring time of 7 min are optimal parameters for the present HRAMMCS; to reduce porosity, wear loss, and the coefficient of friction while increasing, ultimate tensile strength, compressive strength, and Vickers microhardness. Moreover, the examination of the tensile and impact fracture surfaces and worn surfaces was carried out using SEM analysis of the alloy and composite produced under the optimal experimental conditions. The results of the fracture surface analysis indicated that the failure of both tensile and impact fractures was due to an amalgamation of ductile and brittle behaviors. The composites exhibited lower ductility than that of the base alloys. A study of the wear mechanism revealed that it was a mixture of adhesive and abrasive wear mechanisms. The SiC and PSSA ceramic reinforcements demonstrate higher hardness compared to the alloy, which restricts the fluid-like movement of the matrix. When these reinforcements were added to the alloy, they substantially decreased the occurrence of severe delamination and the formation of adhesive wear particles.

The effect of welding speed on the microstructure, mechanical properties, and fatigue failure of Q690D high-strength steel

This study analyzes the effect of welding speed on the microstructure and mechanical properties of CO2 gas-shielded welded joints of 4 mm thick Q690D high-strength steel. The results show that the weld zone is mainly composed of acicular ferrite. The coarse-grained zone and fine-grained zone contain lath bainite and lath martensite. As the welding speed increases, the degree of recrystallization in the weld zone initially increases and then decreases. At the optimal welding speed of 38 cm/min, the tensile strength of the welded joint reached 692.1 MPa, with an elongation of 9.63 %. The maximum microhardness of the welded joint was 303 HV, and the residual stress was a tensile stress of 167 MPa. After fitting the S-N curve, the ultimate fatigue strength of the welded joint was 210 MPa. Both fatigue and tensile fracture surfaces displayed second-phase precipitate particles, impacting the mechanical properties.

Effect of temperature on the mechanical behavior of pvc foams

Experiments were conducted to characterize the mechanical behavior of Divinycell PVC foams over a wide range of environmental temperatures, from −60 to +80°C. Transversely isotropic properties of the foams, including modulus, strength, and ductility, were found to vary with temperatures between the ductile-to-brittle transition temperature (−60 to −50°C) and just under the glass transition temperature (95 to 100°C). The elastic modulus and yield strength decreased linearly as the temperature increased from −60 to +80°C. Compressive strength also decreased steadily with increasing temperature over the entire temperature range. In contrast, tensile and shear strengths only showed a significant decrease in values as the temperature rose above 23°C (room temperature). Below 23°C, there was a minor change in tensile and shear strengths. Tensile and shear ductility decreased sharply as the temperature decreased from +80°C to −40°C and stabilized between −60 and −40°C, which is close to the ductile-to-brittle transition region. Fractography of the tensile and shear fracture surfaces confirmed brittle fracture at −60°C and ductile tearing at +60°C. Equations were derived to predict modulus, yield strength, compressive, tensile and shear strengths, and ductility at any temperature in terms of room temperature values.

Experimental study on the influence of non-penetrating crack spatial distribution on brittle fracture process

To gain insights into the spatial distribution of non-penetrating cracks during the rock fracture process, a comprehensive uniaxial compression test is conducted on cubic gypsum specimens (100 mm × 100 mm × 100 mm) containing two non-penetrating cracks. The two pre-formed cracks are rectangular, with dimensions of 25 mm length, 2 mm width, and depths of 80 mm and 35 mm on adjacent sides of the specimen. The depth of the 80 mm crack can be adjusted from 0° to 150° in increments of 30°, while the other is fixed at a 45° angle. The results show that the spatial distribution of non-penetrating cracks can significantly influence the strength of the specimen. Initially, the strength of the specimen exhibits an upward trend and subsequently declines as the pre-crack inclination angle of the main rupture plane increases, ultimately reaching its pinnacle at 90°. The total percentage of tensile cracks in specimens with different inclinations are found to be 57%, 57%, 63%, 77%, 68%, and 61%, respectively. This change aligns seamlessly with the fluctuation in specimen strength as influenced by the angle of inclination. Non-penetrating cracks can also induce spalling on the specimen surface and give rise to anti-wing cracks, thereby exacerbating the spalling on the specimen surface. The inclinations of non-penetrating cracks can inevitably exert a certain influence on the propagation of neighboring non-penetrating cracks. Additionally, the macro-scale shear fracture of the specimen often occurs on the side of the non-penetrating crack that is deeper. The curved tensile fracture surface formed by the extension of the non-penetrating crack bears resemblance to the non-penetrating region in its ability to somewhat restrain the propagation of new cracks. Even under uniaxial compression, the spalling surface of the specimen containing spatial non-penetrating cracks frequently exhibits fracture characteristics belonging to I-III mode fracture, while its interior may display characteristics belonging to I-II-III mode fracture. These findings hold significant implications for comprehending and elucidating the genuine fracture process and three-dimensional fracture theory of rocks.

A Study on the Application Performance of High-Aspect-Ratio Nano-Ettringite in Photocurable Resin Composites.

In this study, the impact of the addition of high-aspect-ratio nano-ettringite to photocurable epoxy acrylate resin was explored. The nano-ettringite samples were modified using γ-Aminopropyltriethoxysilane (KH-550) and γ-methacryloxypropyl trimethoxy silane (KH-570). Then, 3 wt% or 6 wt% KH-550-modified, KH-570-modified, and unmodified nano-ettringite samples were dispersed into resin via ultrasonic treatment in conjunction with mechanical stirring. The grafting effects of nano-ettringite onto KH-550 or KH-570 were analyzed through scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric (TG) analysis. The results demonstrate that KH-550 and KH-570 have been successfully grafted onto the surface of nano-ettringite. In addition, this study also focuses on the variations of composite materials in the viscosity, shrinkage, tensile strength, and elongation at break. The results indicate that increased dosages of unmodified, KH-550-modified, and KH-570-modified nano-ettringite led to increased viscosity of the composite while reducing shrinkage. At the same dosage, the photocurable resin containing KH-570-modified nano-ettringite demonstrated a lower shrinkage and a higher tensile strength. From the analysis of tensile fracture surfaces, it was observed that compared to the KH-550 modified and unmodified variants, the KH-570 modified nano-ettringite exhibits superior dispersibility in photocurable epoxy acrylate resin. Notably, when the amount of KH-570-modified nano-ettringite was 3 wt%, the highest tensile strength of the composite was 64.61 MPa, representing a 72.57% increase compared to the blank sample. Furthermore, the incorporation of KH-570-modified nano-ettringite as a filler provides a new perspective for improving the performance of photocurable epoxy acrylate resin composites.

Bingham and herschel-bulkley fluids flow regimes in rough-walled rock fractures

Flow of typical non-Newtonian fluids such as cement grouts can experience different regimes as the Reynolds number (Re) changes, understanding of which is important for design and operation of rock grouting in various rock engineering applications. Here, flow regimes of representative non-Newtonian fluids, i.e., Bingham and Herschel–Bulkley (H–B) fluids, are numerically investigated with experimental validations. Three tensile rock fracture surfaces originated from a fine-grained sandstone, a medium-grained sandstone and a medium-grained granite samples are used to create rough-walled fracture models with variable aperture structures. Flow of groundwater, Bingham and H–B fluids through these fractures is numerically simulated respectively, by solving the full mass and momentum conservation equations with the Re ranging from 0.01 to 1000. The regimes for these fluids flowing through the fractures are characterized. Laboratory flow tests are conducted in a cylindrical granite fracture sample to verify the characterized flow regimes. The results reveal important differences of flow regimes between Newtonian and non-Newtonian fluids. Specifically, the transmissivity for water flow is constant when Re is relatively small until the Re reaches certain critical values; the transmissivity for Bingham and H–B fluids flow increases with increasing Re until asymptotically reaches certain peak values, followed by a descending stage when Re is relatively large. The critical (water) and peak (Bingham and H–B fluids) values are affected by surface roughness, that is, a rougher surface results in smaller critical and peak values as well as greater discrepancies compared to the analytical solutions based on the smoothed parallel plates model. These results show that a peak or optimum transmissivity is achievable in a specific range of Re (Re = 10–100 for the fractures studied). This new finding can potentially help optimize the injection pressure or flow rate in rock grouting practices.

Joining Behaviour of Thick Plate Using High-Frequency Induction Assisted Arc Welding

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ.

The effect of laser post-treatment on the microstructure and properties of Al coating on the PEEK substrate

To improve the bonding strength and electrical conductivity(σ) of cold-sprayed Al coatings on polyetheretherketone(PEEK) substrates, laser post-treatment was employed as an effective strengthening method without decomposition of the polymer substrates. Optical and electron microscopy observations were used to examine the microstructures and tensile fracture surfaces of the Al coatings fabricated with various laser powers. X-ray diffraction and electron backscatter diffraction were employed to investigate the phase composition and grain information of each coating. Hardness, pull-out adhesion, and electrical conductivity tests were performed to investigate the effect of laser power on the mechanical and physical properties of cold-sprayed Al coatings. The results revealed that despite the formation of several hundred micrometer-sized pores on the PEEK side, the porosity of the laser post-treated Al coatings significantly decreased, and the particle–particle interfaces were greatly healed with increasing laser power. The heat input induced large-scale recrystallization and significantly reduced the dislocation density in the samples. The XRD pattern revealed that no oxidation phase appeared following the laser treatment under the protection of Ar. The electrical conductivity and bonding strength of the Al coatings increased by up to 40 % and 167.4 %, respectively, after the laser post-treatment.

The Influence of MAPP and MAPE Compatibilizers on Physical and Mechanical Properties of 3D Printing Filament Made of Wood Fiber/Recycled Polypropylene

This study aims to develop 3D printing filament composites that support sustainability and waste reduction goals by utilizing wood waste and recycled polypropylene. This study evaluated the effect of Maleic Anhydride Polyethylene (MAPE) and Maleic Anhydride Polypropylene (MAPP) compatibilizers on the mechanical properties of the filament. The study found that r-WoPPc filament with MAPP and MAPE had higher tensile strength compared to r-WoPPc with significant increments of 13% and 74%, respectively, compared to v-WoPPc. The flexural strength of r-WoPPc increased by 18% and 60% after adding optimum loading MAPP and MAPE, respectively. The finding also reveals a significant enhancement in the tensile and flexural strength of the composite, proportional to the increase in MAPP percentage. In contrast, as the MAPE content increases, the tensile strength and flexural strength of the r-WoPPc experience a gradual decrease. Consequently, the addition of MAPP and MAPE improved the interfacial adhesion between wood and polypropylene, as revealed by the surface morphology of the r-WoPPc tensile fractured surface. Moreover, the reduced water absorption in r-WoPPc is attributed to the enhanced interfacial adhesion between wood fibers and the r-PP matrix, associated with improved tensile and flexural strength. The highest tensile strength of r-WoPPc with MAPP absorbs 14% water, while the lowest tensile strength absorbs 26%. Likewise, the highest tensile strength of r-WoPPc with MAPE absorbs only 0.8% water, compared to the lowest strength, which absorbs 2% water. This study demonstrated the potential for producing 3D printing filament from recycled polypropylene and wood waste, which benefits sustainability.

Ductility fracture mechanisms of Al-7Si-Mg casting alloys considering Si particles: A combined experimental and crystal plasticity study

Al-7Si-Mg casting alloys are widely utilized for their excellent formability, though they commonly exhibit poor ductility. This study comprehensively investigates the factors influencing the ductility of Al-7Si-Mg casting alloys, proposing a fracture mechanism and developing a model for ductile fracture of the alloy. Tensile tests were conducted on samples subjected to different aging times, with analysis of the alloy’s microstructure and tensile fracture surfaces. The findings reveal that fracture initiation occurs at clusters formed by the aggregation of Si particles, followed by the coalescence of cracks within these clusters, leading to macroscopic fracture. Different tensile strains were applied to specimens subjected to under-aging and over-aging treatments. The distribution of geometrically necessary dislocations (GNDs) in stretched samples indicates that the Si cluster area undergoes greater localized plastic deformation compared to the Al matrix, and this disparity increases with the applied strain. It has been observed that the reduced elongation observed in over-aged alloys is due to the coalescence of Si clusters under lower strain conditions. Representative volume elements with the characteristics of Si cluster is proposed, and the crystal plasticity finite element method is used for tensile simulations. The simulation results show that the proposed model is more consistent with experimental findings pertaining to elongation than with the results of a conventional void model. A longer aging time reduces ductility owing to a more intense strain localization under same tensile strain.

Combined effects of high temperature and lithology on the tensile mechanical damage and fracture surface morphology of reservoir rocks

Combined effects of high temperature and lithology on the tensile mechanical damage and fracture surface morphology of reservoir rocks

Viscoelastic behaviour of yttrium oxide and reduced graphene oxide embedded epoxy nanocomposite

In this work, two different types of nanofillers yttrium oxide (Y2O3) or yttria and reduced graphene oxide (RGO) are used to reinforce with epoxy polymer for the synthesis of epoxy nanocomposites by using the ultrasonication dual mixing approach. Raman spectroscopy has been done to analyze the microstructure of yttria and conformation of the formed RGO from Graphene oxide. The viscoelastic behavior of epoxy nanocomposites is evaluated with the help of the dynamic mechanical analyzer. Further Storage modulus is used to determine the cross-link density ‘νe’, coefficient of effectiveness ‘C factor’, and reinforcement efficiency factor ‘r factor’. The damping coefficient (Tan δ) helps in determining the glass transition temperature of the epoxy and its nanocomposites. The results demonstrate that at 1.6 wt% Y2O3 & 0.8 wt% RGO reinforcement in pure epoxy matrix showed maximum enhancement in terms of storage modulus, loss modulus, and glass transition temperature. The semi-circular shape that resulted from the study of the Cole-Cole plot of all the nanocomposites demonstrated the homogenous dispersion of nanoparticles and efficient bonding between epoxy and nanoparticles. Field Emission Scanning Electron Microscopy (FESEM) has been used to identify the interfacial interaction between nanoparticle and epoxy matrix through tensile fracture surfaces.

Microstructure and properties nonuniformity of Ti6Al4V component fabricated by high-power laser melting deposition

High-power laser melting deposition provides an efficient solution for the fabrication of large-sized titanium alloy components. In this study, Ti6Al4V blocks with well-formed structures were prepared using a 7 kW laser power, and their internal defect distribution, microstructure along the deposition direction, tensile properties, and fatigue performance were investigated. The results showed that the density of the as-deposited Ti6Al4V blocks could reach 99.94%, and the main internal defects were cavities, primarily spherical and dispersed, with a maximum diameter of 326.7 μm. Among them, 65.53% of cavities had a diameter smaller than 100 μm, and 92.76% had a diameter smaller than 200 μm. The microstructure at the top region of the specimen consisted of a needle-shaped α phase, the middle region had a mixture of needle-shaped and lamellar α-phase, and the bottom region showed a lamellar α-phase structure. With an increase in deposition height, the aspect ratio of α-phase increased, and the average width decreased from 3.22 μm to 0.88 μm. The internal structure was mainly composed of a basket-weave structure, with a small amount of Widmanstätten structure present at grain boundaries. Hardness and tensile properties exhibited significant non-uniformity along the deposition height. The tensile strength and yield strength at the top region were approximately 50 MPa higher than those in the middle and bottom regions, while the elongation was about 2% lower. The top region's tensile fracture surface displayed a sawtooth pattern, whereas the middle and bottom regions exhibited fractures along the 45° direction of the principal stress. The length of α-bundles and the interface density within the bundles were crucial factors affecting crack propagation. In the top region, α bundles were the longest, and the interface density was the highest. During crack propagation, when the crack extended perpendicular to the α bundles, it encountered high resistance, and when it extended non-perpendicular, it rapidly propagated along the bundle boundaries, exhibiting high strength and low plasticity. The fatigue performance of the Ti6Al4V specimens fabricated by high-power laser melting deposition showed significant dispersion, with cracks originating from subsurface lack of fusion defects. At different stages of fatigue crack propagation, the role of α phase laths varied: during the fatigue source region, cracks primarily propagated along the boundaries of α laths, displaying significant cleavage fracture characteristics. In the fatigue propagation region, crack propagation velocity was mainly influenced by the direction of the laths, and in the fatigue final rupture region, ductile fracture was predominant. Α laths parallel to the tensile direction exhibited the best plasticity, promoting the formation of large dimples and high tear ridges.

Nano-Sized Al2O3-Gr Reinforced Al7075 Hybrid Composite: Impact of Cooling Agents on Mechanical, Wear, and Fracture Behavior.

Aluminum metal cast composites (AMCCs) are frequently used in high-tech sectors such as automobiles, aerospace, biomedical, electronics, and others to fabricate precise and especially responsible parts. The mechanical and wear behavior of the metal matrix composites (MMCs) is anticipated to be influenced by the cooling agent's action and the cooling temperature. This research paper presents the findings of a series of tests to investigate the mechanical, wear, and fracture behavior of hybrid MMCs made of Al7075 reinforced by varying wt % of nano-sized Al2O3 and Gr and quenched with water and ice cubes. The heat-treated Al7075 alloy hybrid composites were evaluated for their hardness, tensile, and wear behavior, showcasing a significant process innovation. The heat treatment process greatly improved the hybrid composites' mechanical and wear performance. The samples quenched in ice attained the highest hardness of 119 VHN. There is a 45.37% improvement in the hardness of base alloy with the addition of 3% of Al2O3 and 1% of graphite particles. Further, the highest tensile and compression strengths were found in the ice-quenched 3% Al2O3 and 1% graphite hybrid composites with improvements of 34.2 and 48.83%, respectively, compared to the water-quenched base alloy. Under the samples quenched in ice, the mechanical and wear behavior improved. The tensile fractured surface showed voids, particle pullouts, and dimples. The worn-out surface of wear test samples of the created hybrid composite had micro pits, delamination layers, and microcracks.

Enhancement of spent coffee grounds as biofiller in biodegradable polymer composite for sustainable packaging

AbstractThis study explores the utilization of Spent Coffee Grounds (SCG), a residual product of the coffee industry, as a microfiller reinforcement in Poly‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate (PHBV) biopolymer composites at varying concentrations (1%, 3%, 5%, and 7%). Melt compounding via a twin‐screw extruder and subsequent compression molding were employed in the fabrication process. The SCG microfiller, with particle diameters ranging from 1.11 to 1.28 μm, exhibited a significant negative charge (zeta potential: −20 mV). Hydrophobicity increased up to 5% filler concentration, as indicated by higher water contact angles, but diminished at highest concentration likelihood of agglomeration of the spent coffee grounds within the biopolymer matrix. The addition of SCG enhanced overall mechanical properties, particularly at a 5% filler concentration. Field Emission Scanning Electron Microscopy (FE‐SEM) and Atomic Force Microscopy (AFM) confirmed the successful incorporation of SCG microfiller, improving structural characteristics. Schematic drawings illustrated the interphase bonding of microfiller and matrix. However, properties diminished at the highest filler content (7%) due to coffee grounds' agglomeration. Despite this, SCG incorporation enhanced functional properties, making the biopolymer composite a promising material for sustainable packaging and various applications.Highlights Enhancement of properties of spent coffee grounds in PHBV biocomposites. Characterization of Biocomposites for multifunctional properties. Fracture and 2D analysis of the tensile fractured surface of biocomposites. A promising material for sustainable and biodegradable packaging.

Effect of Al addition on the microstructure and mechanical properties of IN718 alloy fabricated by laser deposition manufacturing

The IN718 alloys with different Al contents were fabricated by laser deposition manufacturing (LDM) technology. The microstructure and tensile properties of LDMed IN718 alloy with different Al contents before and after homogenization-solution-double aging (HSA) treatment were analyzed. The as-deposited samples show dendrite structure which develops with the addition of Al element. The microstructure of the as-deposited samples mainly consists of the γ matrix, Laves phases and a small amount of carbides. The HSA treatment improves the precipitation of γ″, γ′ and δ strengthening phases, and with the Al content increasing, the γ′ phase increases, but the γ″ phase decreases. With the increasing of Al content, the tensile strength of as-deposited samples increases, but the elongation decreases. For HSA-treated samples, the IN718+0.5Al alloy shows the highest tensile strength and elongation. The tensile fracture surfaces of LDMed IN718 alloys show dimpled surfaces, indicating the transgranular ductile failure mode.

Exploring the influence of pin geometry on metallurgical and mechanical characteristics of dissimilar aluminum TIG welds via friction stir processing

This study explored the effect of friction stir processing (FSP) on tungsten inert gas (TIG)-welded AA6061-T6 and AA7075-T6 joints by utilizing three different tool pin geometries, namely simple cylinder (SC), threaded cylinder with triflat faces (THF), and simple square (SS). The metallurgical aspects of unprocessed and processed weld regions were analyzed and correlated with the ultimate tensile strength, impact toughness, and microhardness properties. Results revealed that the post-FSP with a THF pin transformed the coarse dendritic structures (AGS of 34.55 µm) of the TIG weld into equiaxed fine structures (AGS of 3.51 µm) and increased the UTS, impact toughness, and microhardness by 71.51%, 95.40%, and 72.46%, respectively. The joint processed with the THF pin resulted in the highest ultimate tensile strength of 279 MPa, impact toughness of 15.02 J, and microhardness of 116.13 HV in the nugget region compared to the other two pin geometries. The highest joint properties of THF pin were attributed to the formation of fine grain structures in the nugget region, high effective strain and heat generation, improved material flow, and the decimation of intermetallic precipitates with their uniform dispersion in the nugget region. The tensile fractured surface of the TIG weldment had noticeable macro voids and coarse dimples with some rough cleavage facet in the fusion region, resulting in a brittle mode of failure. However, the tensile fractured surface of TIG + FSP weldments showed ductile failure due to the presence of fine and deep dimples with tear ridges without any void.

Introduction to subpressure-driven soft deformation method for removing inherent voids in green components manufactured by material extrusion

This study introduces a post-treatment process, the subpressure-driven soft deformation method, to reduce inherent voids in Material Extrusion (MEX) components. By subjecting printed green components to heat treatment under subpressure, the process enhances viscosity, effectively filling voids formed between deposited tracks. The average porosities of the samples sintered from the green components without and with soft deformation are calculated to be 3.55% and 2.36%, respectively. A comparison of the tensile strengths and fracture surfaces of the sintered samples with and without soft deformation treatment indicated that the sintered samples with soft deformation treatment exhibited narrower standard deviation for the various mechanical properties. Capillary rheometer calculations indicate feedstock viscosity to be between 450.34 and 1018.31 Pa s under subpressure, diminishing inter-track voids without sizeable dimensional changes. Molecular dynamics simulation demonstrates a 3.7-fold increase in bond strength, indicating intertrack voids effectively eliminated. Reduced inter-particle distances facilitate necking, grain growth, and improved sintered density.