Search Results (1,048)

Comprehensive studies of hydrogen embrittlement in high-strength austenitic alloys under cryogenic conditions are scarce, leaving the combined effect of hydrogen charging and extreme temperatures largely unexplored. Given the demands of cryogenic applications such as hydrogen storage and transport, understanding material behavior under these conditions is crucial. Here, we present the first systematic study of hydrogen’s effect at liquid helium temperature (4.2 K) on the mechanical properties of precipitation hardened austenitic alloys, specifically the nickel-based Alloy 718 and austenitic stainless steel A286. Both materials were subjected to pressurized hydrogen charging at 473 K followed by slow strain rate tensile testing at room temperature and at 4.2 K. Hydrogen charging caused significant ductility loss at room temperature in both alloys. In contrast, testing at 4.2 K resulted in increased strength and no evidence of hydrogen embrittlement. Notably, materials pre-charged with hydrogen and tested at 4.2 K exhibited higher stress drop amplitudes and increased strain accumulation during serration events, suggesting persistent hydrogen–dislocation interactions and possible enhanced dislocation pinning by obstacles such as Lomer–Cottrell locks. These results indicate that while hydrogen influences plasticity mechanisms at cryogenic temperatures, embrittlement is suppressed, providing new insight into the safe development of austenitic alloys in cryogenic hydrogen environments. Full article

Cold-spray additive manufacturing (CSAM) is an emerging solid-state deposition technology that effectively mitigates common defects associated with conventional thermal processes, such as oxidation, phase transformation, and residual stresses. In this study, copper–titanium (Cu-Ti) composite coatings were fabricated via high-pressure CSAM using mixed powders with Ti contents of 3, 6, and 10 wt.%. The influence of Ti content and post-heat treatment (350–400 °C) on the tensile properties of the composites was systematically investigated. The results indicate that the ultimate tensile strength (UTS) remained consistently within the range of 265–285 MPa under all conditions, showing only a mild positive correlation with Ti content. In contrast, ductility was significantly influenced by Ti addition, with elongation decreasing markedly as the Ti content increased. Notably, the composite with 3 wt.% Ti heat-treated at 400 °C exhibited a well-balanced combination of tensile strength (270 MPa) and ductility (20% elongation). These findings demonstrate that CSAM-fabricated Cu-Ti composites possess attractive mechanical properties, which can be tailored through Ti content and heat treatment. Full article

In the present study, aluminum matrix composites (AMCs) were fabricated by friction stir processing (FSP) using Ni-Cu particles. Ni-Cu particles were added to the Al matrix in two ways. First, without any treatment and in the form of a mixture of as-received powders. Second, treated through mechanical alloying to form Monel solid-solution particles. The particles were added to a groove to be processed by the FSP tool to produce a local AMC. To investigate the kinetics of intermetallic compounds (IMCs) growth in reinforcement particles, the produced AMCs were annealed at 500 °C for 2 h. To characterize the reinforcing particles, several analyses were performed on the samples. Field-emission scanning electron microscopy (FE-SEM) was used to study the size, morphology, and IMC thickness. TEM was performed to characterize the IMCs through high-resolution chemical analyses. Tensile testing was used to understand the mechanical properties and fracture behavior of AMCs. Tensile testing revealed a noticeable improvement in strength for the as-mixed sample, with a UTS of 90.3 MPa, approximately 22% higher than that of the base aluminum. In contrast, the mechanical alloying sample with annealing heat treatment exhibited a severe drop in ductility, with elongation decreasing from 17.98% in the as-mixed sample to 1.52%. The results showed that heat treatment thickened the IMC layer around the reinforcing particles formed during the FSP process with as-mixed particles. In the AMC reinforced with mechanically alloyed Ni-Cu powders, IMC formation during FSP was significantly suppressed compared to that of as-mixed particles, despite the finer size resulting from milling. Additionally, the heat treatment resulted in only a slight increase in IMC thickness. The IMC layer thickness after heat treatment in both the mechanically alloyed sample and the as-mixed sample was approximately 2 µm and 20–40 µm, respectively. The reason behind this difference and its effect on the fracture behavior of the composite were elaborated in this study, giving insights into metal-matrix production with controlled reaction. Full article

Nanoporous gold (NPG), characterized by a bicontinuous network of nanoscale solid ligaments and pore channels, exhibits exceptional physical and chemical properties. However, the limited strength and stiffness of traditional isotropic NPG (INPG) have constrained its engineering applications. To effectively enhance the mechanical properties of NPG, this work proposes an innovative anisotropic NPG (ANPG) architecture featuring unidirectional ligament orientation. By controlling spinodal decomposition parameters, ANPG models with preferentially aligned ligaments and INPG with random ligament orientation are constructed, spanning relative densities from 0.30 to 0.50. The ligament length and diameter of ANPG along the out-of-plane direction are twice those along other directions. Molecular dynamics simulations of tensile tests show that ANPG exhibits superior out-of-plane Young’s modulus and yield strength but reduced fracture strain compared to INPG. Crucially, ANPG maintains toughness comparable to INPG at relative densities below 0.4, offering an optimal strength-toughness balance for practical applications. Scaling law analysis demonstrates INPG follows classical bending-dominated Gibson-Ashby behavior, while ANPG exhibits a hybrid deformation mechanism with significant ligament stretching contribution. Atomic-scale analysis reveals that both structures develop dislocation-mediated plasticity initially, but ANPG transitions to localized ligament necking and fractures more rapidly, explaining its reduced ductility. Strain localization quantification, measured by atomic shear strain standard deviation, confirms the intensifier deformation concentration in ANPG at large plastic strain. These findings suggest anisotropic design as a powerful strategy for developing high-performance NPG for actuators, sensors, and catalytic systems where simultaneous mechanical robustness and functional performance are required. Full article

This study successfully produced a magnesium alloy bar featuring a bimodal microstructure with high strength via an asymmetric upsetting–extrusion process. The evolution of microstructure, texture, and mechanical properties was systematically investigated using finite element simulation, room-temperature tensile tests, optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Results demonstrate that the bimodal structure forms under the combined effects of shear deformation in the upsetting stage and low-speed, high-ratio deformation in the extrusion stage. This structure consists of coarse deformed grains containing high-density dislocations surrounded by fine dynamically recrystallized grains. A strong <10-10>//ED basal fiber texture also developed, which effectively suppresses basal slip. Continuous dynamic recrystallization was the primary grain refinement mechanism. The 370 °C extruded alloy achieved a high tensile strength of 457.9 MPa, but its elongation was limited to 3.96%. This combination of strength and ductility is attributed to the synergistic influence of the bimodal microstructure, strong basal texture, and high dislocation density. Full article

We report a scalable route to hybrid aluminum matrix composites (AMCs) based on Al6060 (as-fabricated condition) reinforced with 2 wt.% TiB₂ and 1 wt.% microsilica, fabricated by ultrasonically assisted stir casting (UASC) followed by radial-shear rolling (RSR). Premixing and preheating of powders combined with acoustic cavitation/streaming during UASC ensured uniform, non-sedimentary particle dispersion and low-defect cast billets. X-ray diffraction of the as-cast composite shows fcc-Al with weak TiB₂ reflections and no reaction products; microsilica remains amorphous. Electron microscopy and EBSD after RSR reveal full erasure of cast dendrites, fine equiaxed grains, weakened texture, and a high fraction of high-angle boundaries due to the concurrent action of particle-stimulated nucleation (micron-scale TiB₂) and Zener pinning/Orowan strengthening (50–350 nm microsilica). Mechanical testing shows that, in the cast state—comparing cast monolithic Al6060 to the cast hybrid-reinforced composite—yield strength (YS) increases from 61.7 to 77.2 MPa and ultimate tensile strength (UTS) from 103.4 to 130.7 MPa, without loss of ductility. After RSR to Ø16 mm (cumulated true strain ≈ 0.893), the hybrid attains YS 101.2 MPa, UTS 150.6 MPa, and elongation ≈ 22.0%, i.e., comparable strength to rolled Al6060 (UTS 145.1 MPa) while restoring/raising ductility by ~9.7 percentage points. Microhardness follows the same trend, increasing from 50.2 HV0.2 to 73.1 HV0.2 when comparing the base cast condition with the rolled hybrid. The route from UASC to RSR thus achieves a favorable mechanical strength–ductility balance using an economical, eco-friendly oxide/boride hybrid reinforcement, making it attractive for formable AMC bar and rod products. Full article

To develop a cost-effective titanium alloy tailored for laser powder bed fusion (LPBF), a novel Ti-5.2Al-5Fe (wt.%) dual-phase alloy was designed and fabricated in this study. The composition was optimized for low density (4.4 g/cm³), high yield strength (1052 MPa), and suitable β-phase stability ([Mo]_eq = 9.3%). The alloy demonstrated excellent formability, achieving high densification (porosity ≤ 2%) and hardness (>400 HV) over a wide volumetric energy density range (48–204 J/mm³). The Al element inhibited balling by improving melt pool wettability, while the Fe element synergistically promoted densification by lowering the liquidus temperature. The as-built microstructure comprised α and β phases, with the α-phase content increasing significantly from 25.4% to 60.8% with higher energy density. While all samples exhibited high tensile strength (>1290 MPa), ductility was limited (<2.6%). EBSD analysis identified the α-phase as the primary carrier of micro-residual stress, with a high density of “zero-solution” points, low-angle grain boundaries, and KAM values. This indicates severe stress concentration from rapid solidification and phase transformation, elucidating the fundamental reason for the low ductility. This study provides systematic insights from composition design to microscopic mechanisms for designing LPBF-dedicated titanium alloys with a wide process window. Full article

Poly(L-lactide) (PLA) is a promising biopolymer for biomedical applications due to its biodegradability and biocompatibility; however, its brittleness restricts its use in fused deposition modeling (FDM). To overcome this limitation, flexible PLA monofilaments with enhanced mechanical performance and printability were developed. In this study, PLA was melt-blended with acetyl triethyl citrate (ATEC, 1.0–5.0 wt%) as a plasticizer and zinc phenyl phosphonate (TMC-200, 0.3 wt%) as a nucleating agent. It was found that the PLA with 3.0 wt% ATEC (PLA/A) exhibited the greatest flexibility, while the addition of TMC-200 further improved tensile strength and ductility. Specifically, the ternary blend of PLA/TMC-200/ATEC (PLA/T/A) exhibited a synergistic effect, achieving superior mechanical properties (tensile strength: 35.0 MPa, elongation at break: 232.0%, compared to 12.1% for pure PLA) and raising the degree of crystallinity (X_c) from 4.7% to 45.0%. Monofilaments (1.70 ± 0.05 mm) fabricated from PLA/T/A exhibited smooth surfaces, balanced mechanical performance, and excellent cytocompatibility (over 99% cell viability in L929 fibroblasts). Moreover, FDM-printed specimens retained enhanced mechanical and thermal performance, demonstrating material stability after processing. Shelf-life testing further confirmed the structural integrity of PLA/T/A monofilament after 8 weeks at 50 °C. Overall, PLA/T/A provides an effective strategy for producing high-performance, medical-grade PLA monofilaments with improved toughness, printability, and biocompatibility, enabling their application in biomedical 3D printing. Full article

Polymers such as PLA, PLA reinforced with carbon fiber (PLA + CF), and PETG are widely employed in utensils, structural components, and biomedical device housings where load-bearing capability and chemical resistance are desirable. This is particularly relevant for reusable applications in which sterilization with hydrogen peroxide (HP) or ethylene oxide (EO) is often required. In this study, the impact of HP and EO sterilization processes on the mechanical, thermal, and structural properties of PLA, PLA + CF, and PETG was evaluated. The mechanical properties assessed included elongation at break, elastic modulus, and tensile strength after sterilization. The thermal properties examined comprised thermal stability and the coefficient of thermal expansion (CTE). Additionally, Fourier Transform Infrared Spectroscopy (FTIR) was performed to detect potential alterations in functional groups. For PLA, sterilization with HP and EO resulted in a 22% increase in ultimate tensile strength (UTS) and a 21% increase in elastic modulus, accompanied by a noticeable reduction in ductility and the appearance of more brittle fracture surfaces. PLA + CF exhibited greater stability under both sterilization methods due to the reinforcing effect of carbon fibers. In the case of PETG, tensile strength and stiffness remained stable; however, HP sterilization led to a remarkable increase in elongation at break (294%), whereas EO sterilization reduced it. Regarding thermal properties, glass transition temperature (Tg) showed variations: PLA presented either an increase or decrease in Tg depending on the sterilization treatment, PLA + CF displayed a Tg reduction after EO sterilization, while PETG exhibited a moderate Tg increase under HP sterilization. CTE decreased at lower temperatures but increased after EO treatment. FTIR analysis revealed only minor chemical modifications induced by sterilization. Overall, HP and EO sterilization can be safely applied to additively manufactured medical components based on these polymers, provided that the structures are not subjected to high mechanical loads and do not require strict dimensional tolerances. Full article

The study of the strain rate effects on the PA6 glass fiber-reinforced polyamide, in this specific case, PA6 GF30 (30% reinforced glass fiber), is critical due to composites widely used in automotive applications where the velocity of loading can vary significantly. Some insights into material safety under high quasistatic strain rate regime are given by understanding tensile behavior with focus on strain and stress at break. For this, using injection molding, dog bone samples were subjected to tensile tests at different strain rates, using a precise displacement control and extensometer to record the engineering stress–strain. The results demonstrate that higher strain rates increased the stiffness and strength of the specimen, shifting the stress–strain behavior to higher stress at break due to the reduced time for the polymer relaxation. However, the strain at break decreases under rapid movement, indicating the fact that the specimens exhibited reduced ductility. The results indicate a pronounced strain rate sensitivity that needs to be evaluated and considered for the design and failure mechanism of the components made of PA6 GF30, highlighting the necessity of strain rate specific mechanical characterization for accurate evaluation of performance under high quasistatic strain rate load cases, leading to a more safe and reliable design. Full article

Lightweight magnesium alloys are gaining increasing attention as potential structural materials for automotive and aerospace applications due to their high specific strength and excellent recyclability. However, their formability and mechanical performance are often limited by strong basal texture and limited recrystallization during thermomechanical processing. In this context, the present study systematically investigates the effect of post-annealing treatment on the microstructural evolution, recrystallization behavior, and mechanical response of a hot-rolled Mg-3Al-1Zn-1Ca alloy. Detailed microstructural characterization revealed that Al₂Ca precipitates were uniformly distributed along grain boundaries in the as-received (AR) condition, where they contributed to significant pinning of boundary migration. Post-annealing treatment (350 °C, furnace cooling) resulted in non-uniform grain coarsening, driven by the interplay of precipitate pinning and differential stored strain energy, while also facilitating particle-stimulated nucleation (PSN) and recrystallization. Electron backscatter diffraction (EBSD) analysis confirmed a substantial increase in the fraction of high-angle grain boundaries and recrystallized grains in the heat-treated (HT) state, with kernel average misorientation (KAM) and grain orientation spread (GOS) analyses indicating pronounced recovery of lattice distortions. Mechanical testing demonstrated a significant decrease in yield strength (263 MPa to 187.4 MPa) and hardness (65.7 to 54.1 HV) due to dislocation annihilation and stress relaxation, while ultimate tensile strength remained nearly unchanged (~338 MPa) and ductility improved markedly (12.6% to 16.4%). These findings highlight the dual role of Al₂Ca precipitates in promoting recrystallization through PSN while simultaneously restricting excessive grain growth through Zener pinning. Full article

This study investigates the development of biodegradable, scented bio-composite filaments incorporating industrial residues, specifically spent coffee grounds (SCG) and lignin (LI), into a PLA matrix for FDM 3D printing. Two fragrance additives, essential oil (EO) and microencapsulated fragrance powder (FP), were introduced (3%) to enhance sensory properties. The research investigates the effects of filler content (5%, 10%, and 15%) and fragrance additives on the surface chemistry (FTIR), thermal stability (TGA and DSC), mechanical properties (Tensile, flexural and impact), microstructure, and dimensional stability (Water absorption test and thickness swelling). Incorporating industrial residues and additives into PLA reduced the thermal stability, the degradation temperature and the glass transition temperature but increased the residual mass and the crystallinity. The effect of lignin was more pronounced than that of SCG, significantly influencing these thermal properties. Increasing the filler content of spent coffee grounds and lignin also led to a progressive decrease in tensile, flexural, and impact strength due to poor interfacial adhesion and increased void formation. However, lignin-based biocomposites exhibited enhanced stiffness at lower concentrations (≤10%), while biocomposites containing 15% SCG doubled their elongation at break compared to pure PLA. Adding fragrance reduced the mechanical strength but improved ductility due to plasticizer-like interactions. Microstructural analysis revealed heterogeneity in the biocomposites’ fracture surface characterized by the presence of pores, filler agglomeration, and delamination, indicating uneven filler dispersion and limited interfacial adhesion, particularly at high filler concentrations. The water absorption and dimensional stability of 3D-printed biocomposites increased progressively with the addition of residues. The presence of essential oil slightly improved water resistance by forming hydrogen bonds that limited moisture absorption. This article adds significant value by extending the potential applications of biocomposites beyond conventional engineering uses, making them particularly suitable for the fashion and design sectors, where multi-sensory and sustainable materials are increasingly sought after. Full article

Al–Zn–Mg–Cu alloys are well known for their outstanding strength, toughness, and corrosion resistance, arising from the balanced addition of Mg, Zn, and Cu. However, conventional casting methods often lead to grain boundary segregation and the formation of coarse Fe-rich phases, which severely limit subsequent heat treatment and plastic processing. To overcome these drawbacks, this study systematically investigates the effects of the Continuous Rheo-Extrusion (CRE) process on the microstructure and mechanical performance of Al–Zn–Mg–Cu alloys using XRD, EBSD, SEM, and TEM analyses. The CRE process refines the average grain size from 53.5 μm to 16.1 μm and raises the fraction of high-angle grain boundaries to 88.8%. Moreover, coarse Fe-rich phases are fragmented to below 5 μm, while the elemental distribution of Zn, Mg, and Cu becomes more homogeneous, effectively reducing grain boundary segregation. The Al₂Cu precipitates are refined from 106.3 nm to 11.7 nm, corresponding to an 88.9% size reduction. These microstructural optimizations yield a remarkable increase in tensile strength (from 204.7 ± 23.7 MPa to 338.0 ± 9.3 MPa) and elongation (from 11.4 ± 2.4% to 13.8 ± 1.3%). Quantitative analysis confirms that dislocation and precipitation strengthening are the dominant contributors to this improvement. Overall, the CRE process enhances microstructural uniformity through the synergistic effects of shear deformation, continuous dynamic recrystallization (CDRX), and dynamic precipitation, thereby providing a solid theoretical and practical foundation for short-process fabrication of high-strength, high-ductility Al–Zn–Mg–Cu alloys. Full article

Laser melting deposition (LMD), one of the novel powder-to-powder welding technologies, has emerged as an ideal method for fabricating lightweight high-temperature Ti₂AlNb alloy. However, the high thermal gradients and heat accumulation during the LMD process typically promote grain growth along the deposition direction, resulting in coarse columnar grains and high internal residual stress. This study investigates the influence of prolonged aging treatment and internal cyclic heat on the microstructure and mechanical properties of Ti₂AlNb alloys. Both long-term aging and internal cyclic heat induce the columnar-to-equiaxed grain morphology transition. A 48 h aging heat treatment at 750 °C facilitates the formation of a B2 + O dual-phase lamellar structure, leading to a significant improvement in room-temperature strength. Internal cyclic heat effectively reduces the cooling rate, eliminates internal stress, and suppresses the precipitation of the brittle and detrimental α₂ phase. This results in a more homogeneous distribution of O-phase laths, raising the room-temperature tensile strength from 938 MPa to 1215 MPa and achieving a high-temperature strength of 1116 MPa at 650 °C. These improvements demonstrate a synergistic enhancement in both room- and high-temperature strength and ductility, which provides an efficient strategy for in situ regulation of the microstructure and mechanical properties of laser-deposited Ti₂AlNb alloys. Full article

T6 aging, involving solution treatment and artificial aging, is a widely adopted strengthening method for magnesium alloys due to its proven effectiveness. However, the integration of three or more sequential thermal treatments has been explored only sparingly, primarily due to the challenges associated with optimizing such multi-parameter processing systems. This study demonstrates that integrating a 12 h deep cryogenic treatment (DCT) before aging in a Mg–Al–Ca–Mn alloy optimizes mechanical performance, achieving a tensile strength of 343 MPa and 27.3% elongation. Microstructural analysis, based on electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), reveals that the strength enhancement results from ~29 nm precipitate refinement, elevated dislocation density, and nanoscale sub-grain formation, while the ductility gains stem from the activation of non-basal slip systems and the suppression of microcrack propagation. These synergistic mechanisms enable superior strain accommodation, providing a clear framework for DCT-enabled sequential heat treatment design in high-performance magnesium alloys. Full article