Search Results (6,580)

Using α-SiC powder as a raw material, with ytterbium oxide and magnesium oxide as liquid-phase sintering aids, silicon carbide ceramics were prepared via spark plasma sintering (SPS) at 1900, 2000, and 2050 °C with a 10 min dwell. As the sintering temperature increased, the grain size grew from 0.54 μm to 17.59 μm, while the thermal conductivity correspondingly increased from 122.4 W/(m·K) to 231.8 W/(m·K). Microstructural analyses revealed that elevated sintering temperatures significantly accelerated the dissolution–precipitation process, thereby inducing abnormal grain growth. Grain size is identified as the dominant factor governing the thermal conductivity of SiC ceramics. Larger grains reduce grain boundary density and interfacial thermal resistance, thereby facilitating phonon transport. Full article

Two aluminum alloys (4043 and 6061) were fabricated using the innovative Molten Metal Deposition (MMD) technique. Three types of samples were produced by varying selected deposition parameters. The quality of the resulting components was assessed in terms of defects, density, and microstructure. In the 4043 alloy, the microstructure consists of α-Al dendrites surrounded by an Al–Si eutectic phase. All 4043 samples exhibited this microstructure, regardless of the deposition parameters. The mechanical response was preliminarily evaluated through HV0.5 microhardness measurements. The indentations produced under a 500 g load enabled the assessment of the contribution of both the α-Al matrix and the surrounding Al–Si eutectic. As for the 6061 alloy, its microstructure is composed of an α-Al matrix containing dispersed Al–Si–Fe intermetallics. Some oxide particles were observed at the grain boundaries, indicating the need for processing under a controlled atmosphere. In this study, no inert shielding atmosphere was used for the fabrication of the samples. Thanks to its high processing speed, sustainability, and ease of deployment, MMD can be regarded as a viable alternative to more conventional additive manufacturing technologies. Full article

To investigate the influence of a second-phase mineral on the rheology of mantle peridotite, we conducted high-temperature deformation experiments on dry olivine–clinopyroxene (Ol-Cpx) aggregates. Cylindrical samples were manufactured using hot-isostatic pressing techniques, with Ol as the matrix phase and Cpx added at volume fractions of f_Cpx = 0.1, 0.3, and 0.5. Deformation experiments were performed in a Paterson gas-medium apparatus at a confining pressure of ~300 MPa, temperatures ranging from 1423 to 1523 K, and strain rates of ~5 × 10⁻⁶ s⁻¹, ~1 × 10⁻⁵ s⁻¹, ~2 × 10⁻⁵ s⁻¹, and ~5 × 10⁻⁵ s⁻¹. The stress exponents (n = 3.4–4.3) for two-phase aggregates are comparable to those reported for both pure Ol and pure Cpx, indicating that dislocation creep remains the dominant deformation mechanism. Increasing Cpx content does not induce a transition of dominant mechanism but leads to a slight decrease in activation energy, consistent with predictions from two-phase rheological models and reflecting the increasing contribution of Cpx to bulk deformation. Normalized flow stresses fall between the Ol and Cpx end-members within the Taylor–Sachs bounds, indicating moderate strain partitioning between phases. Aggregates with f_Cpx = 0.5 show slightly reduced strength and lower effective stress exponents. This is attributed to enhanced dynamic recrystallization, which triggers grain-size reduction and thereby increases the contribution of diffusion-assisted deformation, even though dislocation creep remains the dominant mechanism. These results suggest that under dry conditions, Cpx primarily modulates the rheology of olivine-rich aggregates through microstructural evolution and strain partitioning rather than by altering the dominant deformation mechanism. Full article

Extreme ultraviolet (EUV) pellicles must exhibit high optical transmittance, thermal, and mechanical stability to withstand the demands of semiconductor fabrication. ZrSi₂ has attracted attention as a pellicle material due to its excellent optical characteristics. The thickness of ZrSi₂ films is being reduced to enhance EUV transmittance (EUVT). Since the mechanical strength of nanoscale thin films can be influenced by grain-size effects described by either the Hall–Petch or inverse Hall–Petch relationship, grain-size control becomes critical. In this study, ZrSi₂/SiN_x free-standing membranes with different ZrSi₂ grain sizes were fabricated by sputter deposition followed by annealing at 425–600 °C. Grazing incidence X-ray diffraction analysis confirmed that the ZrSi₂ thin films retained their orthorhombic structure up to 600 °C. Scanning transmission electron microscopy showed a gradual increase in grain size with increasing annealing temperature. EUVT remained almost unchanged regardless of the ZrSi₂ grain size. In contrast, the ultimate tensile strength increased with grain size up to 64 nm and decreased with further grain growth. These results indicate that although the optical properties of ZrSi₂-based EUV pellicles are grain-size independent, their mechanical strength can be optimized through microstructural engineering, consistent with the Hall–Petch relationship. Full article

Sulphatic evaporites represent a critical challenge for underground engineering due to their high solubility, swelling potential, and sensitivity to changing hydraulic and thermal conditions. In this study, we investigate the temperature-dependent dissolution behavior and microstructural evolution of Triassic sulphate rocks consisting of anhydrite and minor portions of gypsum from the Western Alps. Twelve cylindrical samples were immersed in CaSO₄-saturated water solutions at 15 °C, 40 °C, and 60 °C for six months. Periodic mass and volume measurements were combined with Scanner Electron Microscope (SEM) imaging to quantify dissolution and document mineralogical transformations. All samples experienced progressive mass loss, whereas volumetric changes remained below measurement resolution. Dissolution pathways varied strongly with temperature. At 15 °C, dissolution occurred mainly along anhydrite grain boundaries, producing rounded crystal edges, while less effect was observed in the gypsum veins, leaving the intergranular layers preserved. In contrast, at 40–60 °C, gypsum was preferentially dissolved, generating porosity around comparatively unaltered anhydrite grains. These results qualitatively reproduce the temperature-controlled solubility inversion between gypsum and anhydrite predicted by thermodynamic models. No secondary gypsum precipitation or swelling features were observed. The experimental evidence highlights the role of temperature and hydraulic regime in controlling the stability of sulphate rocks and provides insights relevant to tunnel excavation, underground storage facilities, and geomechanical modeling in evaporitic settings. Full article

To synergistically integrate piezoelectric and varistor functionalities in a single material, PNN-PZT piezoelectric powder (abbreviated as P) and ZnO-based varistor powder (abbreviated as Z) were utilized to fabricate PZT-ZnO composite ceramics (denoted as PZm) via conventional solid-state sintering. The P/Z molar ratio was regulated to 1/0.9, 1/1.05, 1/1.2, 1/1.35, and 1/1.5 to systematically study its influence on the phase composition, microstructure, and electrical properties of the composites. XRD, SEM, EDS characterization, and electrical performance tests were carried out. Results indicate that all PZm samples exhibit the biphasic coexistence of perovskite (piezoelectric phase) and wurtzite (varistor phase) without impurity phases, consisting of large perovskite grains with distinct edges and small wurtzite grains with smooth surfaces. The PZ3 sample (P/Z = 1/1.2) achieves optimal comprehensive properties: d₃₃ = 161 pC/N, k_p = 0.25, Ɛ_r = 2527, tan δ = 3.83%, E_1mA = 1396 V/mm, I_L = 8.2 mA, α = 22.06. This work confirms the synergistic optimization of piezoelectric and varistor properties in PZT-ZnO composites, providing a reliable experimental basis for the formulation design and performance regulation of multifunctional ceramics. Full article

Alumina-spinel refractory bricks, composed of 82 wt.% alumina and 18 wt.% MgAl₂O₄ spinel phases, are used in steel ladles due to their ability to resist chemical attack and thermal shock. Thermal shock resistance is determined, in part, by the thermal conductivity of the material. Thermal conductivity measurements for alumina-spinel refractory, three model alumina ceramics, and single crystal sapphire were made with the laser-flash technique from 20 °C to 1000 °C. At room temperature, these gave 6.5 W m⁻¹ K⁻¹ for the refractory, 5.8 to 22 W m⁻¹ K⁻¹ for the alumina ceramics, and 36 W m⁻¹ K⁻¹ for sapphire, despite all materials containing >81 vol.% of alumina. The differences are explained by the roles of porosity, grain boundary thermal resistance, and the spinel phase (refractory). In order to estimate the thermal conductivity of alumina grains in each material, these microstructural effects are modelled with Landauer’s relation for porosity and thermal resistors in series for grains combined with grain boundaries. For two alumina ceramics, the grains yielded similar behaviour to the single crystal. By taking the spinel phase into account with a two-phase mixture relation, the alumina grains in the refractory were estimated with a value of 31 ± 2 W m⁻¹ K⁻¹, close to sapphire. Full article

Manufacturing heavy-gauge high-strength steel plates with uniform through-thickness properties is challenging due to the limited hardenability and significant cooling rate variations inherent to heavy sections. However, the mechanism governing microstructural homogenization across such large cross-sections remains not fully understood. This study investigates the through-thickness microstructure and mechanical properties of a 60 mm thick high-Nb microalloyed Q690 steel plate processed by direct quenching (AQ) and subsequent tempering at 530 °C and 580 °C. Characterization was performed at the surface (0t), quarter-thickness (1/4t), and core (1/2t) locations. Results revealed a pronounced gradient in the as-quenched state: while the surface consisted of fine lath martensite/bainite, the core formed coarse granular bainite containing blocky martensite–austenite (M-A) constituents. This microstructural heterogeneity resulted in poor core toughness (~24 J). High-temperature tempering at 580 °C promoted the complete decomposition of these metastable M-A constituents into ferrite and fine carbides, significantly improving the core impact energy to ~49 J. However, a toughness gradient persisted compared to the quarter-thickness (>120 J), attributed to the inherited coarse matrix and the formation of grain boundary carbides. Notably, high yield strength was maintained across the thickness despite matrix recovery. This is primarily attributed to a potent anti-softening effect provided by thermally stable (Nb,Ti,Mo)C nanoprecipitates, which generate strong Orowan strengthening. These findings highlight the critical role of optimizing the trade-off between M-A decomposition and carbide evolution in promoting the microstructural and property homogenization of heavy-gauge steels. Full article

H13 tool steel is widely used in the hot work die industry owing to its excellent mechanical properties. However, the inherent anisotropy of its microstructural and mechanical properties during additive manufacturing (AM) via laser powder bed fusion (L-PBF) hinders its broader application. In the current study, Ce-containing and as-built samples were prepared in both vertical and horizontal directions, and their microstructures and tensile properties were investigated. Notably, the grain size of the vertical samples is approximately 2.7 μm, which is 19.2% smaller than that of the horizontal samples in L-PBF H13 steel. In addition, the retained austenite (RA) content in the vertical samples reaches as high as 19.7%, whereas in the horizontal samples, it is only 0.4%. After the addition of Ce, the columnar grains of the building direction (BD) samples transform into equiaxed grains. The RA content of the scanning direction (SD) samples and BD samples is 6.3% and 5.7%, respectively. The tensile test results further demonstrate that Ce-containing BD samples exhibit a tensile strength of 2025.3 MPa and an elongation of 17.3%, with the elongation difference between the two directions being only 0.2%. The addition of Ce reduces microstructural anisotropy, resulting in a significant decrease in the mechanical property anisotropy of the formed parts. Full article

Understanding the mechanisms of microstructure evolution and defect formation, and their influence on mechanical properties and fracture mechanisms (from crack initiation to failure stage), is essential for manufacturing high-strength, fatigue-resistant A7075 alloy by selective laser melting (SLM). In this investigation, the A7075 alloy was fabricated using a laser power of 350 W with various hatch spacings of 1.0, 1.5, and 2.0 μm, and scanning speeds of 800, 1100, and 1300 mm/s. The results show that the alloy exhibits an equiaxed grain structure, which varies from coarse grains at small hatch spacing and low scanning speed to fine grains with increasing hatch spacing and scanning speed. The alloys exhibit low tensile strength due to solidification cracking and pores. However, this tensile strength increases with hatch spacing, while it decreases with scanning speed. At small hatch spacing and low scanning speed, fracture occurs through the coalescence of pores and solidification cracking along the weakly bonded grain boundaries (GBs) due to eutectic growth along these boundaries. In contrast, with increasing hatch spacing and scanning speed, fracture occurs through solidification cracking and coalescence of pores. This research provides valuable insights into the microstructure evolution, defect formation, and fracture mechanisms of the A7075 alloy under common processing conditions. Full article

This study systematically investigates the microstructural characteristics and mechanical properties of resistance spot-welded joints in 3 mm thick non-heat-treatable die-cast AlSi₇MnMg alloy, with particular focus on the influence of element segregation and secondary phase behavior on fracture mechanisms and the process window. The results indicate that the weld nugget exhibits a typical dual structure consisting of columnar and equiaxed grain zones, with a corresponding “M”-shaped microhardness profile. Significant segregation of Si, Fe, and Mn elements at the nugget boundary was observed, leading to the formation of low-melting-point eutectic regions and secondary phase bands. These features induce microporosity along segregation trajectories, serving as crack initiation sites and resulting in a notably narrowed spot welding process window. From the perspective of microstructure and solute behavior during non-equilibrium solidification, this work elucidates the intrinsic mechanisms governing joint performance and process stability in non-heat-treatable die-cast aluminum alloys, providing a theoretical basis for their engineering applications. Full article

This study significantly enhances the mechanical properties of an Al-Zn-Mg-Cu alloy through the implementation of a pre-aging process. By optimizing the microstructure of the Al-Zn-Mg-Cu alloy with different pre-aging treatments, the evolution of the microstructure and mechanical properties of the alloy initially containing GP I, GP II, and η′ phases is systematically investigated during aging at 140 °C. The experimental results show that, under the three pre-aging processes, the peak tensile strengths are 590.8 MPa, 594.0 MPa, and 612 MPa, respectively, while the corresponding elongation rates are 8.2%, 8.4%, and 10.3%. When pre-aging produces an initial microstructure containing GP I and GP II, these GP zones rapidly coarsen within the grains during subsequent aging. This makes it difficult for solute atoms to diffuse to the grain boundaries, resulting in finer grain boundary precipitates and ultimately leading to a lower alloy strength. When the pre-aging temperature is 120 °C, the pre-aging process can reduce the vacancy concentration, thereby suppressing the phase transformation from η′ to η precipitates. For samples pre-aged to the η′ phase, solute atoms diffuse to the grain boundaries, resulting in grain boundary precipitates with a greater length during subsequent aging compared to the other two samples. These grain boundary precipitates exhibit a discontinuous distribution along the grain boundaries, which contributes to the improved elongation of the alloy. The present work provides a novel heat treatment strategy for producing high-strength Al alloys while effectively achieving a favorable balance between strength and ductility. Full article

Aluminum–lithium (Al-Li) alloys are extensively employed in aerospace and space structures because of their low density, high specific stiffness, and excellent fatigue resistance. However, welding of these alloys remains challenging, since the joints typically exhibit unique microstructural features, including equiaxed grain zones (EQZ) along the fusion boundary and coarse columnar grains in the fusion zone, which degrade mechanical performance and increase susceptibility to cracking. This review provides an overview of the generational evolution of Al-Li alloys and their associated weldability, highlights the advantages and limitations of major welding processes, such as laser, arc, and hybrid techniques, and systematically examines the formation mechanisms of EQZ, columnar grains, and equiaxed grain bands. Various strategies for microstructural control are compared, including filler design, pulsed current, and external-field-assisted welding. Special attention is given to grain refinement achieved through heterogeneous nucleation, dendrite fragmentation, and columnar-to-equiaxed transition. Finally, prospects for advanced microstructural control strategies are discussed, with the goal of achieving high-quality welds for next-generation lightweight structural applications. Full article

Magnesium alloys’ poor corrosion resistance limits their applications as biodegradable bone repair materials. Alloying tailors Mg alloys’ microstructure and properties. The present study investigates the effect of 2 wt.% Ag addition on the microstructure and initial corrosion behavior of hot-rolled Mg-1Ca alloy. Mg-1Ca and Mg-1Ca-2Ag alloys were prepared by melting using Mg-2Ca and Mg-4Ag master alloys, followed by homogenization at 400 °C for 2 h, hot rolling, and stress-relief annealing at 400 °C for 6 h. The alloys were systematically characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). Initial corrosion behavior was evaluated via 3 h immersion tests in simulated body fluid (SBF). Results reveal Ag’s high thermal diffusivity promotes segregation at tensile twin boundaries, forming Ag₃Mg nanoparticles. These nanoparticles hinder grain boundary migration and, with increased deformation, facilitate grain rotation and high-angle grain boundary formation, weakening texture. Internal stress accumulation near twin boundaries—driven by grain orientation variation and nanoparticles—induces ~86° rotation of {10–12} tensile twins around the c-axis, forming double twins. During corrosion, nanoparticles and double twins synergistically promote dense protective film formation, significantly reducing corrosion rates. Full article

With surging demand for oil and gas resources, staged fracturing is becoming extremely important, and fracturing material is the key factor in exploration. Recently developed Mg-Al alloys cannot simultaneously achieve high strength and rapid degradation, limiting their widespread application in the exploration. To address this issue, this study utilized the rapid densification technology of spark plasma sintering (SPS) to sinter Mg, Al, and Fe powders at a ratio of Mg-5Al-Fe (0, 2, 4, 6 wt.%) under a temperature of 510 °C and a pressure of 35 MPa for 800 s. And this study conducted investigations on the microstructure, mechanical strength and degradation rate of the alloy through scanning electron microscope, hardness and compression tests, as well as immersion experiments. The results indicated that SPS enabled rapid powders densification and grain refinement, and the addition of Fe particles formed a second-phase strengthening which could block dislocation, thereby increasing mechanical strength. The ultimate compressive strength (UCS) was increased from 189.37 ± 6.12 MPa for Mg-5Al to 421.21 ± 12.31 MPa for Mg-5Al-6Fe. Furthermore, the addition of Fe accelerated the degradation rate, with the Mg-5Al-6Fe alloys reaching 45.26 ± 2.6 mm/year. Meanwhile, the alloys also had a low density of 1.38 ± 0.027–1.53 ± 0.030 g/cm³, which could effectively reduce the pumping energy consumption of fracturing fluids. These characteristics met the core requirements of degradable fracturing balls, showing the great potential of Mg-5Al-Fe alloys for staged fracturing. Full article