Search Results (79)

SU-8 photoresist is extensively used as a structural and passivation layer in microelectromechanical systems, microfluidic devices, and related microscale technologies. The long-term reliability of these devices critically depends on the mechanical integrity and viscoelastic behaviour of the SU-8 coating. In this study, the mechanical and viscoelastic behaviour of SU-8 polymer thin films was systematically investigated using nanoindentation at different baking stages representative of standard photolithographic processing. SU-8 layers were spin-coated on silicon wafers and subjected to pre-bake, post-bake, and hard-bake treatments to evaluate the effects of progressive cross-linking. Static nanoindentation revealed that the elastic modulus did not change significantly during the baking phases and remained near 6.2 GPa; however, a significant change in hardness was observed from 0.173 ± 0.012 GPa after pre-bake to 0.365 ± 0.011 GPa and 0.364 ± 0.016 GPa after post- and hard bake, respectively. Creep tests analysed by the Burgers viscoelastic model showed a significant increase in both the retarded modulus and viscosity parameters with thermal curing, indicating the suppression of long-term viscoelastic deformation. The combined results demonstrate that nanoindentation provides a sensitive, nondestructive tool for monitoring the evolution of cross-linking and viscoelastic stability in SU-8 films, offering valuable insight for process optimization and mechanical reliability in MEMS and microfluidic applications. Full article

In the aerospace sector, integrating advanced materials with high mechanical capabilities represents the forefront of material science, especially in the field of rocketry. Bimetallic structures are increasingly used in aerospace applications due to their combination of high strength-to-weight ratio, thermal conductivity, and corrosion resistance. Among these, Inconel-copper (In718-Cu) systems are particularly promising, although large differences in thermophysical and mechanical properties between the two materials can induce residual stresses, cracks, and other interfacial defects, requiring careful process control. This study evaluates the fabrication of In718-Cu structures through Direct Energy Deposition (DED), in which In718 was deposited onto a copper substrate using an innovative deposition strategy. Interface quality and microstructure were characterized by SEM/EDS and X-ray diffraction, whereas the mechanical properties were evaluated by nanoindentation, indentation creep, and tensile testing. The results showed that crack-free samples can be achieved, with strong diffusion bonding at the interface and efficient precipitation strengthening on the copper side already in the as-built condition. A uniform distribution of precipitates and consistent penetration depth were also observed, confirming the effectiveness of the deposition strategy for producing reliable In718-Cu components. Full article

This study investigates the synergistic effect of phenolic resin impregnation on the mechanical and adhesive properties of hydrothermally treated bamboo composites further reinforced with a silica nanoparticle sol–gel catalyzed by Fe₃O₄ (SiO₂/Fe₃O₄). The hydrothermal pre-treatment was found to enhance cellulose crystallinity, as confirmed through XRD analysis. Dynamic mechanical analysis (DMA) and nanoindentation tests revealed that the hybrid treatment significantly influences the viscoelastic response. Composites treated only with hot water and resin (GB-W) exhibited superior short-term creep resistance and higher elasticity, attributed to their optimized crystalline structure. In contrast, the silica-reinforced composites (GB-M) demonstrated the most viscous behavior and lowest stress relaxation, making them most effective at minimizing elastic springback. Nanoindentation further showed that GB-W had the highest nano-adherence at the fiber cell wall level. FTIR analysis indicated a stronger interaction between the phenolic resin and the hydroxyl groups of the bamboo matrix in GB-0 and GB-W compared to GB-M, where the silica layer potentially altered this interface. Microscopy confirmed a resin penetration depth of at least 1 mm, primarily into porous tissues. The results demonstrate that while silica reinforcement enhances relaxation properties, the hydrothermal pre-treatment combined with phenolic resin creates a more favorable interface, leading to better overall creep resistance and adherence. Full article

This study investigates the impact of increased extrusion ram speed—achieved by utilizing liquid nitrogen as a die cooling agent—on the mechanical properties of a 6060-aluminum alloy. Mechanical characterization of the extruded profiles was performed using both tensile and nanoindentation tests. In addition, nanoindentation was employed to evaluate creep behaviour and to extract key parameters, such as the steady-state creep strain rate. The findings indicate that while the enhanced ram speed has a minimal influence on Ultimate Tensile Strength (UTS) and Yield Tensile Strength (YTS), it has a more noticeable effect on elongation. Finite Element Analysis (FEA) was used in conjunction with nanoindentation data to model the mechanical behaviour of the alloy, showing good agreement with experimental tensile test results. This confirms the effectiveness of FEA-assisted nanoindentation as a reliable tool for mechanical assessment. Moreover, the results demonstrate that creep displacement is significantly influenced by the increased ram speed. However, the steady-state creep strain rate remained largely unaffected by variations in ram speed with the use of liquid nitrogen as a coolant. Notably, the creep stress exponent (n) was found to increase with higher ram speeds enabled by liquid nitrogen cooling. Full article

Tuning structural heterogeneity in metallic glasses is key to improving their mechanical performance. Here we examine how carbon micro-alloying modulates the relaxation dynamics and creep of Fe-based amorphous ribbons. Increasing carbon content lowers the crystallization temperature, amplifies β-relaxation, and reduces hardness, consistent with enhanced atomic mobility. Nanoindentation creep, fitted with a stretched-exponential model, shows a decreasing exponent with carbon addition, indicating broader relaxation–time distributions and stronger dynamic heterogeneity. Nanoscale force-mapping further reveals a larger fraction of liquid-like regions and pronounced viscoelastic heterogeneity in carbon-rich samples. These changes facilitate the activation of shear-transformation zones and promote room-temperature creep flow. Together, the results establish a direct link between structural heterogeneity, relaxation processes, and mechanical response, providing guidance for the design of ductile metallic glasses. Full article

Mg-Sc body-centered cubic (BCC) phase-structured alloys not only exhibit superior room-temperature ductility and quasi-isotropic deformation behaviors compared to conventional hexagonal close-packed (HCP) Mg alloys in mechanical applications, but they also demonstrate a shape-memory effect that is applicable to intelligent devices. Due to the introduction of a dual-phase microstructure feature, the unveiled strengthening/toughening mechanism, and the potential benefit of Sc alloying in BCC creep deformation, it is necessary to investigate the composition and time-dependent creep behaviors of BCC Mg-Sc alloys, such as creep resistance and strain rate sensitivity at room temperature, through nano-indentation on the Mg-Sc diffusion couple. A critical finding is that as the Sc content increases from 23.01 at.% to 33.56 at.%, the BCC Mg-Sc alloy exhibits a progressive enhancement in creep resistance at room temperature, evidenced by the creep stress exponent (n) rising from 49.02 to 66.22. Furthermore, the strain rate sensitivity (m) increases from 0.02 at 26.94 at.% Sc to 0.11 at 32.63 at.% Sc, along with the Sc composition gradient. These phenomena can be attributed to the formation of ordered structures with the increasing Sc concentration, which introduce short-range local barriers to dislocation motion, as confirmed through atomic-scale microstructural analysis. Full article

Al-Mg-Si (6XXX) series aluminum alloys are widely applied in aerospace and transportation industries. However, exploring how varying compositions affect alloy properties and deformation mechanisms is often time-consuming and labor-intensive due to the complexity of the multicomponent composition space and the diversity of processing and heat treatments. This study, inspired by the Materials Genome Initiative, employs high-throughput experimentation—specifically the kinetic diffusion multiple (KDM) method—to systematically investigate how the pop-in effect, indentation size effect (ISE), and creep behavior vary with the composition of Al-Mg-Si alloys at room temperature. To this end, a 6016/Al-3Si/Al-1.2Mg/Al KDM material was designed and fabricated. After diffusion annealing at 530 °C for 72 h, two junction areas were formed with compositional and microstructural gradients extending over more than one thousand micrometers. Subsequent solution treatment (530 °C for 30 min) and artificial aging (185 °C for 20 min) were applied to simulate industrial processing conditions. Comprehensive characterization using electron probe microanalysis (EPMA), nanoindentation with continuous stiffness measurement (CSM), and nanoindentation creep tests across these gradient regions revealed key insights. The results show that increasing Mg and Si content progressively suppresses the pop-in effect. When the alloy composition exceeds 1.0 wt.%, the pop-in events are nearly eliminated due to strong interactions between solute atoms and mobile dislocations. In addition, adjustments in the ISE enabled rapid evaluation of the strengthening contributions from Mg and Si in the microscale compositional array, demonstrating that the optimum strengthening occurs when the Mg-to-Si atomic ratio is approximately 1 under a fixed total alloy content. Furthermore, analysis of the creep stress exponent and activation volume indicated that dislocation motion is the dominant creep mechanism. Overall, this enhanced KDM method proves to be an effective conceptual tool for accelerating the study of composition–deformation relationships in Al-Mg-Si alloys. Full article

Nickel-based superalloys are widely utilized in critical hot-end components, such as aeroengine turbine blades, owing to their exceptional high-temperature strength, creep resistance, and oxidation resistance. During service, these components are frequently subjected to complex localized loading, leading to non-uniform plastic deformation and microstructure evolution within the material. Combining nanoindentation experiments with the crystal plasticity finite element method (CPFEM), this study systematically investigates the effects of loading rate and crystal orientation on the elastoplastic deformation of DD6 alloy under spherical indenter loading. The results indicate that the maximum indentation depth increases and hardness decreases with prolonged loading time, exhibiting a significant strain rate strengthening effect. The CPFEM model incorporating dislocation density effectively simulates the nonlinear characteristics of the nanoindentation process and elucidates the evolution of dislocation density and slip system strength with indentation depth. At low loading rates, both dislocation density and slip system strength increase with loading time. Significant differences in mechanical behavior are observed across different crystal orientations, which correspond to the extent of lattice rotation during texture evolution. For the [111] orientation, crystal rotation is concentrated and highly regular, while the [001] orientation shows uniform texture evolution. This demonstrates that anisotropy governs the deformation mechanism through differential slip system activation and texture evolution. Full article

This study investigates the elevated-temperature mechanical and viscoelastic properties of a PDMS–silica-based superhydrophobic nanocomposite coating using nanoindentation and a nano-dynamic mechanical analysis over a temperature range of 24 °C to 160 °C. The nanoindentation load–displacement curves exhibited consistent hysteresis, indicating a stable energy dissipation across the temperature range. Creep tests revealed an increased displacement and accelerated deformation at elevated temperatures, displaying a two-stage creep profile characterized by rapid primary and steady-state secondary creep. The hardness decreased with the creep time, while the strain rate sensitivity remained relatively stable, suggesting consistent deformation mechanisms. A time-dependent creep model incorporating linear and logarithmic terms accurately captured the experimental data. The nano-dynamic mechanical analysis results showed a decrease in the storage modulus with depth, while the loss modulus and tan δ peaked at shallow depths. These findings are crucial for the evaluation and design of superhydrophobic nanocomposite coatings. Full article

This study aimed to evaluate the nanomechanical surface properties and water uptake of a flowable short-fiber-reinforced composite (SFRC) using various restorative techniques in order to assess its potential as a standalone restorative material. Nanoindentation and compressive creep testing were employed to characterize material performance. Three resin composites were examined: a flowable SFRC (everX Flow), a bulk-fill particulate filler composite (PFC), and a conventional PFC. Five experimental groups were established based on the restorative technique: layered PFC, layered SFRC, bulk SFRC, bulk PFC, and a bi-structure combining SFRC and PFC. Ninety standardized specimens (n = 18/group) were fabricated. Static and creep nanoindentation tests were conducted to assess surface properties, and water uptake was measured over a 30-day period. Data were analyzed using one-way ANOVA and Bonferroni post hoc tests. Nanoindentation revealed significant differences in hardness, with bulk PFC exhibiting the lowest values (p < 0.001). Creep testing indicated changes in modulus and viscosity following water storage. Notably, bulk SFRC showed the lowest water absorption (p < 0.001). Overall, bulk-applied SFRC demonstrated favorable nanomechanical properties and reduced water uptake, demonstrating its suitability as a standalone restorative material. Further clinical investigations are recommended to validate its long-term performance. Full article

The rheological properties of concrete paste significantly influence its tensile creep behavior. In this study, the tensile creep behavior of high-volume fly ash concrete (HVFAC) employing the same cementitious pastes was experimentally investigated, and the rheological properties of the paste containing a high volume of fly ash using the nanoindentation (NI) technique was investigated in order to explore the influence of the paste’s rheological properties (such as micro-mechanical properties and microscopic creep) on the early-age tensile creep of HVFAC. The results demonstrated that the micro-strain of paste containing a high volume of fly ash (HVFA) showed a larger value than that without fly ash. As the test age extends, a decreasing trend in microscopic creep was observed which could be attributed to the growth of the content of HD C–S–H (high density C–S–H) gel. Moreover, within the same age period, the experimental data revealed that the incorporation of fly ash resulted in the reduction of the values of the creep modulus C and characteristic time τ. The effects of fly ash dosages and loading age on the creep properties of concrete was consistent with the micro-creep properties of the cementitious paste. The tensile specific creep values derived from the ZC (“ZC” are initials for the word ‘‘self-developed” in Chinese) model based on nanoindentation data closely match those obtained from experiments. Full article

In fossil fuel and nuclear power plants, welded joints continuously experience creep-fatigue loading, which can result in premature cracking during the in-service term. To study the creep-fatigue interactive (CFI) behavior, the CFI test of P92 steel was performed with different strain rates at 823 K. Results indicate that the short cycle life is measured with the increasing strain rate. Relying on the scanning electron microscope, the fracture mechanism of P92 steel gradually changes from fatigue-dominating to creep-fatigue interactive damage with the increasing strain rate. The hardness (H), elastic modulus (E) and creep deformation were then measured by nanoindentation, and the strain rate sensitivity (m) was estimated. The relation between the degenerated mechanical properties and microstructural evaluations, i.e., enhanced grain size and nucleation of creep voids, was established, and the damage mechanism was discussed. Full article

Nanoindentation has been used to characterize the mechanical and creep properties of various materials. However, research on the viscoelastic and creep properties of superhydrophobic surfaces remains limited. In this study, a superhydrophobic coating was developed and its corrosion resistance was evaluated initially. Electrochemical impedance spectroscopy (EIS) results quantitatively confirm the enhanced anti-corrosion performance of the superhydrophobic coating. Subsequently, this study investigates the creep, hardness, strain rate sensitivity, and viscoelastic behavior of the superhydrophobic surface at the nanoscale before and after accelerated corrosion exposure. Our findings reveal that during the creep tests, the logarithmic values of creep strain rate and stress exhibited a good linear relationship. Additionally, the surface retains its key viscoelastic properties (hardness, storage modulus, loss modulus, and tan δ) even after exposure to corrosion. These results highlight the surface’s robustness under corrosive conditions, a crucial factor for applications requiring both mechanical integrity and environmental resilience. Full article

The effects of aging treatment and the volume fraction of precipitation particles on the nano-hardness and nano-indentation morphology of Ni-based single crystal superalloys are systematically investigated. Using nano-indentation tests and atomic force microscopy (AFM), this study examined the mechanical properties and related physical mechanisms of Ni-based superalloys that have two volume fractions of precipitation particles and four aging treatment times. Results analyzed using the Oliver–Pharr method indicate that prolonging the aging time or increasing the volume fraction of particles enhances the nano-hardness and creep resistance of Ni-based single crystal superalloys and reduces the indentation-affected area. Additionally, the nano-hardness and elastic modulus decrease gradually with increasing applied force, revealing an obvious indentation size effect. These variations are closely linked to the size and density of particles and work hardening rate, as well as to the topologically close-packed (TCP) phases, which influence dislocation movement and accumulation within the material and lead to various nano-indentation behavior in Ni-based single crystal superalloys. The related study provides theoretical guidance and experimental data to support the design and application of superalloys. Full article

To improve the performance of AlCoCrFeNi_2.1 eutectic high-entropy alloys (EHEA) to meet industrial application requirements, Zr_xAlCoCrFeNi_2.1 high-entropy alloys (x = 0, 0.01, 0.05, 0.1) were synthesized through vacuum induction melting. Their microstructures were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Additionally, the hardness, low-temperature compressive properties, nanoindentation creep behavior, and corrosion resistance of these alloys were evaluated. The results showed that AlCoCrFeNi_2.1 is a eutectic high-entropy alloy composed of FCC and B2 phases, with the FCC phase being the primary phase. The addition of Zr significantly affected the phase stability, promoting the formation of intermetallic compounds such as Ni₇Zr₂, which acted as a bridge between the FCC and B2 phases. Zr addition enhanced the performance of the alloy through solid-solution and dispersion strengthening. However, as the Zr content increased, Ni gradually precipitated from the B2 phase, leading to a reduction in the fraction of the B2 phase. Consequently, at x = 0.1, the microhardness and compressive strength decreased at room temperature. Furthermore, a higher Zr content reduced the sensitivity of the alloy to loading rate changes during creep. At x = 0.05, the creep exponent exceeded 3, indicating that dislocation creep mechanisms dominated. In the Zr_xAlCoCrFeNi_2.1 (where x = 0, 0.01, 0.05, 0.1) alloys, when the Zr content is 0.1, the alloy exhibits the lowest self-corrosion current density of 0.034197 μA/cm² and the highest pitting potential of 323.06 mV, indicating that the alloy has the best corrosion resistance. Full article