Search Results (734)

Metal/graphene composites with a metal matrix and graphene reinforcement are very promising innovative materials due to their improved mechanical and physical properties. In this paper, the possibility of fabricating a composite from a graphene network filled with nickel (Ni), copper (Cu) and aluminum (Al) nanoparticles is shown by molecular dynamics simulation. Composites are obtained by hydrostatic compression at 0.7 of the melting temperature of the metal nanoparticles. It is found that the Ni/graphene composite exhibits the highest ultimate tensile strength (89.5 GPa) and Young’s modulus (296.9 GPa) compared to 35.1 and 65.9 GPa for Cu/graphene and 36.8 and 109.1 GPa for Al/graphene, respectively. The Ni nanoparticles were uniformly distributed throughout the graphene network, providing high strength. Indentation simulations confirm this trend: the Ni/graphene composite exhibits a hardness 1.7 times higher than that of pure crumpled graphene, while Al/graphene shows a value 2.2 times lower, which directly correlates with the tensile strength. The Cu/graphene composite has the best ductility (fracture strain of 0.75 versus 0.45 for Ni/graphene and 0.47 for Al/graphene) due to the easier sliding between the Cu nanoparticles and the graphene during tensile loading. The Al/graphene composite has low strength and ductility because the Al nanoparticles tend to coagulate inside the graphene network and hardly interact with the graphene. For Cu/graphene and Al/graphene composites, fracture occurs at the metal/graphene interface. The results show that it is possible to fabricate metal/graphene composites that are much stronger than pure metal by deformation-temperature treatment. In addition, the mechanical properties can be modified by varying the type of metal. Full article

The manuscript aims to analyze the properties of gray cast iron EN GJL-250 as a function of the charge composition with an emphasis on microhardness and indentation size effect (ISE). Three compositions of cast iron were used: cast iron A as traditionally produced cast iron, B and C as inoculated and overheated cast iron micro-alloyed with FeTi70. The authors used the cutting method to assess residual stresses in castings with a stress grid designed according to Sipp. The specimens from thick and thin bars of the grid, after determination of residual stresses, were used for uniaxial tensile tests, measurement of the hardness (HBW, HV, and Vickers microhardness), metallographic, and fractographic analysis. Results of microhardness were used for the determination of ISE indices, and “true hardness” was calculated. The effect of composition has a statistically significant effect (single ANOVA; specimens from thick and thin bars are considered together) only for Meyer index n, and in the case of thick bars, also for HBW and HV. Full article

This study investigates flexoelectricity in the pyramid- and truncated-pyramid-patterned contact interface of a NOA-63/Ecoflex (N/E) triboelectric nanogenerator (TENG) operating in contact–separation mode. Microscale pyramidal and truncated pyramidal arrays were fabricated using silicon molds and paired with an Ecoflex™ 00-10 elastomer substrate, and the structural integrity of the arrays was confirmed by scanning electron microscopy. Combining experimental results with established knowledge of soft-polymer indentation mechanics and hard-to-hard flexoelectric behavior, the surface charge density (σ) and flexoelectric coefficient (μ_flexo) were determined to be 8.48 × 10⁻⁶ C/m² and 2.95 × 10⁻¹¹ C/m, respectively. These parameters were incorporated into a total charge equation to estimate charge output for both pyramidal and truncated pyramidal N/E TENG arrays under varying applied loads. The proposed model can adequately predict the charge output of pyramidal and truncated pyramidal N/E TENGs. Full article

With the development of three-dimensional high-density integration, low-temperature co-fired ceramic (LTCC) technology has become an important substrate platform for electronic packaging. However, screen-printed Au films on LTCC substrates often contain boundary roughness, local thickness variation, pores, and particle-packing non-uniformity caused by the printing process. These features may affect both the macroscopic resistivity of printed patterns and the local mechanical response of the film. In this study, edge-related structural non-uniformity in screen-printed Au/LTCC films was evaluated using SEM observation, macroscopic resistivity–temperature fitting, nano-indentation, XRD, and nano-scratch testing. The resistivity results show that the stripe pattern has approximately 10–13% higher resistivity than the grid patterns within the measured temperature range, indicating a geometry-dependent electrical response. Nano-indentation results reveal large spatial dispersion in reduced modulus and hardness, and statistical analysis shows that differences among annealing conditions are not significant at the 0.05 level when indentation data alone are considered. Therefore, nanomechanical data are treated as an indirect structural indicator rather than a direct proof of local electrical uniformity. Among the investigated temperatures, 200 °C provides a favorable balance of local hardness, scratch resistance, and microstructural stability, whereas 300 °C should be interpreted cautiously because the higher scratch load is not supported by direct post-scratch failure analysis. Overall, the results provide a cautious but clear structure–property correlation for screen-printed Au/LTCC conductors and identify 200 °C as the preferred annealing condition among the investigated temperatures. These results provide practical guidance for evaluating structural non-uniformity in screen-printed Au/LTCC conductors. Full article

The optimization and the engineering development of additive manufacturing (AM) products both require accurate, non-destructive techniques to extract their mechanical performances. The Instrumented Indentation Test (IIT) has such a potential, although it currently lacks standard procedures that are suitable for analyzing materials which are affected by internal residual stress (RS). Additionally, nanoindentation testing suffers from the presence of indentation size effects (ISE), which hamper the possibility of correlating the measured mechanical performance at different indentation depths or peak loads using the standard indentation hardness (H_IT) and modulus (E_IT). This paper presents a novel IIT methodology that is based on new indentation parameters, namely the loading stiffness rate (LSR) and the rate-derived hardness (H_R), which are then used to assign the desired mechanical performances of an L-PBF 316L austenitic stainless-steel alloy obtained via multiload/multiscale IIT strategy. The mean values of LSR, H_R, H_IT, and E_IT on the macroscale were 57.3 ± 1.4 GPa, 2.33 ± 0.059 GPa, 2.41 ± 0.13 GPa, and 201 ± 7.8 GPa, respectively, whereas on the nanoscale they were 56.1 ± 5.1 GPa, 2.30 ± 0.21 GPa, 3.00 ± 0.36 GPa, and 219 ± 24 GPa, respectively. Unlike the standard H_IT, the new indentation parameters of the nano- and macro-IITs are within the standard deviation, proving their ISE-free property. The obtained E_IT was slightly higher than the reference Young’s modulus (~190 GPa) of the 316L stainless steel. The loading secant stiffness versus depth plot can be used to assess the susceptibility of RS to relax during indentation, which is an important performance factor for the engineering design of AM components. The successful correlation that has been found between electron backscatter diffraction (EBSD) analysis (in terms of crystal anisotropy, grain size, and dislocation density) and nanoindentation testing at three subregions of the core zone of the investigated deposit confirms the validity of the proposed methodology. The proposed methodology is a step towards the full determination of the three Ps, that is, process, properties, and performance of advanced AM products. Full article

ZERODUR glass-ceramic is widely used in ultra-precision optical components because of its extremely low thermal expansion and excellent dimensional stability. However, its two-phase microstructure, composed of crystalline and amorphous phases with different mechanical properties, may cause non-uniform material removal during magnetorheological polishing, thereby limiting further improvement of nanoscale surface quality. To address this issue, this study investigates the effect of oxide abrasives on the surface homogenization of ZERODUR. A single-particle abrasive–workpiece contact model based on modified Hertz contact theory and elastoplastic contact analysis was established to compare the indentation responses of CeO₂, SiO₂, and ZrO₂ abrasives in the two constituent phases. Magnetorheological polishing experiments were conducted under identical process parameters, and the polished surfaces were characterized by AFM over scan areas of 2 μm × 2 μm, 5 μm × 5 μm, and 10 μm × 10 μm. The results show that all three abrasives improved the surface quality of the ring-polished substrate, with ZrO₂ achieving the best surface homogenization performance. The lowest roughness, Ra = 0.104 nm, was obtained at a 2 μm field of view, and the ZrO₂-polished surface showed more stable roughness evolution across different scan sizes than the CeO₂- and SiO₂-polished surfaces. These results indicate that the elastic modulus, hardness, and mechanical compatibility of abrasives with ZERODUR play key roles in governing contact stress, indentation behavior, and final surface quality. This work addresses the lack of mechanistic understanding of abrasive-dependent surface homogenization in the magnetorheological polishing of two-phase ZERODUR glass-ceramic. The main innovation is the integration of contact-mechanics-based abrasive–workpiece modeling with multi-scale AFM characterization to clarify how abrasive mechanical compatibility affects nanoscale surface uniformity and to guide abrasive selection for ultra-smooth optical manufacturing. Full article

This study investigates the properties of WC–10Ni cermet coatings deposited by plasma spraying using two different plasma torches: a conventional A60 torch (APS) and an advanced Axial III torch (HV-APS). The aim of the work was to compare the microstructure, porosity, surface roughness, phase composition, and mechanical properties (hardness and instrumented indentation), as well as erosion, scratch response, and resistance to tribological wear of the obtained coatings. The coatings were deposited onto S235 steel substrates using WC–10Ni (WOKA 3302) powder. The results revealed that both coatings exhibit a typical lamellar structure characteristic of plasma-sprayed materials; however, distinct differences in surface roughness, porosity, and mechanical response were observed. The coating produced using the Axial III torch showed lower porosity (~6%) and higher hardness (~1000 HV) compared to the coating deposited with the A60 torch (~12% porosity and ~831 HV). Phase analysis confirmed the presence of WC, W₂C, and Ni in both coatings, indicating partial decarburization of carbides during the spraying process. Erosion resistance tests did not reveal significant differences between the coatings. Erosion testing revealed comparable performance for both coatings, with erosion rates of approximately 0.7 mg/min. Scratch testing showed significantly lower acoustic emission activity for the Axial III coating, indicating less intensive fracture-related events during loading and confirming its more compact microstructure. In contrast, ball-on-disk tribological tests demonstrated comparable wear rates for both coatings (≈9 × 10⁻⁵ mm³·N⁻¹·m⁻¹), despite the substantially higher hardness of the Axial III coating (1010 HV0.2 compared with 792 HV0.2 for the A60 coating). These results indicate that the improvements in hardness and coating densification achieved by the HV-APS process did not result in a measurable reduction in steady-state sliding wear under the applied test conditions. Full article

The mesomechanical properties of dolostone are critical for reservoir stimulation. Focusing on the dolostone from the Shunbei Oil and Gas Field, this study employed nanoindentation combined with SEM, EDS, and XRD to investigate its micromechanical behavior. The samples are predominantly composed of dolomite, with minor amounts of calcite and silicates, exhibiting heterogeneity in both mineral phases and pore structures. Nanoindentation results indicate that the elastic moduli are concentrated in the range of 90–120 GPa, with hardness values of 3–5 GPa and maximum indentation depths of 1.0–1.4 μm, reflecting high brittleness. Dense regions with a modulus of 149.09 GPa exhibit few cracks, whereas low-modulus regions at 109.2 GPa develop radial cracks. The fracture toughness ranges from 3.6 to 10.3 MPa·m^0.5, and microdefects significantly degrade this toughness. The elastic modulus shows a moderate positive correlation with hardness; meanwhile, fracture toughness correlates positively with the elastic modulus and weakly with hardness, reflecting the synergistic control exerted by dense crystalline domains and defects. Furthermore, the elastic modulus varies nonlinearly with indentation depth, and fracture toughness exhibits a negative power-law correlation with depth, confirming the coupling effect between depth dependence and heterogeneity. This study establishes quantitative correlations among micromechanical heterogeneity, mineral phases, and pores. It provides a mesomechanical basis for fracturing optimization and wellbore stability in ultra-deep carbonate reservoirs, thereby expanding the application of nanoindentation techniques. Full article

CoCrFeMnNi high-entropy alloy (HEA) coatings were fabricated on an S41500 stainless steel substrate by laser cladding and subsequently strengthened using machine hammer peening (MHP) at three hammering energies of 1.7 J, 3.5 J, and 5.0 J. The effects of MHP treatment on the phase structure, surface morphology, microhardness, and tribological properties of the coatings were systematically investigated. The results showed that all coatings retained a single-phase face-centered cubic (FCC) structure after MHP treatment, indicating excellent microstructural stability during impact-induced strengthening. With increasing hammering energy, the surface morphology gradually evolved from discrete hammering indentations to a more continuous orange-peel-like texture, while the surface roughness initially increased and then decreased. MHP significantly enhanced the surface hardness of the coatings. In particular, the MHP3.5 sample exhibited the highest surface hardness of approximately 420 HV, representing an increase of about 120% compared with the untreated coating. Under dry sliding conditions at a load of 30 N, the MHP3.5 sample exhibited the lowest and most stable friction coefficient, maintaining a steady-state value of approximately 0.40–0.45. Its specific wear rate decreased by nearly 45% compared with that of the untreated coating. The improved wear resistance was mainly attributed to the combined effects of strain hardening, grain refinement, and dislocation strengthening induced by machine hammer peening. Considering the hardness, friction coefficient, and specific wear rate results together, a hammering energy of 3.5 J was identified as the most suitable MHP parameter under the low-load wear conditions investigated in this study. Full article

To develop the applications of nanoindentation in a liquid environment, a higher requirement has been presented for evaluating measured errors of micromechanical performance, particularly for the immersion indentation. In this study, a numerical investigation was conducted to explore the influence of buoyancy and surface roughness on the indentation responses of EH36 steel. The results show that a difference in indentation load–depth curves and mechanical properties with and without the buoyancy effect is observed as the indentation depth increases. The relative calculated errors of reduced modulus and indentation hardness are more than 25.35% and 1.92%, respectively. Meanwhile, as the surface roughness increases, a pronounced increase in the data scatter of indentation responses is observed, especially at shallow nanoindentations. The coupling effects of buoyancy and surface roughness on the deviation of indentation data exhibit a competitive relationship rather than a simple cumulative effect. The measured errors of reduced modulus at roughness values below 0.10 μm are predominantly affected by buoyancy during immersion indentations, while the surface roughness is the main factor in other cases. This study provides a comprehensive understanding of these factors and predicts the qualitative variations in micromechanical responses under assumed immersed conditions. Full article

This study investigates the mechanical performance of a pulsed laser butt-welded IN792 DS joint and its relationship to its microstructure by means of grid nanoindentation. A new ISE-free (rate-derived) hardness parameter (H_R) has been introduced to account for the local bulk elastoplastic behavior of the material in combination with the stable contribution of residual stress, thus overcoming the limitations of the current standard codes. It allows performance comparability between different welding experiments, materials, and joint configurations. It offers an alternate means to mechanically determine the HAZ width when microscopic and metallurgical methods fail to detect it. Moreover, the spectra of two independent indentation parameters have been utilized as an input within an iterative statistical deconvolution scheme to estimate the composition of the relevant phases present within the fused zone. While one parameter spectrum acted as a predictor in the first stage, the second one served as a corrector for the final estimation of the four detected phases, thereby self-validating the iteration procedure with 5% tolerance. The validity of phase estimation was first determined over the entire FZ and then at three levels of the weald seam (top, neck and bottom) for further validation. The results indicate that the γ-matrix and ultrafine fine/hard second phases in the fused zone amounted to 54% and 43% volume fractions, respectively. The associated deconvoluted mechanical performance, expressed in terms of E_IT, H_IT, and H_R, corresponded to approximately 209 ± 4.5, 6.3 ± 0.2, 4.4 ± 0.1 and 224 ± 7.0, 6.7 ± 0.1, and 4.6 ± 0.1 GPa, respectively. A correlation between the estimated phases and the local mechanical performance via the conventional indentation parameter (H_IT and E_IT) and the new H_R parameter in the three relevant regions of the fused zone was discussed while discerning the effect of cooling rate on precipitate size, heterogeneity, porosity, residual stresses, and grain orientation. Further validation studies on different sample geometries, materials and joint configurations are needed to confirm the generality of the proposed methodology. Full article

Flexible polyurethane (PUR) foams and latex rubber foams are widely used in furniture and mattress cushioning, yet conventional standardized mechanical tests only partially capture comfort-relevant behavior, particularly in layered constructions where material interactions and sequencing can alter elastic response. This study aimed to compare the mechanical (elastic) properties of selected three-layer composites of approximately 60 mm thickness (composed of conventional PUR, high-resilience PUR, low-resilience PUR, and latex foam) and to preliminarily assess whether combining foam types improves support of such setup and whether changing layer order modifies elasticity and support. Indentation hardness testing of multilayer cushions was conducted by ISO 2439:2008 Method E. Six three-layer systems (Alpha–Zeta) were assembled in two groups. Group X showed nearly identical support factors (2.6–2.7), high recovery (64.3–66.2%), low hysteresis loss (24.3–24.5%), and overlapping force–indentation (IFD) curves, indicating minimal effect of layer order and dominance of the PUR layers. Group Y exhibited higher but more sequence-dependent support (3.1–3.7), markedly reduced, wider range recovery (30.0–45.9%), increased hysteresis (33.0–34.7%), and more dispersed IFD curves. Placing high-resilience foam at the top partially improve recovery, whereas locating low-resilience foam at the surface increase energy loss. The research contributes in part to the body of knowledge about the behavior of the tested materials according to standardized rules. These preliminary results can be compared with other research findings and used in the preparation of testing models for multilayer foam composites, thereby generating new knowledge to improve the design of future experiments, which will result in increased sitting and lying comfort. Full article

High Velocity Oxy-Fuel (HVOF) thermal spraying enables the deposition of dense coatings with low porosity, high hardness, and good fracture resistance. Tungsten carbide–cobalt (WC-Co) coatings are widely used in industrial and aerospace applications due to their excellent wear resistance; however, improving crack resistance and coating–substrate adhesion remains a key challenge. In this study, WC-Co+Ni composite coatings were deposited on ductile cast iron, with emphasis on the role of Ni addition in controlling microstructure development under HVOF conditions. Microstructural characterization was performed using optical, scanning, and transmission electron microscopy (OM, SEM, TEM), while phase composition and chemical analysis were determined by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The coatings exhibited a dense, low-porosity microstructure composed of fine WC and W₂C carbides embedded in a Co–Ni binder, with locally nanocrystalline regions. XRD analysis confirmed WC and W₂C as the dominant phases, with weak reflections corresponding to the η-phase (Co₆W₆C), indicating local decarburization. The addition of Ni increases the fraction of the transient liquid phase during particle flight, enhancing carbide dissolution and mass transport in the binder, which accelerates decarburization kinetics and promotes η-phase formation. Simultaneously, Ni modifies the binder into a more ductile Co–Ni matrix, reducing the detrimental effect of brittle η-phase on coating integrity. Mechanical and tribological testing (instrumented indentation and scratch testing) demonstrated improved crack resistance, wear resistance, and adhesion. The results show that Ni addition enables process-driven microstructural tailoring of HVOF-sprayed WC-Co coatings, leading to enhanced performance despite the presence of η-phase. Full article

The nanoindentation analysis of zirconium carbide (ZrC) has been studied through molecular dynamics simulations, focusing on various factors such as temperature, stoichiometric ratio, and crystal orientation. The findings show that as temperature increases, both the critical pop-in load and the maximum load decrease, while atomic strain, von Mises stress, and residual indentation depth increase. High temperatures facilitate the nucleation and propagation of 1/2<110> dislocations, which enhance the material’s ability to undergo plastic deformation. Both indentation hardness and Young’s modulus decrease linearly as temperature rises or the concentration of C vacancy increases. For stoichiometric ZrC, as the temperature rises from 10 K to 2100 K, the hardness decreases from 45.04 GPa to 20.36 GPa, and Young’s modulus drops from 396.28 GPa to 254.45 GPa. At 10 K, when the C/Zr ratio is reduced to 0.5, the hardness and Young modulus decrease to 25.32 GPa and 192.09 GPa, respectively. This reduction is attributed to the weakening of Zr-C bonds, which also reduces stress concentration. At elevated temperatures, the impact of C vacancies on the nanoindentation process diminishes due to the thermal softening of the substrate, which lessens the effects of vacancy-induced softening. Regarding anisotropy, Young’s modulus at room temperature decreases from 383.39 GPa on the (001) plane to 335.93 GPa on the $(1\stackrel{\mathrm{-}}{1}0)$ plane, and it reduces further to 303.31 GPa on the $(1\stackrel{\mathrm{-}}{1}1)$ plane; hardness shows a similar decreasing trend. This trend is primarily due to differences in slip systems, surface energies, and the angles between the plane normal and the Zr-C bond axis located directly beneath the surface atoms. Overall, these results may provide theoretical support for the processing and application of ZrC. Full article

Drilling in deep hard formations poses significant challenges for conventional polycrystalline diamond compact (PDC) cutters, which often suffer from low rock-breaking efficiency and premature failure due to severe cutter-face wear, high thermal loads, and stick-slip vibrations. To overcome these limitations, this study proposes a chisel-shaped PDC cutter and systematically investigates its rock-breaking and thermal characteristics. A coupled temperature–displacement finite element model (FEM) of cutter–granite interaction and a single-cutter indentation model were developed based on elastoplastic mechanics and the Drucker–Prager failure criterion. The rock constitutive parameters used in both models were validated through uniaxial compression tests. Using these models, the influences of cutter shape, back rake angle, and depth of cut (DOC) were analyzed. Compared with a conventional cylindrical cutter, the chisel cutter reduces the cutting force by 13.4% and the axial penetration reaction force by 22%. The cutting force of the chisel cutter remains consistently lower across all tested depths. The optimal back rake angle is 20–25°, and the optimal DOC is 1.5 mm. Full-bit simulations further demonstrate that the chisel-cutter bit creates a more concentrated bottomhole stress field, increases the rate of penetration (ROP) by 19.7%, reduces average torque by 11.34%, and produces smoother torque fluctuations, indicating higher drilling stability. Thermal analysis reveals that the chisel cutter exhibits lower and more stable cutter-face temperatures. Both simulation and experimental results confirm that the chisel design reduces the friction contact area between cuttings and the cutter face, thereby lowering temperature accumulation. Field drilling data corroborate the reliability of the conclusions. These findings provide guidance for the design of PDC bits intended for deep hard formations. Full article