Search Results (15)

Surface roughness significantly affects the performance of microelectromechanical systems (MEMS) and piezoelectric films. This study investigates the impact of surface roughness on the mechanical properties of thin piezoelectric films using nanoindentation and scanning probe microscopy (SPM). Four piezoelectric films with different thicknesses (220, 350, and 450 nm) and substrate configurations (LNO/SiO₂/Si or LNO/Si) were analyzed. A discriminant analysis revealed that the fractal dimension is more effective than the arithmetic mean height (Sa) for distinguishing surfaces, with only 2% misclassification versus 25% for Sa. A multiscale analysis identified the Smr2 parameter with low-pass filtering at 140 nm as highly effective for surface discrimination, achieving only 0.1% misclassification. The analysis of the roughness parameter Sa at various scales showed that band-pass filtering at 500 nm yielded a 0.7% misclassification rate, indicating its relevance for fractal roughness characterization. Most relevant roughness parameters for mechanical property correlation were found: Smr2 with low-pass filtering at 500 nm correlated best with hardness (R² = 0.82), and Vvc with low-pass filtering at 2 nm correlated best with reduced elastic modulus (R² = 0.84). These results demonstrate that surface roughness features like valley volume and voids significantly impact the apparent mechanical properties of piezoelectric films. Full article

The investigation of new composite materials possessing low weight but not at the expense of their mechanical performance is of great interest in terms of reducing energy consumption in many industrial applications. This study is focused on the nanomechanical characterization of high-density polyethylene (HDPE)-based composite specimens modified with equal loadings of graphene nanoplatelets (GNPs) and/or multiwall carbon nanotubes (MWCNTs). Quasi-static nanoindentation analysis revealed the impact of the carbon nanofillers on the receiving of nanocomposites with higher nanohardness and reduced modulus of elasticity, reaching values of 0.146 GPa and 3.57 GPa, respectively. The role of the indentation size effect in elastic polymer matrix was assessed by applying three distinct peak forces. Nanoscratch experiments depicted the tribological behavior of the composite samples and inferred the influence of the carbon nanofillers on the values of the coefficient of friction (COF). It seems that the incorporation of 4 wt% GNPs in the polymer structure improves the scratch resistance of the material, resulting in a higher value of the exerted lateral force and therefore leading to the detection of a higher coefficient of friction at scratch of 0.401. A considerable pile-up response of the scratched polymer specimens was observed by means of in-situ SPM imaging of the tested surface sample area. The sway of the carbon nanoparticles on the composite pile-up behavior and the effect of the pile-up on the measured friction coefficients have been explored. Full article

The A356 aluminum alloy is a very commonly used alloy in the automotive industry, for parts such as pistons, cylinder heads, and connecting rods, for which the mechanical properties can be effectively increased by anodizing. In this work, oxide layers were formed in oxalic acid solution with defined parameters on A356 aluminum alloy and then studied by using a novel combination of the scanning electron microscope (SEM) and in-situ nanoindentation. The purpose of this research is to understand the relationship between the substrate and the oxide layer by examining its microstructure and nanohardness. Based on the experimental results showing special composite microstructure and corresponding high hardness, this alloy seems to be a good alternative for replacing steel brake disks in an environmentally conscious manner. Full article

We present a systematic density functional theory study to determine the electronic structure of bending 2H-MoS₂ layers up to 75° using information from in-situ nanoindentation TEM observations. The results from HOMO/LUMO and density of states plots indicate a metallic transition from the typical semiconducting phase, near Fermi energy level (E_F) as a function of bending, which can mainly occur due to bending curvatures inducing a stretching and contracting of sulfur-sulfur chemical bonds located mostly over basal (001)-plane; furthermore, molybdenum ions play a major role in such transitions due to reallocation of their metallic d-character orbitals and the creation of “free electrons”, possibly having an overlap between Mo_-dx²_-y² and Mo_dz² orbitals. This research on the metallic transition of 2H-MoS₂ allows us to understand the high catalytic activity for MoS₂ nanostructures as extensively reported in the literature. Full article

In situ nanoindentation is extensively employed for online observing deformation and mechanical behaviors of bio-materials. However, the existing designs of the positioning stages have limited performances for testing soft or hard biomaterials. Consequently, this paper proposes a new structural design of a compliant one degree of freedom (01-DOF) stage with faster response. In addition to a new design, this article applies an analytical method to estimate the kinematic and dynamic behaviors of the stage. Firstly, the 01-DOF stage is designed with two modules, including a displacement amplifier with six levers and a symmetric parallelogram mechanism. Secondly, a kinetostatic diagram of the stage is built by pseudo-rigid-body method. Then, the dynamic equation of the proposed stage is formulated using the Lagrange method. In order to speed up the response of the indentation system, the structural optimization of the stage is conducted via the Firefly algorithm. The results showed that the theoretical first-order resonant frequency is found at about 226.8458 Hz. The theoretical consequences are nearby to the verified simulation. Besides, this achieved frequency of the presented stage is greater than that of previous stages. In an upcoming study, the prototype will be fabricated by additive manufacturing method or a computerized wire cutting method in order to verify the analytical results with experimental results. Full article

In-situ electrochemical nanoindentation (ECNI) has been used to study the effect of hydrogen on the mechanical properties of austenitic stainless steel AISI 316L. Changing the electrode potential (via electrochemical charging) revealed the interconnected nature of the hydrogen effect on the nanomechanical properties of the stainless steel. At more positive cathodic potentials, a softening effect of hydrogen can be noticed, while significant hardening can be observed at more negative cathodic potentials. The hydrogen effects on the nanomechanical properties were analyzed in terms of the homogeneous dislocation nucleation (HDN) and the hydrogen-dislocation interactions from the energy point of view. The effects can be explained with the framework of the defactant theory and the hydrogen-enhanced localized plasticity (HELP) mechanism. Full article

Beyond the current commercial materials, refining the grain size is among the proposed strategies to manufacture resilient materials for industrial applications demanding high resistance to severe environments. Here, large strain machining (LSM) was used to manufacture nanostructured HT-9 steel with enhanced thermal stability, mechanical properties, and ductility. Nanocrystalline HT-9 steels with different aspect rations are achieved. In-situ transmission electron microscopy annealing experiments demonstrated that the nanocrystalline grains have excellent thermal stability up to 700 °C with no additional elemental segregation on the grain boundaries other than the initial carbides, attributing the thermal stability of the LSM materials to the low dislocation densities and strains in the final microstructure. Nano-indentation and micro-tensile testing performed on the LSM material pre- and post-annealing demonstrated the possibility of tuning the material’s strength and ductility. The results expound on the possibility of manufacturing controlled nanocrystalline materials via a scalable and cost-effective method, albeit with additional fundamental understanding of the resultant morphology dependence on the LSM conditions. Full article

Commercial Co/WC/diamond composites are hard metals and very useful as a kind of tool material, for which both ductile and quasi-brittle behaviors are possible. This work experimentally investigates their damage evolution dependence on microstructural features. The current study investigates a different type of Co/WC-type tool material which contains 90 vol.% Co instead of the usual <50 vol.%. The studied composites showed quasi-brittle behavior. An in-house-designed testing machine realizes the in-situ micro-computed tomography ($\mathsf{\mu }$CT) under loading. This advanced equipment can record local damage in 3D during the loading. The digital image correlation technique delivers local displacement/strain maps in 2D and 3D based on tomographic images. As shown by nanoindentation tests, matrix regions near diamond particles do not possess higher hardness values than other regions. Since local positions with high stress are often coincident with those with high strain, diamonds, which aim to achieve composites with high hardnesses, contribute to the strength less than the WC phase. Samples that illustrated quasi-brittle behavior possess about 100–130 MPa higher tensile strengths than those with ductile behavior. Voids and their connections (forming mini/small cracks) dominant the detected damages, which means void initiation, growth, and coalescence should be the damage mechanisms. The void appears in the form of debonding. Still, it is uncovered that debonding between Co-diamonds plays a major role in provoking fatal fractures for composites with quasi-brittle behavior. An optimized microstructure should avoid diamond clusters and their local volume concentrations. To improve the time efficiency and the object-identification accuracy in $\mathsf{\mu }$CT image segmentation, machine learning (ML), U-Net in the convolutional neural network (deep learning), is applied. This method takes only about 40 min to segment more than 700 images, i.e., a great improvement of the time efficiency compared to the manual work and the accuracy maintained. The results mentioned above demonstrate knowledge about the strengthening and damage mechanisms for Co/WC/diamond composites with >50 vol.% Co. The material properties for such tool materials (>50 vol.% Co) is rarely published until now. Efforts made in the ML part contribute to the realization of autonomous processing procedures in big-data-driven science applied in materials science. Full article

The need for control of the elastic properties of architected materials has been accentuated due to the advances in modelling and characterization. Among the plethora of unconventional mechanical responses, controlled anisotropy and auxeticity have been promulgated as a new avenue in bioengineering applications. This paper aims to delineate the mechanical performance of characteristic auxetic and anisotropic designs fabricated by multiphoton lithography. Through finite element analysis the distinct responses of representative topologies are conveyed. In addition, nanoindentation experiments observed in-situ through scanning electron microscopy enable the validation of the modeling and the observation of the anisotropic or auxetic phenomena. Our results herald how these categories of architected materials can be investigated at the microscale. Full article

The severe deformation and temperature paths in the stir zone, also called weld nugget, of friction stir welded joints result, at very local levels, in significant microstructural variations, such as major differences in grain size or precipitation. One of the most common features of friction stir welds is the presence of successive material layers, known as onion rings; however, little data is available on the mechanical properties of the different regions of the weld nugget, and particularly within the onion ring bands. Such information becomes very important for the integrity of large size friction stir welded structures. In the present study, a comprehensive characterization of onion rings produced during friction stir welding of a 6082-aluminum alloy was carried out. Advanced techniques such as in-situ SEM nanoindentation, EBSD, and high-resolution EDS were used to validate and compare the characteristics of the different bands in the onion rings. The analyses consisted of quantifying variations in grain size, precipitate composition and distribution, crystallographic orientations, and mechanical properties in each band. Furthermore, the tensile strengths of different regions of the weld nugget were evaluated using shear punch testing and correlated with those for the onion ring region in order to determine the impact of the presence of onion rings on weld nugget mechanical properties. The main difference between the alternate bands in the onion ring was found to be due to the difference in their grain size, misorientation, and precipitate content. It was also observed that the bands originate from the base metal and stir zone successively due to the nature of the stirring process, which pulls BM into SZ. Comparison of the shear punch testing results in different regions of the nugget revealed that, in spite of having local differences in the hardness of alternate bands in the onion ring, the presence of onion rings has no significant impact on the deterioration of the mechanical properties of the weld nugget. Full article

To explore the macro-fracture mechanism of a friction welded joint between TiAl alloy and GH3039 superalloy, the micromechanical properties of intermediate phases at the joint interface are characterized and the relationship between the macro-fracture and micro-fracture of the joint is established. The indentation technique has been employed to calculate the nano-hardness and fracture toughness of the intermediate phases. The dynamic in-situ tensile test in SEM has been applied to observe the initiation and propagation process of cracks at the interface. It has been found that Al₃NiTi₂ and AlNi₂Ti have the highest nano-hardness and elastic recovery rates, while TiAl and GH3039 base metals have the lowest nano-hardness and elastic recovery rates. This indicates that the harder the materials, the more prone they are to elastic deformation. Nevertheless, the fracture toughness of Al₃NiTi₂ and AlNi₂Ti are the two lowest, which were 1.7 MPa·m^1/2 and 2.7 MPa·m^1/2, respectively. The cracks sprouted from Al₃NiTi₂ and AlNi₂Ti and then spread throughout the entire intermediate phase zone. In other words, the fracture mainly happened in these two phase layers. It has been concluded that Al₃NiTi₂ and AlNi₂Ti were the two weakest phases at the interface and their poor fracture toughness results in low joint strength. Full article

Zr-based bulk metallic glasses (Zr-BMGs) are potentially the next generation of metallic biomaterials for orthopaedic fixation devices and joint implants owing to their attractive bulk material properties. However, their poor tribological properties and long-term biocompatibility present major concerns for orthopaedic applications. To this end, a novel surface modification technology, based on ceramic conversion treatment (CCT) in an oxidising medium between the glass transition temperature and the crystallisation temperature, has been developed to convert the surface of commercially available Zr₄₄Ti₁₁Cu₁₀Ni₁₁Be₂₅ (Vitreloy 1b) BMG into ceramic layers. The engineered surfaces were fully characterised by in-situ X-ray diffraction, glow-discharge optical emission spectroscopy, scanning electron microscopy, transmission electron microscopy, and scanning transmission electron microscopy. The mechanical, chemical, and tribological properties were evaluated respectively by nano-indentation, electrochemical corrosion testing, tribological testing and the potential biocompatibility assessed by a cell proliferation assay. The results have demonstrated that after CCT at 350 °C for 40 h and at 380 °C for 4.5 h the original surfaces were converted into to a uniform 35–55-nm-thick oxide layer (with significantly reduced Ni and Cu concentration) followed by a 200–400-nm-thick oxygen-diffusion hardened case. The surface nano hardness was increased from 7.75 ± 0.36 to 18.32 ± 0.21 GPa, the coefficient of friction reduced from 0.5–0.6 to 0.1–0.2 and the wear resistance improved by more than 60 times. After 24 h of contact, SAOS-2 human osteoblast-like cells had increased surface coverage from 18% for the untreated surface to 46% and 54% for the 350 °C/40 h and 380 °C/4.5 h treated surfaces, respectively. The significantly improved tribological properties and biocompatibility have shown the potential of the ceramic conversion treated Zr-BMG for orthopaedic applications. Full article

The mechanical properties such as compressive strength and nanohardness were investigated for Pinctada margaritifera mollusk shells. The compressive strength was evaluated through a uniaxial static compression test performed along the load directions parallel and perpendicular to the shell axis, respectively, while the hardness and Young modulus were measured using nanoindentation. In order to observe the crack propagation, for the first time for such material, the in-situ X-ray microscopy (nano-XCT) imaging (together with 3D reconstruction based on the acquired images) during the indentation tests was performed. The results were compared with these obtained during the micro-indentation test done with the help of conventional Vickers indenter and subsequent scanning electron microscopy observations. The results revealed that the cracks formed during the indentation start to propagate in the calcite prism until they reach a ductile organic matrix where most of them are stopped. The obtained results confirm a strong anisotropy of both crack propagation and the mechanical strength caused by the formation of the prismatic structure in the outer layer of P. margaritifera shell. Full article

Reduced activation ferritic and martensitic steel like EUROFER (9Cr-1W) are considered as potential structural materials for the first wall of the future next-generation DEMOnstration Power Station (DEMO) fusion reactor and as a reference material for the International Thermonuclear Experimental Reactor (ITER) test blanket module. The primary motivation of this work is to study the re-deposition of the main constituent materials of EUROFER, namely tungsten (W), iron (Fe), and chromium (Cr), in a DEMO type reactor by producing and analyzing complex W_xCr_yFe_1−x−y layers. The composite layers were produced in laboratory using the thermionic vacuum arc (TVA) method, and the morphology, crystalline structure, elemental composition, and mechanical properties were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-X-ray fluorescence (micro-XRF), and glow discharge optical emission spectrometry (GDOES), as well as nanoindentation and tribology measurements. The results show that the layer morphology is textured and is highly dependent on sample positioning during the deposition process. The formation of polycrystalline W_xCr_yFe_1−x−y was observed for all samples with the exception of the sample positioned closer to Fe anode during deposition. The crystalline grain size dimension varied between 10 and 20 nm. The composition and thickness of the layers were strongly influenced by the in-situ coating position, and the elemental depth profiles show a non-uniform distribution of Fe and Cr in the layers. The highest hardness was measured for the sample positioned near the Cr anode, 6.84 GPa, and the lowest was 4.84 GPa, measured for the sample positioned near the W anode. The tribology measurements showed an abrasive sliding wear behavior for most of the samples with a reduction of the friction coefficient with the increase of the normal load. Full article

Al–Si–Mg based alloys can provide high strength and ductility to satisfy the increasing demands of thin wall castings for automotive applications. This study has investigated the effects of T6 heat-treatment on the microstructures, the local mechanical properties of alloy phases and the fracture behavior of high vacuum die-cast AlSiMgMn alloys using in-situ scanning electron microscopy (SEM) in combination with nano-indentation testing. The microstructures of the alloys at as-cast and T6 treated conditions were compared and analyzed. It is found that the T6 heat treatment plays different roles in affecting the hardness and the Young’s modulus of alloy phases. This study also found that the T6 heat treatment would influence the failure modes of the alloys. The mechanisms of crack propagation in the as-cast and T6 treated alloys were also analyzed and discussed. Full article