RESUMEN

ScAlMgO4 (SCAM), which can be used as an epitaxial substrate material of GaN in power devices, faces the challenge of achieving a high-quality surface by ultra-precision polishing due to its brittle and easily cleaved characteristics, which are closely associated with its mechanical properties. The micromechanical properties of SCAM single crystals were evaluated by nanoindentation and microscratch tests using different indenters. The elastic modulus EIT and the indentation hardness HIT of SCAM obtained by nanoindentation were 226 GPa and 12.1 GPa, respectively. Leaf-shaped chips and the associated step-like planes of SCAM can be found in the severely damaged regime during scratching by Berkovich and Vickers indenters with sharp edges due to the intersection of intense radial and lateral cracks. The fracture toughness (Kc = 1.12 MPa·m1/2) of SCAM can be obtained by using a scratch-based methodology for a spherical indenter based on linear elastic fracture mechanics (LEFM) under an appropriate range of applied loads. An optimal expression for calculating the fracture toughness of easily cleaved materials, including SCAM, via the Vickers indenter-induced cracking method using a Berkovich indenter was recommended.

RESUMEN

In this paper, the morphological, micromechanical and tribological characteristics of the Ti-6Al-4V ELI alloy after thermal oxidation (TO) were identified. TO was carried out at temperatures of 848 K, 898 K and 948 K over a period of 50 h. Microscopic examination revealed that an increase in temperature resulted in an improved uniformity of coverage and an increased oxide grain size. Micromechanical tests showed that TO of the Ti-6Al-4V ELI alloy led to an increase in hardness and deformation resistance. Following oxidation, a decrease (by approximately 10-22%) was observed in the total mechanical work of indentation, Wtotal, compared to the as-received material. The formation of protective oxide films on the Ti-6Al-4V ELI alloy also led to the improvement of tribological characteristics, both when tested under dry friction conditions and in Ringer's solution. The sliding wear resistance increased with an increase in the oxidation temperature. However, a greater degree of wear reduction (by approximately 30-50%) was found for the lubricated contact in comparison with the dry friction tests. Surface roughness also increased with the increase in temperature.

RESUMEN

To investigate the damage mechanisms in granite's physical and mechanical properties after high-temperature water quenching, this study employed MTS815.04 for uniaxial compression tests on thermally treated specimens, with concurrent acoustic emission monitoring, and utilized nanoindentation for micromechanical analysis. The results show that with increasing temperature, granite's peak strength and elastic modulus decrease, with a sharp decline after 400-500 °C, corresponding to a significant increase in the internal damage, which can be detected by acoustic emission monitoring. Below 500 °C, macroscopic mechanical degradation is due to mineral thermophysical property differences, while above 500 °C, microcrack development is the main deterioration factor. The failure mode shifts from tensile to tensile-shear complex to shear failure, with transition points at 400 °C and 800 °C. The results of this study are of certain reference value for improving the efficiency of extracting thermal energy from dry-hot rocks and providing security guidance for the tunnel restoration process following fire damage.

RESUMEN

In order to investigate the cross-scale effects of the interaction between the hard and soft segments of stiff polyurethane foam on the material's mesoscopic pore structure and macroscopic compression characteristics in various negative-temperature environments, this paper used molecular dynamics to calculate the interaction differences between hard and soft segments in different negative-temperature environments. The effects of various negative-temperature settings on the cell structure of stiff polyurethane foam were investigated using scanning electron microscopy and Image J software. Finally, macro experiments were used to determine the influence of a negative-temperature environment on the characteristics of stiff polyurethane foam (such as compressibility). The molecular simulation calculation results show that in a negative-temperature environment, decreasing temperature gradually increases the interaction between hard segment molecules and soft segment molecules, resulting in an increase in the molecules' modulus and cohesive energy density. The scanning electron microscope results reveal that a negative-temperature environment gradually increases the pore diameter of stiff polyurethane foam. The compression experiment findings demonstrate that, for the same service duration, the compressive strength in the -20 °C environment is 27.53% higher than that in the 0 °C environment. The study's findings reveal a microscopic mechanism for the following receiving alterations and toughness enhancement of rigid polyurethane foam throughout service in negative-temperature conditions.

RESUMEN

The healthcare-associated infections (HAIs) and pandemics caused by multidrug-resistant (MDR) and new-generation pathogens threaten the whole world community. Cu and its alloys have been attracting widespread interest as anti-contamination materials due to the rapid inactivation of MDR-superbugs and viruses. Applying thin Cu-based foils on pre-existing surfaces in hygiene-sensitive areas represents a quick, simple, cost-effective self-sanitising practice. However, the influence of chemical composition and microstructure should be deeply investigated when evaluating the antimicrobial capability and durability of Cu-based materials. The effect of composition on micromechanical and antiviral properties was investigated by comparing Cu15Zn and Cu18Ni20Zn (foil thickness from 13 to 27 µm) with Phosphorous High-Conductivity (PHC) Cu. The influence of recrystallisation annealing of PHC Cu was also investigated. Microstructural characterisation was carried out by optical (OM) and scanning electron (FEG-SEM) microscopy, Energy-dispersive Spectroscopy (EDS) and Electron-Backscattered Diffraction (EBSD). The micromechanical behaviour was assessed by microhardness, microscale abrasion and scratch tests. Cu-based foils were exposed to SARS-CoV-2 for different time points in quasi-dry conditions (artificial sweat solution), evaluating their antiviral capability by quantitative Reverse-Transcriptase Polymerase Chain Reaction (qRT-PCR). Surface morphology, contact angle measurements and Cu release were measured. All Cu-based surfaces completely inactivated SARS-CoV-2 in 10 min: pure Cu was the best option regarding antiviral efficiency, while Cu15Zn showed the best trade-off between micromechanical and antiviral properties.

RESUMEN

Nanostructured cemented carbides with Co binders have shown excellent mechanical properties in various applications. Nevertheless, their corrosion resistance has shown to be insufficient in different corrosive environments, leading to premature tool failure. In this study, WC-based cemented carbide samples with different binders were produced using 9 wt% of FeNi or FeNiCo with the addition of Cr3C2 and NbC as the grain growth inhibitors. The samples were investigated using electrochemical corrosion techniques: the open circuit potential Ecorr, the linear polarization resistance (LPR), the Tafel extrapolation method, and the electrochemical impedance spectroscopy (EIS) at room temperature in the solution of 3.5% NaCl. Microstructure characterization, surface texture analysis, and instrumented indentation were conducted to investigate the influence of corrosion on the micro-mechanical properties and the surface characteristics of the samples before and after corrosion. The obtained results indicate a strong binder chemical composition's effect on the consolidated materials' corrosive behavior. Compared to the conventional WC-Co systems, a significantly improved corrosion resistance was observed for both alternative binder systems. The study shows that the samples with the FeNi binder are superior to those with the FeNiCo binder since they were almost unaffected when exposed to the acidic medium.

RESUMEN

This paper aims to study the microstructural and micromechanical variations of solder joints in a semiconductor under the evolution of thermal-cycling loading. For this purpose, a model was developed on the basis of expectation-maximization machine learning (ML) and nanoindentation mapping. Using this model, it is possible to predict and interpret the microstructural features of solder joints through the micromechanical variations (i.e. elastic modulus) of interconnection. According to the results, the classification of Sn-based matrix, intermetallic compounds (IMCs) and the grain boundaries with specified elastic-modulus ranges was successfully performed through the ML model. However, it was detected some overestimations in regression process when the interfacial regions got thickened in the microstructure. The ML outcomes also revealed that the thermal-cycling evolution was accompanied with stiffening and growth of IMCs; while the spatial portion of Sn-based matrix decreased in the microstructure. It was also figured out that the stiffness gradient becomes intensified in the treated samples, which is consistent with this fact that the thermal cycling increases the mechanical mismatch between the matrix and the IMCs.

RESUMEN

This contribution lays the foundation for the European database of explanted UHMWPE liners from total joint replacements. Three EU countries (Czech Republic, Italy and Spain) have joined their datasets containing anonymized patient data (such as age and BMI), manufacturer data (such as information on UHMWPE crosslinking, thermal treatment and sterilization), orthopedic evaluation (such as total duration of the implant in vivo and reasons for its revision) and material characterization (such as oxidative degradation and micromechanical properties). The joined database contains more than 500 entries, exhibiting gradual growth, and it is beginning to show interesting trends, which are discussed in our contribution, including (i) strong correlations between UHMWPE oxidative degradation, degree of crystallinity and microhardness; (ii) statistically significant differences between UHMWPE liners with different types of sterilization; (iii) realistic correlations between the extent of oxidative degradation and the observed reasons for total joint replacement failures. Our final objective and task for the future is to continuously expand the database, involving researchers from other European countries, in order to create a robust tool that will contribute to the better understanding of structure-properties-performance relationships in the field of arthroplasty implants.

RESUMEN

High entropy metal sub-lattice stabilized nitride coatings based on multicomponent refractory transition metals (TM = Ti, Nb, V, Ta, Zr, Hf) are promising candidates for extreme conditions due to their high thermal, mechanical, and corrosion properties. The aims of the current work included the investigations of the possibilities of the novel High Target Utilization Sputtering (HiTUS) technique applied to reactive sputtering of TiNbVTaZrHf-xN coatings from the viewpoints of hysteresis behavior during reactive sputtering as well as the structure, composition, stoichiometry, and mechanical properties of the resulting coatings. With increasing nitrogen content, coating structures varied from amorphous in metallic alloy coatings to textured nano-columnar fcc structures. Despite certain deviations of TM from equiatomic concentrations, homogeneous solid solutions corresponding to single-phase multicomponent nitride analogous to high entropy stabilized compounds were obtained. Mechanical properties were found to be proportional to nitrogen content. The highest hardness HIT ~ 33 GPa and indentation modulus EIT ~ 400 GPa were found in a slightly sub-stoichiometric (~42 at% nitrogen) composition. HIT/EIT and limited pillar split measurements suggested that these coatings exhibit low fracture toughness (around 1 MPa.m1/2). The work confirmed that reactive HiTUS is suitable for the preparation of multicomponent nitrides with the control of their stoichiometry and mechanical properties only via nitrogen additions.

RESUMEN

In the present work a comprehensive characterization of the hierarchical architecture of the walnut shell (Juglans regia L.) was carried out using scanning electron microscopy (SEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). Furthermore, micromechanical properties (hardness, HIT and elastic modulus, EIT) of plant tissues were evaluated at cell wall level by applying the instrumented indentation technique (IIT). The complex architecture of the material was described in terms of four hierarchical levels (HL): endocarp (H1), plant tissues (H2), plant cells (H3) and cell wall (H4). Our findings revealed that the walnut shell consists of a multilayer structure (sclerenchyma tissue, ST; interface tissue, IT; porous tissue, PT; and flattened parenchyma tissue, FPT), where differences in the microstructure and composition of plant tissues generate parallel gradients along the cross-section. The indentation tests showed a functional gradient with a sandwich-like configuration, i.e., a lightweight and soft layer (PT, HIT = 0.04 GPa) is located between two dense and hard layers (ST, HIT = 0.33 GPa; FPT, HIT = 0.28 GPa); where additionally there is an interface between ST and PT (IT, HIT = 0.16 GPa). This configuration is a successful strategy designed by nature to improve the protection of the kernel by increasing the strength of the shell. Therefore, the walnut shell can be considered as a functionally graded material (FGM), which can be used as bioinspiration for the design of new functional synthetic materials. In addition, we proposed some structure-property-function relationships in the whole walnut shell and in each of the plant tissues.

Asunto(s)

RESUMEN

We report a reproducible preparation and characterization of highly homogeneous thermoplastic starch/pol(ε-caprolactone) blends (TPS/PCL) with a minimal thermomechanical degradation and co-continuous morphology. These materials would be suitable for biomedical applications, specifically for the local release of antibiotics (ATB) from the TPS phase. The TPS/PCL blends were prepared in the whole concentration range. In agreement with theoretical predictions based on component viscosities, the co-continuous morphology was found for TPS/PCL blends with a composition of 70/30 wt.%. The minimal thermomechanical degradation of the blends was achieved by an optimization of the processing conditions and by keeping processing temperatures as low as possible, because higher temperatures might damage ATB in the final application. The blends' homogeneity was verified by scanning electron microscopy. The co-continuous morphology was confirmed by submicron-computed tomography. The mechanical performance of the blends was characterized in both microscale (by an instrumented microindentation hardness testing; MHI) and macroscale (by dynamic thermomechanical analysis; DMTA). The elastic moduli of TPS increased ca four times in the TPS/PCL (70/30) blend. The correlations between elastic moduli measured by MHI and DMTA were very strong, which implied that, in the future studies, it would be possible to use just micromechanical testing that does not require large specimens.

RESUMEN

The objective of this study was to evaluate the effect of the presence of calcium oxalate (CaOx) crystals on the micromechanical properties of sclerenchyma tissue from the pecan nutshell (Carya illinoinensis). The microstructure of the cross-section nutshell was examined using light microscopy (LM) and atomic force microscopy (AFM). Using an instrumented indentation system, indentation tests with maximum loads of 500 mN were made on the biological material where the variables studied were the number of crystals present in the evaluated area and the size of individual crystals. Microscopic analysis revealed that the pecan nutshell consists of sclerenchyma tissue with multiple CaOx crystals randomly distributed throughout the material, exhibiting prismatic shapes and various sizes. The results of the indentation tests showed that the examined areas where there were crystals (1, 2 or up to 3) presented values of hardness and elastic modulus significantly higher (P < 0.05) compared to the sclerenchyma (without crystals). Likewise, there were no significant differences (P > 0.05) between the values of the micromechanical properties of the areas evaluated as a function of the number of crystals. On the other hand, it was observed that the size of the crystals did not show a direct correlation with the mechanical properties evaluated as expected. In conclusion, the biomineralization phenomenon is a successful strategy designed by nature to improve the rigidity of the pecan nutshell, where the CaOx crystals strengthen the structure by increasing the micromechanical properties.

Asunto(s)

RESUMEN

Articular cartilage is a multiphasic, anisotropic, and heterogeneous material. Although cartilage possesses excellent mechanical and biological properties, it can undergo mechanical damage, resulting in osteoarthritis. Thus, it is important to understand the microscale failure behavior of cartilage in both basic science and clinical contexts. Determining cartilage failure behavior and mechanisms provides insight for improving treatment strategies to delay osteoarthritis initiation or progression and can also enhance the value of cartilage as bioinspiration for material fabrication. To investigate microscale failure behavior, we developed a protocol to initiate fractures by applying a microindentation technique using a well-defined tip geometry that creates localized cracks across a range of loading rates. The protocol includes extracting the tissue from the joint, preparing samples, and microfracture. Various aspects of the experiment, such as loading profile and solvent, can be adjusted to mimic physiological or pathological conditions and thereby further clarify phenomena underlying articular cartilage failure. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Harvesting and dissection of the joint surfaces Basic Protocol 2: Preparation of samples for microindentation and fatigue testing Basic Protocol 3: Microfracture using microindentation Basic Protocol 4: Crack propagation under cyclic loading.

Asunto(s)

RESUMEN

This study utilized a statistical nanoindentation analysis technique (SNT) to measure the amount of organic and inorganic constituents of twenty different brands of dental resin-based composites (RBCs) and tested whether their macro-property such as flexural modulus could be approximated by the proportions of constituents' micromechanical signatures using various rules of mixtures. The probability density function (PDF) of constitutive moduli per RBC brand were measured for three groups, comprised of different indent arrays and inter-indent spacings. SNT was then applied to deconvolute each PDF, from which the effective filler (µF) and matrix (µM) moduli and filler (VF) and matrix (VM) volume fractions per RBC brand were computed. VF and VM values obtained via SNT were strongly correlated with VF and VM obtained via Thermogravimetric Analysis and Archimedes method. The "observed" flexural modulus (EcFS) measured under macro-experiment were well associated with "predicted" effective modulus (EcEff) measured under nano-experiment, thereby establishing that global modulus was strongly affected by the constituents' micromechanics. However, the "predicted" EcEff were proportionally higher than the "observed" EcFS. VF was a confounder to EcFS and EcEff, whereby the influence of VF on both modular ratios (EcFS/µM and EcEff/µM) was best modeled by an exponential regression.

Asunto(s)

RESUMEN

Phenol-formaldehyde (PF) resin, modified using nano-copper with varying contents (0 wt%, 1 wt%, 3 wt%), was manufactured to improve the mechanical properties of Chinese fir. The morphology, chemical, micromechanical and micromechanical properties of the samples were determined by transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental scanning electron microscopy (ESEM), Fourier transform infrared spectroscopy (FTIR), nanoindentation (NI) and traditional mechanical testing. The TEM and AFM results indicated that the in situ synthesized nano-copper particles were well-dispersed, and spherical, with a diameter of about 70 nm in PF resin. From the FTIR chemical changes detected by FTIR inferred that the nano-copper modified PF resin penetrated into the Chinese fir cell walls and interacted with the acetyl groups of hemicellulose by forming a crosslinked structure. Accordingly, the micro-mechanical properties of the Chinese fir cell walls were enhanced after treatment with nano-copper modified PF resin. The filling of the PF-1-Cu resin (1 wt% nano-copper) in the wood resulted in 13.7% and 22.2% increases in the elastic modulus (MOE) and hardness, respectively, of the cell walls. Besides, the impact toughness and compressive strength of the Chinese fir impregnated with PF-1-Cu resin were 21.8% and 8.2% higher than that of the PF-0-Cu resin. Therefore, in situ synthesized nano-copper-modified PF resin is a powerful treatment method for Chinese fir due to improved diffusive properties and reinforcement of the mechanical properties.

RESUMEN

In the present work, an oxygen hardening of near-ß phase Ti-13Nb-13Zr alloy in plasma glow discharge at 700-1000 °C was studied. The influence of the surface treatment on the alloy microstructure, tribological and micromechanical properties, and corrosion resistance is presented. A strong influence of the treatment on the hardened zone thickness, refinement of the α' laths and grain size of the bulk alloy were found. The outer hardened zone contained mainly an oxygen-rich Ti α' (O) solid solution. The microhardness and elastic modulus of the hardened zone decreased with increasing hardening temperature. The hardened zone thickness, size of the α' laths, and grain size of the bulk alloy increased with increasing treatment temperature. The wear resistance of the alloy oxygen-hardened at 1000 °C was about two hundred times, and at 700 °C, even five hundred times greater than that of the base alloy. Oxygen hardening also slightly improved the corrosion resistance. Tribocorrosion tests revealed that the alloy hardened at 700 °C was wear-resistant in a corrosive environment, and when the friction process was completed, the passive film was quickly restored. The results show that glow discharge plasma oxidation is a simple and effective method to enhance the micromechanical and tribological performance of the Ti-13Nb-13Zr alloy.

RESUMEN

Laser-based technologies are extensively used for polymer surface patterning and/or texturing. Different micro- and nanostructures can be obtained thanks to a wide range of laser types and beam parameters. Cell behavior on various types of materials is an extensively investigated phenomenon in biomedical applications. Polymer topography such as height, diameter, and spacing of the patterning will cause different cell responses, which can also vary depending on the utilized cell types. Structurization can highly improve the biological performance of the material without any need for chemical modification. The aim of the study was to evaluate the effect of CO2 laser irradiation of poly(L-lactide) (PLLA) thin films on the surface microhardness, roughness, wettability, and cytocompatibility. The conducted testing showed that CO2 laser texturing of PLLA provides the ability to adjust the structural and physical properties of the PLLA surface to the requirements of the cells despite significant changes in the mechanical properties of the laser-treated surface polymer.

RESUMEN

Carbonation of hydrated cement paste (HCP) causes numerous chemo-mechanical changes in the microstructure, e.g., porosity, strength, elastic modulus, and permeability, which have a significant influence on the durability of concrete structures. Due to its complexity, much is still not understood about the process of carbonation of HCP. The current study aims to reveal the changes in porosity and micromechanical properties caused by carbonation using micro-beam specimens with a cross-section of 500 µm × 500 µm. X-ray computed tomography and micro-beam bending tests were performed on both noncarbonated and carbonated HCP micro-beams for porosity characterization and micromechanical property measurements, respectively. The experimental results show that the carbonation decreases the total porosity and increases micromechanical properties of the HCP micro-beams under the accelerated carbonation. The correlation study revealed that both the flexural strength and elastic modulus increase linearly with decreasing porosity.

RESUMEN

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·m1/2 and 2.7 MPa·m1/2, 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.

RESUMEN

Resilin-like polypeptides (RLPs) are an important class of intrinsically disordered multistimuli-responsive bioelastomers. The nanostructure of RLPs in solution has been extensively studied in the past few years, from dilute to molecular crowding conditions, and with the addition of rigid biopolymers. Modification of the hierarchical network structure of RLP hydrogels using graphene oxide (GO) as an additive is a burgeoning prospect for their application in the bioelectronic and biomedical fields. In this work, we systemically study the influence of incorporating GO into RLP (Rec1) hydrogels for tuning their physicochemical properties and understanding the gel-cell interactions. The nature of GO interaction with the Rec1 hydrogel is deduced from the change in structure and properties. Contrast-matching small-angle and ultra-small-angle neutron-scattering techniques were used to investigate the network structure of the Rec1 hydrogel and how this structure is modified in the presence of GO. Incorporation of GO in the Rec1 hydrogel matrix results in an increase in the micromechanical resilience, equilibrium water swelling ratio, micropore size, cross-linked domain size; with a decrease in the cross-link density, mass fractal cluster size, local compressive elastic modulus, and cell inert characteristics. These property combinations achieved with the addition of GO further open up the available structure-property design window for RLP applications.