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Coatings with tunable refractive index and high mechanical resilience are useful in optical systems. In this work, thin films of HfO2 doped with Al2O3 were deposited on silicon at 300 °C by using plasma-enhanced atomic layer deposition (PE-ALD). The mainly amorphous 60–80 nm thick films consisted Al in the range of 2 to 26 at.%. The refractive indexes varied from 1.69 to 2.08 at the wavelength of 632 nm, and they consistently depended on the composition. The differences were higher in the UV spectral region. At the same time, the hardness of the films was from 12–15 GPa; the modulus was in the range of 160–180 GPa; and the mechanical properties did not have a good correlation with the deposited compositions. The deposition conditions, element contents, and refractive indexes at respective wavelengths were correlated. The results indicated that it is possible to tune optical properties and retain mechanical properties of atomic layer-deposited thin films of HfO2 with Al2O3 as doping oxide. Such films could be used as mechanically resilient and optically tunable coatings in, for instance, micro- or nano-electromechanical systems or transparent displays. [ABSTRACT FROM AUTHOR]

Elaborating an instrumented nanoindentation is to exercise nondestructive tests to be applied to volumes of polymethylmetacrylate (PMMA) materials in miniature. This work focuses on factors that explain the trends variation of mechanical properties like Young's modulus (E), contact hardness (H) and indentation force (P). The evolution of E and H with depth (h) and P shows a 2.77 nm inflection point at low penetrations, separating two zones: the first increasing and the second decreasing. This is respectively explained by the surface hardening induced by preparing the material surface, and the existence of a surface hardness gradient denoted by an indentation size effect (ISE) observed at very low depths. Moreover, In addition, a critical penetration depth of 9.71 nm below which the surface effect dominates the variation of the penetrating load is detected. E and H results differences between dynamic and static modes are 8.46% and 6.44% inducing an overestimation of 35 MPa in E value, and an underestimation of 1.23 MPa in H value. This tends to affect the expected nanoscale precision of the indentation to determine the nanomechanical properties of PMMA. [ABSTRACT FROM AUTHOR]

One of the major obstacles restricting the wide applications of Mg alloys is their low Young's modulus at ∼45 GPa, which is uncompetitive to Al alloy over 60 GPa. To resolve this issue, we proposed a new strategy of designing ultra-light Mg-Li alloys by employing the microscale compounds in both HCP and BCC grains to achieve high Young's modulus. HCP or BCC alone cannot achieve a high modulus due to the segregation of solutes at the grain boundaries and the formation of brittle intermetallics in the interdendritic region. We designed chemistry that is so perfect to arrest the excess solutes inside the BCC matrix during solidification and engulf pre-solidified rare earth particles by HCP primary grains which have such a lean chemical composition that has almost no segregation. During solution heat treatment, the dissolution of solutes pushes the BCC boundary towards HCP grains by Ostwald ripening (BCC structures are interconnected but the HCP structures are isolated). During low-temperature aging heat treatment, nucleation of HCP structure on the rare earth particles inside the BCC grain is found, degrading the strength. Therefore, a novel Mg-Li-Al-Zn-Y-Mn-Gd (LAZWMV) alloy with a very high modulus was designed which reaches Young's modulus as high as 61.4 GPa. Micro-compounds (AlLi and Al-X) with average equivalent diameters of 3.76 µm and 6.55 µm were quantified in 3D using X-ray computed tomography and nanoindentation tests for establishing the microstructure-modulus correlation. The influence of Li addition on Mg-Mg was calculated by DFT calculations and the mechanism of modulus improvements has been proposed. [Display omitted] • Ultra-light Mg-Li alloy was designed with high strength and high modulus. • Super-high Young's Modulus of 61.4 GPa was first reported for a novel Mg alloy. • Nanoindentation uncovers the principles of modulus increase in Mg-Li alloys. • Quantitative 3D characterization of high modulus phase using XCT prectict alloy properties. • DFT calculation of Mg-Mg bonds explores the effects of heat treatments. [ABSTRACT FROM AUTHOR]

LiCoPO4 is a promising cathode material for use in high voltage Li-ion batteries. One of the problems with LiCoPO4 is limited cycle life. One possible cause for the limited cycle life of LiCoPO4 is mechanical degradation. As a consequence, the mechanical properties, elastic modulus, E, and fracture toughness, KIC, of hot-pressed dense (~98%) polycrystalline (15-20 µm) single phase LiCoPO4 were investigated. E for the hot-pressed LiCoPO4 specimen is ~137 GPa while the E value for the LiCoPO4 specimen after annealing at 600 °C is ~106 GPa. The fracture toughness of the hot-pressed LiCoPO4 sample is ~0.41 MPa m1/2, which increased to ~0.53 MPa m1/2 after annealing. These low KIC values reveal that LiCoPO4 is a brittle material. It is believed that the decrease in E and increase in KIC with annealing is associated with a reduction in residual stress. [ABSTRACT FROM AUTHOR]

Nanoindentation is widely used to investigate the surface-mechanical properties of biocomposites. In this study, polypropylene random copolymer (PPRC) and biowaste rice husk (BRH) were used as the main raw materials, and glass-fiber-reinforced polypropylene and talc were also used with BRH to enhance the mechanical characterization of the biocomposites. The interfacial bonding between the polymer and the rice husk was increased by treating them with maleic anhydride and NaOH, respectively. The results obtained from the nanoindentation indicated that the plastic behavior of the biocomposites was prominent when untreated BRH was used and vice versa. The modulus and hardness of the biocomposite improved by 44.8% and 54.8% due to the neat PPRC, respectively. The tribological properties were studied based on the hardness-to-modulus ratio and it was found that BRH- and talc-based biocomposites were better than other samples in terms of low friction and wear rate. The creep measurements showed that untreated rice husk biocomposite exhibited high resistance to load deformation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hardness of cured UF resins was evaluated by nanoindentation technique. [•] Both HB and HM value was consistently changed as a function of F/U mole ratio. [•] However, both Er and Es of cured UF resins displayed inconsistent trend. [•] Both HM and Er showed much greater in the COV at lower F/U mole ratios 1.0 and 1.2. [•] Crystalline structures in the low F/U mole UF resins contributed to this variability. [ABSTRACT FROM AUTHOR]

Abstract: Nanoindentation was applied to determine the elastic moduli in the compression mode of films of fluorinated ethylene propylene copolymers (FEP) foamed by means of supercritical carbon dioxide. For this purpose, a flat punch indenter with a diameter larger than the average cell size of the foams was found to be appropriate. The dependence of the mechanical properties of the films on their cellular structure was investigated by varying material and process parameters: molar mass of the FEP, the magnitude of the pressure drop and the temperature during the foaming process. The elastic modulus showed a strong influence of the cellular structure of the films. A decrease of the molar mass of FEP as well as an increase of pressure drop and foaming temperature considerably reduced the elastic modulus of the foams generated. This lowering of the stiffness correlated with the decrease of foam density. In addition, a significant contribution of the cellular morphology and the thickness of the compact skin layers of the foams could be noted. A further reduction of the foam stiffness was achieved by a biaxial stretching of the foams, which deformed the cells into a lens shape. [Copyright &y& Elsevier]

In materials science and engineering, a significant amount of research has been carried out using indentation techniques in order to characterize the mechanical properties and microstructure of a broad range of natural and engineered materials. However, there are many unresearched or partly researched areas, such as, for example, the investigation of the shape of the indentation load–displacement curve, the associated mechanism in porous materials with clastic texture, and the influence of the texture on the constitutive behavior of the materials. In the present study, nanoindentation is employed in the analysis of the mechanical behavior of a benchmark material composed of plaster of Paris, which represents a brand of highly porous-clastic materials with a complex structure; such materials may find many applications in medicine, production industry, and energy sectors. The focus of the study is directed at the examination of the influence of the porous structure on the load–displacement response in loading and unloading phases based on nanoindentation experiments, as well as the variation with repeating the indentation in already indented locations. Events such as pop-in in the loading phase and bowing out and elbowing in the unloading phase of a given nanoindentation test are studied. Modulus, hardness, and the elastic stiffness values were additionally examined. The repeated indentation tests provided validations of various mechanisms in the loading and unloading phases of the indentation tests. The results from this study provide some fundamental insights into the interpretation of the nanoindentation behavior and the viscoelastic nature of porous-clastic materials. Some insights on the influence of indentation spacing to depth ratio were also obtained, providing scope for further studies. [ABSTRACT FROM AUTHOR]

Abstract: Thin organic films of octadecyltrichlorosilane (OTS) and aminopropyltriethoxysilane (APTES) were deposited on oxidized Si(111) substrates and characterised using atomic force microscopy (AFM) and nanoindentation methods. Films derived from a novel alkylsilane, 4-[N,N-(2-pyridyl)aniline]triethoxysilane (NDTS), which has properties similar to related electroluminescent and fluorescent compounds, were also examined. This latter compound could be used to directly couple a fluorescent or electroluminescent centre to a semiconductor surface, with applications in microfluidics or other microelectronic-based sensors. AFM images showed that when OTS or APTES was deposited from ethanol solution onto the oxidized Si surface, an inhomogeneous film was formed, containing both smooth regions and polymerised particles of the alkylsilanes up to 200nm in diameter. Nanoindentation force/displacement curves could clearly distinguish these two regions of the film, and they showed quite different mechanical properties. When deposited from a solution of ethanol and CH2Cl2, OTS films were smooth and completely covered the surface. Discontinuities in the force/displacement curves, corresponding to a breakthrough by the indentor through the film into the substrate showed that these films were some 2nm in thickness. When OTS, APTES or NDTS were deposited from CH2Cl2 solution, similar discontinuities could be observed, and showed that the film thickness increased, and roughness decreased, as the concentration of alkylsilane in solution was decreased. The results are discussed in the context of using nanoindentation methods as a means of characterising organic thin films. [Copyright &y& Elsevier]

In this work, the effects of chemical pretreatment and different fiber loadings on mechanical properties of the composites at the sub-micron scale were studied through nanoindentation. The composites were prepared by incorporating choline chloride (ChCl) pretreated rice husk waste (RHW) in low-density polyethylene (LDPE) using melt processing, followed by a thermal press technique. Nanoindentation experiments with quasi continuous stiffness mode (QCSM) were performed on the surface of produced composites with varying content of pretreated RHW (i.e., 10, 15, and 20 wt.%). Elastic modulus, hardness, and creep properties of fabricated composites were measured as a function of contact depth. The results confirmed the appreciable changes in hardness, elastic modulus, and creep rate of the composites. Compliance curves indicated that the composite having 20 wt.% of pretreated RHW loading was harder compared to that of the pure LDPE and other composite samples. The values of elastic modulus and hardness of the composite containing 20 wt.% pretreated RHW were increased by 4.1% and 24% as compared to that of the pure LDPE, respectively. The creep rate of 42.65 nm/s and change in depth of 650.42 nm were also noted for the composite with RHW loading of 20 wt.%, which showed the substantial effect of holding time at an applied peak load of 100 mN. We believe that the developed composite could be a promising biodegradable packaging material due to its good tribo-mechanical performance. [ABSTRACT FROM AUTHOR]

In this study, the influence of alloying elements on the mechanical properties of iron borides FeB and Fe2B formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) alloys were evaluated using instrumented indentation measurement. The microstructural characterization of the alloys was performed by means of X-ray diffraction and scanning electron microscope equipped with an energy dispersive X-ray analyzer. The fraction of the phases present in the alloys was determined either by the lever rule or by image analysis. The hardest and stiffest FeB formed in Fe-B-X (X = C, Cr, Mn) alloys was observed in the Fe-B-Cr alloys, where indentation hardness of HIT = 26.9 ± 1.4 GPa and indentation modulus of EIT = 486 ± 22 GPa were determined. The highest hardness of Fe2B was determined in the presence of tungsten as an alloying element, HIT = 20.8 ± 0.9 GPa. The lowest indentation hardness is measured in manganese alloyed FeB and Fe2B. In both FeB and Fe2B, an indentation size effect was observed, showing a decrease of hardness with increasing indentation depth. [ABSTRACT FROM AUTHOR]

The physico-chemical properties of the Uranium intermetallic compound are of technological importance for improvement of the safety and compatibility of nuclear engineering systems. Diffusion couple samples with U and Cu were assembled and U-Cu intermetallic compounds were fabricated at interface by hot pressure diffusion method at a treatment temperature of 350 °C to 650 °C and at a pressure of 168 MPa in a vacuum furnace. The microstructure and element distribution of the compound phase have been studied by means of SEM, EDS, and XRD. The result showed that a new phase was developed to a thickness of approximately 10 μm with a ration of U:Cu with 1:5. Mechanical properties such as elastic moduli and hardness of the compound have been studied by means of nanoindentation. The nanoindentation testing on sample indicated that hardness of Uranium intermetallic compound are higher than that of metal U and Cu. Uranium intermetallic compound and U have a Young's moduli with 121 GPa, 160 GPa respectively. The elastic/plastic responses of U-Cu intermetallic compound and U under nanoindentation tests were also discussed in detail. [ABSTRACT FROM AUTHOR]