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Abstract: Since hardness is a quantitative measure of bulk mechanical properties, it can be used to examine the kinetics of crack propagation inside YBa2Cu3O7−δ (YBCO or Y-123) ceramics. YBCO samples with a tetragonal phase were oxygenated at a range of temperatures (from 250°C to 750°C) for different times. For each oxygenation temperature and time, hardness was measured by the nanoindentation technique, to study the defects (macro-/microcracks and porosity) produced along the c-axis. These defects were visualized by optical microscopy. The main purpose of this study was to establish the oxygenation kinetics for YBCO samples, which were textured by the top-seeded melt growth technique. We studied the evolution of hardness perpendicular to the ab-plane, as measured by the nanoindentation technique at a maximum penetration depth of 150nm. The results indicate that the nanoindentation technique can be used successfully to monitor oxygenation and to establish the kinetics of the process. [Copyright &y& Elsevier]

Abstract: This paper reviews commonly used methods of analyzing and interpreting friction, adhesion and nanoindentation with an AFM tip test data, with a particular emphasis of the testing of single crystals, metals, ceramics and ceramic coatings. Experimental results are reported on the friction, mechanical and adhesion properties of these materials. The popularity of AFM testing is evidenced by the large quantity of papers that report such measurements in the last decade. Unfortunately, a lot of information about these topics is scare in the literature. The present paper is aimed to present the basic physical modelling employed and also some examples using each technique. [ABSTRACT FROM AUTHOR]

Abstract: The Young’s modulus (E), hardness (H) and fracture toughness (KIC ) of various compositions of gadolinia doped-ceria (GDC, Gd x Ce1− x O2− x /2, 0.1⩽ x ⩽0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol–gel method, formed by uniaxial pressure and sintered at 1400°C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500mN. The results were interpreted by the Oliver–Pharr method and values of KIC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and KIC of GDC decreased with increasing gadolinia concentration, due to the oxygen vacancies generated by the dopant addition. As a result, the mechanical properties of GDC were significantly lower than those of YSZ electrolyte. [Copyright &y& Elsevier]

Abstract: The mechanical properties of CeO2 layers that are undoped or doped with other elements (e.g. Zr and Ta) are a topic of special interest specially in the manufacturing of superconductor buffer layers by pulsed electron deposition. Nowadays, the trend is to produce small devices (i.e. coated conductors), and the correct mechanical characterization is critical. In this sense, nanoindentation is a powerful technique widely employed to determine the mechanical properties of small volumes. In this study, the nanoindentation technique allow us determine the hardness (H) and Young''s modulus (E) by sharp indentation of different buffer layers to explore the deposition process of CeO2 that is undoped or doped with Zr and Ta, and deposited on Ni–5%W at room temperature. This study was carried out on various samples at different ranges of applied loads (from 0.5 to 500mN). Scanning electron microscopy images show no cracking for CeO2 doped with Zr, as the doping agent increases the toughness fracture of the CeO2 layer. This system, presents better mechanical stability than the other studied systems. Thus, the H for Zr–CeO2 is around 2.75·106 Pa, and the elastic modulus calculated using the Bec et al. and Rar et al. models equals 249·106 Pa and 235·106 Pa respectively. [Copyright &y& Elsevier]

As the changes on the mechanical properties with depth of indentation provide valuable information that may be suitable for design purposes, nanoindentation is an adequate technique for investigating the nanomechanical changes in the surface and in the inner polymers. This research focuses on the study of the nanomechanical properties of two grades of polypropylene (PP) after the long term exposure to an organic fluid, such as paraffin wax used as a phase change materials (PCM). PCM are used for thermal energy storage (TES) in buildings applications for passive systems or heating and cooling usages. In any of these uses PCM must be encapsulated and PP is a possibility within the container materials used. Four different samples of the polypropylene were evaluated: PP, filled polypropylene with 60% Mg(OH) 2 (PP-60Mg), PP-60Mg with PCM (RT-25), and PP-60Mg with PCM (RT-42). It was studied the thermal stability by Thermogravimetrical analysis of these samples, and also it was evaluated the Hardness ( H ), Elastic modulus ( E ) and Loss modulus ( E loss ) for the unfilled PP and PP-60Mg in contact with two different PCM at different temperatures (30 °C, 45 °C and 60 °C for RT-25 and 45 °C for RT-42) for 32 days. Results show that the mechanical properties H , E , and E loss are higher for PP-60Mg than for PP. Nevertheless, these properties decrease significantly when the PP and the PP-60Mg are in contact with PCM, because it acts as a plasticizer, softening the polymer. Besides, the higher PCM’s melting point, the lowest mechanical properties were observed. [ABSTRACT FROM AUTHOR]

Unlike other engineered ceramic products, alumina (Al 2 O 3) displays interesting mechanical and physical properties, which makes it an ideal candidate for a wide range of uses in different fields and in particular for catalytic applications. However, the manufacturing of ceramic components has still a major drawback in production of highly complex three-dimensional (3D) shapes, microfeatures or structures with tailored porosity. Direct Ink Writing (DIW), also known as robocasting, is a material extrusion Additive Manufacturing technology and is one of such versatile methods with unique flexibility in material and geometry. In this work, α -Al 2 O 3 ceramic materials were designed and produced by DIW to determine the most suitable sintering treatment and ceramic ink composition to design new components for catalytic applications. Several thermal treatments varying sintering temperature and time were tested previously to the preparation of inks with different ceramic loadings, up to 75 wt%. A systematic study of the DIW specimens sintered at the optimal sintering temperature – time combination, in terms of microstructure (density and porosity) and mechanical properties (hardness and indentation fracture toughness), was performed to determine the optimize ceramic loading. Finally, finite element modeling and catalytic experiments conducted for the optimal ceramic ink showed that 3D printed parts with a rectilinear infill pattern and 40% infill density favored catalytic performance. [ABSTRACT FROM AUTHOR]

The changes in mechanical properties, hydrothermal degradation and cell adhesion were studied in 3Y-TZP under two different superficial modification patterns (uni- and multidirectional) with a surface roughness ranging from 16 to 603 nm. In this sense, mechanical properties (i.e. hardness, indentation fracture toughness and scratch) and accelerated tests in water steam were measured to evaluate the influence of the surface treatments on the superficially modified layer. Moreover, a detailed characterization through micro-Raman spectroscopy and X-Ray diffraction was performed. Finally, SaOS-2 osteoblasts were used for the evaluation of the cell adhesion behaviour on the surfaces. Overall, ground/polished specimens increased the mechanical properties and ageing resistance of mirror-like polished specimens, although resistance to degradation was maximum at intermediate conditions (S a ≈ 40−180 nm). The studied surfaces allowed cell attachment, but promoted contact guidance (i.e. cell alignment) only on unidirectionally ground surfaces above Sa = 150 nm. [ABSTRACT FROM AUTHOR]

Zr 1−x Mo x thin films were synthesized on glass substrates by co-sputtering molybdenum and zirconium targets in the presence of argon with x in the 0.32–0.95 range. From X-ray diffraction analyses and transmission electron microscopy images it was possible to observe an evolution of the samples structure from a nano-crystalline solid solution of Zr in the bcc lattice of Mo to clusters of Zr(Mo) nano-crystalline in an amorphous matrix. The coherence length deduced from X-ray diffractograms was around 1 nm–8 nm depending on the composition. Mechanical measurements show that the films exhibited high hardness H , low Young's modulus E and therefore high H ∕ E ratio compared with the bulk of Zr and Mo. We also found a low friction coefficient values for all the samples. Finally, an inverse Hall-Petch effect was observed for coherence length lower than 6 nm. [ABSTRACT FROM AUTHOR]

Cycling contact fatigue indentation tests in dry and wet conditions were conducted in cemented carbides CVD-coated with Ti(C,N)/α-Al 2 O 3 and Zr(C,N)/α-Al 2 O 3 systems. In dry contact experiments, all imprints presented a deformed area where the coating was still present after the test. Formation of cracks was visible at the edge of the contact point of the imprint. On the other hand, under wet conditions, almost all imprints presented a ring where the α-Al 2 O 3 had been removed, driven by a corrosion-fatigue process. Exceptionally, for Cr-containing cemented carbides combined with Zr(C,N)/α-Al 2 O 3 coating, no delamination of α-Al 2 O 3 was observed after the test under wet conditions. This result suggests that the combination of fine-grained cemented carbides and coating systems with low coefficient of thermal expansion may be of advantage to resist degradation by cyclic contact fatigue. Furthermore, the response to fatigue by contact loads can be enhanced by tailoring/combining cemented carbides and CVD coating systems which present higher chemical stability, and both higher intrinsic plasticity and resistance to plastic deformation. • Contact fatigue response in wet and dry conditions for CVD coated cemented carbides. • Resistance to cracking dominated by carbide/coating system response to deformation. • Substrates with higher plasticity present higher load bearing capacity and resistance to cracking. • Resistance to cracking in CVD systems dominated by low CTE and high intrinsic plasticity. • Suitable carbide/coating systems developed by considering intrinsic plasticity and low CTE. [ABSTRACT FROM AUTHOR]

The main goal of this work is to obtain a reliable value of the fracture toughness of single grains of tungsten carbide (WC). It is attempted by testing microcantilever and micropillar samples shaped out, by means of focused ion beam milling, of individual WC particles embedded within a WC-Co cemented carbide grade. Experimental testing included the use of a nanoindenter for inducing microcantilever bending and micropillar splitting, as well as sampling WC grains with basal and prismatic orientations. Experimental results are compared with those previously assessed through implementation of the indentation microfracture technique. Bending of notched microcantilevers yielded more consistent results than those measured out of micropillar splitting tests. In this regard, the average value of fracture toughness for single WC grains, within the two-phase interpenetrated network existing in cemented carbides, is found to be 5.6 ± 0.8 MPa·m1/2. Such a relatively high value – coherent with local plastic features evidenced in nanoindentation imprints - is in satisfactory agreement with results indirectly estimated from other macromechanical tests. • Fracture toughness of single WC grains is measured by micromechanical methods. • Microcantilevers produce the most consistent results. • Fracture toughness of WC grains of cemented carbides, is found to be 5.6 MPa·m1/2. [ABSTRACT FROM AUTHOR]