Evaluation of microwave processed glass–ceramic coating on nimonic superalloy substrate

MgO–Al₂O₃–TiO₂ based glass–ceramic coatings were formed on nimonic superalloy substrates by microwave and conventional heat treatment processes. The resultant glass–ceramic coatings were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), image analysis, nanohardness and Young's modulus evaluation by depth sensitive indentation (DSI) technique. Nanohardness and Young's modulus values of the microwave heat treated glass–ceramic coatings were improved in comparison to those of the conventionally treated glass–ceramic coatings due to presence of finer sized crystallites in the microwave processed coatings. Slight enhancement in the nanohardness and Young's modulus values with soaking time for the microwave processed coatings were explained in terms of the microstructural refinement and the reinforcement of the parent glass matrix.     

Damage Tolerance and Extensive Plastic Deformation of β‐Yb2Si2O7 from Room to High Temperatures

β‐Yb₂Si₂O₇ is a promising environmental barrier coating (EBC) material and recently attracted attention for its damage tolerance. To investigate the mechanisms of its damage tolerance and possible plasticity, dense β‐Yb₂Si₂O₇ sample was synthesized by in situ reaction/hot‐pressing method, and its mechanical properties were measured from room to high temperatures. The low magnitudes of hardness to Young's modulus ratio H_V/E, shear modulus to bulk modulus ratio G/B, and high fracture toughness to strength ratio K_IC/σ provide evidences of damage tolerance of β‐Yb₂Si₂O₇. β‐Yb₂Si₂O₇ exhibits extensive plastic deformation in Hertzian contact tests at both room and high temperatures. Transmission electron microscopy (TEM) observations show that the deformation mechanisms are different at low and high temperatures. Deformation twinning and parallel dislocation arrangement occur in plastic deformation at room temperature. Above the brittle‐to‐ductile transition temperature (between 1200°C and 1300°C), plastic deformation brings out extensive slip and climb of dislocations, while twinning is seldom observed. Measurement of temperature‐dependent dynamic Young's modulus demonstrates excellent elastic stiffness retention up to 1300°C.     

An estimate of quartz content and particle size in porcelain tiles from young's modulus measurements

The influence of quartz particle size, weight content and firing temperature on the Young's modulus of porcelain tiles was studied. To simulate a porcelain tile microstructure, an albite glass matrix with added crystalline quartz particles was developed. Average particle size of quartz (3.4 and 31 µm) and volume content (18.5 and 37.6 vol%) were varied. An acoustic impulse excitation technique was used to measure the elastic modulus from room temperature up to 700 °C. Results showed that quartz has a major influence on the elastic modulus of porcelain tiles. At temperatures below 573 °C, a hysteresis area between the Young's modulus curves during heating and cooling was closely related to quartz particle size. Between 573 and 700 °C, the variation of the Young's modulus was related to the quartz volume fraction. By using those correlations, a prediction of quartz content and quartz particle size in commercial porcelain materials can be carried out from Young´s modulus data.     

The elastic property of polyvinyl alcohol gel with boric acid as a crosslinking agent

The elastomers of polyvinyl alcohol gel were made from the polyvinyl alcohol polymer, with boric acid added as a crosslinking agent, in the mixed solvent of dimethyl sulfoxide and water. From the experimental results, the viscosity of polyvinyl alcohol solution is found to increase not only with an increment of boric acid content, but also with the temperature in the range of 70°C ∼ 100°C, although the viscosity is decreased in the range of 30°C ∼ 70°C. Moreover, the molecular mass between junctions of polyvinyl alcohol gel is calculated from the rubber elastic theory and found to be decreased with the increment of boric acid content. We also evaluated the values of Young's modulus of polyvinyl alcohol gel, E, E*, and the elastic parameters C₁ and C₂ of the Mooney‐Rivlin equation, according to Hook's law and theory of rubber elasticity. Based on these, the polyvinyl alcohol gel behaves as a good rubberlike elastic property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3046–3052, 1999     

Preparation and characterization of poly(vinyl chloride)–continuous carbon fiber composites

In this article, we report on the preparation and characterization of novel poly(vinyl chloride) (PVC)–carbon fiber (CF) composites. We achieved the reinforcement of PVC matrices with different plasticizer contents using unidirectional continuous CFs by applying a warm press and a cylinder press for the preparation of the PVC–CF composites. We achieved considerable reinforcement of PVC even at a relatively low CF content; for example, the maximum stress (σ_max) of the PVC–CF composite at a 3% CF content was found to be 1.5–2 times higher than that of the PVC matrix. There were great differences among the Young's modulus values of the pure PVC and PVC–CF composites matrices. The absolute Young's modulus values were in the range 1100–1300 MPa at a 3% CF content; these values were almost independent of the plasticizer content. In addition, we found a linear relationship between σ_max and the CF content and also recognized a linear variation of the Young's modulus with the CF content. The adhesion of CF to the PVC matrix was strong in each case, as concluded from the strain–stress curves and the light microscopy and scanning electron microscopy investigations. The mechanical properties of the PVC–CF composites with randomly oriented short (10 mm) fibers were also investigated. At low deformations, the stiffness of the composites improved with increasing CF content. Dynamic mechanical analysis (DMA) was used to determine the glass‐transition temperature (T_g) of the PVC–CF composites. The high increase in the Young's modulus entailed only a mild T_g increase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Elastic behaviour of zirconium titanate-zirconia bulk composite materials at room and high temperature

Zirconium titanate-zirconia composites have potential for applications involving variations of temperature. Elastic characterization is necessary to evaluate stresses developed in materials which may be used in these kinds of applications. In this work, Young's and shear modulus and Poisson's ratio of two zirconium titanate-zirconia bulk composites (Z(Y)T70 and Z(Y)T50) have been determined at room temperature by the Impulse Excitation Technique (IET). Furthermore, Young's modulus (E) has been determined at high temperature (up to 1400 °C) for both composites. Young's modulus of Z(Y)T70 composite decreases ≈6% between room temperature and 400 °C due to the presence of zirconia. From 400 to 1400 °C, the decrease of E (≈14%) is due to the presence of zirconium titanate. Young's modulus behaviour at high temperature of Z(Y)T50 composite is determined by the degree of microcrack healing, which depends on the maximum temperature reached.     

Elastic anisotropy and thermodynamics properties of BiCu2PO6, BiZn2PO6 and BiPb2PO6 ceramics materials from first-principles calculations

In present work, the elastic properties, anisotropy in elasticity and thermodynamics properties for BiCu₂PO₆, BiZn₂PO₆ and BiPb₂PO₆ ceramics materials were investigated using the first-principles calculation. The formation enthalpy and phonon frequencies confirm that three BiX₂PO₆ (X = Cu, Zn, and Pb) compounds exhibit the structural stability. The calculated elastic constants and elastic moduli indicate that BiZn₂PO₆ has the better mechanical properties than BiCu₂PO₆ and BiPb₂PO₆ at ground state. The values of B/G confirm that three BiX₂PO₆ compounds all exhibits the ductile behavior. The values of anisotropic parameters, three-dimensional surface constrctions and two-dimensional projection curves of the Young's modulus reveal the anisotropic degree of three BiX₂PO₆ compounds. The thermodyanmic parameters indicate that three BiMn₂XO₆ materials show the thermal stability from 0 to 1000 K. The obtained physical parameters can provide the useful data for the further experimental investigations.     

Thermomechanical properties of Y-substituted SrTiO3 used as re-oxidation stable anode substrate material

Re-oxidation robustness is important to warrant a reliable operation of anode-supported solid oxide fuel cell systems. The current work concentrates on the mechanical properties of re-oxidation stable Y-substituted SrTiO₃ ceramic for the use as anode substrate material. Room temperature micro-indentation yielded Young's modulus and hardness of 160 and 7 GPa, respectively, whereas the temperature-dependent modulus was measured with a resonance-based method up to ∼950 °C. The effective Young's modulus as a function of porosity was measured at room temperature and compared with fracture strength data. The fracture toughness was assessed using a combination of pre-indentation cracks and bending test. Creep rates were measured at 800 and 900 °C in a 3-point bending configuration. Post-test fractographic analysis performed using stereo, confocal and scanning electron microscopy, revealed important information on fracture origins and critical defects in the material. A methodology to assess the mechanical properties of porous materials is suggested.     

First-principles calculations on structural energetics of Cu-Ti binary system intermetallic compounds in Ag-Cu-Ti and Cu-Ni-Ti active filler metals

Structural, mechanical and thermodynamic properties, as well as the electronic structures of Cu-Ti binary system intermetallic compounds in Ag-Cu-Ti and Cu-Ni-Ti active filler metals were calculated systematically using a first-principles density functional theory (DFT). The calculated formation enthalpy index that all the Cu-Ti intermetallic compounds are thermodynamic stable from degradation to pure metals and the relationship between Cu content (x) and formation enthalpy (y) for tetragonal structure meets the function y=0.572+(−1.005/(0.048*sqrt(3.142/2)))*exp(−0.5*((x−47.167)/13.533)^2). The mechanical properties, including bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio v, and elastic anisotropy were derived from the elastic data C_ij. For the tetragonal Cu-Ti intermetallic compounds, the shear modulus G and Young's modulus E are negatively related to the formation enthalpy, while for the orthorhombic Cu-Ti intermetallic compounds, G and E are positively related to the formation enthalpy. Moreover, the elastic anisotropy increases in the following order: Cu₄Ti<CuTi₃<Cu₄Ti₃<Cu₂Ti<CuTi<CuTi₂<Cu₃Ti₂. The thermodynamic properties were estimated from the electronic structures and elastic constants simultaneously, and the results found that Cu₄Ti possess the best thermal conductivity and heat capacity among all the Cu-Ti intermetallic compounds, while CuTi₃ shows the worst ones. Finally, the relationship between electronic structures and physical properties was discussed, and get the inference that for the Cu-Ti intermetallic compounds, the mechanical properties are positively related to the strength of the covalent bond, while the thermophysical properties are influenced by the ionic character and covalent character simultaneously and the ionic character shows the dominant role, therefore, CuTi and Cu₄Ti₃ show the strongest mechanical properties due to the strongest covalent character, while Cu₄Ti shows the strongest thermal conductivity and heat capacity due to the strongest ionic character.     

Preparation and properties of LixLa0.5TiO3 perovskite oxide electrolytes

Solid electrolytes with high lithium ionic conductivity and outstanding mechanical stability are essential for all solid‐state lithium ion batteries. Perovskite Li_xLa_0.5TiO₃ is one of the most promising as solid electrolytes candidates. Li_xLa_0.5TiO₃ with various initial Li₂O (0.5≤x≤0.569) is synthesized by traditional solid‐state reaction at high temperatures. The crystal structure is not remarkably affected by the Li₂O quantity, yet higher porosity is obtained as a result of excess Li₂O. The Young's modulus, hardness, and fracture toughness are evaluated with indentation method. The Young's modulus increases from 72 to 148 GPa with increasing Li₂O, which means that a small variation of Li quantity in Li_xLa_0.5TiO₃ results in over a 100% change in Young's modulus. However, the fracture toughness exhibits an opposite trend with that of the Young's modulus. The high Young's modulus and fracture toughness could guarantee the structural integrity during cycle operations.     

Elastic Properties of Ceramic Composite Materials (of Cermet Type) Based on Refractory Oxides

Results of a study of cermets based on Al₂O₃ and ZrO₂ reinforced by a metallic skeleton of steel 12Kh18N9T are presented. The Young's modulus, the shear modulus, the compression modulus, and the Poisson coefficient are determined by the dynamic method. Formulas for computing the moduli of elasticity of cermets are derived proceeding from the additivity of the phases contained in the composition.     

Elastic behaviour of zirconium titanate bulk material at room and high temperature

Zirconium titanate (ZrTiO₄) is a well known compound in the field of electroceramics, however, its potential for structural applications has never been analysed. Moreover, it is compatible with zirconia, thus, zirconium titanate–zirconia composites might have potential for structural applications in oxidizing atmospheres. Nevertheless, there are currently no data about elastic properties of zirconium titanate materials in the literature. In view of the importance of these properties for the structural integrity of components subjected to high temperature and mechanical strains, an attempt was done in this work to determine the elastic properties of ZrTiO₄, both at room and high temperature. Young's modulus (161 ± 4 GPa), shear modulus (61 ± 1 GPa) and Poisson's ratio (0.32 ± 0.01) values at room temperature have been estimated for a fully dense single phase ZrTiO₄ material from experimental data of sintered single phase ZrTiO₄ materials with different porosities (6–19%). Values for room temperature Young's modulus are in agreement with those obtained by nanoindentation. Young's modulus up to 1400 °C shows an unusual dependence on temperature with no significant variation up to 500 °C an extremely low decrease from 500 to 1000 °C (≈0.02–0.03% every 100 °C) followed by a larger decrease that can be attributed to grain boundary sliding up to 1400 °C.     

Additive manufacturing of complex-shaped and porous silicon nitride-based components for bionic bones

Si₃N₄ is a novel implant material with promising applications in the replacement of human hard tissues. The biomimetic human bone structure used in this study was created using digital light-processing technology. The effect of pore-forming agent content on the curing and mechanical properties of Si₃N₄ ceramics was studied. The obtained results indicated that with an increase in the pore-forming agent content, the cure depth of the ceramic suspension first increased and then decreased, while the excess cure width decreased. Furthermore, as the pore-forming agent content increased, the porosity of the sample increased, whereas the compressive strength and Young's modulus decreased. The maximum porosity of the sample at the optimal mass ratio (pore-forming agent: Si₃N₄ = 5:10) is 58.48 ± 0.49%, and the compressive strength and Young's modulus are 79.01 ± 6.78 MPa and 18.18 ± 0.26 GPa, respectively.     

One-pot hydrothermal synthesis of MoS2 nanosheets/C hybrid microspheres

Uniform MoS₂ nanosheets/C hybrid microspheres with mean diameter of 320 nm have been successfully synthesized via a facile one-pot hydrothermal route by sodium molybdate reacting with sulfocarbamide in d-glucose solutions. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). XRD patterns showed that the MoS₂ was kept as a two-dimensional nanosheet crystal and C was retained as amorphous even after their annealing treatment at 800 °C. TEM and SEM images indicated that the MoS₂ nanosheets were uniformly dispersed in the amorphous carbon. The experiment results also revealed that the appropriate amount of d-glucose had an obvious effect on the formation of uniform MoS₂ nanosheets/C hybrid microspheres. A possible formation process of MoS₂ nanosheets/C hybrid microspheres was preliminarily presented.     

Ferromagnetism in freestanding MoS2 nanosheets

Freestanding MoS₂ nanosheets with different sizes were prepared through a simple exfoliated method by tuning the ultrasonic time in the organic solvent. Magnetic measurement results reveal the clear room-temperature ferromagnetism for all the MoS₂ nanosheets, in contrast to the pristine MoS₂ in its bulk form which shows diamagnetism only. Furthermore, results indicate that the saturation magnetizations of the nanosheets increase as the size decreases. Combining the X-ray photoelectron spectroscopy, transmission electron microscopy, and electron spin resonance results, it is suggested that the observed magnetization is related to the presence of edge spins on the edges of the nanosheets. These MoS₂ nanosheets may find applications in nanodevices and spintronics by controlling the edge structures.     

In situ hot pressing/reaction synthesis,mechanical and thermal properties of Lu2SiO5

Lu₂SiO₅ is a promising candidate of environmental barrier coatings (EBC) for silicon based ceramics due to its excellent high temperature stability. However, little information is available for the mechanical and thermal properties of Lu₂SiO₅, which frustrated evaluation of its performances for EBC applications. In this paper, dense Lu₂SiO₅ ceramic is successfully fabricated from Lu₂O₃ and SiO₂ powders by in situ hot pressing/reaction sintering at 1500 °C. Mechanical properties, including Young's modulus, bulk modulus, shear modulus, Poisson's ratio, fracture toughness, Vickers hardness, and bending strength are reported for the first time. Lu₂SiO₅ possesses excellent high temperature mechanical properties up to at least 1300 °C. Thermal stress for the case of Lu₂SiO₅ or Y₂SiO₅ coating on silicon bond coat and thermal stress resistance parameter are also estimated based on the experimental mechanical and thermal properties. The present results suggest that Lu₂SiO₅ has better reliability than Y₂SiO₅ in harsh thermal environment.     

Fracture surface and correlation of buckling force with aspect ratio of C60 crystalline whiskers

The structure and mechanical properties of crystalline whiskers with an average diameter of 600 nm, composed of C₆₀ molecules were studied by transmission electron microscopy combined with nanonewton force measurements used in atomic force microscopy. C₆₀ nanowhiskers with a body-centered tetragonal structure are compressed along their long axis. Young's modulus of the C₆₀ nanowhiskers was estimated to be 28 ± 5 GPa. The buckling stress was correlated to the aspect ratio of length to diameter of the C₆₀ nanowhiskers. The (100) surface was the principal fracture surface of the C₆₀ nanowhiskers.     

Enhanced Thermo‐Mechanical Stiffness,Thermal Stability,and Fire Retardant Performance of Surface‐Modified 2D MoS2 Nanosheet‐Reinforced Polyurethane Composites

This article reports new‐generation 2D‐MoS₂ nanosheet‐containing polyurethane (PU) composite materials with improved thermo‐mechanical stiffness, thermal stability, and fire retardation properties. The surface of 2D‐MoS₂ nanosheets is modified with melamine (M‐MoS₂), and then PU composites with varying M‐MoS₂ loadings are synthesized using an in situ polymerization method. During polymerization, 3‐amino‐propyl‐trimethoxy silane is introduced to create silicate functionality on the PU chains, which further improves the compatibility between PU and M‐MoS₂. Microscopy studies confirm the distribution of highly intercalated and agglomerated M‐MoS₂ nanosheets in the PU matrix. The PU composite containing 5 wt% M‐MoS₂ shows a 65% higher storage modulus (at 30 °C) than that of pure PU. The thermal stability of pure PU is significantly improved (62 °C) after composite formation. Thermogravimetric analysis in combination with FTIR spectroscopy shows that the PU/M‐MoS₂ composites release less toxic gases during thermal degradation compared to pure PU. Moreover, the composite containing 5 wt% M‐MoS₂ shows improved fire retardation properties, with 45% and 67.5% decrease in the peak heat and total heat release rates, respectively, as compared with those of pure PU. In summary, 2D‐MoS₂ is shown to have potential as an advanced nano‐filler to obtain stiffer PU composite with improved fire retardant property for structural application.     

Nanomechanical properties of zirconia- yttria and alumina zirconia- yttria biomedical ceramics,subjected to low temperature aging

Samples of ZTA composites {80 wt%Al₂O₃+20 wt%TZ-3Y}, ATZ composites {20 wt%Al₂O₃+80 wt%TZ-3Y}, tetragonal polycrystalline zirconia (3Y-TZP), and cubic stabilized zirconia (8Y-CSZ) were prepared to study the nanomechanical properties by nanoindentation before and after low temperature aging or degradation. Moreover, structural properties and crystalline present phases were evaluated by X-Ray Diffraction (XRD) and Electron Diffraction Patterns from transmission electron microscopy (TEM). The 8Y-CSZ ceramic showed the best mechanical behavior among all the analyzed materials (ZTA, ATZ and 3Y-TZP), the 8Y-CSZ sample did not showed any phases transformations when subjected to low temperature degradation (LTD). Absolute nanohardness, Young's modulus and fracture toughness after the LTD were carried out in different samples, the obtained results, in a decreasing order were: 8Y-CSZ>ZTA>3Y-TZP>ATZ, 8Y-CSZ>3Y-TZP>ZTA>ATZ and 8Y-CSZ>3Y-TZP>ATZ>ZTA, respectively. The 8Y-CSZ ceramic, did not showed any variations in nanomechanical properties due to the absence of anisotropic behavior, manifesting high hardness, elastic modulus and relative values of fracture toughness. Perhaps this material could be candidate for biomedical applications.     

Characterization of morphology and mechanical properties of block copolymers using atomic force microscopy: Effects of processing conditions

The effect of preparation methods and processing conditions on morphology and mechanical properties of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) triblock copolymer were investigated with atomic force microscopy (AFM) tapping mode and nanomechanical mapping, tensile testing, and gel permeation chromatograph (GPC). It was found that the samples prepared by solution casting and melt processing show large difference in morphology and mechanical properties. High shear rate does not induce alignment of lamellar block copolymer melts but leads to serious degradation of SEBS. As increase of rotational speed from 0 to 400 rpm, the molecular weight including M_n and M_w decreases from 67,100 to 26,000 and 70,000 to 43,000, respectively. Such large molecular weight decrease causes greatly decreased tensil strength but there is almost no evident effect on the well-phase separated morphology and Young's modulus of the SEBS. The Young's modulus distribution revealed by nanomechanical mapping becomes narrow as the increase of rotational speed. The amount of SEBS molecular having higher Young's modulus, which play a very important role in tensile strength of SEBS, also decreases.