Production, microstructural characterization and mechanical properties of as-cast Ti-10Mo-xNb alloys

Beta titanium (Ti) alloys are one of the most promising groups of Ti alloys for biomedical applications. This work presents the production, microstructural characterization, and mechanical properties of as-cast Ti-10Mo-xNb (x = 0, 3, 6, 9, 20, and 30) alloys. They were produced via arc melting and characterized by scanning electron microscopy and X-ray diffraction. The density of each alloy was measured by the Archimedes method and the mechanical characterization was carried out by using the Vickers microhardness test and Young`s modulus measurements. The results show a near beta microstructure for niobium (Nb) contents lower or equal to 9 wt% while beta single-phase microstructure was obtained for higher Nb additions. The microhardness values decreased with the increase of Nb content in the alloys. The elastic modulus values of Ti-10Mo-3Nb and Ti-10Mo-20Nb alloys were lower than those of cp Ti and Ti-6Al-4V.

Evaluation of rock mechanical behaviors under uniaxial compression with reference to assessed weathering grades

A weathering classification for granitic rock materials from southeastern Brazil was framed based on core characteristics. The classification was substantiated by a detailed petrographic study. Indirect assessment of weathering grades by density, ultrasonic and Schmidt hammer index tests was performed. Rebound values due to Schmidt hammer multiple impacts at one representative point were more efficient in predicting weathering grades than averaged single impact rebound values, P-wave velocities and densities. Uniaxial compression tests revealed that a large range of uniaxial compressive strength (214-153 MPa) exists in Grade I category where weathering does not seem to have played any role. It was concluded that variability in occurrences of quartz intragranular cracks and in biotite percentage, distribution and orientation might have played a key role in accelerating or decelerating the failure processes of the Grade I specimens. Deterioration of uniaxial compressive strength and elastic modulus and increase in Poisson`s ratio with increasing weathering intensity could be attributed to alteration of minerals, disruption of rock skeleton and microcrack augmentation. A crude relation between failure modes and weathering grades also emerged.

Mechanical and tribological properties of a sintered glass-ceramic compared to granite and porcelainized stoneware

Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 degrees C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile. (C) 2011 Elsevier B.V. All rights reserved.

Composite materials of thermoplastic starch and fibers from the ethanol-water fractionation of bagasse

The aim of this study was to evaluate the potential of the fibrous material obtained from ethanol-water fractionation of bagasse as reinforcement of thermoplastic starches in order to improve their mechanical properties. The composites were elaborated using matrices of corn and cassava starches plasticized with 30 wt%glycerin. The mixtures (0,5,10 and 15 wt% bagasse fiber) were elaborated in a rheometer at 150 degrees C. The mixtures obtained were pressed on a hot plate press at 155 degrees C. The test specimens were obtained according to ASTM D638. Tensile tests, moisture absorption tests for 24 days (20-23 degrees C and 53% RH, ASTM E104), and dynamic-mechanical analyses (DMA) in tensile mode were carried out. Images by scanning electron microscopy (SEM) and X-ray diffraction were obtained. Fibers (10 wt% bagasse fiber) increased tensile strength by 44% and 47% compared to corn and cassava starches, respectively. The reinforcement (15 wt% bagasse fiber) increased more than fourfold the elastic modulus on starch matrices. The storage modulus at 30 C (E(30 degrees C)`) increased as the bagasse fiber content increased, following the trend of tensile elastic modulus. The results indicate that these fibers have potential applications in the development of biodegradable composite materials. (c) 2011 Elsevier B.V. All rights reserved.

Residual stresses in TiN, DLC and MoS(2) coated surfaces with regard to their tribological fracture behaviour

Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03-4 GPa on steel substrate and 0.1-1.3 GPa on silicon. MoS(2) coatings had tensional stresses in the range of 0.8-1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 mu m TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS(2) and DLC coatings, being K(C) = 4-11, about 2, and 1-2 MPa M(1/2), respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface. (C) 2009 Elsevier B.V. All rights reserved.

Energy dissipation in depth-sensing indentation as a characteristic of the nanoscratch behavior of coatings

Wear behavior of coatings has usually been described in terms of mechanical properties such as hardness (H) and effective elastic modulus (E*). Alternatively, an energy approach appears as a promising analysis taking into account the influence of those properties. In a nanoindentation test, the dissipated energy depends not only on the hardness and elastic modulus, but also on the elastic recovery (W(e)). This work aims to establish a relation between plastic deformation energy (E(p)) during depth-sensing indentation method and the grooving resistance of coatings in nanoscratch tests. An energy dissipation coefficient (K(d)) was defined, calculated as the ratio of the plastic to the total deformation energy (E(p)/E(t)), which represents the energy dissipation of materials. Reactive depositions using titanium as the target and nitrogen and methane as reactive gases were obtained by triode magnetron sputtering, in order to assess wear and nanoindentation data. A topographical, chemical and microstructural characterization has been conducted using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), wave dispersion spectroscopy (WDS), scanning electron (SEM) and atomic force microscopy (AFM) techniques. Nanoscratch results showed that the groove depth was well correlated to the energy dissipation coefficient of the coatings. On the other hand, a reduction in the coefficient was found when the elastic recovery was increased. (C) 2009 Elsevier B.V. All rights reserved.

High temperature flexural strength and fracture toughness of AlN with Y(2)O(3) ceramic

The effects of temperature on the fast fracture behavior of aluminum nitride with 5 wt% Y(2)O(3) ceramic were investigated. Four-point flexural strength and fracture toughness were measured in air at several temperatures (30-1,300 A degrees C). The flexural strength gradually decreased with the increase of temperature up to 1,000 A degrees C due to the change in the fracture mode from transgranular to intergranular, and then became almost constant up to 1,300 A degrees C. Two main flaw types as fracture origin were identified: small surface flaw and large pores. The volume fraction of the large pores was only 0.01%; however, they limited the strength on about 50% of the specimens. The fracture toughness decreased slightly up to 800 A degrees C controlled by the elastic modulus change, and then decreased significantly at 1,000 A degrees C due to the decrease in the grain-boundary toughness. Above 1,000 A degrees C, the fracture toughness increased significantly, and at 1,300 A degrees C, its value was close to that measured at room temperature.

Instrumented indentation testing of an epoxy adhesive used in automobile body assembling

Instrumented indentation has been used to investigate the mechanical properties of BETAMATE 1496 (R) Epoxy adhesive. The properties of the adhesive were analyzed by measuring its hardness and its Young`s modulus in samples extracted from six different positions of the front door of a commercial passenger vehicle in two phases of processing: after application of the adhesive in the door assembling (""pre-cured"" state) and after final cure in the painting oven (""cured"" state). Special attention was given to setting the optimal parameters (""creep"" time and unloading time step) for the instrumented indentation testing for the present application. Young`s modulus values around 1.1 +/- 0.2 GPa and hardness values around 0.15 +/- 0.05 GPa were obtained for all samples, irrespective of the variation of the indentation parameters in the testing procedure and of the relative position of the adhesive in the door frame in both states. (C) 2008 Elsevier Ltd. All rights reserved.

Electrical and Mechanical Properties of Post-annealed SiC(x)N(y) Films

Amorphous SiC(x)N(y) films have been deposited on (100) Si substrates by RF magnetron sputtering of a SiC target in a variable nitrogen-argon atmosphere. The as-deposited films were submitted to thermal anneling in a furnace under argon atmosphere at 1000 degrees C for 1 hour. Composition and structure of unannealed and annealed samples were investigated by RBS and FTIR. To study the electrical characteristics of SiC(x)N(y) films, Metal-insulator-semiconductor (MIS) structures were fabricated. Elastic modulus and hardness of the films were determined by nanoindentation. The results of these studies showed that nitrogen content and thermal annealing affect the electrical, mechanical and structural properties of SiC(x)N(y) films.

Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress (sigma(r)), the film elastic modulus (E) and the film work hardening exponent (n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of sigma(r). Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only sigma(r). The numerical analyses were also used to further understand the effect of sigma(r) on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio VIE, where Y is the yield strength of the film. In an additional analysis, four ratios (R/h(max)) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and sigma(r) on the indentation load-displacement curves. In this case, or did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by sigma(r) and n. (C) 2010 Elsevier B.V. All rights reserved.

Determination of mechanical properties of PECVD silicon nitride thin films for tunable MEMS Fabry-Pérot optical filters

This paper reports an investigation on techniques for determining elastic modulus and intrinsic stress gradient in plasma-enhanced chemical vapor deposition (PECVD) silicon nitride thin films. The elastic property of the silicon nitride thin films was determined using the nanoindentation method on silicon nitride/silicon bilayer systems. A simple empirical formula was developed to deconvolute the film elastic modulus. The intrinsic stress gradient in the films was determined by using micrometric cantilever beams, cross-membrane structures and mechanical simulation. The deflections of the silicon nitride thin film cantilever beams and cross-membranes caused by in-thickness stress gradients were measured using optical interference microscopy. Finite-element beam models were built to compute the deflection induced by the stress gradient. Matching the deflection computed under a given gradient with that measured experimentally on fabricated samples allows the stress gradient of the PECVD silicon nitride thin films introduced from the fabrication process to be evaluated.

Characterization of mechanical properties of silicon nitride thin films for MEMS devices by nanoindentation

An experimental investigation of mechanical properties of thin films using nanoindentation was reported. Silicon nitride thin films with different thicknesses were deposited using plasma enhanced chemical vapor deposition (PECVD) on Si substrate. Nanoindentation was used to measure their elastic modulus and hardness. The results indicated that for a film/substrate bilayer system, the measured mechanical properties are significantly affected by the substrate properties. Empirical formulas were proposed for deconvoluting the film properties from the measured bilayer properties.

Long-term stability of dentin matrix following treatment with various natural collagen cross-linkers

Objectives: Collagen disorganization is one of the main degradation patterns found in unsuccessful adhesive restorations. The hypothesis of this study was that pretreatment using natural collagen cross-linking agents rich in proanthocyanidin (PA) would improve mechanical properties and stability over time of the dentin collagen and, thus, confer a more resistant and lasting substrate for adhesive restorations. Methods: PA-based extracts, from grape seed (GSE), cocoa seed (CSE), cranberry (CRE), cinnamon (CNE) and acai berry (ACE) were applied over the demineralized dentin. The apparent elastic modulus (E) of the treated dentin collagen was analyzed over a 12 month period. Specimens were immersed in the respective solution and E values were obtained by a micro-flexural test at baseline, 10, 30, 60, 120 and 240 min. Samples were stored in artificial saliva and re-tested after 3, 6 and 12 months. Data was analyzed using ANOVA and Tukey test. Results: GSE and CSE extracts showed a time-dependent effect and were able to improve [240 min (MPa): GSE = 108.96 +/- 56.08: CSE = 59.21 +/- 24.87] and stabilize the E of the organic matrix [12 months (MPa): GSE = 40.91 +/- 19.69; CSE = 42.11 +/- 13.46]. CRE and CNE extracts were able to maintain the E of collagen matrices constant over 12 months [CRE = 11.17 +/- 7.22; CNE = 9.96 +/- 6.11; MPa]. ACE (2.64 +/- 1.22 MPa) and control groups immersed in neat distilled water (1.37 +/- 0.69 MPa) and ethanol-water (0.95 +/- 0.33 MPa) showed no effect over dentin organic matrix and enable their degradation and reduction of mechanical properties. Significance: Some PA-based extracts were capable of improving and stabilizing collagen matrices through exogenous cross-links induction. (C) 2011 Elsevier Ltd. All rights reserved.

Do Low-shrink Composites Reduce Polymerization Shrinkage Effects?

Progress in polymer science has led to continuous reduction of polymerization shrinkage, exemplified by a new generation of ""low-shrink composites"". The common inference that shrinkage stress effects will be reduced in teeth restored with such restoratives with lower shrinkage was tested in extracted human premolars. Mesio-occluso-distal slot-shaped cavities were cut and restored with a conventional (SupremePlus) or low-shrink (RefleXions, Premise, Kalore, and LS) composite (N = 5). We digitized the coronal surfaces before and 10 min after restoration to determine cuspal deflection from the buccal and lingual volume change/area. We also determined the main properties involved (total shrinkage, post-gel shrinkage, degree of conversion, and elastic modulus), as well as microleakage, to verify adequate bonding. It was shown that, due to shrinkage stresses, buccal and lingual surfaces pulled inward after restoration (9-14 microns). Only Kalore and LS resulted in significantly lower tooth deformation (ANOVA/Student-Newman-Keuls post hoc, p = 0.05). The other two low-shrink composites, despite having the lowest and highest total shrinkage values, did not cause significant differences in cuspal deflection. Deflection seemed most related to the combination of post-gel shrinkage and elastic modulus. Therefore, even for significantly lower total shrinkage values, shrinkage stress is not necessarily reduced.

Understanding Contradictory Data in Contraction Stress Tests

The literature shows contradictory results regarding the role of composite shrinkage and elastic modulus as determinants of polymerization stress. The present study aimed at a better understanding of the test mechanics that could explain such divergences among studies. The hypothesis was that the effects of composite shrinkage and elastic modulus on stress depend upon the compliance of the testing system. A commonly used test apparatus was simulated by finite element analysis, with different compliance levels defined by the bonding substrate (steel, glass, composite, or acrylic). Composites with moduli between 1 and 12 GPa and shrinkage values between 0.5% and 6% were modeled. Shrinkage was simulated by thermal analogy. The hypothesis was confirmed. When shrinkage and modulus increased simultaneously, stress increased regardless of the substrate. However, if shrinkage and modulus were inversely related, their magnitudes and interaction with rod material determined the stress response.