Logomarca do periódico: Materials Research

Open-access Materials Research

Publication of: ABM, ABC, ABPol
Area: Engenharias
ISSN printed version: 1516-1439
ISSN online version: 1980-5373
Creative Common - by 4.0

Table of contents

Materials Research, Volume: 17, Issue: 5, Published: 2014

Materials Research, Volume: 17, Issue: 5, Published: 2014

Document list
Documents
Regular Articles
Mechanical performance of concrete with incorporation of coarse waste from the marble industry Martins, Pedro Brito, Jorge de Rosa, Alexandra Pedro, Diogo

Abstract in English:

The waste resulting from marble extraction process is usually disposed of in landfills or dumps and its accumulation is causing serious environmental and landscaping problems. One way of reusing marble waste is to consider its incorporation in structural concrete as a non-primary aggregate. This research work attempts to alleviate the situation and provide information on the mechanical performance of concrete as a function of the replacement ratio of primary aggregates (PA) with coarse waste marble aggregates (CMA). Three concrete families, including reference concrete (RC) mixes, were studied that were made with primary aggregates of basalt (BCA), limestone (LCA) and granite (GCA) (these are the main sources of primary aggregates in the southern and central parts of Portugal), and concrete mixes with replacement ratios of 20%, 50% and 100% of PA by CMA. To evaluate their quality and mechanical performance mixes were tested for: slump (in the Abrams cone test), specific density, compressive strength, splitting tensile strength, Young's modulus of elasticity and resistance to abrasion. The results suggest a tendency for the values of all mechanical properties to decline. However, this tendency is clearly weaker than those observed for the majority of the research involving other types of non-primary recycled aggregates, which are already used in certain proportions in structural concrete, according to the limits imposed by the standards and specifications. The mechanical properties of concrete made with CMA were assessed within the scope of concurrent work also undertaken at Instituto Superior Técnico (Lisbon, Portugal), concerning the durability-related materials of the same type of concrete.
Regular Articles
A characterization for the constitutive relationships of 42CrMo high strength steel by Artificial Neural Network and its application in isothermal deformation Quan, Guo-zheng Liang, Jian-ting Lv, Wen-quan Wu, Dong-sen Liu, Ying-ying Luo, Gui-chang Zhou, Jie

Abstract in English:

In hot working process, the prediction of material constitutive relationship can improve the optimization design process. Recently, the artificial neural network models are considered as a powerful tool to describe the elevated temperature deformation behavior of materials. Based on the experimental data from the isothermal compressions of 42CrMo high strength steel, an artificial neural network (ANN) was trained with standard back-propagation learning algorithm to predict the elevated temperature deformation behavior of 42CrMo steel. The inputs of the ANN model are strain, strain rate and temperature, whereas flow stress is the output. According to the predicted and experimental results, it indicates that the developed ANN model shows a good capacity of modeling complex hot deformation behavior and can accurately tracks the experimental data in a wide temperature range and strain rate range. In addition, the predicted data outside of experimental conditions were obtained, indicating good prediction potentiality of the developed ANN model. The θ -σ curves outside of experimental conditions indicate that the predicted strain-stress curves exhibit a typical dynamic recrystallization softening characteristic of high temperature deformation behavior. Through the coupling of the ANN model and finite element model, the hot compression simulations at the temperature of 1273 K and strain rates of 0.01~10 s-1 were conducted. The results show that the predicted constitutive data outside the experimental conditions successfully improved the prediction accuracy of forming load during the FEM simulation.
Regular Articles
Quenching and partitioning heat treatment in ductile cast irons Silva, Anderson José Saretta Tomaz da Goldenstein, Hélio Guesser, Wilson Luiz Campos, Marcos Flávio de

Abstract in English:

A commercial ductile iron alloy was submitted to a quenching and partitioning heat treatment. Samples were austenitized at 900 ºC for two hours, quenched at 160 ºC and kept at this temperature for 2 minutes and finally were re-heated at temperatures between 300 and 450 ºC during time intervals between 2 and 180 minutes. The microstructural evaluation was performed with SEM and X-ray diffraction and the mechanical properties were measured using tensile strength and Charpy tests. In general, the quenching and partitioning treatment is viable to achieving expressive fractions of retained austenite in ductile cast irons. Generally, higher partitioning temperatures produce a higher fraction of retained austenite after shorter times. This behavior can be explained by the increase on diffusion rate of carbon at higher temperatures. For all tested conditions it was possible to see a well-defined process window and the combination of mechanical properties is very similar to the austempered ductile irons.
Regular Articles
Study of oxide nanoparticles as additives for vegetable lubricants Trajano, Marinalva Ferreira Moura, Edja Iandeyara Freitas Ribeiro, Kandice Suane Barros Alves, Salete Martins

Abstract in English:

Currently, vegetable oils have been studied as biolubricants in order to reach new environmental standards. Besides being non-renewable, mineral oils from petroleum bring consequences to the environment due to its low biodegradability. Thus, the aim of this work is to develop a biolubricant and to add oxide nanoparticles (ZnO and CuO) in order to improve abrasion resistance and friction. This product must be biodegradable and has better performance under boundary lubrication. The methodology consisted of the synthesis of biolubricants using vegetable oils (soybean and sunflower) by epoxidation reaction. The tribological performance was evaluated by HFRR (High Frequency Reciprocating Rig). The developed biolubricants showed good tribological properties besides being more adapted to the environment. Also, it was possible to verify that biolubricants without additives are slightly more tribologically effective than lubricants with additives.
Regular Articles
Laboratory comparison of aging characteristics of warm mix asphalts involving natural and synthetic water containing additives Topal, Ali Dokandari, Peyman Aghazadeh

Abstract in English:

When comparing the aging characteristics of hot and warm mix asphalts from a technical point of view, it can intuitively be expected that a warm mix asphalt would be less subjected to aging-induced failures due to lower application temperatures. Since the side effects of warm asphalt technology should be investigated distinctly. This study addresses the aging investigation of properties of bituminous mixtures containing two (i.e., natural and synthetic zeolite) water based additives available on the market. Within the scope of this study, short- and long-term aging conditions were simulated on mixtures containing various contents of additives as well as on control specimens. The aging indices were determined based on the hardness ratio employing indirect tensile strength values in order to investigate the aging induced failures betide by time. Aging indices showed that the specimens with water containing additives demonstrate relatively better resistance against hardening than conventional hot mix asphalt specimens.
Regular Articles
Effect of phase transformations on hardness in Zn-Al-Cu Alloys Villegas-Cardenas, Jose David Saucedo-Muñoz, Maribel Leticia Lopez-Hirata, Victor Manuel Dorantes-Rosales, Hector Javier Gonzalez-Velazquez, Jorge Luis

Abstract in English:

Sixteen Zn-Al-Cu alloy compositions were prepared by melting pure elements. The as-cast alloys were homogenized at 350 °C for 180 h. Both the as-cast and homogenized alloys were analyzed with X-ray diffractometer and EDX-scanning electron microscope. The Rockwell “B” hardness of both the as-cast and homogenized alloys was determined using the standard procedure. The X-ray diffraction patterns and scanning electron micrographs indicated the presence of several phases in the as-cast alloys. Some of them do not correspond to those shown in the equilibrium Zn-Al-Cu phase diagram at low temperatures. However, the homogenized alloys showed most of the phases predicted by the equilibrium diagram. The hardness of alloys increases with the Cu content because of the presence of Cu-containing phases such as, the θ and τ’ phases in both alloys. The hardness of the homogenized alloys was lower than that of the as-cast alloys as a result of the elimination of the dendritic structure.
Regular Articles
Natural additives for poly (hydroxybutyrate - CO - hydroxyvalerate) - PHBV: effect on mechanical properties and biodegradation Brunel, Daiane Gomes Pachekoski, Wagner Maurício Dalmolin, Carla Agnelli, José Augusto Marcondes

Abstract in English:

In this work, the improvement of mechanical properties in biodegradable materials was obtained through the incorporation of natural and also biodegradable plasticizers and nucleation agents into the PHBV copolymer. PHBV production with different quantities of additives was obtained by extrusion followed by injection. The additives in the copolymer were efficient, resulting in an adequate processing due to the presence of nucleate and an improvement of the mechanical properties of the resulting material provided by the action of the plasticizer. The formulation with the minimum amount of additive content, 5% epoxidized cottonseed oil and 0.1% Licowax, was the most effective showing 35% reduction in the elastic modulus, and 18% in the PHBV crystallinity; 58% increase in impact resistance and 46% increase in elongation. Furthermore, it is important to emphasize that the natural additives were very efficient for biodegradation, showing a mass loss higher of pure PHBV.
Regular Articles
Solvent effect on the morphology of the bee: structure observed by atomic force microscopy on bitumen sample Backx, Bianca Pizzorno Simão, Renata Antoun Dourado, Erico Rodrigues Leite, Leni Figueiredo Mathias

Abstract in English:

The objective of this work was to characterize the asphaltic cement penetration grade 30/45 (CAP 30/45) based on the morphology of nanostructures called "bee" structure observed and its modification when the binder was diluted in heptanes or toluene. The morphology of CAP30/45, toluene and heptane films was studied by Atomic Force Microscopy (AFM) tapping mode and showed typical "bee" structure in asphaltic cement films, but this structure is not visible on the other films. While, toluene completely dissolved the bees, films attacked with heptane still presented some structures left.
Regular Articles
Mechanical properties of castor oil polymer mortars Reis, João Marciano Laredo dos Motta, Eduardo Pereira

Abstract in English:

In the last years, ecological concerns have resulted in the interest to substitute petroleum-based materials by renewable resources-based ones. Natural oils constitute an excellent alternative for the development of natural composites. The aim of this work is to evaluate the use of natural polymer, manufactured from castor oil, as substitute to synthetic, epoxy and polyester, in polymer mortars matrices, with particular regards to compressive, flexural and fracture properties. Mechanical properties of castor oil polymer mortars are similar to epoxy based ones and significantly higher than polyester polymer mortars with improved flexural properties and less brittle failure.
Regular Articles
Mechanical and microstructural characterization of Nodular Cast Iron (NCI) with Niobium Additions Souza, Tânia Nogueira Fonseca Nogueira, Rogéria Alves Perilo Sousa Franco, Francis José Saldanha Aguilar, Maria Teresa Paulino Cetlin, Paulo Roberto

Abstract in English:

Nodular cast irons (NCIs) involve the inoculation and nodulization of 0.03 to 0.06wt% Magnesium, as well as the addition of Molybdenum, Chromium, Nickel, Copper and Vanadium, although the presence of Niobium is not common. The literature reports that Niobium leads to better mechanical properties of the NCIs, and recent results indicate that 0.5wt% Niobium increases the strength and the Charpy notch toughness of NCIs, but decreases its hardness, in relation to a similar NCI without Niobium. The present report studies the addition of 0.23, 0.47, 0.67, and 0.85wt% Niobium to a NCI covering the effects on the microstructures, yield and tensile strengths, tensile elongations and Charpy toughness. The NCIs were prepared in a 120 kg medium frequency induction furnace, and samples were obtained following the ASTM A842 standard; the various test specimens were extracted from these samples according to specific standards for each test. Fracture analysis was performed in fractures specimens after the Charpy tests. It was shown that the volume fraction of pearlite increases as the Niobium content is raised, leading to increments in the yield and tensile strengths and hardness of these materials. Modest increment of tensile ductility and Charpy toughness are observed only for an addition of 0.23% Niobium. Fracture analysis revealed typical brittle cleavage surfaces and decohesion between grains and grain - graphite nodules interfaces, and very low porosity
Regular Articles
Compatibility analyses of BICUVOX.10 as a cathode in yttria-stabilized zirconia electrolytes for usage in solid oxide fuel cells Piva, Roger Honorato Piva, Diógenes Honorato Souza, Marcelo Tramontin Morelli, Márcio Raymundo

Abstract in English:

Copper-substituted bismuth vanadate has been considered a promising material for composite cathodes in SOFC. However, high reactivity of BICUVOX.10 towards the electrolytes still has been its greatest shortcoming. This paper describes reactions between BICUVOX.10 and yttria-stabilized zirconia (YSZ) electrolytes. Secondary phases formed were evaluated by X-ray diffraction, scanning electron microscopy and a.c. impedance spectroscopy. A deleterious interaction between BICUVOX.10 and YSZ was observed, mainly regarding the yttrium depletion from ZrO2 lattice through reaction with VO2.5, resulting in YVO4 phase nucleation and destabilization of the tetragonal and cubic ZrO2 polymorphs to monoclinic. The ZrO2 destabilization and YVO4 nucleation are related phenomena and were interpreted through a theoretical mechanism using charge-compensating dopants description. Thus, these reactions were seen as detrimental to the cathode/electrolyte contact, especially regarding the highly resistive layer formed in the BICUVOX.10/YSZ junction, discouraging further usage of BICUVOX.10 as a cathode in yttria-stabilized zirconia electrolytes.
Regular Articles
Microstructural developments of poly (p-phenylene terephthalamide) fibers during heat treatment process: a review Ahmed, Dawelbeit Hongpeng, Zhong Haijuan, Kong Jing, Liu Yu, Ma Muhuo, Yu

Abstract in English:

Poly (p-phenylene terephthalamide) fibers prepared by wet or dry-jet wet spinning processes have a notable response to very brief heat treatment (seconds) under tension. The modulus of the as-spun fiber can be greatly affected by the heat treatment conditions (temperature, tension and duration). The crystallite orientation and the fiber modulus will increase by this short-term heating under tension. Poly (p-phenylene terephthalamide) fibers have a very high molecular orientation (orientation angle 12-20°). Kevlarï and Twaronï fibers are poly (p-phenylene terephthalamide) fibers. This review reports for PPTA fibers the heat treatment techniques, devices and its process conditions. It reports in details the structural relationships between the fiber properties which are influenced by the heat treatment process. In particular, focused deeply on the effect of the crystal structure and the morphology of the fibers on the mechanical properties of PPTA fibers.
Regular Articles
Evaluation of different methods of cooling-lubrication in cylindrical grinding of advanced ceramic dip Simões, Rafael Plana Bianchi, Eduardo Carlos Oikawa, Marcos Hiroshi Aguiar, Paulo Roberto de Droppa Júnior, Roosevelt Canarim, Rubens Chinali

Abstract in English:

The current work presents a study of alternative methods of cooling-lubrication for the external plunge grinding of advanced ceramics using diamond wheels. These two alternative methods, which are intended to reduce cutting fluid expenses, are commonly referred to as the optimized cooling-lubrication method and minimal quantity of lubrication (MQL). The techniques were evaluated by process monitoring and by the assessment of output variables such as tangential cutting force, G ratio, roundness errors, surface roughness, microstructure and residual stresses measured by X-ray diffraction. The obtained results showed that the two proposed techniques can replace the conventional cooling-lubrication method, i.e., flood coolant. In particular, optimized cooling-lubrication method reduced wheel wear and produced workpieces with the best geometric and dimensional finishes, while MQL significantly reduced the amount of fluid employed in the process without harming the workpiece quality.
Regular Articles
Plasma-spray synthesis and characterization of ti-based nitride and oxide nanogranules Antipas, Georgios S. E.

Abstract in English:

The synthesis of nanosized Ti-based nanogranules via plasma spraying is reported. The synthesis route involved use of both nitrogen and oxygen gases with varying results. In the case of nitrogen, a mixture of titanium nitrides were produced, yielding both the Ti2N and the sub-stoichiometric TiN0.61 compounds. In the case of oxygen, both the stoichiometric rutile and TiO ceramic phases were indexed. Based on EDS analysis, even fractional oxygen concentrations caused tungsten impurities which originated from the cathode electrode. The method yielded particle mass median sizes of the order of 15nm and the smallest particles detected were 5nm.
Regular Articles
Elliptical and circular bonded composite repair under mechanical and thermal loading in aircraft structures Benyahia, Faycal Albedah, Abdulmohsen Bouiadjra, Bel Abbes Bachir

Abstract in English:

In this study, the three-dimensional finite element method is used to achieve a comparison between the semi circular and semi elliptical patch repairs in aircraft structures. The comparison was done by the analysis of : the mechanical and thermal stress intensity factors (SIF and TSIF) at the tip of repaired crack and the distribution of the adhesive stresses for the two patch shapes. The obtained results show that the semi circular shape of the patch presents lower stress intensity factor at the crack tip, which is beneficial for the fatigue life and lower adhesives stresses, which is beneficial for the repair durability. In addition the circular patch is subjected to less significant thermal residual stresses compared to the elliptical shapes.
Regular Articles
2D upper bound analysis of ECAE through 2θ-dies for a range of channel angles Perig, Alexander V.

Abstract in English:

Equal Channel Angular Extrusion (ECAE), sometimes referred to as Equal Channel Angular Pressing (ECAP), is a Severe Plastic Deformation technique. However the energy-power parameters of ECAE have not been fully addressed in previous known publications. The present article is focused on the punching pressure, accumulated plastic strain, and dead metal zone geometry estimation during ECAE of metal workpieces through a 2θ-die with a channel intersection angle of 2θ>0º and 2θ≠90º. Computational analytical results for ECAE technological parameters have been analytically derived for planar flow of a plastic, incompressible, non-hardening metal workpiece in an angular Segal die with 2θ>0º and 2θ≠90º. This is accomplished through the use of an Upper Bound Method (UBM) with Discontinuous Velocity Field (DVF) introduction. The development of the Dead Zone (DZ) for metal ECAE through a 2θ-die with 2θ>0º and 2θ≠90º has been analytically investigated. The obtained computational results for 2θ-die have been compared with the slip line analytic solutions of Segal for non-rectangular 2θ-dies of the same geometry. Good agreement between the two computational results has been found. The physical modeling techniques using plasticine have confirmed the appearance of a dead zone and material flow dynamics during ECAE through the Segal 2θ-die.
Regular Articles
Microstructure and microtexture assessment of delamination phenomena in charpy impact tested specimens Haskel, Hudison Loch Pauletti, Ederson Martins, Juliana de Paula Carvalho, André Luis Moreira de

Abstract in English:

In this article the delamination phenomena, which occurs in the X70 steel during fracture process from the Charpy impact tests, was investigated. Microstructure, microtexture and Taylor factor map analyses were performed by scanning electron microscopy, light microscopy and electron backscatter diffraction, respectively. In a cross-section of two fractured surface regions namely, in the perpendicular and parallel regions to the propagation fracture direction where delamination occurred, it was possible to notice that delamination showed a key role in the anisotropy of impact toughness between the L-T and T-L orientations. The results also revealed that the cause of the delamination can be attributed to the presence of microstructural banding and elongated ferrite grains aligned in a rolling direction. The presence of (100)[011] and (111)[110] crystallographic orientations, with Taylor factors close to 2.7 and 4.5, respectively, were identified in the delamination region. They contribute to the occurrence of cleavage delamination during the fracture process.
Regular Articles
Evaluation of sample temperature and applied power on degradation of stearic acid in inductively coupled radio frequency plasma Farias, Carlos Eduardo Bianchi, José Carlos Oliveira, Paulo Roberto de Borges, Paulo César Bernardelli, Euclides Alexandre Belmonte, Thierry Mafra, Márcio

Abstract in English:

Plasma cleaning is a promising technology in surface treatments, despite technological interest its use is limited because its mechanisms still are not entirely understood. This work aims to evaluate how the applied power of an inductively coupled RF discharge at 13,56 MHz, with Ar and Ar+10%O2 atmospheres, affects its capabilities to etch an organic molecule. Mass variation rate was used as direct characterization of degradation process and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was performed to search for residual molecular modifications. Additionally, optical emission spectroscopy (OES) measurements were performed to monitor the offer of active species in the gaseous volume. In experimental conditions was possible attain mass reduction from sample, with higher mass loss rate when applied power is increased. Material characterization shows the possibility of attain a high etch rate, while no structural modifications were detected, if the temperature is controlled.
Regular Articles
History of development of thermoelectric materials for electric power generation and criteria of their quality Polozine, Alexandre Sirotinskaya, Susanna Schaeffer, Lírio

Abstract in English:

An analysis of results, obtained in the development of thermoelectric materials for electricity generation during the last 130 years, shows that they are comparable to those obtained as early as the nineteenth century. One of the main factors responsible for the stagnation in this area is the use of inappropriate criteria for the evaluation of material quality. The most popular criterion used for this purpose is the Thermoelectric Figure of Merit. The criterion of usefulness proposed in this paper is free of imperfections of the Thermoelectric Figure of Merit and may be considered as alternative to it. The criterion of usefulness shows, among other things, that it is reasonable to develop thermoelectric pairs both with high and relatively low thermoelectric efficiency. Its application would make it possible to avoid the creation of useless materials. This is especially important under conditions of limited research funding.
Regular Articles
Phase transition and elasticity of gallium arsenide under pressure Güler, Emre Güler, Melek

Abstract in English:

Geometry optimization calculations were performed for some structural, elastic and mechanical properties of gallium arsenide (GaAs) under pressures up to 25 GPa. In contrast to previous works, a recent Stillinger-Weber type potential was used for the first time to elaborate the pressure dependence aspects of GaAs. B3→B1 phase transition pressure was determined as 17 GPa. Pressure dependence of density, typical cubic elastic constants, bulk, shear, and Young moduli, Poisson ratio, elastic velocities, anisotropy parameter, Kleinman parameter, elastic anisotropy degree, and stability conditions of GaAs were also evaluated. Overall, our results are satisfactory and can be helpful for future investigations of GaAs under pressure.
Regular Articles
Hot corrosion behavior of monel 400 and AISI 304 dissimilar weldments exposed in the molten salt environment containing Na2SO4 + 60% V2O5 at 600 °C Ramkumar, K. Devendranath Arivazhagan, N. Narayanan, S. Mishra, Debidutta

Abstract in English:

This research work investigates the use of pulsed current for joining two dissimilar metals Monel 400 and AISI 304 using Pulsed Current Gas Tungsten Arc welding using three different filler metals such as ER309L, ERNiCu-7 and ERNiCrFe-3. Microstructure observations showed the presence of Partially Melted Zone (PMZ) at the heat affected zone (HAZ) of all the weldments. The formation of secondary phases was witnessed at the HAZ of Monel 400 on using ERNiCu-7 filler. Tensile studies corroborated that the bimetallic combinations employing ERNiCu-7 offer better tensile properties as compared to ER309L and ERNiCrFe-3 weldments. Parent metal Monel 400 exhibited better corrosion resistance as compared to other zones of the weldments when exposed in the synthetic molten salt environment containing Na2SO4 - 60% V2O5 environment at 600 °C. A detailed structure - property relationship was made using the combined techniques of optical microscopy and SEM. Also the hot corrosion products were revealed using the thermogravimetric plots, XRD and SEM/EDAX analysis.
Regular Articles
Post-consumer polyethylene terephthalate and polyamide 66 blends and corresponding short glass fiber reinforced composites Novello, Marcus Vinicius Carreira, Lilian Gasparelli Canto, Leonardo Bresciani

Abstract in English:

Blends of bottle-grade post-consumer polyethylene terephthalate (PET) and virgin polyamide 66 (PA66), over the complete composition range, and corresponding short glass fiber (SGF) reinforced composites were investigated. These materials were compounded in a twin-screw extruder and injection molded as standard specimens. Morphological investigation of the composites revealed that the short glass fibers have a good size distribution and are homogenously dispersed within a polymeric matrix. The PET/PA66/SGF composites showed good mechanical performance in flexural, tensile and impact tests demonstrating that the addition of SGFs to PET/PA66 blends is an interesting approach to obtaining new thermoplastic composites. In addition, this represents a potential application for post-consumer PET, an abundant and cheap material, in the well-established market of PA66/SGF composites, which are widely used in technical parts requiring high mechanical and thermal properties.
Regular Articles
Influence of radiopacifier additives on calcium aluminate cement properties Oliveira, Ivone Regina de Andrade, Talita Luana de Matsuo, Daniele Coelho Parreira, Renata Martins Jacobovitz, Marcos Pandolfelli, Victor Carlos

Abstract in English:

The aim of this study was to determine the best radiopaque additive to be incorporated to calcium aluminate cement (CAC) to promote radiopacity. Measurements of optical density were carried out on white MTA and CAC with and without additives such as: polymeric dispersant, plasticizer and various radiopacifiers. The effects of the radiopacifying addition on some properties of CAC were also evaluated. The radiopacity value for CAC-Bi2O3 (25%) was higher than the other radiopacifying agents tested. The addition of ZnO (25%) and 15%ZnO:10%Bi2O3 increased the compressive strength of CAC, whereas for Bi2O3 (25%) containing samples the strength was lower than for the CAC. The ZnO (25%) and 15%ZnO:10%Bi2O3 additions also reduced the apparent porosity. CAC does not have sufficient radiopacity to be distinguished from adjacent anatomic structures, such as dental tissues and bone. The addition of 15%ZnO:10%Bi2O3 can be suggested as the most suitable one to obtain the best compromise between good physical and mechanical properties and ideal radiopacity for clinical purposes.
Regular Articles
Study of expanded austenite formed in plasma nitrided AISI 316L samples, using synchrotron radiation diffraction Campos, Marcelo Souza, Sylvio Dionysio de Martinez, Luis Gallego Olzon-Dionysio, Maristela

Abstract in English:

AISI 316L stainless steel samples nitrided at different conditions of temperature and time, showing different properties, such as nitrogen concentration (C N) and nitrided layer thickness, were studied. Expanded austenite (γN) diffraction peaks up to the (222) reflection were observed using suitable wavelength synchrotron radiation. XRD patterns were fitted by Le Bail method, using a special triclinic crystal structure (with a lattice distortion n) for γN, whose peaks were decomposed in a few subpeaks, to consider C N gradient across the nitrided layer. Our results indicate that regarding γN magnetic behavior, which was observed for the samples nitrided at 450 °C, it seems to be correlated not only to high C N (≥31at.%), but also to higher η (≥2.4°), which reaches up to 5.6°. This distortion h decreases when C N increases, consequently, with its minimum close to the surface. On the other hand, for paramagnetic samples (350 °C),η increases up to 1.4° when C N increases up to 30 at.%.
Regular Articles
Combined effect of thermoplastic and thermosetting adhesives on properties of particleboard with rice husk core Kwon, Jin Heon Ayrilmis, Nadir Han, Tae Hyung

Abstract in English:

This study investigated the combined effect of adhesive type and content on the dimensional stability and mechanical properties of three-layer particleboards made from a mixture of wood particles (face layer: 30 wt %) and rice husk particles (core layer: 70 wt %). Two types of thermosetting adhesives, liquid urea-formaldehyde (UF) and phenol-formaldehyde (PF), and thermoplastic adhesive (low density polyethylene: LDPE) powder were used as binder in the experiments. Thickness swelling and water absorption of the particleboards significantly decreased with increasing content of the LDPE powder. The incorporation of LDPE powder into the core layer of particleboard greatly improved the internal bond strength.
Regular Articles
Feasibility of RF Sputtering and PIIID for production of thin films from red mud Antunes, Maria Lúcia Pereira Cruz, Nilson Cristino da Delgado, Adriana de Oliveira Durrant, Steven Frederick Bortoleto, José Roberto Ribeiro Lima, Vivian Faria Santana, Pericles Lopes Caseli, Luciano Rangel, Elidiane Cipriano

Abstract in English:

During the extraction of aluminum from bauxite, a waste of oxides containing traces of heavy metals in a highly alkaline matrix, called Red Mud (RM), is produced. In this study RM is characterized and the feasibility of using it as a precursor for the production of thin films by Plasma Sputtering and by Plasma Immersion Ion Implantation and Deposition (PIIID) is demonstrated. The chemical structure and composition, surface morphology, topography, and wettability of the films prepared using such methodologies were investigated. The films consist mainly of the elements aluminum, silicon, iron and carbon. Infrared spectroscopic analyses reveal the presence of C=O, C-H2, Fe(OH), Al-O and Si-C functionalities. RF Sputtering produced films with smoother surfaces, whereas PIIID produced granular surface structures. Surface contact angle measurements showed that despite the presence of oxides and hydroxides, the films are hydrophobic, thus exhibiting an interesting link between the physical and thermodynamical properties.
Regular Articles
Prediction of Friction Stir Welding defect-free joints of AISI 304 austenitic stainless steel through axial force profile understanding Plaine, Athos Henrique Alcântara, Nelson Guedes de

Abstract in English:

Friction Stir Welding (FSW) joints of AISI 304 austenitic stainless steel (304 SS) using position controlled mode were investigated in order to understand and relate axial force behavior to welding quality. Joints were produced using two tools and four combinations of specific parameters. The results showed coherence between the axial force profiles and the low-magnification overviews of the welded joints. For defect-free joints, only a natural oscillation on axial force occurred after tool plunge. In contrast, abnormal or abrupt oscillations were directly associated with common welding defects, such as voids and nugget collapse.
Regular Articles
Analysis of thin bifacial silicon solar cells with locally diffused and selective back surface field Moehlecke, Adriano Osório, Vanessa da Conceição Zanesco, Izete

Abstract in English:

The aim of this work is to present the development and comparison of thin n+pp+ industrial bifacial silicon solar cells produced with the local screen-printed Al back surface field (BSF) to those with the selective BSF doped with aluminum-boron. To produce solar cells with selective BSF, the boron diffusion based on spin-on dopant was introduced in the process sequence. The thin SiO2 layer (10 nm) thermally grown did not produce good passivation on the rear face and wafers were contaminated during aluminum diffusion in the belt furnace. The implementation of selectively doped BSF improved the efficiency by reflecting minority charge carriers and the wafer contamination by belt furnace was compensated by boron diffusion. The bifacial solar cells with B-Al selective BSF achieved an efficiency of 13.7% / 8.9% (front / rear illumination) and presented lower sensitivity to the belt furnace processing and to the quality of the rear surface passivation.
Regular Articles
Effects of post weld heat treatments on the microstructure and mechanical properties of dissimilar weld of supermartensític stainless steel Tavares, Sérgio Souto Maior Rodrigues, Clóvis Ribeiro Pardal, Juan Manuel Barbosa, Edvan da Silva Abreu, Hamilton Ferreira Gomes de

Abstract in English:

A supermartensitic stainless steel with composition 12.2%Cr-5.8%Ni-1.90%Mo-0.028%C (%wt.) was welded by gas tungsten arc welding (GTAW) with superduplex stainless steel filler metal. Post weld heat treatments (PWHT) at 650 ºC for different periods of time were performed in order to decrease the hardness in the heat affected zone (HAZ). This paper deals with the effect of these heat treatments on the microstructure and mechanical properties of the joint. Mechanical strength of the weld joint was slightly inferior to the base metal, but was not affected by heat treatments. Precipitation of intermetallic phases in the weld metal (WM) due to prolonged PWHT was detected by scanning electron microscopy. The impact toughness of the weld metal decreased with the increase of time of heat treatment, due to intermetallic precipitation. However, even in the specimen treated for 1h, the Charpy energy remained above 27J at -46 ºC. It was found that optimum mechanical properties can be obtained with heat treatment for 30 minutes at 650 ºC.
Regular Articles
A model for evaluation of effective thermal conductivity of periodic composites with poorly conducting interfaces Escarpini Filho, Romildo dos Santos Marques, Severino Pereira Cavalcanti

Abstract in English:

This paper presents a new micromechanical extension of the parametric finite-volume theory for evaluation of effective thermal conductivities of periodic unidirectional fiber reinforced composites. Such materials are assumed as composed of repeating unit cells with arbitrary internal architectural arrangements of fiber coated by thin interphase with low thermal conductivity. The parametric homogenization approach uses quadrilateral subvolumes for discretization of the repeating unit cell microstructure, thereby allowing an efficient modeling of the details of fibers with arbitrarily shaped cross sections. The interphases are replaced by imperfect interface elements with continuity in normal heat flux and discontinuity in temperature. The performance of the homogenization model is demonstrated for several numerical examples, including two-and three-phase composites with regular squared and hexagonal arrays of fibers. The ability of the model to accurately predict the effective thermal conductivity of those composites is demonstrated by means of comparisons of results obtained using finite-element and analytical solutions.
Regular Articles
Abrasive blasting contamination in Super Duplex and carbon steels - a quantification approach by rietveld analysis Rocha, Adriana da Cunha Nascimento, Áquila Vieira do Margarit-Mattos, Isabel Cristina Pereira Assis, Kioshy dos Santos Mattos, Oscar Rosa

Abstract in English:

A methodology for quantifying the contamination after abrasive blasting by Aluminum Oxide and Martensitic Carbon Steel particles in Super Duplex and Carbon Steel substrates has been developed. The method consisted of performing x-ray diffraction in the blasted steel substrates and calculating the particle contamination using Rietveld Quantitative Method. In this way, it is possible to evaluate the substrate volume in which the abrasive particles have been trapped (taking into account the surface roughness) rather than solely performing visual examination, as indicated by standards documents. Equations describing the intensity model of the diffracted peaks as well as those describing the quantitative measurements are presented. Correction functions are also employed to compensate the effect of the surface roughness generated on the metallic substrates after blasting. Alumina and martensitic steel abrasives contaminations were detected and quantified in both steel substrates. Results showed that Super Duplex Steel substrates revealed a higher degree of contamination when compared to the Carbon Steel substrates, both for alumina abrasives as for martensitic abrasives. Also, the abrasive that generated the lower degree of contamination was the Martensitic Carbon Steel, for both substrates.
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