Scielo RSS <![CDATA[Materials Research]]> vol. 20 num. lang. en <![CDATA[SciELO Logo]]> <![CDATA[Editorial]]> <![CDATA[Microstructure and Hardness Evolution in Magnesium Processed by HPT]]> High pressure torsion provides an opportunity to process materials with low formability such as magnesium at room temperature. The present work shows the microstructure evolution in commercially pure magnesium processed using a pressure of 6.0 GPa up to 10 turns of rotation. The microstructure evolution is evaluated using electron microscopy and the hardness is determined using dynamic hardness testing. The results show that the grain refinement mechanism in this material differs from materials with b.c.c. and f.c.c. structures. The mechanism of grain refinement observed at high temperatures also applies at room temperature. The hardness distribution is heterogeneous along the longitudinal section of the discs and is not affected by the amount of deformation imposed to the material. <![CDATA[Surface Modification of Ti6Al4V Alloy by Pulsed Lasers: Microstructure and Hydrophobic Behavior]]> In many aerospace applications, it is important to produce hydro-repellent surfaces because water and ice accumulation could lead to malfunctioning of the part or component with a potential critical failure. In this study, it was investigated the texturing of a titanium alloy (Ti6Al4V) by applying a pulsed Nd:YAG laser, aimed at the surface characterization by microscopy, X-ray diffraction, roughness and nano-indentation tests as well as free fall drop test. The experimental procedure aimed to understand the influence of three variables: (N) the number of laser runs 1, 2, 5 and 10; (V) laser speeds of 25, 50 and 100 cm/s and (P) laser power of 5, 10 and 20 W on the microstructure and the hydrophobic behavior. The Vickers hardness and elastic modulus of laser processed surfaces were similar to the untreated surfaces. When the number of the laser runs (N) increased, a TiO phase amount increases as a result of increasing heat input. The measured roughnesses decreased with increasing P as a direct result of remelting. As the number of runs (N) increases the surface became more and more flat, consequently the overlapping runs induced polishing of the titanium surfaces. The mean roughness Ra attained 0.23 µm after 10 runs at V=100m/s and P=10W, compared to Ra=0.41 µm of the virgin surface. The water repellent conditions were N1V50P05, N1V100P05, N2V25P05, N2V50P05, N5V25P05, N5V50P05, N5V100P10 and N10V25P10. These conditions were associated with a homogeneous remelted layer, low power, partial superposition of the laser shots of 50% or 75%, and a surface finish slightly rougher than the original material. <![CDATA[Complete Band Gaps in Nano-Piezoelectric Phononic Crystals]]> We study the band structure of elastic waves propagating in a nano-piezoelectric phononic crystal consisting of a polymeric matrix reinforced by BaTiO3 inclusions in square, rectangular, triangular, honeycomb and Kagomé lattices. We also investigate the influence of inclusion cross section geometry - circular, hollow circular, square and rotated square with a 45º angle of rotation with respect to x and y axes. Plane wave expansion method is used to solve the governing equations of motion of a piezoelectric solid based on classical elasticity theory, ignoring nanoscopic size effects, considering two-dimensional periodicity and wave propagation in the xy plane. Complete band gaps between XY and Z modes are observed for all inclusions and the best performance is for circular inclusion in a triangular lattice. Piezoelectricity influences significantly the band gaps for hollow circular inclusion in lower frequencies. We suggest that nano-piezoelectric phononic crystals are feasible for elastic vibration management in GHz. <![CDATA[Examining the Thermal Stability of an Al-Mg-Sc Alloy Processed by High-Pressure Torsion]]> An Al-3%Mg-0.2%Sc alloy was solution treated and subjected to 10 turns of high-pressure torsion (HPT). Thereafter, the HPT-processed material was annealed for 1 hour at temperatures ranging from 423 to 773 K and its mechanical properties and microstructural evolution were examined using microhardness measurements and EBSD analysis. The results demonstrate that the Al-Mg-Sc alloy exhibits an average microhardness of ~190 Hv and an average grain size of ~140 nm immediately after HPT processing and also after further annealing at 423 K. Conversely, it is shown that annealing at temperatures above 473 K leads to a substantial decrease in the hardness values as well as a sharp increase in the grain size of the material previously processed by HPT. In addition, detailed EBSD analysis revealed the formation of a bi-modal distribution of grains after annealing at temperatures from 623 to 773 K, and this becomes more uniform with increasing temperatures. <![CDATA[Using Severe Plastic Deformation to Fabricate Strong Metal Matrix Composites]]> The processing of bulk metals through the application of severe plastic deformation leads to significant grain refinement and a consequent strengthening of the material. High-pressure torsion (HPT) generally refers to the processing of disk samples and this technique is especially effective in producing extremely small grains. Recently, new experiments were conducted in which disks of two different alloys, based on aluminum and magnesium, were stacked together and then processed by HPT for up to 20 turns at room temperature. Analysis after processing revealed the formation of a multi-layered structure in the central region of the disks but with a true nanoscale microstructure containing different types of intermetallic compounds within an Al matrix leading to the formation of metal matrix nanocomposites at the disk edges. Measurements showed a lowering of density at the disk edges, thereby confirming the potential for using HPT to fabricate materials with exceptionally high strength-to-weight ratios. <![CDATA[Optical Properties of Blown Films of PA6/MMT Nanocomposites]]> In this work blown films of polyamide 6 (PA6) nanocomposites were produced at different processing conditions, with the addition of montmorillonite (MMT), pure and surface modified by an organic salt. The films' optical properties were evaluated according to ASTM D-1003 and the results correlated with the degree of crystallinity, nanoparticle's dispersion state and processing conditions. It was observed that the thinner the film, the lower the haze and higher the clarity, due to the presence of less internal scattering structures in the direction of the incident light. The PA6 films with the unmodified MMT had the lowest clarity values, due to nanoparticles' agglomeration. The organic modification of the montmorillonite led to its exfoliating through the PA6 matrix, resulting in an optimization of the films' optical properties (decreased haze and increased clarity) when compared to the pure PA6 films. <![CDATA[Severe Plastic Deformation and Additive Distribution in Mg-Fe to Improve Hydrogen Storage Properties]]> Magnesium (Mg) is a light metal with relatively low cost. Its hydride (MgH2) is interesting for the safe hydrogen storage in solid state and has a high gravimetric capacity of 7.6%. Practical application of Mg is still hampered by high reaction temperatures and slow kinetics. In order to improve it and focus on more viable industrial processing conditions, Mg plates, with or without iron (Fe) addition, in the form of wires and powders, were submitted to severe plastic deformation (SPD) in air, starting with extensive cold rolling (ECR), followed by repetitive rolling (ARB). The samples were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning (SEM) and transmission electron microscopy (TEM). H2 storage properties were evaluated by differential scanning calorimetry (DSC) and Sievert's volumetric method. Mg processed by ECR+ARB resulted in larger grain refinement and densities of cracks than ECR. In addition, Fe in the form of continuous wires was fragmented and resulted in a better distribution of particles than powders, which agglomerated. Thus, finally, the synergetic effect of microstructural features and Fe as catalyst and its distribution improved activation, kinetics and hydrogen storage capacity. <![CDATA[Assessing Collaboration and Knowledge Flow on Coatings of Metallic Glasses Obtained From Thermal Spraying Processes Using Bibliometrics and Science Mapping]]> Coatings of amorphous metallic alloys can be obtained using different thermal spraying processes, such as HVOF, plasma spraying, cold spraying and others. Although many studies focused on investigating scientific issues concerning apply amorphous metallic coatings using thermal spraying, less attention have been paid to evaluate how research institutes and companies are collaborating and influencing each other to promote new technologies. In this paper, we assessed the collaboration of organizations and the knowledge flow on this relatively new field using bibliometrics and science mapping. The method relies on scientific publications indexed in Web of Science and clustered into research areas using the CWTS Publication-level Classification System. These results provide useful insights about how players are organized and may be used in the context of R&amp;D management, science policy and decision making. <![CDATA[Study of the Young's Modulus in Microstructures through the Resonance Frequency Technique for Applications in Commercial CMOS Processes]]> The companies that manufacture devices with techniques inherited from microelectronics, called foundries, generally provide the electrical characteristics of the layers of their manufacturing processes, but they do not provide the mechanical parameters, which prevents the mechanical optimization of any design used in this manufacturing. Thus, the extraction of mechanical properties from the layers of a commercial process is important and it requires specific techniques and microstructures for this purpose. This work presents a study on the Young's modulus of cooper thin films using the resonance frequency technique to extract this parameter. The microstructures used for the application of the technique are cooper cantilevers with lengths of 100-700 µm, width 40 µm and thickness 2 µm suspended in such a way that it is possible to measure their resonant frequency. These structures are also simulated using the finite element method. The experimental results are compared with the simulations and presented equivalence. <![CDATA[Hydrogen Uptake Enhancement by the Use of a Magnesium Hydride and Carbon Nanotubes Mixture]]> Studies show that the carbon nanotubes (CNTs) serve as hydrogen diffusion channels, when used with magnesium hydride. The hydrogen sorption study, of a MgH2 and 5wt% of multiwalled carbon nanotubes mixture, was the main purpose of this work. The samples were analyzed by means of X-ray diffraction (XRD) and also studied in a differential scanning calorimeter (DSC). The carbon nanotubes, that were ball milled during 20 min to the MgH2, were observed in the scanning electron microscopy (SEM) images. The mixture of MgH2-CNT turned out to enhance the hydrogen sorption when compared to pure MgH2 and in 5 min it desorbed around 5 wt% of hydrogen, at 350oC and 0.1 bar. <![CDATA[Thermal Spraying Processes and Amorphous Alloys: Macro-Indicators of Patent Activity]]> Thermal spraying processes allows high cooling rates and can favor the formation of amorphous microstructures. Amorphous metallic coatings can result in superior mechanical and functional properties. To follow new technological development and innovation paths, indicators based on patent data can be assembled to support technological forecasting assessments and decision making. This study mapped the technological development on amorphous alloys processed by thermal spraying using patent indicators from documents indexed in the Derwent Innovations Index database between the years 1997 and 2014. We evaluate the patent activity, the role of countries, the main technological subdomains and markets of interest, as well as the main metallic alloys explored as coating. We conclude that new technological developments should be expected in near future and these advances both in amorphous alloys and thermal spraying shall be constantly monitored in the coming years. <![CDATA[Production of TiO<sub>2</sub> Coated Multiwall Carbon Nanotubes by the Sol-Gel Technique]]> In recent years, efforts in developing high strength-low density materials are increasing significantly. One of the promising materials to attend this demand is the carbon nanotube (CNT), to be used mainly as a reinforcing phase in lightweight metal matrix composites (MMC). In the present work, the sol-gel technique has been employed to obtain TiO2 coating on the surface of commercial multiwall carbon nanotubes (MWCNT). The aim of such coating is to improve the thermal stability of MWCNT in oxidize environment, which is necessary in most of MMC processing routes. Calcination in inert atmosphere was performed in order to crystallize a stable coating phase. The hybrid CNT/TiO2 nanocomposite was characterized by X-Ray Diffractometry (XRD), Raman spectroscopy, Thermogravimetry (TGA) and Field Emission Gun - Scanning Electron Microscopy (FEG-SEM). The coating structure was observed to change from anatase to rutile, as the calcination temperature increases from 500 to 1000°C. Results from thermogravimetric analysis showed that the samples calcined at 1000 ºC were more resistant to oxidation at high temperatures. <![CDATA[Aqueous Nanofluids Based on Copper MPA: Synthesis and Characterization]]> The application and use of efficient cooling fluids have become increasingly important due to the increasing industrial and energy demand associated with the miniaturization of various electronic devices. The search for high-efficiency heat exchanger fluids in the early 1990s led to the development of a new class of refrigerants called nanofluids. The use of nanofluids is linked to obtaining stable colloidal dispersions which exhibit high thermal conductivity. For this purpose, the efficiency of a nanofluid will depend on the type of fluid used and the dispersed nanomaterial. In this work, a stable aqueous nanofluid based on mercaptopropionic acid-coated copper sulfide nanoparticles (Cu2S/MPA), synthesized by the chemical reduction method, was developed. The nanofluid presented colloidal stability in alkaline medium and an average increase of 36% in thermal conductivity for a volumetric fraction of 0.05%. <![CDATA[Influence of Nanoxides on Diffusivity and Solubility of Hydrogen in Pd-based alloys]]> The hydrogen interaction in palladium alloys with addition of Ce, Zr and Y was studied. These alloys are produced by arc-melting and then cold rolled into thin foils. Heat treatment at 800ºC for 24h in air atmosphere is applied to induce internal oxidation. Hydrogen permeation tests and TDS (Thermal Desorption Spectroscopy) are carried out to evaluate hydrogen interaction with three different microstructures which can be characterized by dislocations, substitutional atoms and nanoxides. For alloys argon annealed, Ce is the element that delays the most hydrogen diffusion, followed by Zr and Y. However alloys with yttrium nanoxides exhibit the highest solubility and the smallest diffusivity due to their small size, spherical shape and dispersion throughout the matrix. Analyzing TDS curves, it is shown that nanoxides are irreversible traps that improve hydrogen stored on palladium alloys. Dislocations and impurity atom on solid solution have little binding energy that detraps hydrogen at smaller temperatures. <![CDATA[Coagulation Bath in The Production of Membranes of Nanocomposites Polyamide 6/Clay]]> Membranes of polyamide 6 and its nanocomposites with 3 and 5% of clay were obtained by the phase inversion method using distilled water and solvent as the coagulation bath, 10 and 30% of acid was used, in order to change the membranes morphology/porosity. By XRD analysis, the obtained nanocomposites showed an exfoliated and/or partially exfoliated structure, it was also seen two characteristics peaks of the polyamide 6 phases (α and γ). For the membranes, the characteristic peak γ of the membrane disappeared, being evident the peaks α1 and α2. By SEM the PA6 membrane almost doesn't have pores in its surface, with an addition of clay had an increase in the quantity of surface pores. In the cross section of the PA6 membrane, an extremely thin selective layer, adding the clay the selective layer became thicker and a better defined porous support was obtained. From the acid in the coagulation bath the PA6 membrane continued with a few pores structure. For the nanocomposites there was an increase in size and a better uniformity of the pores. In the cross section the presence of the bath decrease the membrane filtering, also modifying a uniformity of the pores. <![CDATA[Improvement of Titanium Corrosion Resistance by Coating with Poly-Caprolactone and Poly-Caprolactone/Titanium Dioxide: Potential Application in Heart Valves]]> Heart diseases affect part of world population and generally involves the functioning of valves. Valves replacement is the most common treatment and the choice between synthetic or natural/biological implants depends on several factors. Synthetic implants have greater durability, whereas biological ones are more biocompatible. This work proposes the use of polymeric coating on titanium metal surface to increase implant biocompatibility. Poly-caprolactone (PCL) has demonstrated greater efficacy for biomedical applications due to its biocompatibility. It can easily form films and coat surfaces. Titanium discs were submitted to alkaline and thermal treatments and coated with 1%PCL and 1%PCL+TiO2. For both conditions, PCL crystals were found in titanium coated surface (SEM and EDX) and X-ray diffractogram confirmed PCL coating. Infrared Spectroscopy spectra showed both PCL and TiO2 characteristic peaks. Moreover, corrosion resistance of coated disc has considerably increased, proving the effectiveness of PCL as coating material and its potential application in cardiac valves. <![CDATA[Experimental Multi-scale analysis of Carbon/Epoxy Composites Nano-Reinforced by Carbon Nanotubes/Multi-layer Graphene]]> Nano-size structures, nanotubes/multi-layer graphene (CNT/MLG), were dispersed into epoxy system by a combination of sonication and high shear mixing. To avoid CNT/MLG agglomeration, a non-covalent functionalization were performed using surfactants, CO890 - Polyoxyethylene (40) nonylphenyl ether and SDBS - sodium dodecyl benzene sulfonate. Raman spectroscopy and Fourier transformed Infra-red analysis indicated that CO890-MLG and SDBS-CNT have strong chemical interactions. Atomic force microscopy revealed formation of "spike-like" nanostructures for SDBS-CNT combination and "wall-like" nano-shape structures for the CO890-MLG ones. Tensile tests data indicate no significant change on stiffness. In average, the ultimate stress increased around 18%, while toughness had an improvement close to 62%. SDBS-CNT and CO890-MLG at small concentrations (0.075 wt. %) are probably the best options for nano-reinforcement of carbon/epoxy composites. <![CDATA[The Carbon Nanotubes Effect into Single-lap Joint Failure Modes and Load Capacity: a Macromechanical Analysis]]> This study investigates the influence of the adhesive (epoxy resin) thickness and the dispersions of non-functionalized carbon based nanostructures (carbon nanotubes - CNT) on mechanical properties of single-lap bonded joints. To achieve this goal, three CNT concentrations (0.5%, 1.0% and 2.0% m/m); and three different bondline thicknesses (0.05 mm, 0.15 mm and 0.40 mm) were evaluated. The mechanical properties were measured using the apparent shear tensile test, based on ASTM D5868. The results showed that the addition of 1.0 wt% CNTs improved the interface strength, leading to an increase on delaminated areas in failure region up to 55.36% and also improving the peak force up to 13.85%. Decrease in adhesive thickness from 0.40 mm to 0.05 mm promoted a stress redistribution inside adhesive layer improving the peak force up to 13.91%. CNT seems to promote changes in failure modes, light fiber tear (LFT) failure significantly increases up to 45.96%, indicating that interface strength between adhesive and adherent was improved. <![CDATA[Effects of Local Heat Input Conditions on the Thermophysical Properties of Super Duplex Stainless Steels (SDSS)]]> The properties of the super duplex stainless steels (SDSS) are strongly affected by the thermal history imposed by welding procedures. The controlled dual phase microstructure (ferrite and austenite) guarantee excellent mechanical properties such as mechanical strength and corrosion resistance, in addition to small thermal expansion coefficient and high thermal conductivity. In this paper, we newly proposed a model able to predict the thermal history of the welding pieces coupled with local mechanical properties developed during welding procedure that combine the effects of temperature and phase changes during welding. We applied inverse method to fit the thermophysical parameters based on measured data. The model was verified by comparing measured and predicted temperature profiles using thermocouples located within the heat affected zone. Thus, an inverse method was implemented to obtain the parameters fitting for the grain growth evolution compatible with the final microstructure and grain size measured using SEM images and stereological techniques. We demonstrated that very small amount of non-equilibrium deleterious phases and nanosized precipitated are expected during the welding procedures depending upon the local conditions of temperature, compositions and alloying dilution evolutions.