RESUMEN Los clásicos mecanismos de deformación basados en defectos de los policristales metálicos no son adecuados para describir el comportamiento mecánico de los materiales metálicos vítreos y nanocristalinos. Su complejidad inherente crea un verdadero desafío para comprender sus complicados fenómenos físicos. El uso de la dinámica molecular (DM) se torna interesante permitiendo evaluar la relación entre la estructura atómica con las propiedades mecánicas. En el presente trabajo, simulaciones de DM fueran utilizadas para estudiar los mecanismos de deformación a nivel de nanoescala de la aleación Al80Ti15Ni5. Los resultados revelaron una dependencia significativa entre el módulo de Young y la estructura atómica. El tipo de estructura a escala atómica, nanocristalina o amorfa, gobierna los mecanismos de la deformación. Para la aleación nanocristalina, el deslizamiento y la difusión del contorno de grano parecen ser los procesos dominantes en la deformación. Además, se observan emisiones de discordancias parciales en los contornos de grano. En el material amorfo, las zonas de transformación por cizallamiento comienzan a formarse en el régimen elástico y se convierten en bandas de cizallamiento actuando como los principales mecanismos en el proceso de deformación. Los resultados indican que las propiedades mecánicas de la estructura amorfa representan un caso límite inferior del nanocristal. Los módulos elásticos determinados en la aleación Al80Ti15Ni5 son muy bajos, por esta razón se evaluaron los efectos de los potenciales interatómicos unarios y ternarios para cada elemento.

ABSTRACT Classical deformation mechanisms based on crystalline defects of metallic polycrystals are not entirely suitable to describe the mechanical behavior of nanocrystalline and glassy materials. Their inherent complexity creates a real challenge to understand the acting physical phenomena. Thus, the molecular dynamics approach becomes interesting because it allows evaluating the mechanical properties and its related atomic structure. To study the atomic structure's influence on the deformation mechanisms at the nanoscale level of the Al80Ti15Ni5 alloy, molecular dynamics simulations, and post-processing techniques were used in the present work. The results revealed a significant dependency between the Young modulus and the atomic structure. Moreover, the type of structure, i.e., nanocrystalline or amorphous, governs the deformation mechanism type. For the nanocrystalline alloy, grain boundary sliding and diffusion seem to be the dominant deformation processes followed by the less essential emissions of partial dislocations from the grain boundaries. Concerning the amorphous material, the shear transformation zones begin to form in the elastic regime evolving to shear bands, these being the main mechanisms involved in the deformation process. The results also indicate the amorphous structure as a lower limit-case of the nanocrystal. The Al80Ti15Ni5 elastic moduli values were below expectations; for this reason, the effects of unary and ternary interatomic potentials were evaluated for each element.

ABSTRACT Mechanical components and structures wear out as a result of friction between surfaces in relative motion. Residual stresses play an important role for the tribological performance of components since compressive residual stresses yield positive effects on wear resistance. However, the real effect of residual stresses on the tribological performance of surfaces is not entirely clear. The objective of this work is to evaluate the residual stress behavior during a pin-on-disk wear test of quenched and tempered AISI 4340 disk specimens against a counter-body of steel AISI E 52100. Tests were performed in shot peened and non-shot peened specimens in six steps and residual stresses were evaluated after each one by X-ray diffraction technique using sin2y method. The results shown that wear rate of the shot peened specimens was approximately fifty percent lower. Shot peening induced compressive residual stresses contributed to this effect even though they were modified during the pin-on-disk test.

Duplex stainless steels (DSS) are corrosion resistant alloys largely used in chemical and petrochemical industries. Some commercial DSS contain 0.5-1.0% copper addition to improve the corrosion resistance by reducing the corrosion rate in non-oxidizing environments. Higher copper addition (≥ 2%) can also hard by precipitation, especially when fine copper precipitates (ε phase) are produced. In this work, a cast copper alloyed DSS type ASTM A890 grade 1B with 3.01%Cu was investigated. Different levels of hardness were produced by solution treatment and aging at 450, 500, 550 and 600 oC for periods of time up to 1 hour. The corrosion resistance of aged DSS was evaluated by electrochemical tests in three media: 0.6 mol/L NaCl, 0.3 mol/L H2SO4 and 0.6 mol/L NaCl + 0.3 mol/L H2SO4 solutions. The results indicate that the effect of Cu addition depends on the media studied. Polarization studies in 0.6 mol/L NaCl showed a small anodic current peak occurred at around 400 mV vs. Ag/AgCl, with a strong influence on the passive film stability. Additionally, chronoamperometric measurements at 400 mV vs. Ag/AgCl showed a high electrochemical activity for the samples in 0.6 mol/L NaCl.

RESUMO A simulação em Dinâmica Molecular (MD) é uma poderosa ferramenta para estudo de ligas amorfas nanométricas. Neste artigo, a MD foi empregada para o estudo da liga Ni80Cu20. As simulações foram realizadas com o código livre LAMMPS, em um sistema contendo 2.000 átomos com interação atômica dada pelo potencial de Finnis-Sinclair (EAM-FS). O aquecimento foi realizado à taxa de 2 K/ps, entretanto, no resfriamento foram utilizadas as taxas de 40, 10, 4, 3, 2 e 1 K/ps, com a finalidade de se observar a evolução estrutural da liga. Taxas superiores a 3 K/ps conduzem à formação de estrutura amorfa. Por outro lado, taxas inferiores a esta permitem ao sistema formar uma estrutura cristalina Cúbica de Face Centrada (CFC). A estrutura da liga foi analisada empregando-se Funções de Distribuição Radial (RDF), os poliedros de Voronoi, e Common Neighbor Analysis (CNA). Além disto, foram realizados estudos de tratamento térmico tanto em modo dinâmico à taxa de resfriamento de 40 K/ps como isotérmico com a finalidade de observar a cristalização da liga amorfa. A curva tensão vs deformação indica que a presença de 20 % de nanocristais eleva a resistência mecânica sem afetar o módulo elástico. Com esta fração, que se forma por efeito do tratamento térmico, o limite de resistência é aumentado em mais de 30 %.

ABSTRACT Molecular Dynamics (MD) is a powerful tool for the study of nanometric amorphous alloys. In the present work, MD was used to investigate the Ni80Cu20 alloy. The simulations were performed by using the free code LAMMPS, for a system containing 2,000 atoms. The atomic interaction was governed by Finnis-Sinclair (EAM-FS) potential. The heating was controlled by a rate 2 K/ps, however, the cooling stage used the following rates 40, 10, 4, 3, 2 and 1 K/ps, in order to observe the structural evolution of the alloy. Rates higher than 3 K/ps produce an amorphous structure. On the other hand, lower rates allow the formation of Cubic Face Centered (CFC) crystals. The alloy structure was analyzed by Radial Distribution Function (RDF), Voronoi polyhedrons, and Common Neighbor Analysis (CNA). Moreover, studies on the heat treatment with cooling rate at 40 K/ps as well as isothermal condition were performed to know the crystallization process of glassy alloy. The stress-strain curve indicates the presence of 20 % of nanocrystal increases the mechanical resistance without jeopardizing the elastic modulus. This fraction, resulting of heat treatment, increases the ultimate tensile strength at least 30 %.

This paper presents the results of Molecular Dynamics (MD) simulations of Cu60.0Zr32.5Ti7.5 alloy through the open source code LAMMPS. Amorphous samples were produced by quenching the molten metal from 2300 to 300 K. The pair distribution functions of the liquid and solid were calculated. Moreover, the atomic short-range order at 800, 700 and 300 K was obtained by using the Voronoi tesselation method. Cu-centered icosahedral clusters were the prevailing configuration. The tensile stress-strain curve showed that the material present plastic deformation, however, shear bands were not observed in the MD simulation. The evolution of viscosity in temperatures higher than its glass transition temperature was also determined. Furthermore, the fragility of the alloy at glass temperature was evaluated.

The use of eco-friendly corrosion inhibitors in metallurgical processing has increased interest due to the reduced environmental impact. Hence, the inhibitory effect of Aniba canelilla (Lauraceae) extract was studied in the corrosion of carbon steel in 1.0 mol∙L-1 hydrochloric acid solution. This acid is used during the surface treatment of steel processing. The carbon steel protection was observed by varying the extract concentration from 50 to 300 mg∙L-1. Polarization curves revealed that this extract acted as an adsorption inhibitor decreasing both anodic and cathodic current densities. A relatively high inhibition corrosion efficiency, close to 97%, was obtained with plant stem extracts by gravimetric measurements. Weight loss measurements showed that the extract remains active for at least 72 hours at room temperature. The adsorption process of this extract is properly represented by the Langmuir isotherm. Atomic force microscopy shows that inhibited acid medium produces a smooth surface.

Heat treatment can modify the corrosion resistance of stainless steels. Thus, the corrosion behavior of ASTM A890/A 890M GR 5A super duplex stainless steels (SDSS) has been investigated in aqueous 60,000 ppm NaCl solution by several electrochemical tests. The specimens were aged for 2, 10, 50 and 100 hours at 475 ºC. Potentiodynamic polarization studies showed that, when the corrosion potential comes to the passivation state, a peak current is detected at about 400 mV vs. Ag/AgCl, with a strong influence on the film stability. The peak current value increased with the aging time; the highest peak value was for the sample aged for 100 h. Three potentials were chosen from the polarization curves in order to evaluate the sample/film/solution behavior and their changes over the passivation range. The results indicate that the passive film was degraded with the increase of the aging time. In addition, the results of the corrosion tests were compared with the evolution of the mechanical properties of the steels by the Vickers microhardness test.

Hydrogen embrittlement is a phenomenon that affects the performance of steel used for oil and gas pipelines. This paper presents a study of the effect of hydrogenation on the residual stresses of an API 5L X65 steel pipe. Residual stresses were analyzed by X-ray diffraction technique using the sin2Ψ method. The hydrogenation of base metal and welded joint specimens was performed by electrochemical tests in a simulated soil solution NS4. Results show that the hydrogenation led to significant changes in residual stress configuration and in the mechanical properties of steel. The hydrogenation increased the magnitude of the longitudinal residual stress of base metal and fusion zone, without changing the tensile/compressive nature. On the other hand, the hydrogenation increased the intensity of the tangential stress of base metal, and changed from compressive to tensile the residual stress of the fusion zone. The microstructural characterization by optical and scanning electron microscopy was used to complement this study.

The inhibitory effect of Bauhinia purpurea (Fabaceae) extract was studied in the corrosion of carbon steel in 1.0 mol∙L-1 sulfuric acid solution. This plant was collected from the Brazilian rainforest. The carbon steel protection was observed by varying the extract concentration from 50 to 500 mg∙L-1. Polarization curves revealed that this extract acted as an adsorption inhibitor decreasing both anodic and cathodic density currents. Weight loss measurements showed that the extract remains stable for at least 72 hours. The adsorption process of this extract obeyed the Langmuir adsorption isotherm. Lastly, Arrhenius plot suggested the physical adsorption of the extract.

Superduplex stainless steel has been frequently employed in new sites of Brazilian Pre-Salt. In these environments, chloride concentration, temperature and carbon dioxide are normally present in higher levels than those at sea water at room temperature. In these conditions, it is expected that the passive films of stainless steel also show modifications. To better understand such modifications, samples of superduplex stainless steel UNS S32750 were submitted to electrochemical impedance measurements in brine media, at two temperatures and under presence/absence of carbon dioxide. The electrochemical impedance results were initially tested using the Kramers-Kronig transform and subsequently fitted by equivalent circuit employing constant phase elements - CPE. Moreover, to quantify the effect of each factor (temperature, chloride, carbon dioxide and microstructure) on the equivalent circuit, their parameters were tested applying statistical analysis. Significant effect of carbon dioxide and temperature was found on related parameters of passive film for heat-treated samples.

A sample of hydroxyapatite was synthesized and its crystalline structure was analyzed by X-ray diffraction by means of the Rietveld method. Two functions were used to fit the peak profiles, modified Voigt (TCHZ) and Pearson VII. The occupational factors and lattice parameters obtained by both models show that the sample does not contain relevant cationic substitutions. The interatomic distances from Ca1 to oxygens O1, O2 and O3 were adequate for a pure hydroxyapatite without defect at site Ca1. Besides, the use of multiple lines in planes (300) and (002) associated with the model Pearson VII resulted in good agreement with the TCHZ model with respect to the size-strain effectswith an ellipsoidal shape of crystallites. In conclusion, the procedures adopted in the synthesis of hydroxyapatite produced a pure and crystalline material. The experimental results of transmission electron microscopy confirmed the predicted shape of crystals.

Hydroxyapatite (HA) is capable of accepting substitute ions within its lattice, including zinc ions. Zinc is a trace element that activates the osteogenesis of osteoblastic cells and therefore plays an important role in the activity of alkaline phosphatase enzyme. The purpose of this work was to produce and characterize 5% mol Zn bioceramic in granular form (Zn-granules) for clinical applications and compare it with granules made from HA by using the same production route. Granules with addition of porogen agents were produced from powders of HA and zinc-containing HA by uniaxial pressing and heat treatment. The granules were subsequently ground and sieved. The results indicated that zinc contributed to the reduction of sample crystallinity and formed a biphasic structure after calcination at 1200 °C. Additionally, zinc release from granular material may have clinical applications as bone graft.

Esse artigo apresenta a análise termodinâmica do ponto de vista do processamento cerâmico para a obtenção de niobatos de potássio. A análise realizada indicou as condições de pH em que seria possível produzir insumos cerâmicos fotoluminescentes por rotas de precipitação química. Para tanto foram consideradas as presenças dos elementos químicos Ca, La, K, Nb e Eu em meio aquoso à temperatura ambiente, que foram estudados considerando os parâmetros potencial e a solubilidade.

This work presents a thermodynamic analysis from ceramic processing point of view to obtain photoluminescent potassium niobate ceramic. The analysis carried out indicated the conditions of pH which the route of processing by chemical precipitation would be done. Therefore, the presence of chemical elements Ca, La, K, Nb and Eu in aqueous medium was considered on potential and solubility parameters at room temperature.