Scielo RSS <![CDATA[Materials Research]]> vol. 23 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Evaluation of Microstructural Characteristics of High-Si Al Alloy Cylindrical Samples Produced by Rheological Squeeze Casting with Bottom-Up Filling and Flow State Analysis of the Alloy Semi-Solid Slurries]]> The microstructures of high-Si Al alloy cylindrical simples produced by rheological squeeze-casting with bottom-up filling were investigated. The effect of process parameters on the distribution of hard phases (primary Si and Fe-rich phase) was evaluated, and flow characteristics of semi-solid slurry of high-Si Al alloy were investigated. Differences in volume fractions (VFs) of hard phases between the middle and upper layers of cylindrical samples decreased as the squeezing speed increased. Moreover, the flow state of the semi-solid alloy slurry transitioned from laminar to turbulent flow as the squeezing speed was increased. Movement of gases throughout the semi-solid alloy slurry filling process was analysed under different process parameters. The results provide insights for improving rheological casting of high-Si Al alloy and other Al matrix composites. <![CDATA[Metallurgical and Mechanical Behaviors of 309L-Si and ERNiCrMo-3 Dissimilar Weld on ASTM A182 F22 Steel]]> The present work aims to evaluate the metallurgical and mechanical behavior of dissimilar weld formed by 309L-Si and ERNiCrMo-3 (Inconel 625) electrodes combination on the ASTM A182 F22 steel with GMAW process. The welded joints were characterized by SEM, OM, tensile test and Vickers microhardness technique. The dissimilar interface formed in buttery of 309L and INC625 showed partially mixed zone (PMZ) formation and solidification microcracks that affected the mechanical properties in welded joint, presenting a fragile behavior. The F22 and INC625 interface presented high hardness regions with peaks greater than 400 HV. These regions were enriched by carbon due to the diffusion from F22 steel into the weld metal caused by tension relief heat treatment (TRHT). <![CDATA[FEM Modeling of the Delamination Process in Fabric Composites]]> Abstract The article presents the process of modeling delamination of a woven composite material by the finite element method. The models contain a detailed mesostructure in the form of weave geometry. The delamination occurs in the DCB (Double Cantilever Beam) test with the critical energy release rate as a propagation criterion. The methods used, especially Virtual Crack Closure Techniques (VCCT), have allowed us to present the delamination front changes during the propagation. To further investigate the influence of the mesostructure, additional fully homogenous models were analyzed. Load-displacement graphs, typical for DCB tests, are presented. The obtained results show how the presence of detailed geometry of the composite influences the development of damage. <![CDATA[Plasma Species and Coating Compositions in Aluminum Treated by PEO Using Shot Square Pulse]]> Abstract Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency (&lt; 1 kHz) pulsed discharge using high concentration alkaline-silicate electrolytic (Na2SiO3 &gt; 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (&gt; 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time. <![CDATA[Failure Analysis of HP40 Steel Tubes utilized in Steam Reformer Units of Petroleum Refinery Plants]]> Abstract This work is focused on the failure analysis of a HP40 steel tube used in steam reformer units, which was operated at about 850 °C for 100000 h. The failure analysis was conducted experimentally and numerically using the Thermo-Calc software. The main results indicated that the failed tube presented slightly different contents of Ni and Cr from the nominal ones, which originated the absence of the interdendritic eutectic microconstituent, composed of austenite and M7C3 carbides. This fact was also corroborated by Thermo-Calc results. This absence of eutectic facilitates the crack propagation on the dendritic zones and then the trangranular brittle fracture propagation through the austenite dendritic zones. <![CDATA[Evaluation of Formic Acid and Cyclohexylamine as Additives in Electrodeposition of Zn Coating]]> Abstract The Zn coatings obtained through electrodeposition are used to protect steel substrates from corrosion. In general, organic additives are added to the deposition bath in order to improve deposition characteristics such as corrosion resistance, hardness and deposition efficiency. Despite of the literature present information about the various organic additives effects on Zn coating properties there is no analysis of organic compounds with free electron-containing radicals, such as formic acid and cyclohexylamine. The formic acid has oxygen atoms with free electrons, whereas cyclohexylamine contains nitrogen with free electrons. Aiming at overcoming this gap, this manuscript presents an analysis of the effect in addition of formic acid mixture and cyclohexylamine on the deposition flow efficiency, corrosion resistance, hardness, roughness and micro-structure of Zn coating on carbon steel AISI 1020. The corrosion resistance evaluation was performed by potentiodynamic polarization determined by polarization resistance and weight loss tests as well. The analisys of morphology and electrodeposited microstructures were made by the Scanning Electron Microscopy (SEM) and Spectrometry X-Ray Diffraction (XRD). The Zn coatings were obtained from chloride deposition baths at constant pH 5. Results showed that corrosion resistance in the 0.5 mol/L NaCl solution of Zn coatings increases with the addition of the mixture of the formic acid and / or cyclohexylamine. Also, the corrosion resistance is higher with mixture than with additives alone. The addition of the mixture formic acid and cyclohexylamine increases the basal plane presence (0 0 2). However, the basal plane presence (0 0 2) does not increase when formic acid and cyclohexylamine are added alone which indicates a synergic effect of formic acid and cyclohexylamine in in the plan promotion (0 0 2). Also, was observed that an addition of formic acid mixture and cyclohexylamine increases the current deposition efficiency, decreases the roughness and raises the Zn coating hardness. <![CDATA[Effects of Different Wire Drawing Routes on Grain Boundary Character Distribution, Microtexture, δ-Phase Precipitation, Grain Size and Room Temperature Mechanical Behavior of Alloy 718]]> Abstract Over the last decades, alloy 718 usage has expanded and requirements imposed by its industrial applications became more critical. The knowledge about grain boundary character distribution (GBCD) in alloy 718 and its effect on properties improvement is mostly built based on iterative processing through cold rolling steps interspersed with solution annealing. Alloy 718 is found in the industry in many different forms and geometries, and fabricated by multiple thermomechanical processes such as wire drawing, rolling, forging or extrusion. The present study focused on understanding how wires respond to deformation mode related to drawing in regard to GBCD evolution, crystallographic orientation, precipitation of δ-phase and grain size. Lastly, assessing the resulting mechanical properties. The findings show that microstructural evolution is a consequence of competing mechanisms such as strain induced boundary migration, recrystallization, grain growth and phase precipitation. The deformation gradient along wire cross section plays an important role in affecting microstructural features, such as δ precipitation, GBCD and microtexture.