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Artigo de evento 1 Citação(ões) na Scopus Pit morphology and its microstructure relation in 850°C aged UNS S31803 (SAP 2205) duplex stainless steel(2003-07-24) Rodrigo Magnabosco; ALONSO-FALLEIROS, N.This work described the relationship between microstructure of UNS S 31803 (SAP 2205) aged at 850°C and pitting morphology after cyclic polarization in chloride aqueous solution. The initial material, solution treated for 30 minutes at 1120°C and water quenched, was aged at 850°C for periods up to 100 hours. Cyclic polarization in 3,5% NaCl aqueous solution was conducted on #600 grounded sample surfaces. After polarization, the samples were sectioned transversal and perpendicular to polarized surface to allow the inner view of pitting corrosion using scanning electron microscope. It was found that sigma phase formation after 850°C aging treatment reduced pitting potential, and pitting corrosion occurred as selective corrosion of chromium and molybdenum impoverished regions, like interfaces between sigma phase and metallic matrix.Artigo 2 Citação(ões) na Scopus New approach for applications of machinability and machining strength(2009-09-05) COPPINI, N. L.; Júlio Cesar Dutra; DOS SANTOSA, E. C.Purpose: The purpose of this paper is to present and discuss the machinability and machining strength concepts under a new viewpoint concerned with both their applications and how to measure then. Despite of the fact that to develop easy to cut steel is a very important task, this work take under consideration entire application of these properties for any kind of materials in terms of how aggressive it can be against the tool material. Design/methodology/approach: A new approach to measure machining strength property is proposed. The reliability of the proposed test was based on experimental data from the literature. The best way to apply machinability index and machining strength index is put forward. Otherwise, at this moment, the authors are doing experimental laboratory research to evaluate the best way to organize appropriate samples to attend different kind products for respective materials makers'. Findings: It was possible to conclude that machinability must be used by means of comparative tests as close as possible to shopping floor conditions. The main application is to select the best steel to be used for a specific cutting process workpart. Research limitations/implications: The main limitation is that the entire new viewpoint presented is very new for the materials makers. The authors must spread the ideas presented here to check the actual materials makers' resistance or acceptance of their applications. Originality/value: The proposed test is very simple and more reliable than that one already published. On the other hand, machining strength is a material intrinsic property. For this reason, it is best employed during easy to cut materials development and measured by a Coppini Index (CI) based on standard tests. As a material intrinsic property it is not related to a standard material. Machinability is supposed to be appropriated for process optimization and not for materials development or characterization. © Copyright by International OCSCO World Press. All rights reserved. 2009.- Reusing Surlyn® Ionomer Scraps in LDPE Blends: Mechanical and Thermal Properties(2023-01-05) BARBOSA, M. F.; Adriana Martinelli Catelli Souza© 2023 Universidade Federal de Sao Carlos. All rights reserved.This study aimed to evaluate the possibility of reusing industrial scraps of Surlyn® ionomer by obtaining blends with Low-Density Polyethylene (LDPE). Blends of LDPE and Surlyn® scraps were obtained by extrusion with compositions ranging from 25 to 75 wt% of the ionomer. Their melt flow index (MFI), morphology (SEM), mechanical (tensile, flexural, impact tests) and thermal properties (DSC, TGA, HDT tests) were analyzed. The morphology of the blends presented two phases, indicating the immiscibility of phases. Surlyn® incorporation promoted a decrease in the degree of crystallinity of LDPE and a slight increase in the thermal decomposition temperature. In addition, Surlyn® decreased the decomposition rate of LDPE. However, the decrease in the degree of crystallinity did not affect the mechanical properties of the blends. Incorporating ionomer in LDPE promoted an increase in tensile and flexural strength, tensile and flexural modulus and strain at break. Impact strength decreased with increasing ionomer concentration.
- Assessment of the Von Mises Stresses and Stress Triaxiality in Notches Using Modified Tensile Specimens(2023-05-26) PEREIRA, L. DOS S.; Gustavo Donato; MATTAR NETO, M.© 2023 Universidade Federal de Sao Carlos. All rights reserved.Complete understanding of the local stress triaxiality and stress concentration is essential to ensuring structural safety of several structures. A combination of mechanical tests with numerical simulations can be used to obtain this information. One way to study stress triaxiality is by modifying the standard tensile test geometry (ASTM E8) with a notch. Based on previous results from the literature, five notches were chosen: 10, 5, 3, 2, and 1 mm. These geometries were tested, and the results were numerically reproduced using the Abaqus/Explicit 2020 software. The models used were a non-linear model with the Gurson-Tvergaard-Needleman damage model to reproduce the failure. The numerical analyses allowed the assessment of the von Mises stress and stress triaxiality near the notch to compare with the standard smooth specimen. Two instants were considered as crack propagation onset; the instant of the maximum von Mises stress in the element at the center of the specimen, where the failure process begins; and the moment of maximum stress in the true stress x true strain curve. For the von Mises stress analysis, the difference between the curves was small. The stress triaxiality is a better variable to visualize the influences of the notch. When the strain is equal to a 0.07 (instant of the maximum force for the standard specimens), for the smaller notches (1 and 2 mm), there is a region where the effective plastic strain is zero. Consequently, the stress triaxiality is larger in this region than in the center. For the crack propagation onset instant, the plastic strain occurs along the whole transversal section. In this instant, the maximum value of stress triaxiality occurs in the center for all specimens. These results demonstrate that the stress triaxiality changes as the strain increases, i.e., varies with time.
- Polyamide 12 Filled with Cross-Linked Polyethylene Waste: Processing, Compatibilization, and Properties(2023-06-05) MORAES, W. G. B.; BONSE, B. C© 2023 Universidade Federal de Sao Carlos. All rights reserved.Cross-linked polyethylene (XLPE) is primarily used as a coating and insulator for electrical wires and cables. The cross-links render recycling through remelting unfeasible, and XLPE waste is usually incinerated or sent to landfills. Previous investigations showed that XLPE increased the impact strength of commodity thermoplastics. Hence, incorporating XLPE in polyamide 12, an engineering thermoplastic, was studied using maleic anhydride grafted polyethylene (PE-g-MA). Formulations were prepared using a co-rotating twin-screw extruder containing 20 wt% XLPE with 0, 2, 4, and 8 wt% compatibilizer. Test specimens were injection-molded. DSC results showed that adding XLPE and compatibilizer reduced PA12 crystallinity but affected little melt and crystallization temperatures. Morphological analyses revealed poor adhesion between polyamide 12 and XLPE, which improved when adding PE-g-MA. The lack of adhesion when XLPE is added strongly reduces the mechanical properties, except for impact strength, which increased by ca.120% compared to the formulation without XLPE; while using 4 wt% compatibilizer this increase was ca. 140%. When adding PE-g-MA as a compatibilizer, some recovery was achieved in tensile strength and strain at break, and impact strength increased furthermore. Flexure and HDT tests showed a decrease in stiffness after adding XLPE. Stiffness was further reduced in compositions containing compatibilizer.
- Processing of Metal Matrix AA2124 Aluminium Alloy Composites Reinforced By Alumina And Silicon Carbide By Powder Metallurgy Techniques(2014) ALVES, S. J. F.; SOUSA, M. M. S.; ARAÚJO, E. R. DE; AMBROZIO FILHO, F.; SANTOS, M. J. DOS; ARAÚJO FILHO, O. O. DE A.© (2014) Trans Tech Publications, Switzerland.This work aims the processing of metal matrix AA2124 aluminium alloy composites reinforced by alumina (Al2O3) and silicon carbide (SiC). The composites were manufactured by powder metallurgy techniques, in a grinding using a ball mill spex type (high energy) at a ratio of balls/ powders of 10:1 and grinding time of 30 and 60 minutes using stearic acid (C18H36O2) as lubricant to each one of the samples. The fractions used in both reinforcements were 5, 10 and 15% in mass. The microstructural characterizations of AA2124 alloy powders with the reinforcements of alumina (Al2O3) and silicon carbide (SiC) powders were obtained by scanning electron microscopy (SEM) and the particles sizes and distribuition of the particle sizes in powders produced were obtained by laser diffraction, whereas the sintered characterizations were obtained by scanning electron microscopy (SEM) and mechanical characterization of the sintered tests was achieved by Vickers hardness (HV). The composites were uniaxially cold compacted (room temperature), at a pressure of 7.0 t/cm², thus forming small pellets that were sintered (at a temperature of 500 °C) in a vacuum furnace at IPEN (SP). There was observed the influence of the respective bulk fractions of reinforcement particles used in mechanical characteristics presented in the resulting composites.
- Preparation of Molybdenum High Speed Tool Steels with Addition of Niobium Carbide by Powder Metallurgy Techniques(2014-12-01) ARÁUJO FILHO, O. O. DE A.; ANTONELLO, R. T.; GONZALEZ, C. H.; URTIGA FILHO, S. L.; AMBROZIO FILHO, F.© (2014) Trans Tech Publications, Switzerland.High speed steels processed by Powder Metallurgy (PM) techniques present better mechanical properties when compared with similar steels obtained by the conventional process of cast to ingot and hot working. PM techniques produce improved microstructures with smaller and better distribution of carbides. Liquid phase sintering high speed steel seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels. The introduction of niobium as alloying element began with the object of replacing elements like vanadium (V) and tungsten (W). Phase liquid sintering consists in a manufacturing technique to process high speed steels by powder metallurgy. The aim of this work of research is to process and obtain AISI M2 and M3:2 with and without the addition of niobium carbide by high energy milling, cold uniaxial compaction and vacuum sintering in the presence of a liquid phase. The powders of the AISI M2 and M3:2 were processed by high energy milling adding a small quantity of niobium carbide (6% in mass), then the powders were characterized by means of X-ray diffraction (XRD) and scanning electron Microscopy (SEM) plus energy dispersion spectroscopy (EDS) in order to evaluate the milling process. The powders of the AISI M2 and M3:2 with the addition of niobium carbide (NbC) were uniaxially cold compacted and then submitted to vacuum sintering. The sintered samples had their microstructure, porosity and carbide distribution observed and evaluated by means of Scanning Electron Microscopy (SEM) and the mechanical property of hardness was investigated by means of Vickers hardness tests. At least five samples of each steel were investigated.
- Improvements on the characterization of heterogeneities in grain size by network analysis(2023-01-05) MOREIRA, V. C.; TSCHIPTSCHIN, A. P.; Júlio Cesar Dutra© 2022Some microstructural heterogeneities, like those observed during abnormal grain growth or right after recrystallization of metals and alloys, may be challenging to evaluate in metric or topological terms, as the variations in both grain size and number of sides distributions are subtle. This work proposes a new methodology for microstructural heterogeneities characterization based on network analysis. The method involves coupling the eigenvector centrality and three newly conceived microstructural network centralities. These microstructural centralities take advantage of existing topological constraints during normal grain growth to overcome the dependency of traditional network centralities on the number of grains in micrographs. The proposed methodology was successfully tested for the characterization of abnormal grain growth and a pre-self-similar state during normal grain growth. This procedure has some advantages over grain size distribution and topological evaluations, and it can be automated for both industrial and research applications, paving the way for the characterization of other heterogeneities in materials microstructures.
- Effect of injection molding conditions on the properties of polyamide 6/calcium carbonate nanocomposite(2023-05-12) AUGUSTO, T. A.; CARASTAN, D. J.; SANTOS, A. N. B.; BONSE, B. C.© 2023 Wiley Periodicals LLC.The application range of polyamide 6 in lightweight part applications can be significantly increased by using appropriate processing parameters and by incorporating additives. Therefore, specimens were manufactured at varying mold temperatures and injection velocities to study the effect of injection molding parameters on the properties of polyamide 6 and its nanocomposite with nano-calcium carbonate. Mechanical properties, degree of crystallinity, density, heat deflection temperature, and melt flow index were measured to assess the effect of injection molding conditions on material properties. Mold temperature was the process factor that most affected polyamide 6 and polyamide 6/nano-calcium carbonate properties. Increasing this parameter increased density, impact strength, flexural strength, flexural modulus, and heat deflection temperature. The nanocomposite's degree of crystallinity, tensile modulus, and melt flow index also increased. High injection velocity reduced only the impact strength of the nanocomposite. The findings indicate that by modifying injection parameters, it is possible to improve mechanical properties and processing efficiency of polyamide 6 and its nanocomposites, bringing them closer to their maximum potential. Incorporating the nanofiller increased almost all properties except for impact strength and elongation at break. Nano-calcium carbonate provided considerable advantages to polyamide 6 mechanical performance and processability while increasing sample weight by only 1.5%.
- Electrochemical characterization of 13Cr low-carbon martensitic stainless steel - Corrosion study with a mini-cell setup(2022-10-27) CALDERON- HERNANDEZ, J. W.; GONZALEZ-RAMIREZ, M. F.; SEPULVEDA-CASTANO, J. M.; SANTOS-MARTINEZ, J. D.; QUISPE-AVILES, J. M.; Rodrigo Magnabosco; Goldenstein H.© 2022 The Authors.13Cr low-carbon martensitic stainless steels also known as supermartensitic stainless steels (SMSS) have superior properties than conventional martensitic stainless steels. The SMSS have better weldability and corrosion resistance. Nevertheless, corrosion resistance depends on phases transformations which are induced generally by heat treatments. In this work, the electrochemical properties of a SMSS were evaluated as a function of the tempering temperature (400 °C-700 °C). The susceptibility to intergranular corrosion was determined throught the degree of sensitization (DOS) using the Double Loop - Electrochemical Potentiokinetic Reactivation technique (DL-EPR) in a conventional three electrodes corrosion cell. On the other hand, the pitting susceptibility was evaluated by potentiodynamic polarization using a homemade corrosion mini-cell (based on a sessile electrolyte droplet), thus avoiding crevice problems typically seen with conventional arrangements. Imaging the microstructure with SEM, XRD analysis and thermodynamic and kinetic simulations were performed to understand the microstructural transformations and their relationship with corrosion resistance. The most severe sensitization occurs at the temperature where reversed austenite transformation is highest.