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URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/795
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- 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.
- Effect of aging heat treatment H950 and H1000 on mechanical and pitting corrosion properties of uns s46500 stainless steel(2018-01-05) BERALDO, C. H.; CALDERON-HERNANDEZ, J. W.; Rodrigo Magnabosco; ALONSO-FALLEIROS, N.© 2018 Universidade Federal de Sao Carlos. All rights reserved.The effect of aging temperature on mechanical and pitting corrosion properties of UNS S46500 was investigated. Tensile and Hardness tests were carried out and the microstructure was analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction; Thermo-Calc simulations helped in the phase identification. Pitting corrosion properties were investigated in 0.6M NaCl electrolyte with sulfate additions by Potentiodynamic Polarization (PP). Hardness, tensile and yield strength of the UNS S46500 steel after lower aging temperature, 510ºC (H950), are higher than the ones found in the 538ºC (H1000) aged steel.This result is explained by microstructure, X-ray diffraction and Thermo-Calc analysis, which indicated the presence of austenite, chi phase and probably Ni3Ti precipitates finely and uniform distributed throughout the martensite matrix. Pitting corrosion resistance is equivalent in both aging temperatures. The sulfate inhibitor effect on UNS S46500 steel was enhanced for 538ºC condition when the electrolyte reaches 1Cl-:1SO4 2- ratio, which is explained by Ni sulfate adsorption and the amount of interfaces in the microstructure resulting in smaller amount of adsorption sites, such as coarsened Ni3Ti precipitates, smaller fraction of chi phase and recovery of dislocations in martensite structure.
- The influence of the milling environment on the sintered structure of a W-Cu composite(2010-10-05) COSTA, F. A.; AMBROZIO FILHO, F.; SILVA, A. G. P.; GOMES, U. U.; LIMA. S. J. G.; ACCHAR, W.This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050°, 1150° and 1200°C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement. © (2010) Trans Tech Publications.
- Corrosion versus mechanical tests for indirect detection of alpha prime phase in UNS S32520 super duplex stainless steel(2011-04-05) FONTE, T. F.; Rodrigo Magnabosco; TERADA, M.; PADILHA, A. M.; COSTA, I.Alpha prime formation leads to material embrittlement and deterioration of corrosion resistance. In the present study, the mechanical and corrosion behavior of super duplex stainless steel UNS S32520 aged at 475°C from 0.5 h to 1,032 h was evaluated using microhardness measurements, Charpy impact tests, electrochemical impedance spectroscopy, and cyclic polarization curves. The sensibility of these tests to the effects of alpha prime phase was investigated. The microhardness test showed a gradual increase in hardness with aging time, whereas the impact tests revealed losses of about 80% in the energy absorption capacity for the material aged for 12 hin comparison with the solution-annealed samples. The most responsive analysis was the impact test, which indirectly revealed the presence of this deleterious phase in samples aged for 0.5 h. The electrochemical impedance spectroscopy and polarization tests were not highly sensitive to the alpha prime phase unless these are present In large amounts in the stainless steel. © 2011, NACE International.
- Production of cellular ceramics by gel casting ceramic emulsions Produção de cerâmicas celulares por emulsão seguida de gelifi cacao(2011) DE SOUSA, E.; DELLU JUNIOR, M.; PANDOLFELLI, V. C.; SA, F.Cellular ceramics have been produced by several methods, resulting in a wide range of structures and properties. This work describes a novel route to produce cellular ceramics based on the gel casting of emulsions consisting of an aqueous ceramic suspension containing water-soluble organic monomers and an emulsifi ed insoluble liquid phase (kerosene). The effects of solids loading and kerosene content on the rheological properties of emulsions were evaluated. SEM of the cellular structure revealed isolated pores for samples with low porosity, which changed to an interconnected network of pores as the porosity increased. Diametrical compression was used to evaluate the strength of sintered samples, which varied in the range of 2.0 and 48 MPa, depending on the porosity.
- Quantification of MgO surface excess on the SnO 2 nanoparticles and relationship with nanostability and growth(2011-02-15) GOUVEA, D.; PEREIRA, G. J.; GENGEMBRE, L.; STEIL, M. C.; ROUSSEL, P.; RUBBENS, A.; HIDALGO, P.; CASTRO, R. H. R.In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO 2 nanoparticles plays an important role in the system's energetics and stability. Using X-ray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO 2 with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO 2 nanoparticles stability. © 2010 Elsevier B.V.
- Test to characterize the machining strength property for the AISI 316L steel(2012-08-05) COPPINI, N. L.; DUTRA, J. C.; BAPTISTA, E. A.; DA SILVA, F. F. A. P.; FERREIRA, F. A. A.; COCCUMAZZO, D.This paper explores the effect of grain size on machining strength in an Fe-Cr-Ni alloy (AISI 316L). Ideal grain growth law [1], was used to obtain the activation energy level for this steel, which was 185 kJ.mol-1 [2]. The initial grain size was measured (12 μm) and considering these values, both temperature and time values needed to achieve a final grain size ten times larger than the initial one, could be calculated, which were 1200°C and 2 hours. Ternary phase diagram analysis showed that austenite was stable at this temperature. Following, samples of 200 mm length were annealed and quenched in water to prevent any formation of sigma (μ) phase. Annealed and as-received bars were then used to compare their machining strength. Results showed that the machining strength is higher in the as received condition than the one after annealing (127 μm). It may be concluded that the bigger the grain size, the lower its machining strength. It is believed that this is caused by the pile-up of dislocations on grain boundaries, since this material exhibits large plastic deformation before fracture.
- Assessment of the utilization of different peroxide dispersion media on the controlled degradation of polypropylene(2013-01-05) MUNOZ, P. A. R.; BETTINI, S. H. P.A two-step investigation of polypropylene-controlled degradation was performed. First the controlled degradation of polypropylene was investigated by assessing the effects of using dicumyl peroxide (DCP) and 2,5-dimethyl-2,5- di(t-butylperoxy) hexane (DHBP) in different suspensions (neat, calcium carbonate, and organically modified montmorillonite). The second part of this research was performed according to a factorial design at two levels (2 2 experimental design) with center point, in which peroxide concentration and reaction time were studied. Polypropylene degradation was assessed by melt flow rate (MFR) and parallel plate rheometry. Results showed that DCP presented higher molar efficiency in polypropylene degradation reactions in relation to DHBP; likely due to radical recombination reactions. The results also indicate that clay may catalyze the recombination reactions of polypropylene radicals. Copyright © 2012 Wiley Periodicals, Inc.
- Effects of hydrogen content in nitrogen-based sintering atmosphere on microstructure and mechanical properties of Fe-0.3%C-0.1%B alloy(2014-10-05) LOBERTO, A.; DA SILVA, M. D. C. A.; AMBROZIO FILHO, F.; DE FLORIO, D. Z.; YOSHIMURA, H. N.© (2014) Trans Tech Publications, Switzerland.For the sintered materials, the mechanical properties are strongly dependent on the density of the final product. A substantial reduction of the porosity can be achieved using additives in the powder mixture which promote the formation of a liquid phase during sintering. Boron is a potential liquid phase promoter in ferrous alloys, when sintering is carried out using hydrogen or argon atmospheres. These atmospheres, however, are costly, and the use of nitrogen containing low content of hydrogen could be beneficial. In this study the effects of 10 to 50% hydrogen in nitrogen atmosphere on the microstructure and mechanical properties of a Fe-0.3%C-0.1%B alloy sintered at 1120 and 1250°C were investigated. Boron addition increased the sintered densities, but lowered the transverse rupture strength and hardness in relation to the control alloy (Fe-0.3%C). No significant differences were observed among the samples sintered in different atmospheres for each alloy. Nitrogen containing up to 50% hydrogen atmosphere is not suitable to sinter Fe-C alloy containing boron since it lowers the mechanical properties with the formation of fragile boron nitride precipitates at the grain boundaries and lower perlite fraction.