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Materials Research, Volume: 14, Número: 2, Publicado: 2011
  • Studies of the properties of heat treated rolled medium carbon steel Regular Articles

    Oluyemi, Daramola O.; Oluwole, Oladele Isiaka; Adewuyi, B. O.

    Resumo em Inglês:

    Investigations were carried out to study critically the effects of heat treatment on the properties of rolled medium carbon steel. Representative samples of as-rolled medium carbon steel were subjected to heat treatment processes which are; Quenching, Lamellae Formation and Tempering in the following order (Q + Q + L + T), (Q + L + T) and (L + T). The steel was heated to the austenizing temperature of 830 ºC and water quenched. The quenched steel was subjected to lamellae formation by reheating it to the ferrite-austenite dual-phase region at a temperature of 745 ºC below the effective A C3 point and then rapidly quenched in water. The lamellae formed was tempered at 480 ºC to provide an alloy containing strong, tough and lath martensite in a soft and ductile ferrite matrix. Mechanical tests were carried out on the samples and the results shows that the steel developed has excellent combination of tensile strength, hardness and impact strength which is very good for structural applications. The corrosion behaviour of the samples; heat treated rolled medium carbon steel and as-rolled medium carbon steel in sodium chloride medium were also investigated from where it was also confirmed that improved corrosion resistance is achievable by the treatment.
  • Effect of different finishing: polishing systems on the surface roughness of two heat-treated composite resins Regular Articles

    Lima, Gabrielle Ribeiro; Maluf, Nathalia Cardoso Baima; Souza, Soraia de Fátima Carvalho; Paiva, Antonio Ernandes Macedo; Souza, Erick Miranda; Santana, Ivone Lima

    Resumo em Inglês:

    The aim of this study was to compare the surface roughness achieved by different finishing/polishing systems on two composite resins for direct use after thermic treatment. The specimens (n = 40 per group (G); G1 = Filtek™ P60; G2 = Fill Magic®) were set up on a matrix of stainless steel with circular internal niches (Ø = 10.0 mm; h = 2.0 mm). Next, they were subjected to thermal treatment in a heated chamber at 170 °C for 10 minutes. They were then divided randomly into four subgroups (Sg) to receive the surface treatment according to the finishing/polishing systems tested (n = 10): Sg A: Control; Sg B: Diamond® felt disc + Diamond Excel® diamond paste; Sg C: Sof-Lex® discs; and Sg D: Enhance™ silicon tips. The mean roughness (Ra) was determined using a digital surface roughnes tester. Data was analyzed by two-way ANOVA and Tukey's post-hoc test (α = 0.05). Differences between the surface treatments were found on both resins (p < 0.05). In G1, the lowest mean Ra values were observed using Sg C (0.07 μm) and the highest for Sg D (0.12 μm) (p < 0.05). There was no difference between Sg B (0.08 μm) and Sg C (0.07 μm) (p = 0.076). In G2, there was a progressive increase in mean Ra values from Sg D (0.05 μm) to Sg C (0.06 μm) and to Sg B (0.07 μm) (p < 0.05). It was concluded that the finishing/polishing systems modified Ra on both resins.
  • Porous stainless steel for biomedical applications Regular Articles

    Mariotto, Sabrina de Fátima Ferreira; Guido, Vanessa; Yao Cho, Liu; Soares, Cristina Pacheco; Cardoso, Kátia Regina

    Resumo em Inglês:

    Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (%) respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 ºC for 5 hours to decompose the carbonate and the second one at 1150 ºC for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (%) of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%). The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide) was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (%) ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.
  • Fracture Toughness (K1C) evaluation for dual phase medium carbon low alloy steels using circumferential notched tensile (CNT) specimens Regular Articles

    Alaneme, Kenneth Kanayo

    Resumo em Inglês:

    The fracture behavior of dual phase medium carbon low alloy steels produced using two different chemical compositions (A - 0.34C, 0.75Mn, 0.12Cr, 0.13Ni steel and B - 0.3C, 0.97Mn, 0.15Cr steel) was investigated using circumferential notched tensile (CNT) specimens. Intercritical treatments were performed on samples with composition A by 1) austenitizing at 860 °C for 1 hour cooling in air, then treating at 770 °C for 30 minutes before oil quenching; 2) austenitizing at 860 °C for 1 hour quenching in oil, then treating at 770 °C for 30 minutes before quenching in oil; and 3) austenitizing at 860 °C for 1 hour, super-cooling to 770 °C and then quenching in oil. Samples of composition B were subjected to intercritical treatment at temperatures of 740, 760, and 780 °C for 30 minutes, followed by quenching rapidly in oil. Tensile testing was then performed on specimens without notches and the CNT specimens. It was observed that the dual phase steel produced from procedure (2) yielded a fine distribution of ferrite and martensite which gave the best combination of tensile properties and fracture toughness for composition A while the dual phase structure produced by treating at 760 °C yielded the best combination of tensile properties and fracture toughness for composition B. The fracture toughness results evaluated from the test were found to be valid (in plain strain condition) and a high correlation between the fracture toughness and notch tensile strength was observed. The fracture toughness values were also found to be in close agreement with data available in literature.
  • Synthesis of Pr0.70Sr0.30MnO3δ and Nd0.70Sr0.30MnO3δ powders by solution-combustion technique Regular Articles

    Vargas, Reinaldo Azevedo; Bonturim, Everton; Chiba, Rubens; Andreoli, Marco; Seo, Emília Satoshi Miymaru

    Resumo em Inglês:

    Powders of Pr0.70Sr0.30MnO3δ (PSM) and Nd0.70Sr0.30MnO3δ (NSM) compositions are being investigated as alternative cathode materials for Intermediate Temperature Solid Oxide Fuel Cells. The compositions were synthesized by a solution-combustion method using metal nitrates and urea as fuel. Combustion synthesis is a highly suitable synthesis route for achieving fine and homogeneous powders at low temperatures. Single phase pseudo-perovskite was obtained by X-ray diffraction after heat treatment of PSM and NSM powders at 900 ºC. The synthesized and milling powders had an average particle size between 0.27 to 0.07 μm. Chemical analyses of the powders calcined was performed by X-ray fluorescence and morphological analysis by scanning electron microscopy. The results were compared with literature values, indicating characteristics adjusted for preparation of ceramic suspensions.
  • Evaluation of the solubility of the HPMC: PVA blends in biological fluids in vitro Regular Articles

    Bianchi, Sara Elis; Angeli, Valeria Weiss; Souza, Kellen Cristhinia Borges de; Miron, Diogo dos Santos; Carvalho, Gláucio de Almeida; Santos, Venina dos; Brandalise, Rosmary Nichele

    Resumo em Inglês:

    Polymers are often used to coat tablets for controlled drug release. The purpose of this study is to evaluate the solubility of the HPMC and PVA blend compared to isolated polymers in solutions with a pH of biological fluids (6 and 1.2) and the dissolution of capsules obtained using theophylline granules produced with the HPMC/PVA 25/75 blend as a matrix and as coating. HPMC is completely solubilized in the medium that simulates the pH of the stomach and intestine, and PVA is the polymer that allows controlling the solubility of the blend in the medium, with a differents pH. The dissolution time was monitored by UV absorbance with maximum theophylline at 269 nm. The theophylline was released immediately in the granules, and in the capsules 78.4% after 30 minutes and 97.4%, after 120 minutes. Thus, PVA can potentially control the drug solubilization, contributing to obtaining modified release systems.
  • Structural and microstructural characterization of tin(II) oxide useful as anode material in lithium rechargeable batteries obtained from a different synthesis route at room temperature Regular Articles

    Macías, Mario Alberto; Martínez, José Antonio Henao; Gauthier, Gilles Henri; Rodriguez, Jorge Enrique; Avila, Humar; Pinto, José; Pinilla, Jesus

    Resumo em Inglês:

    Tin (II) oxide has been proposed as potential anode material in lithium rechargeable batteries. Different methods to obtain such compound have been developed with relative difficulty due to the fact that Sn(II) is easily oxidized to Sn(IV). We have applied a different methodology to synthesize SnO-romarchite by modifying the solvent nature of the controlled precipitation route using acetic acid and not water. Although the formation of Sn(IV) oxide could not be completely avoided, X-ray diffraction analysis confirmed the synthesis of metastable tin(II) oxide as major phase at room temperature. In depth analysis using Popa's model for Rietveld refinement allows to precise that the material corresponds to small and distorted crystallites, very anisotropic in size. SEM technique confirmed the microstructure is build of flower-like agglomerates of ~15 µm, in turn made of plate-like individual grains that remind the crystallite structure anisotropy.
  • The Effects of ZnO2 nanoparticles on strength assessments and water permeability of concrete in different curing media Regular Articles

    Nazari, Ali; Riahi, Shadi

    Resumo em Inglês:

    In this study, the effect of limewater on strength assessments and percentage of water absorption of concrete incorporating ZnO2 nanoparticles has been investigated. Portland cement was partially replaced by ZnO2 nanoparticles with the average particle size of 15 nm and the specimens were cured in water and saturated limewater for specific ages. The results indicate that ZnO2 nanoparticles up to 2.0 weight percent could produce concrete with improved strength and water permeability when the specimens cured in saturated limewater while this content is 1.0 weight percent for the specimens cured in tap water. Although the limewater reduces the strength of concrete without nanoparticles when compared with the specimens cured in water, curing the specimens bearing ZnO2 nanoparticles in saturated limewater results in more strengthening gel formation around nanoparticles causes improved permeability together with high strength. In addition, ZnO2 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that ZnO2 nanoparticles could improve mechanical and physical properties of the specimens.
  • Stress prediction in a central incisor with intra-radicular restorations Regular Articles

    Amarante, Martha Vasconcellos; Pereira, Marcos Venicius; Darwish, Fathi Aref; Camarão, Arnaldo Freitas

    Resumo em Inglês:

    A 2D finite element analysis was applied to calculate shear and von Mises equivalent stresses developed, under masticatory loading, in an upper central incisor restored with cast gold post and carbon fiber reinforced epoxy resin post. Based on the predicted shear stress levels, it is concluded that the gold post model is more prone to shear failure along the post-dentin interface. Whereas shear stress concentration also occurs in both models at the core-crown interface, the stress level predicted there is higher for the carbon fiber post model which would be more susceptible to crown displacement. Finally, the prediction of von Mises equivalent stress indicates a non-uniform distribution, with the stress preferentially concentrated in the gold post along its interface with the tooth dentin. For the carbon fiber post restored model, on the other hand, the von Mises stresses are more uniformly distributed achieving its maximum level in the tooth dentin.
  • The effect of adding boron in solidification microstructure of dilute iron-carbon alloy as assessed by phase-field modeling Regular Articles

    Furtado, Henrique Silva; Bernardes, Américo Tristão; Machado, Romuel Figueiredo; Silva, Carlos Antônio

    Resumo em Inglês:

    Alloying element like boron, even in small addition, is well known to improve hardenability of steels. Its application can improve mechanical properties of steels and reduce alloying costs. Despite these benefits is not easy to cast boron steels, mainly in dynamical solidification process like continuous casting, due to their crack susceptibility1,2. The strategy of using Phase-Field simulation of the solidification process is based on its proved capacity of predicting realistic microstructure that emerge during solidification under conditions even far from equilibrium3-5. Base on this, some comparative simulations were performed using a three component dilute alloy in a two dimensional domain under unconstrained (isothermal) and constrained (directional) solidification. Simulation results suggested two fragile mechanisms: one related to a deep dendritic primary arms space and other due to the remelting of this region at low temperature. Both resulted mainly from the high boron segregation in interdendritic regions.
  • Behavior of surface integrity in cylindrical plunge grinding using different cooling systems Regular Articles

    Silva, Leonardo Roberto; Mattos, Mariana Faccio; Amaral, Lucimar Venâncio; Corrêa, Elaine Carballo Siqueira; Brandão, Joel Romano

    Resumo em Inglês:

    The superficial texture of the material can exert a decisive influence on the application and performance of the machined component. The conventional fluids used in grinding processes are environmental risk and can also be dangerous to the health. The disposal of these toxic fluids is expensive and the contamination in the proximities of the machines can present risks to the health for the personnel in the shop floor. This paper analyzes the performance of the minimum quantity lubricant (MQL) technique and compares it with the conventional cooling method, developing an optimized fluid application method using a specially designed nozzle, through which a minimum amount of oil is sprayed in a compressed air flow. This paper also explores and discusses the concept of the MQL in the grinding process of hardened AISI 4340 steel. The performance of the MQL technique in grinding was evaluated based on an analysis of the surface integrity (roughness, microstructure and microhardness). As a result, it was realized that the MQL technique provides very similar characteristics to conventional process and can be applied in industry, thus contributing to an environment friendly manufacturing.
  • Deposition of SiOx thin films on Y-TZP by reactive magnetron sputtering: influence of plasma parameters on the adhesion properties between Y-TZP and resin cement for application in dental prosthesis Regular Articles

    Queiroz, José Renato Calvacanti de; Duarte, Diego Alexandre; Souza, Rodrigo Othávio de Assunção e; Fissmer, Sara Fernanda; Massi, Marcos; Bottino, Marco Antonio

    Resumo em Inglês:

    In this paper SiOx thin films were deposited on Y-TZP ceramics by reactive magnetron sputtering technique in order to improve the adhesion properties between Y-TZP and resin cement for applications in dental prosthesis. For fixed cathode voltage, target current, working pressure and target-to-substrate distance, SiOx thin films were deposited at different oxygen concentrations in the Ar+O2 plasma forming gas. After deposition processes, SiOx thin films were characterized by profilometry, energy dispersive spectroscopy (EDS), optical microscopy and scanning electron microscopy (SEM). Adhesion properties between Y-TZP and resin cement were evaluated by shear testing. Results indicate that films deposited at 20%O2 increased the bond strength to (32.8 ± 5.4) MPa. This value has not been achieved by traditional methods.
  • Chemical deposition of La0.7Ca0.3MnO3±δ films on ceramic substrates Regular Articles

    Morilla-Santos, Cássio; Schreiner, Wido Herwig; Lisboa-Filho, Paulo Noronha

    Resumo em Inglês:

    In this paper, it is reported the growth of La0.7Ca0.3MnO3±δ films using a chemical solution deposition method (CSD) by the spin-coating technique. Such solution was prepared through a route based on modified polymeric precursor method. Spin-coating deposition on different ceramic substrates was performed and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The magnetic response of the prepared specimens was studied using a SQUID magnetometer. The obtained results indicated uniform deposition on SrTiO3 and LaAlO3 substrates with similar characteristics. Furthermore, significant differences were detected in the Mn3+/Mn4+ valence ratio and a corresponding diverse magnetic response was observed. The sample prepared on SrTiO3 and LaAlO3 presented a critical temperature around 270 K as expected.
  • Enhanced DLC wear performance by the presence of lubricant additives Regular Articles

    Costa, Romina Paula de Castro; Marcian, Fernanda Roberta; Oliveira, Deiler Antônio Lima; Trava-Airoldi, Vladimir Jesus

    Resumo em Inglês:

    Lubricant additives play significant role for reducing friction and wear of mechanical elements. The additives presented in 5W30 oil were developed for metal surfaces. However, they have been used in engine pieces covered with DLC coatings because they also offer the potential to reduce friction losses and wear in automotive applications. The friction and wear tests were carried out by using a UMT-CETR ball-on-disk tribometer in rotational mode under 5W30 synthetic oil at 100 °C. The X-ray photoelectron spectroscopy (XPS) showed the presence of Mo and S in the wear tracks. These elements are from decomposition of ZDDP and MoDTC additives producing MoS2 in DLC surface, which offers enhanced durability by low wear rate.
  • Chloride diffusivity in red mud-ordinary portland cement concrete determined by migration tests Regular Articles

    Ribeiro, Daniel Véras; Labrincha, João Antonio; Morelli, Márcio Raymundo

    Resumo em Inglês:

    Red mud, which is a solid waste produced in the alumina production process, is classified as dangerous due to its high pH. In this work, the concentration of chlorides was monitored by measuring the conductivity of the anolyte, which initially was distilled water. The steady and nonsteady-state chloride diffusion coefficients were estimated from the "time lag"� and "equivalent time" between diffusion and migration experiments. The capillary water absorption, apparent porosity and pore size distribution of concretes were also analyzed. The addition of red mud apparently ensured lower chloride diffusion in the tested mixtures due to its superfine particle-size distribution and its "filler"� effect. Red mud lengthened the service life of the concrete to 35 years (double that of the reference concrete). This finding is very positive since it indicates a delay in the onset of the rebar corrosion process caused by the migration of chloride ions.
  • Effect of antioxidant agents on bond strength of composite to bleached enamel with 38% hydrogen peroxide Regular Articles

    Silva, Juliane Marcela Guimaraes da; Botta, Ana Carolina; Barcellos, Daphne Câmara; Pagani, Clovis; Torres, Carlos Rocha Gomes

    Resumo em Inglês:

    This study evaluated the effect of antioxidant agents on microtensile bond strengths (mTBS) of composite to bleached enamel. Fifteen freshly extracted human third molars were selected and randomly assigned to 6 groups (n = 5): (NB) enamel not bleached, (B) bleached enamel, (BR7) bleached enamel and restored 7 days later, (BSA) bleached enamel+sodium ascorbate, (BMC) bleached enamel+malvidin chloride, (BPC) bleached enamel+pelargonidin chloride. The groups were bleached with 38% hydrogen peroxide (HP - Opalescence Xtra Boost) and restored with Single Bond+Filtek Z350. The specimens were thermocycled and submitted to a microtensile load at 1 mm/min crosshead speed. The data were evaluated by ANOVA and Tukey test at 5% of significance. The mean and standard-deviation for all groups were: NB: 30.95(±11.97)a; BSA: 30.34(±8.73)a, BPC: 22.81(6.00)b, BR7: 21.41(±6.12)b, B: 14.10(±4.45)c, BMC: 13.25(±6.02)c. Sodium ascorbate reversed the bond strengths to enamel immediately after bleaching.
  • Compression specific toughness of normal strength steel fiber reinforced concrete (NSSFRC) and high strength steel fiber reinforced concrete (HSSFRC) Regular Articles

    Marara, Khaled; Erenb, Özgür; Yitmena, İbrahim

    Resumo em Inglês:

    Compression toughness tests were carried out on concrete cylinders reinforced with three different aspect ratios of hooked-end steel fibers 60, 75, and 83 and six different percentages of steel fibers 0.5, 1.0, 1.25, 1.5, 1.75, and 2.0% by volume of concrete. The w/c ratio used for the normal strength steel fiber reinforced concrete mixes (NSSFRC) was 0.55, and the water-cementitious ratio (w/c+s) for the high strength fiber reinforced concrete mixes (HSSFRC) was 0.31. For each mix, three test cylinders were tested for compression specific toughness. The effect of fiber reinforcement index: volume of fibers × length/diameter ratio on compression specific toughness and also on the relationship between these two properties is presented in this paper. As a result, (a) equations are proposed to quantify the effect of fibers on compression toughness ratio of concrete in terms of FRI, (b) equations obtained in terms of FRI and compression specific toughness of plain concrete to estimate both compression specific toughness of NSSFRC and HSSFRC (N.m), (c) equations obtained which represent the relationship between compression toughness index and FRI for NSSFRC and HSSFRC, respectively, and (d) equations obtained to quantify the relationship between compression specific toughness index and fiber reinforcement index for NSSFRC and HSSFRC, respectively. The proposed equations give good correlation with the experimental values.
  • Properties of high-workability concrete with recycled concrete aggregate Regular Articles

    Safiuddin,; Alengaram, Ubagaram Johnson; Salam, Abdus; Jumaat, Mohd Zamin; Jaafar, Fahrol Fadhli; Saad, Hawa Binti

    Resumo em Inglês:

    This study presents the effects of recycled concrete aggregate (RCA) on the key fresh and hardened properties of concrete. RCA was used to produce high-workability concrete substituting 0-100% natural coarse aggregate (NCA) by weight. The slump and slump flow of fresh concretes were determined to ensure high workability. In addition, the compressive, flexural and splitting tensile strengths, modulus of elasticity, and permeable voids of hardened concretes were determined. The test results revealed that RCA significantly decreased the workability of concrete. RCA also affected the compressive strength, modulus of elasticity, and permeable voids of concrete. At the age of 28 days, the concrete with 100% RCA provided 12.2% lower compressive strength and 17.7% lesser modulus of elasticity than the control concrete. Also, 100% RCA increased the permeable voids of 28-day old concrete by 8.2%. However, no significant negative impact of RCA was observed on the flexural and splitting tensile strengths of concrete.
  • Study of epoxy/CNT nanocomposites prepared via dispersion in the hardener Regular Articles

    Pizzutto, Caio Enrico; Suave, Jaqueline; Bertholdi, Jonas; Pezzin, Sérgio Henrique; Coelho, Luiz Antonio Ferreira; Amico, Sandro Campos

    Resumo em Inglês:

    In this study, carboxylated (SWCNT-c) and pristine (SWCNT) single-walled carbon nanotubes were randomly dispersed in a hardener prior to mixing it with an epoxy resin. The influence of several parameters on the dispersion process were investigated. The produced samples were characterized by infrared spectroscopy, differential scanning calorimetry, dilatometry, dynamic mechanical analysis, scanning electron microscopy and mechanical testing (tensile, flexural and microhardness). The results obtained with the nanocomposites with SWCNT-c suggested that the lowest time and amplitude of sonication improved the mechanical properties. The use of a solvent (acetone) was important to improve dispersion, ultimately increasing microhardness and Young's Modulus up to 32%. Nanocomposites with 0.25 wt. (%) SWCNT-c presented superior mechanical properties compared to those with 0.50 wt. (%) SWCNT. Two simple mathematical models (rule of mixtures and Halpin-Tsai) were used to predict Young's Modulus of the composites yielding results very close to the experimental ones.
  • Effect of different precursors in the chemical synthesis of ZnO nanocrystals Regular Articles

    Gusatti, Marivone; Barroso, Gilvan Sérgio; Campos, Carlos Eduardo Maduro de; Souza, Daniel Aragão Ribeiro de; Rosário, Jeane de Almeida do; Lima, Raquel Bohn; Milioli, Camila Cardoso; Silva, Laura Abreu; Riella, Humberto Gracher; Kuhnen, Nivaldo Cabral

    Resumo em Inglês:

    This work evaluates the effect of ZnCl2 and Zn(NO3)2.6H2O as precursors in the synthesis of ZnO nanocrystals. The materials were obtained at 90 ºC by a simple solochemical route. The resulting samples were characterized regarding phase composition, particle size and morphology, by means of XRD and TEM. The analysis have provided evidences that the material obtained applying Zn(NO3)2.6H2O as precursor has hexagonal crystalline structure, typical of the ZnO, and dimensions in the nanoscale. However, applying ZnCl2 as precursor results in a mixture of ZnO and Zn5(OH)8Cl2.H2O phases. For both precursors, the predominant morphology of the obtained ZnO nanocrystals was the rod-like structure.
  • Evolution of eutectic spacing during unidirectional solidification of Al-Ni alloys Regular Articles

    Araujo, Igor Jefferson Cabral; Silva, Bismarck Luiz da; Spinelli, José Eduardo; Garcia, Amauri

    Resumo em Inglês:

    Hypoeutectic Al-Ni alloys show a ductile phase α distributed with a β phase Al3Ni fragile where β serves as reinforcement of the structure of the material. The eutectic composition alloys obey the relationship: λ2.v = C, where λ is the eutectic spacing, v is a tip growth rate and C is a constant. The aim of this study is to establish correlations between λ and v for hypoeutectic Al-1%, 3% and 5% Ni alloys. Unsteady-state upward directional solidification experiments were performed, as well as metallography, dissolution of the aluminum matrix and scanning electron microscopy (SEM). The interphase spacing of the three Al-Ni alloys decreased with increasing tip growth rate, with a predominance of a rod-like morphology on intermetallic. It was observed that parameters such as tip growth rate, cooling rate and temperature gradient decreases as the solidification front advances. It was further observed that a single experimental law λ = 1.2 v-0, 5 illustrates the evolution of the interphase spacing for any examined alloy.
  • Comparative studies of WC-Co and WC-Co-Ni composites obtained by conventional powder metallurgy Regular Articles

    Martins, Vinícius; Rodrigues, Wilson Corrêa; Ferrandini, Peterson Luiz; Villarinho, Denis Jardim; Knörnschild, Gerhard Hans; Schaeffer, Lírio

    Resumo em Inglês:

    The present work reports a comparative study of cemented carbides of compositions WC-6Co, WC-10Co, WC-20Co, WC-6Co-6Ni and WC-12Ni-6Co. The purpose was to study the powder metallurgical production process of these compositions starting from a commercial WC-6Co powder, obtaining the desired compositions by mass balance with pure Co and pure Ni powders. During the process steps mixing, milling, compacting and sintering the powders were described by its apparent density, green density, shrinkage and sintered density. Lower densities were observed in composites with higher binder content. The process was monitored by scanning electron microscopy and EDS analysis to evaluate the homogeneity of the powders, to detect contaminations by the process and to characterize the microstructure of the sintered materials. A finer microstructure was found when the binder contained Ni. Potentiodynamic polarization tests in sulfuric acid revealed pseudo-passive behavior for all the tested hard metals.
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