Desenvolvimento de recobrimento submicrométrico de óxido de nióbio para aplicação em tubulações de prospecção de petróleo

Pós-graduação em Engenharia Mecânica - FEG

Implantes nanotopograficamente modificados pela ação do laser Yb-YAG

Titanium has proven its suitability as an implant material in surgery over many years. Excellent biocompatibility and corrosion resistance are outstanding features. Implant surfaces always causes concern and interest in scientific communities, due to its close relationship with the time required for osseointegration. Surface modification can be performed by several methods, being laser irradiation one of them. Titanium implants with two different surfaces were inserted in rabbits: Group I (G-I: machined surface, control group), and group II (G-II: laser irradiated, test group) being processed 30 and 60 days after surgery for histological analysis. Surface characterization was performed with SEM-EDS, contact angle measurement, and mean roughness (Ra) parameters. Surface analysis in the GII group showed a nanomorphology affected by melt and quick solidification zones following laser irradiation (SEM), as well as total wettability and Ra mean values significantly higher than in the G-I group. The laser treatment resulted in a homogenized, porous surface, with increased surface area and volume. Histological analysis of bone-implant contact linear extension (BIC) showed better results in G-II at 30 days (39.26 ± 18.23 and 68.41 ± 13.68 for G-I and G-II groups, respectively). Titanium implants modified by laser irradiation showed important features that may accelerate early osseointegration.

Caracterização do fator de intensidade de tensão em corpos trincados através do método dos elementos finitos

The industry generally has sought materials with high mechanical resistance, low density, thermal stability and corrosion resistance. In the aerospace industry, for example, the use of aluminum alloys, such as Al 2024-T351 and Al 7075-T7351, have become essential. However, the use of these materials often do not resulted in a satisfactory performance of the component, since the presence of cracks can cause total rupture of the component, even with a tension below the yield stress of the material, unexpectedly. In this work, these aluminum alloys were analyzed and samples were modeled by the finite element method. Moreover, in the models were applied two different types of cracks, central and edge crack, a vertical force was applied to result in a tension 70% of the yield stress of the material analyzed. Through stress asymptotic distribution in the region near the crack tip were calculated the values of the stress intensity factors for each crack length, after the stress intensity factors characterized were compared graphically with the values of fracture toughness found in the available literature

Influência do tratamento superficial 3IP na vida em fadiga dos aços ABNT 4340 e 15-5PH para aplicação aeronáutica

Pós-graduação em Engenharia Mecânica - FEG

Efeito de elementos susbstitucionais e intersticiais nas propriedades mecânicas e na biocompatibilidade de ligas do sistema Ti-15Zr-xMo

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Utilização de metaheurísticas combinada a diferentes métodos de aglutinação para a otimização de um processo de torneamento com múltiplas respostas

Pós-graduação em Engenharia Mecânica - FEG

Filmes híbridos PMMA-siloxano modificados com nanotubos de carbono para proteção de materiais metálicos contra corrosão

Using the sol-gel process, organic-inorganic hybrid coatings were synthesized by incorporation of different concentrations of functionalized carbon nanotubes, to improve their mechanical strength and thermal resistance without changing its passivation character. The siloxane-PMMA hybrids were prepared by radical polymerization of methyl methacrylate (MMA) with 3-methacryloxipropiltrimethoxisilane (MPTS) using the thermal initiator benzoyl peroxide (BPO), followed by acid catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS). The analysis of pristine and functionalized carbon nanotubes was carried out using Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy and Raman Spectroscopy. Structural analysis of hybrids was performed by Nuclear Magnetic Resonance, Atomic Force Microscopy and Raman Spectroscopy. For analysis of mechanical strength and thermal stability were performed mechanical compression tests and thermogravimetric analysis, respectively. Electrochemical Impedance Spectroscopy was used to evaluate the corrosion resistance in saline environment. The results showed an effective functionalization of carbon nanotubes with carboxyl groups and conservation of its structure. The hybrids showed high siloxane network connectivity and roughness of approximately 0.3 nm. The incorporation of carbon nanotubes in the hybrid matrix did not change significantly their thermal stability. Samples containing carbon nanotubes exhibit good corrosion resistance (on the order of MΩ in saline environment), but the lack of complete dispersion of carbon nanotubes in the hybrid, resulted in a loss of mechanical and corrosion resistance compared to hybrid matrix.

Análise experimental da resistência à corrosão e da velocidade de corrosão: uma proposta pedagógica

In this work it is proposed the use of a chemical activity, in which a corrosion process occurs, aiming to provide to the student relationship among the learning concepts and corrosion phenomena that occur everyday. It is suggested that the experiment development is based on Vygotsky theory, so that students work in groups, which may facilitate social interaction among students and results discussion among groups under professor guidance. This proposal can provide the involved concepts learning, as well as student training such as a critical and reflexive individual.

Influência do aporte térmico da soldagem GTAW no balanço de fases Ferrita/Austenita do Aço Inoxidável Duplex UNS S32205

Pós-graduação em Engenharia Mecânica - FEIS

Desenvolvimento e caracterização de ligas de Co-Cr-Mo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização da liga Ti-15Zr visando aplicações biomédicas

With advances in health care, has been na increase of demand for material that could replace the functions of the human body parts, thus evolved biomedic prosthesis which today are responsible for the constant improvement of the quality of life. The Titanium alloys are widely used as implants due to its properties, like high mechanical resistance, biocompatibility and corrosion resistance, and the addition alloying elements like Zirconium, may improve some of those properties. Such properties are related to the microstructure and consequently to the type of processing performed. The purpose of this dissertation was to characterize the experimental alloy Ti15Zr after route of processsing and heat treatment in order to extend the knowledge about this alloy. The latter has been abtained by fusion of pure metals in a arc melting furnace with an inert argon atmosphere. The material has been homogenized in a tube furnace at 950ºC for 24h and cold worked by swaging, after that, bars with 10 mm of diameter were obtained by the process of rotary forging. The samples were solubilized at 900º C for 2 hours and quenched in water. After that, 4 samples were submitted to the aging, at 400º C, 450º C, 500º C and 550º C. The microstructure and phase analysis was done by optical microscopy and X-rays diffraction (XRD), the mechanical characterization was carried out by microhardness test and finally, evaluation of corrosion resistance of the alloy by electrochemical tests. The XRD and the optical microscopy made it possible to analyze that the heat treatment influenced the phase shifting from α to α', and probably affected the alloy hardness, at the first aged sample at 500º Chas been a sudden increase in the value of hardness, probably by appearance of omega phase, unwanted phase to the medical application duo to great fragility, and finally ... (Complete abstract click electronic access below)

Caracterização da liga Ti-15Zr visando aplicações biomédicas

With advances in health care, has been na increase of demand for material that could replace the functions of the human body parts, thus evolved biomedic prosthesis which today are responsible for the constant improvement of the quality of life. The Titanium alloys are widely used as implants due to its properties, like high mechanical resistance, biocompatibility and corrosion resistance, and the addition alloying elements like Zirconium, may improve some of those properties. Such properties are related to the microstructure and consequently to the type of processing performed. The purpose of this dissertation was to characterize the experimental alloy Ti15Zr after route of processsing and heat treatment in order to extend the knowledge about this alloy. The latter has been abtained by fusion of pure metals in a arc melting furnace with an inert argon atmosphere. The material has been homogenized in a tube furnace at 950ºC for 24h and cold worked by swaging, after that, bars with 10 mm of diameter were obtained by the process of rotary forging. The samples were solubilized at 900º C for 2 hours and quenched in water. After that, 4 samples were submitted to the aging, at 400º C, 450º C, 500º C and 550º C. The microstructure and phase analysis was done by optical microscopy and X-rays diffraction (XRD), the mechanical characterization was carried out by microhardness test and finally, evaluation of corrosion resistance of the alloy by electrochemical tests. The XRD and the optical microscopy made it possible to analyze that the heat treatment influenced the phase shifting from α to α', and probably affected the alloy hardness, at the first aged sample at 500º Chas been a sudden increase in the value of hardness, probably by appearance of omega phase, unwanted phase to the medical application duo to great fragility, and finally ... (Complete abstract click electronic access below)

Characterization of a new beta titanium alloy, Ti-12Mo-3Nb, for biomedical applications

In recent years, different beta titanium alloys have been developed for biomedical applications with a combination of mechanical properties including a low Young's modulus, high strength, fatigue resistance and good ductility with excellent corrosion resistance. From this perspective, a new metastable beta titanium Ti-12Mo-3Nb alloy was developed with the replacement of both vanadium and aluminum from the traditional Ti-6Al-4V alloy. This paper presents the microstructure, mechanical properties and corrosion resistance of the Ti-12Mo-3Nb alloy heat-treated at 950 degrees C for 1 h. The material was characterized by X-ray diffraction and by scanning electron microscopy. Tensile tests were carried out at room temperature. Corrosion tests were performed using Ringer's solution at 25 degrees C. The results showed that this alloy could potentially be used for biomedical purposes due to its good mechanical properties and spontaneous passivation. (c) 2011 Elsevier B.V. All rights reserved.

Niobium Effects on the Recrystallization Behavior on a Full Austenitic 15Cr-15Ni Stainless Steel Investigated Using Adaptive Neural Networks (ANN)

A new series of austenitic stainless steels-Nb stabilized, without Mo additions, non-susceptible to delta ferrite formation and devoid of intemetallic phases (sigma and chi), without deformation induced martensite is being developed, aiming at high temperature applications as well as for corrosive environments. The base steel composition is a 15Cr-15Ni with normal additions of Nb of 0.5, 1.0 and 2 wt%. Mechanical properties, oxidation and corrosion resistance already have been invetigated in previous papers. In this paper, the effects of Nb on the SFE, strain hardening and recrystallization resistance are evaluated with the help of Adaptive Neural Networks (ANN).

Detorque evaluation of dental abutment screws after immersion in a fluoridated artificial saliva solution

Purpose: Implant-abutment connections still present failures in the oral cavity due to the loosening of mechanical integrity by detorque and corrosion of the abutment screws. The objective of this study was to evaluate the detorque of dental abutment screws before and after immersion in fluoridated solutions. Materials and Methods: Five commercial implant-abutment assemblies were assessed in this investigation: (C) Conex˜aoR , (E) EmfilsR , (I) INPR , (S) SINR , and (T) Titanium FixR . The implants were embedded in an acrylic resin and then placed in a holding device. The abutments were first connected to the implants and torqued to 20Ncmusing a handheld torque meter. The detorque values of the abutments were evaluated after 10 minutes. After applying a second torque of 20 Ncm, implant-abutment assemblies were withdrawn every 3 hours for 12 hours in a fluoridated solution over a period of 90 days. After that period, detorque of the abutments was examined. Scanning electronicmicroscopy (SEM) associated to energy dispersive spectroscopy (EDS) was applied to inspect the surfaces of abutments. Results: Detorque values of systems C, E, and I immersed in the fluoridated solution were significantly higher than those of the initial detorque. ANOVA demonstrated no significant differences in detorque values between designs S and T. Signs of localized corrosion could not be detected by SEM although chemical analysis by EDS showed the presence of elements involved in corrosive processes. Conclusion: An increase of detorque values recorded on abutments after immersion in fluoridated artificial saliva solutions was noticed in this study. Regarding chemical analysis, such an increase of detorque can result from a corrosion layer formed between metallic surfaces at static contact in the implant-abutment joint during immersion in the fluoridated solutions.