Jefferson Lins

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Caracterização microestrutural de um aço IF deformado via ECAP

Cadernos UniFOA, Feb 4, 2019

As ligas metalicas com microestrutura ultrafina podem ser obtidas por processos baseados na aplic... more As ligas metalicas com microestrutura ultrafina podem ser obtidas por processos baseados na aplicacao de deformacao plastica severa. Estes materiais possuem propriedades superiores e existe por parte do setor produtivo um grande interesse comercial. O processo de prensagem por canais equiangulares (“Equal Channel Angular Pressing” – ECAP) e uma tecnica bastante atrativa por nao alterar as dimensoes da secao transversal do material. O processo consiste em se forcar um corpo-de-prova previamente lubrificado a escoar numa matriz que possui dois canais de secoes transversais identicas. Esta tecnica visa promover a deformacao via cisalhamento simples. Foi verificada experimentalmente a simulacao computacional do processo ECAP a partir da aplicacao das rotas A e C num aco IF estabilizado ao titânio apos 2 passes de deformacao. O aco IF possuia tamanho de grao grosseiro (~55 μm) e textura aleatoria, sendo considerado como um material modelo por ser praticamente isotropico. Os resultados experimentais apresentados foram analisados de forma comparativa visando esclarecer os mecanismos envolvidos no processo de refinamento microestrutural provocado por cada rota investigada. Os dados fornecidos pelos ensaios de dureza foram correlacionados com as observacoes das microestruturas com o auxilio da tecnica de microscopia eletronica de varredura. A verificacao experimental do processo avaliou de forma quantitativa a carga aplicada e tambem as propriedades mecânicas do material deformado atraves de ensaios de dureza. Um intenso refinamento dos graos aconteceu independente da rota aplicada, porem a rota C se mostrou a mais eficiente em termos de fragmentacao da microestrutura e energia armazenada.

Analysis of the bonding interface in human dentin of two adhesive systems with and without the use of chlorhexdine in the cementation of ceramic restorations

The degradation of the adhesive interface of indirect ceramic and dentin restorations results fro... more The degradation of the adhesive interface of indirect ceramic and dentin restorations results from the interaction of several factors, including an enzyme called metalloproteinase. The objective of this study was to evaluate the interface of ceramic-dentin bonding by varying the use of chlorhexidine and of the conventional and self-etching adhesive systems. The dentin surface was divided into four areas: mesiobuccal, distobuccal, mesiolingual, and distolingual, forming four groups (n=4): G1 (MB) SB + SCL; G2 (DB) SB + CCL; G3 (ML) EO + SCL; G4 (DL) EO + CCL. Two mesiodistal cuts were made, thus, exposing the dentin interface-adhesive systems. The results showed that the use of chlorhexidine in the G2 formed a thicker hybrid layer, and in the G4 it acted to close the interface. It was concluded that the quality of the bonding interface of indirect ceramic restorations is related to the type of adhesive system used.

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Microstructural and textural characterization of a hot-rolled IF steel

Journal of Materials Science, Aug 1, 2007

The present paper reports the experimental results on the microstructural and textural characteri... more The present paper reports the experimental results on the microstructural and textural characterization of a hot-rolled IF steel. The IF steel was hot-rolled in multiple passes in the austenitic field (1,070 °C) followed by air-cooling. SEM, TEM, and LOM were used to image the microstructure of the material. The global texture was determined by X-ray diffraction (XRD) technique. The mesotexture of

Analysis of the Effect of Cyclic Fatigue on the Flexural Strength of a Ceramoceramic System Used in Dental Prostheses

Materials Science Forum, Sep 1, 2018

The aim of this study was to analyze the flexural strength of ceramics based on yttria-stabilized... more The aim of this study was to analyze the flexural strength of ceramics based on yttria-stabilized zirconia (YTZP) , used in the manufacture of dental prostheses infrastructure before and after aging with cyclic fatigue in moisture. The samples were made by pre-sintered blocks of ZirkonTransluzent (Zirkonzahn GMHB) from YTZP ceramics with and without feldspathic ceramic coating, divided into groups: G1 = YTZP control; G2 = YTZP aged; G3 = YTZP + feldspathic; G4 = YTZP + aged feldspathic. The samples were submitted to a three-point bending test with a speed of 0.5 mm / min. The mean values of the flexural strength values were G1 = 645 MPa (DP ± 124), G2 = 681 MPa (DP ± 129), G3 = 904Mpa (DP ± 157) and G4 = 954Mpa (DP ± 243). The values of groups G1 and G2; G3 and G4 were statistically similar, depending on the presence or absence of coating. Cyclic stresses did not affect the flexural strength of the material

Effect of Surface Treatment of Yttria Stabilized Zirconia for Dental Prostheses

Materials Science Forum, Aug 1, 2012

group patients received a prosthetic treatment executed with the Cresco system. Control group pat... more group patients received a prosthetic treatment executed with the Cresco system. Control group patients received a screw retained fixed prosthetic manufacture made with traditional lab procedure. On the day of the surgery implants were submerged and reopened after 3 months. Randomization was made after implant reopening. Implant survival and success rate were monitored during a 3-year time. Standardized radiographs were taken on the day of the surgery, during 1st, 2nd and 3rd year follow up. The survival and success of the prosthetic rehabilitation was also considered. Results: The success rate was 100% for Cresco implants and 94.28% for screwed implants. No statistically significant difference in success rate was found between Cresco and screwed implants. Success was reported in 78.57% of the patients restored with Cresco implants and 64.70% of patients restored with screwed implants. No statistically significant difference emerged among the frequencies of success, surgical complications and prosthodontic complications in patients restored with Cresco implants and screwed implants. Conclusions: This clinical trial did not show differences in survival and success rates of implants and prosthesis randomly realized using Cresco system or traditional lab procedures.

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Simulação numérica do Processo Ecap (Prensagem em Canais Equiangulares) utilizando o aço VMB 300

Cadernos UniFOA, 2017

O processo ECAP é uma técnica de deformação plástica severa, onde um tarugo é forçado a escoar nu... more O processo ECAP é uma técnica de deformação plástica severa, onde um tarugo é forçado a escoar numa matriz com dois canais de seções transversais idênticas formando um determinado ângulo entre si. Uma das vantagens deste processo é que o material deformado não sofre alteração dimensional, além de poder ser processado em temperatura ambiente. A deformação do tarugo ocorre numa estreita zona localizada na intersecção entre os dois canais da matriz, sob condições de cisalhamento. Foram analisadas as distribuições das tensões e deformações causadas no material durante o processo, por meio de simulação numérica utilizando o programa ANSYS (versão 8.1) adotando condições isotérmicas e estado plano de deformação. Os resultados mostraram que as deformações ocorreram por cisalhamento num ângulo de 45º próximo à intersecção dos canais. A parte inicial do tarugo não apresentou deformação, o que explica a necessidade de descartar esta região do material no término do processo.

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Evaluation of Static and Dynamic Hardness Tests of Dental Structures and Resin Restorative Composite

Materials Science Forum, 2019

The goal of this study was to characterize the mechanical behavior of dentin, dental enamel and a... more The goal of this study was to characterize the mechanical behavior of dentin, dental enamel and a nanoparticulate composite resin, used in dental restorations. This characterization was performed through the static and dynamic Vickers hardness test. As for the biological tissue assays, third included human molars were used. The nanoparticulate resinous composite was condensed into a matrix, measuring approximately 10x10x2mm. The obtained HV values were represented by hardness maps. The distribution of hardness values along the enamel and dentin structures occurred unevenly in the two hardness analyzes. For dental enamel, there were differences in hardness values when compared dynamic to static tests. This difference did not occur in dentin. It was observed that the mechanical behavior of the resinous composite resembled more the behavior of the dentin than the enamel.

Evaluation of Morphology and Roughness of the Surface of a Ceramic Based on Lithium Disilicate, after Conditioning with Acid Hydrofluoric the 5% and 10%

Materials Science Forum, 2015

The aim of the study was to evaluate the difference in the surface of dental ceramics, the basis ... more The aim of the study was to evaluate the difference in the surface of dental ceramics, the basis of lithium disilicate, varying the concentration and time of application of the acid. Samples of IPS e.max Press (Ivoclar) were divided into: G1-control; G2 hydrofluoric acid 10% - 20 sec; G3 hydrofluoric acid 10% - 40 sec; G4 hydrofluoric acid 5% - 20 sec G5 and hydrofluoric acid 5% - 40 sec. The samples were analyzed under SEM (Carl Zeiss) confocal microscope and (Carl Zeiss). The qualitative morphologic analysis showed that 40 seconds of conditioning promoted the dissolution of the vitreous component and the ceramic crystal display for the two concentrations. Hydrofluoric acid 10% showed higher values of roughness. One can conclude that conditioning for 40 seconds is more effective than the 20 seconds for the two concentrations hydrofluoric acid and 10% promoted a higher surface roughness in the ceramic.

Evaluation of Mechanical Properties of Composite Materials Used in Dentistry Varying the Inorganic Composition

Materials Science Forum, 2015

The aim of this study was to determine the hardness and the elasticity modulus of the two composi... more The aim of this study was to determine the hardness and the elasticity modulus of the two composite resins base of BISGMA with different inorganic particles: a nanoparticulated with a ceramic withload, (Filtek Z350XT-3M) with and without thermal activation and a microhybrid with no ceramic load (Opallis-FGM). The samples were prepared and subjected to the tests of Vickers hardness (Shimadzu HMV) and acoustic excitation pulse (Sonelastic ®). The samples were divided into three groups: G1-Filtek Z350 XT; G2-Filtek Z350XT MO (subject to further polymerization microwave) and G3-Opallis. The results showed that the hardness of G2 was significantly higher than the groups G1 and G3. The elastic modulus was higher than the G2 to G1 and G3. One can conclude that the resins filled with inorganic ceramic filler showed higher hardness and elastic modulus. The thermal activation increased the hardness and the elasticity modulus of the resin with ceramic load.

Analysis of Flexural Strength of Ceramics Based on Zirconia Stabilized by Yttria with Ceramic Cover

Materials Science Forum, 2015

The aim of this study was to analyze the flexural strength of ceramics based on yttria-stabilized... more The aim of this study was to analyze the flexural strength of ceramics based on yttria-stabilized zirconia ( Y-TZP) , used in the manufacture of dental prostheses infrastructure with different types of coating ceramics. The rectangular samples measuring 18mm x 4mm x 1.2 mm were divided into groups (n = 10): G1 = control Y-TZP, G2= Y-TZP + sintered feldspathic ceramic and G3= Y-TZP + pressable feldspathic ceramic and submitted to assay of three points with a speed of 0.5 mm / min. Compared to the control group (G1), the group that showed the greatest resistance to bending was the G2, however, not significant relative to G3. No group provided the infrastructure fracture. It was observed by means of the methodology applied to all groups are suitable for use in dental prostheses.

The role of the friction during the equal channel angular pressing of an IF-steel billet

Materials Science and Engineering: A, 2008

It is well known that high levels of friction induce adherence effects in materials processed by ... more It is well known that high levels of friction induce adherence effects in materials processed by equal channel angular pressing (ECAP) promoting some degree of heterogeneity along the deformation zone. In the present paper, the role of the friction in relation of die geometry considering frictionless, ideal lubrication and severe friction conditions of an interstitial free (IF) steel deformed by ECAP technique using plane strain finite element models was investigated in details. The analysis of adherence at the billet-die contact region during only one pass of deformation was carried out in a quasi-static form at room temperature. Independent of the die channels intersection angle (90 • or 120 •) analyzed an adherence phenomenon was observed under determined friction conditions. It can be concluded that it is necessary to establish an upper limit to the friction coefficient in order to avoid the adherence effect in two-dimensional finite element simulations.

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Analysis of the Y-TZP Ceramic Substucture in Blasting with Aluminum Oxide before and after Sintering

Materials Science Forum, 2014

The objective of this study was to evaluate the microstructure of a ceramic based on yttria stabi... more The objective of this study was to evaluate the microstructure of a ceramic based on yttria stabilized zirconia (Y-TZP) in blasting with aluminum oxide and its effect on the sintering. 25 pre-sintered Y-TZP blocks were obtained. Ten samples were blasted with alumina, and then all samples were sintered and divided into the groups: Control-no treatment; alumina G1-blasted with alumina and sintered; alumina and Rocatec G1-blasted, sintered, and Rocatec; alumina G2-sintered, alumina blasting; alumina and Rocatec G2-sintering, alumina blasting, and Rocatec. The samples were evaluated by a scanning electron microscopy. The qualitative analysis showed that the treated samples had an increase in the surface texture and that group 1– alumina and Rocatec– presented the silica incorporation to be regular and homogeneous. It was concluded that the treatment of pre-sintered surfaces is a good alternative in the bonding strength between the Y-TZP and the resin cements.

Annealing effects on the microstructure and texture of a multifilamentary Cu–Nb composite wire

Scripta Materialia, 2004

We report the microstructural evolution of a Cu-15%Nb composite annealed from 100 to 1050°C. The ... more We report the microstructural evolution of a Cu-15%Nb composite annealed from 100 to 1050°C. The microstructure was characterized by scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). Boundary splitting is the predominant mechanism to explain the spheroidization of niobium. A simple model describing this phenomenon is proposed.

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Numerical and experimental investigation of microporosity formation in a ternary Al–Cu–Si alloy

Journal of Alloys and Compounds, Jul 1, 2010

Abstract Macrosegregation and porosity formation are investigated by both a numerical model and t... more Abstract Macrosegregation and porosity formation are investigated by both a numerical model and transient directional solidification experiments. The macrosegregation pattern, and the theoretical and apparent densities are presented as a function of the casting length. X-ray fluorescence spectrometry was used to determine the experimental macrosegregation profiles. The measurement of microporosity was performed by a pyknometry procedure. The local composition along an Al–6 wt%Cu–1 wt%Si casting length is used as an input parameter for simulations of microporosity evolution. The results show that the addition of 1 wt% silicon to the Al–Cu alloy composition increases significantly the volumetric fraction of pores as compared with the corresponding porosity exhibited by an Al–6 wt%Cu alloy casting. It is also shown that the use of a carbon steel chill mold induced an abnormal increase in the fraction of pores close to the casting cooled surface which was caused by a higher Fe concentration provoked by the diffusive flux of iron from the chill.

Complex coacervates obtained from interaction egg yolk lipoprotein and polysaccharides

Food Hydrocolloids, 2013

Proteinepolysaccharide coacervates formation was evaluated under influence of pH (3.0, 4.0, 6.5, ... more Proteinepolysaccharide coacervates formation was evaluated under influence of pH (3.0, 4.0, 6.5, 8.5 and 10.0), temperature (10, 20, 30, 40 and 50 C) and polysaccharide mass (0.025, 0.033 and 0.050 g). It was possible to observe that solutions with lower turbidity values were found in pH band 3.0 to 4.0. Statistical analysis of turbidity data have shown that for all polymers pH was meaningful in coacervate formation, although for some, besides pH, temperature and polymer concentration could also influence significantly (p < 0,05) in coacervate formation. Encapsulates morphology made by coacervation was directly linked to the kind of polymer used and its interactional degree. Dehydrated coacervates have presented heterogeneous morphology, different from their original structures.

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Microstructural Analysis of Commercially Pure Magnesium Processed by ECAP at Room Temperature

In this paper, the evolution and distribution of the deformation structures and the hardness of p... more In this paper, the evolution and distribution of the deformation structures and the hardness of pre homogenized commercially pure magnesium were analyzed after a severe plastic deformation processing called ECAP (equal channel angular pressing). The tests were performed at room temperature and the heat treatment was done to optimize the process in this condition, trying to avoid the appearance of defects such as cracks and fissures. To perform the analyzes were used: optical microscope to obtain the microstructure after processing, and a hardness map, in order to compare the evolution of the mechanical properties.

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A microstructural investigation of adiabatic shear bands in an interstitial free steel

Materials Science and Engineering: A, 2007

We report the microstructural characterization of induced adiabatic shear bands (ASB) in a hot-ro... more We report the microstructural characterization of induced adiabatic shear bands (ASB) in a hot-rolled interstitial free (IF) steel deformed at high strain rates (>2.8 × 10 4 s −1) in a split Hopkinson bar under controlled conditions at −50 and 25 • C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used to reveal the degree of subdivision within ASB and neighboring grains. Deformation twins were found in adjacent grains suggesting that twinning occurs before the flow associated to shear banding. Progressive subgrain misorientation (PriSM) recrystallization is a plausible mechanism to explain the development of a new structure consisting of weakly textured ultrafine grains (0.1-0.5 m) within the ASB. Recrystallization is proposed to occur by the formation and mechanical rotation of subgrains during deformation, coupled with boundary refinement via diffusion during shear band cooling. The presence of elongated subgrains and grains perfectly aligned within regions resembling a former lamellar structure within bands supports the occurrence of such a mechanism.

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Caracterização de Uma Liga Nanoestruturada à Base de Mg para Uso como Armazenador de Hidrogênio

Estudo da Influência do Boro no Aço 10B45 (Fio Máquina e Arame Trefilado) analisando propriedades mecânicas e microestruturas

Cadernos UniFOA, 2018

O presente trabalho avaliou as influências da adição de diversos teores de boro nas característic... more O presente trabalho avaliou as influências da adição de diversos teores de boro nas características mecânicas e microestruturais do fio-máquina e arame trefilado no aço 10B45. Foi verificado que a adição de boro reduz a resistência do material, atuando sobre os mecanismos de envelhecimento, pois associa-se ao nitrogênio formando o nitreto de boro (BN) no contorno de grão. Assim, quanto maior a adição de boro, menor resistência à trefilação, o que pôde ser comprovado pelo ensaio de torção nos arames. Ainda foi possível avaliar o modo de fratura relacionado com a quantidade de boro adicionada. Nesse ponto, não foi possível atribuir maior ductilidade à amostra com maior teor de boro.

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Análise Microestrutural De Um Aço Inoxidável Duplex Uns S32304 Submetido Ao Processo De Soldagem Gmaw

Anais do Congresso Anual da ABM, Sep 1, 2017

Resumo O presente trabalho teve como objetivo analisar as diferentes microestruturas do aço inoxi... more Resumo O presente trabalho teve como objetivo analisar as diferentes microestruturas do aço inoxidável duplex UNS S32304 obtidas pelo processo de soldagem Gas Metal Arc Welding (GMAW). As regiões do metal base, zona fundida e zona afetada pelo calor foram investigadas nos corpos de prova com diferentes aportes térmicos. As microestruturas obtidas foram caracterizadas utilizando-se a microscopia óptica (MO). As imagens de Mo obtidas na zona afetada pelo calor mostram que a fração de austenita aumentou com o aumento do aporte térmico. Este aumento está relacionado ao alto teor de cromo e molibdênio presentes no metal de adição utilizado na soldagem. Na zona fundida, a fração de austenita de widmansttaten foi observada com maior frequência na microestrutura do corpo de prova soldado com o aporte térmico de 1,87KJ/mm. Essa maior fração de austenita de widmansttaten observada para o aporte térmico de 1,87KJ/mm está relacionada com o maior tempo de permanência em altas temperaturas deste corpo de prova em relação aos outros corpos de prova investigados. Vale ressaltar que a adição de nitrogênio também promove a formação desta fase. De modo geral, os resultados da metalografia quantitativa mostram que a porcentagem de ferrita foi superior a 65% nas zonas termicamente afetadas e fundidas.

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