Doutorado em Engenharia Mecânica

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Estudo do compósito aço/ceramico AISI-316L/Sr1,8Y0,2CrReO6 produzido através da metalurgia do pó
(Universidade Federal do Espírito Santo, 2019-06-05) Salvador, Jose Firmino; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/; http://lattes.cnpq.br/0061402424211214; Franco Junior, Adonias Ribeiro ; https://orcid.org/; http://lattes.cnpq.br/6677652514776940; Passamai Junior, Jose Luis ; https://orcid.org/0000-0001-6866-1460; http://lattes.cnpq.br/5445869592199028; Passos, Carlos Augusto Cardoso; https://orcid.org/2528679879816545; http://lattes.cnpq.br/2528679879816545; Vieira, Estefano Aparecido; Cavichini, Arthur Sant Ana
This work studies the sintering of a steel/ceramic composite with stainless steel AISI 316L and Sr1.8Y0.2CrReO6 double perovskite (316L/SYCRO) by powder metallurgy. The goal was to produce a material that could be used in additive manufacture with structurally impact, corrosion and magnetic properties. AISI 316L stainless steel is a corrosion resistant material, but not magnetic. Sr1.8Y0.2CrReO6 (SYCRO) ceramic shows magnetic propriety until ~360 ºC (~640 K). 90% of 316L powder was mixed with 10% of SYCRO powder. The mixture was homogenized in a ball milling at low temperature (~77 K). The obtained powder was compacted in cylindrical forms, sealed in a evacuated quartzo tube and submitted to termal treatment for sintering. As a comparative standard, samples of 316L powder were sintered as the similar way of 316L/SYCRO samples. The sintered samples were evaluated by Scanning Electron Microscopy (SEM), X-ray Powder Diffraction (XRD), X-ray Computed Microtomography, Magnetic Susceptibility and Mechanical Compression test. The 316L/SYCRO composite showed a similar magnetism of SYCRO ceramic and a diferente mechanical behavior of sintered 316L sample. Taken into account this work it was demonstrated that it is possible to produce steel/ceramic composites with controllable contents.
Superlubricidade no deslizamento de cerâmicos lubrificados com água
(Universidade Federal do Espírito Santo, 2019-11-22) Strey, Nathan Fantecelle; Scandian, Cherlio; https://orcid.org/0000-0002-4393-719X; http://lattes.cnpq.br/8466752738430250; https://orcid.org/0000-0002-2568-116X; http://lattes.cnpq.br/3613706957012460 ; Sinatora, Amilton; https://orcid.org/0000-0002-5004-4947; http://lattes.cnpq.br/2988437176012972; Souza, Roberto Martins de; https://orcid.org/; http://lattes.cnpq.br/; Bozzi, Antonio Cesar; https://orcid.org/0000-0003-4857-0216; http://lattes.cnpq.br/3017292130810807; Murray, Henara Lillian Costa
Superlubricity is the state of a tribosystem characterized by extremely low friction coefficients, with μ < 0.01. The superlubricity of ceramic pairs sliding in water has been reported for several similar and dissimilar tribopairs: Si3N4-Si3N4; SiC-SiC, Al2O3-Al2O3, ZrO2-ZrO2, Si3N4-SiC, Si3N4 Al2O3, Al2O3-SiC, ZrO2-SiC, etc. By hypothesis, some requirements must be satisfied for superlubricity in these tribosystems to occur: low enough mean contact pressure, adequate surface finish, a mild wear regime during running-in where tribochemical mechanisms are dominant, and formation of a soft tribofilm adhered to surfaces. These conditions were reevaluated through different approaches: (i) the polishing process parameters were optimized during the preparation of engineering ceramics used in tribological components and a better surface finish was obtained for SiC surfaces when compared to Al2O3 or ZTA ones; (ii) wear maps were developed for several dissimilar ceramics pair sliding in water which showed that the combination of tribologically compatible ceramic counterparts extends the operating conditions range of ceramic sliding bearings and that the mild wear regime is a necessary but not sufficient condition for the occurrence of superlubricity. Finally, (iii) the construction of Stribeck curves for Si3N4-SiC, ZrO2-SiC, Si3N4-Al2O3 and SiO2-SiO2 pairs showed that superlubricity is associated with mixed or hydrodynamic lubrication regime, depending on operating conditions, and that the ratio between the minimum thickness of the hydrodynamic film and the amplitude of the surface roughness peaks (λ ratio) is the parameter that best explains the friction coefficient of these tribosystems.
Dinâmica em meios setorialmente homogêneos com o método dos elementos de contorno usando as técnicas de interpolação direta e de superposição de domínios
(Universidade Federal do Espírito Santo, 2019-12-12) Barbosa, Joao Paulo; Neto, Carlos Friedrich Loeffler; https://orcid.org/0000-0002-5754-6368; http://lattes.cnpq.br/3102733972897061; https://orcid.org/; http://lattes.cnpq.br/; Santiago, Jose Antonio Fontes; https://orcid.org/0000-0003-3089-954X; http://lattes.cnpq.br/6891803842511248; Mansur, Webe Joao; https://orcid.org/0000-0001-6033-9653; http://lattes.cnpq.br/9499429606822923; Telles, Jose Claudio de Faria; https://orcid.org/; http://lattes.cnpq.br/9055052467152337; Lara, Luciano de Oliveira Castro; https://orcid.org/0000000313292957; http://lattes.cnpq.br/1675675424615229; Bulcao, Andre; Cezario, Flavio
The Domain Superposition Technique (DST) is a new alternative to the Boundary Element Method (BEM) for solving piecewise homogeneous problems where the complete domain is divided into a surrounding homogeneous domain and other complementary subdomains with different constitutive properties. In this work, the DST is coupled to the direct interpolation technique with radial basis functions (DIBEM) to solve problems governed by the Helmholtz equation, by properly transforming the domain integral, relative to the inertia of the system, into a boundary integral. Thus, we generate a dynamic model capable of calculating the natural frequency spectrum in piecewise homogeneous domains with non-regular boundaries and internal inclusions, for both two-dimensional and three-dimensional cases. In the treatment of two-dimensional problems, linear isoparametric elements are used, while in three-dimensional cases the discretization is done by flat triangular isoparametric elements, of linear variation, with multiple nodes at the edges. To assess the numerical consistency of the more general model, simpler problems such as the three-dimensional homogeneous problems governed by the Laplace and Helmholtz equations were previously examined. Piecewise homogeneous three dimensional cases governed by the Laplace Equation were solved as well, in which the DST was also applied, including examples with geometric irregularities in the contour. The methodology proposed here provides a new model based on a BEM formulation simpler and faster than the previous related formulations, with satisfactory accuracy and convergence ensured with the mesh refinement. The work is also justified considering the use of the well-known advantages of BEM, such as its greater flexibility in mesh redefinition, its natural extension to open domain cases and suitability to fracture and contact problems, provided that the computational cost in these applications is not prohibitive.
O método dos elementos de contorno com interpolação direta aplicado à solução de problemas escalares funcionais em duas dimensões
(Universidade Federal do Espírito Santo, 2019-12-13) Barcelos, Hercules de Melo; Loeffler Neto, Carlos Friedrich ; https://orcid.org/0000-0002-5754-6368; http://lattes.cnpq.br/3102733972897061; https://orcid.org/0000-0001-6325-8429; http://lattes.cnpq.br/3388431029793400; Santiago, Jose Antonio Fontes; https://orcid.org/0000-0003-3089-954X; http://lattes.cnpq.br/6891803842511248; Mansur, Webe Joao; https://orcid.org/0000-0001-6033-9653; http://lattes.cnpq.br/9499429606822923; Telles, Jose Claudio de Faria; https://orcid.org/0000-0002-9940-4798; http://lattes.cnpq.br/9055052467152337; Lara, Luciano de Oliveira Castro; https://orcid.org/0000000313292957; http://lattes.cnpq.br/1675675424615229; Campos, Lucas Silveira; Bulcao, Andre
Recently, major challenges have emerged with the advances of modern engineering, and with this, the search for more elaborate model solutions becomes necessary. In this context, the numerical formulations to treat domain integrals present in these models
Development, calibration and deployment of an electrical resistance tomography system for multiphase flow experiments
(Universidade Federal do Espírito Santo, 2020-04-15) Moura, Bruno Furtado de; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; https://orcid.org/0000-0003-1912-3732; http://lattes.cnpq.br/4593797108698590; Silva, Wellington Betencurte da; https://orcid.org/0000-0003-2242-7825; http://lattes.cnpq.br/6900925458823632; Dutra, Julio Cesar Sampaio; https://orcid.org/0000-0001-6784-4150; http://lattes.cnpq.br/5331990513570911; Oliveira, Luiz Affonso Henderson Guedes de; https://orcid.org/0000-0003-2690-1563; http://lattes.cnpq.br/7987212907837941; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/3879935393431243; Ramos, Rogerio; https://orcid.org/0000000344932435; http://lattes.cnpq.br/2975022316691139; Palma, Francisco Hernán Sepúlveda; https://orcid.org/0000-0002-1930-3859
Electrical Impedance Tomography (EIT) is a soft-field tomography technique for imaging in industrial and medical applications. The method consists of injecting a bidirectional known current through electrodes inside a domain and measuring the subsequent voltages at the boundaries formed due to these injections, considering only non-ionizing radiation, unlike hard-field tomography. These measurements are acquired by a data acquisition system and are used to solve an inverse problem. The result is a distribution of the conductivities inside the domain. Thus, the image is formed by differences in electrical conductivity that may be present in this distribution. The present work aims to develop a data acquisition system and reconstruction software focused on multiphase flow measurement. A low-cost EIT system is developed, capable of 30.61 images/s with a signal-to-noise ratio of 57.47 dB. Further, the performance of the system is evaluated and it is drawn new guidelines from a validated model to develop the next version of the hardware. To extend the frequency response of the system, the parasitic capacitances, which are unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit, must be compensated or eliminated from the circuits. Methods to directly measure these quantities are scarce and limited. Therefore, a technique to statistically estimated with Maximum a Posterior and Markov Chain Monte Carlo method is presented in this work as an alternative. Since there is a concern in estimating sharp images by determining the position of the boundary, a new statistical and recursive application based on the particle filter is presented to estimate the conductivities inside the domain. The results demonstrated the capability of reconstructing fast-moving inclusions properly.
A novel pathway to recover hydrocarbons from polyethylene residues through the combustion-driven pyrolysis process
(Universidade Federal do Espírito Santo, 2021-02-24) Duque, João Vitor Ferreira; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; https://orcid.org/0000-0001-6639-1209; http://lattes.cnpq.br/4157383685655204; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; Pessoa, Fernando Luiz Pellegrini; https://orcid.org/; http://lattes.cnpq.br/6669992155373315; Rocha, Ana Maura Araujo; https://orcid.org/0000-0002-9146-4104; http://lattes.cnpq.br/6136430581477315; Debenest, Gérald; https://orcid.org/0000-0002-9597-5729; Perre, Patrick Gilbert Georges; https://orcid.org/0000-0001-6822-2775
Global production of plastic materials has grown drastically, but the technologies adopted by industry and the policies of combining waste streams, collection, treatment, and disposal have not followed this rapid growth rate. Several methods of thermochemical conversion of plastic waste into useful products have been investigated in the last decades; however, in terms of energy efficiency, the search for a technique that results in the recovery of noble products from plastic wastes is still a challenge, as is the understanding of its thermal degradation behavior. Therefore, the thesis’s general objective was to develop a self-sustainable energy device that uses low-grade fuels as heat-drive to pyrolysis, perform the polyethylene waste thermal cracking, and recover an energy-dense material. The steps toward achieving these objectives were to characterize a recycled polyethylene waste to determine its molecular composition and kinetics pathway from a single-step to a multi-step perspective; to launch a novel device in which the input energy for pyrolysis is driven by a combustion front propagating in a porous matrix, at this step, a new methodology was established to obtain a longitudinal temperature profile (LTP) for reactors with temperature increasing with time; to describe quantitatively and qualitatively for the first time, the propagation of a smoldering front in annular space - through temperature in time, gas analysis, and LTP - that wraps a concentric cylinder chamber in which the heat released by the combustion front is transferred for waste conversion; and finally, to conduct experiments toward the production and recovering of an energy-dense pyrolysis product in the form of wax and to characterize the wax employing FTIR to identify the functional groups, and a detailed kinetic analysis. The research results show that the polyethylene undergoing thermal and mechanical stress in its cycle life has functional groups with long carbon chains while weakening the compounds’ bonds. The main consequence was that recycled polyethylene need less activation energy to degrade thermally, modifying the pyrolysis pathway’s chemical groups. The designed combustion-driven reactor (C-DPyR) could perform polyethylene plastic waste pyrolysis. The proposed LTP served to explore the heat inputted to the pyrolysis chamber, ratifying that a self-sustaining combustion process carried enough energy to supply pyrolysis. The index Energy Availability showed that in the worst case, it remains 11% of energy underused, and at higher thermal energies conditions, just about 5% of the energy is consumed to convert the plastics. The primary outcome was that the volume ratio energy from combustion/energy to pyrolysis could be reduced by increasing the pyrolysis chamber’s volume to convert more kg of plastic per batch. The conclusion can also be drawn that different heat inputs were used to pyrolyze the polyethylene waste, resulting in different pyrolysis products’ yields. A maximum of about 87 wt.% of wax was recovered from an experiment at low thermal energy, confirming that low-grade fuel combustion is an alternative heat source capable of pyrolyzing plastic waste. The enthalpies of the recovered products hovered around 2115 J/g, and according to FTIR results, the wax’s functional groups identified were like the ones in low-density polyethylene’s waste. Therefore, the operational conditions attained by C-DPyR were able to recover a polyethylene wax. That means the C-DPyR process has the potential benefits of feedstock recycling in plastic waste management.
Otimização de superestruturas para a recuperação de calor residual de uma termelétrica brasileira a motores alternativos de combustão interna
(Universidade Federal do Espírito Santo, 2021-08-31) Morawski, Alexandre Persuhn; Santos, José Joaquim Conceição Soares; https://orcid.org/0000-0003-3695-2014; http://lattes.cnpq.br/6666040476009642; https://orcid.org/0000-0002-1158-3083; http://lattes.cnpq.br/0116066750864705; Carvalho, Monica; https://orcid.org/0000-0002-8524-3452; http://lattes.cnpq.br/7491245049317833; Silva, Julio Augusto Mendes da; http://lattes.cnpq.br/3724171990188048; Lora, Electo Eduardo Silva; https://orcid.org/0000-0001-8969-3541; http://lattes.cnpq.br/5479717772667720; Ramos, Rogerio; https://orcid.org/0000000344932435; http://lattes.cnpq.br/2975022316691139; Donatelli, João Luiz Marcon; http://lattes.cnpq.br/2019757368415541
The Brazilian thermal power plants were originally designed to serve as standby energy security for the grid, which is mainly supported by hydroelectric plants. The internal combustion engine (ICE) power plants eliminate copious amounts of residual heat through exhaust gases and cooling water. The current scenario has led to an increase in the operational times of these plants. An attractive solution for increasing power and efficiency in this situation is waste heat recovery (WHR). A variety of technologies and configurations can be used for WHR. The selection of the best WHR system is not a simple task, and the solution should not be generalized for different applications. In this context, optimization approach using mathematical programming has the advantage of providing a domain-independent systematic framework. In this thesis, a superstructure method is used for structural and parametric thermoeconomic optimization, selecting the best WHR for a Brazilian ICE power plant, considering UTE Viana as case study. The specificities and uncertainties of the Brazilian electricity scenario are taken into account through different operational and economic boundary conditions. The selection of the most suitable objective function that characterize the specificities of a Brazilian power plant is analyzed, as well as the influence of these objective functions on the optimization results. Moreover, is evaluated the influence of different heat carriers and economies of scale application. Four technologies are considered: conventional Rankine cycle (CRC), organic Rankine cycle (ORC), Kalina cycle (KC), and absorption chillers for intake air cooling (ChA). The adopted objective functions are: operating profit, net power, specific cost of investment, and specific cost of the generated power. The results demonstrate that the optimization responses are highly influenced by the objective functions, especially when different types of technologies are compared. The results analysis showed that the operating profit is the most suitable objective function to WHR of Brazilian power plants, accounting the uncertainties of the Brazilian scenario by means of annual dispatch hours and variable unit cost (VUC). The ORC alternative presented the best results when maximizing the operating profit, being indicated as the best alternative for WHR of Brazilian ICE power plants. The importance of a complete and simultaneous structural and parametric thermoeconomic optimization using the superstructure method was verified with the extensive variation of the optimum synthesis and parameters of the ORC. The optimization results showed that the influence of different objective functions, operational and economic boundary conditions, heat carries and economies of scale are present both in the variation of parametric variables, as in structural variables. For an optimistic scenario of dispatch and variable unit cost of electricity, the WHR using ORC systems can increase the power plant generation capacity up to 9.4%. For a more realistic scenario of boundary conditions, using an ORC system can increase the power plant generation capacity up to 5.4%. Keywords: Superstructure. Thermoeconomic optimization. Waste heat recovery. Brazilian thermal power plants. Internal combustion engines.
Diagrama abrangente e desagregação da exergia : Uma proposta de sistematização generalizada da modelagem termoeconômica
(Universidade Federal do Espírito Santo, 2021-12-22) Barone, Marcelo Aiolfi; Santos, José Joaquim Conceição Soares; https://orcid.org/0000-0003-3695-2014; http://lattes.cnpq.br/6666040476009642; https://orcid.org/0000-0001-9290-0062; http://lattes.cnpq.br/7099654064340324; Arrieta, Felipe Raul Ponce; https://orcid.org/0000-0001-7107-4929; http://lattes.cnpq.br/8666505917329368; Ramos, Rogério; https://orcid.org/0000000344932435; http://lattes.cnpq.br/2975022316691139; Errera, Marcelo Risso; https://orcid.org/0000-0002-9394-2712; http://lattes.cnpq.br/1262935578021391; Flórez-Orrego, Daniel Alexander; https://orcid.org/0000-0003-0103-7326; http://lattes.cnpq.br/1046064227631606
Some factors can interfere in the cost formation process, making it more arbitrary and less systematized. The objective of this thesis is to propose a generalized systematization of thermoeconomic modeling. The comprehensive diagram was created to eliminate the arbitrariness of the subsystems interconnections and limitations present in the conventional diagram, given that it represents the physical and productive flows in the same diagram, in addition to allowing the cost calculation of both flows. In turn, physical exergy disaggregation was used to isolate dissipative equipment and waste treatment. From the comprehensive unit, the localized exergy disaggregation technique was presented, which performs the physical exergy disaggregation only in the desired device. The results showed that the comprehensive diagram systematized the cost formation process, eliminating the interconnections arbitrariness in addition to allowing the treatment of the dissipative equipment. Only with the disaggregation of physical exergy it was possible to isolate the dissipative equipment and treat the residue systematically. The localized disaggregation obtained coherent unit exergetic cost values in addition to the reduction of complexity. Therefore, the comprehensive diagram is a solution to the interconnections arbitrariness and together with the physical exergy disaggregation it systematized and generalized the cost formation process. The best solution was the comprehensive diagram with the physical exergy disaggregation in Models H&S, UFS and UFS+, which showed a systematic cost formation process, regardless of the existence of dissipative equipment or waste.
Formação de poeira no empilhamento de materiais a granel
(Universidade Federal do Espírito Santo, 2022-06-29) Leão, Rodrigo Xavier de Almeida; Belich Junior, Humberto; https://orcid.org/0000-0002-8795-1735; http://lattes.cnpq.br/3879935393431243; https://orcid.org/0000-0002-0408-0410; http://lattes.cnpq.br/5311312721609904; Mesquita, Andre Luiz Amarante; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; Machado, Luis Paulo Silveira; Amorim, Leandro Silva
This is a study on the formation of dust that occurs during the stacking of bulk materials. Dust formation occurs by the suspension of microparticles easily transported to the atmosphere and over large distances by low-intensity air currents. Presents authorial methods for modeling and analysis of dust formation, including the development of a Lagrangian Particle Displacement Model (MLDP), analytical solution of the pressure field, computational solution of the velocity field through Computational Fluid Dynamics (CFD), evaluation of air flow regions, a model for the induced air flow and the mapping of particle dimensions capable to be transport by the fluid medium. The results demonstrate that if the stacking has a drop height greater than the critical one, the boundary layer acceleration at the core-fluid interface gives rise to a pressure gradient leading to the formation of a toroidal vortex near the impact zone, follow by expansion and detachment of the dust boundary layer. The velocity field undergoes a meaningful change and develops ascending updrafts and preferential escape paths for the microparticles. The probability of the process generating dust depends fundamentally on the physical dimensions of the stacking, as well as the type and granulometry of the material whose collisions between the grains generates nanoparticles that remain suspended in the surrounding air, altering the nearby environment and the dust’s ability to diffuse.
MICROESTRUTURA E TEXTURA CRISTALOGRÁFICA DOS AÇOS INOXIDÁVEIS MARTENSÍTICOS AISI 410, AISI 420 e EM 1.14116
(Universidade Federal do Espírito Santo, 2022-09-30) Moura, Ariane Neves de; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/; http://lattes.cnpq.br/; Fichtner, Paulo Fernando Papaleo; https://orcid.org/0000-0003-4574-2262; http://lattes.cnpq.br/3107128880946249; Rossi, Jesualdo Luiz; https://orcid.org/; http://lattes.cnpq.br/0763948174052925; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; Mucsi, Cristiano Stefano; Macedo, Marcelo Camargo Severo de; http://lattes.cnpq.br/5530638975120211
Martensitic transformation in martensitic stainless steel occurs only after the final conformation in the quenching process. Ferrite grains and Cr-rich carbides are observed in the microstructure during the hot rolling, cold rolling and annealing industrial processes. In this context, this study investigated the microstructures and textures of AISI 410, AISI 420 and EN 1.4116 stainless steels with different carbide fractions, initial grain sizes and textures after 50 % cold rolling reduction and annealing. Analysis of the experimental results showed the initial texture influenced the intensity and existence of texture gradient in the recrystallized samples. The stored energy after cold rolling and grain growth during annealing were mainly influenced by the (Cr,Fe)23C6 carbide fraction, which was identified as Cr15.58Fe7.42C6 type. Reducing initial grain size caused a change in the deformation mode to larger grain boundary constraints, weakening the {110}<001> Goss component in recrystallized textures. The recrystallized microstructures of AISI 420 and EN 1.4116 steels were heterogeneous owing to the (Cr,Fe)23C6 carbide bands in the as-received condition. In addition, the selective particle drag caused the γ- steels.
A fase oleosa e a degaseificação do CO2 na precipitação de CaCO3: implicações, modelagem, simulação numérica, validação e desenvolvimento de protótipo experimental
(Universidade Federal do Espírito Santo, 2022-11-21) Cosmo, Rafael de Paula; Soares, Edson José; http://lattes.cnpq.br/4485206584533650; https://orcid.org/0000-0002-4243-7871; http://lattes.cnpq.br/6932882950751155; Pereira, Fabio de Assis Ressel; https://orcid.org/0000-0002-1500-2952; http://lattes.cnpq.br/5476118728173549; Siqueira, Renato do Nascimento; https://orcid.org/0000-0002-8397-8180; http://lattes.cnpq.br/9791817633014124; Aldeia, Wagner; https://orcid.org/0000-0002-9914-819X; http://lattes.cnpq.br/5721602276797687; Fontes, Rosane Alves; Dariva, Claudio; Junqueira, Silvio Luiz de Mello; Martins, Andre Leibsohn
Precipitation and scaling are recurring problems in many water-handling processes. In oil production, particularly, such occurrences are critical due to the infeasibility or extreme difficulty of remedying precipitation or removing scale. This is due to adverse operating conditions: high pressures and temperatures; the action of corrosive gases such as CO2 and H2S; high salinity; and a confined system in a rocky medium. Pre-Salt carbonate reservoirs are notable for the high CO2 content in their fluids, with this acid gas being a variable affecting several stages of the exploitatory process. The relationship between CO2 and calcium carbonate (CaCO3) is evident in the reaction Ca2+(aq) + 2 HCO3 – (aq) ⇆ H2O + CaCO3(s) + CO2(aq). The pressure drop inherent to the production degass the CO2 (CO2(aq) → CO2(g)), which shifts the equilibrium to the right and implies the formation of CaCO3(s). An applied review of the role of CO2 in precipitation, considering the water, oil and gas phases, was carried out with field data from the Pre-Salt. Likewise for the aqueous, the oily CO2 degasses (CO2(o) → CO2(g)) and also implies more CaCO3, with the partitioning of the CO2 between phases governing the phenomenon. An experimental procedure developed to quantify the CaCO3 that precipitates directly due to pressure and temperature variation, and that which precipitates indirectly due to the escape of CO2, allows the estimation of the weight of the CO2 degassing in CaCO3 precipitation. This procedure was numerically simulated with MultiScale™ software for the H2O–CO2–CaCO3 system, indicating that CO2 escape contributes with 55% to 93% of precipitation. Five geothermal energy production assets (without oil) around the world reporting problems with carbonate precipitation have been investigated. As a result, the CO2 flash contributes with 66% to 93%. In simulations with real data from a Pre-Salt well (with oil), the contribution was 65% for the operating condition of the well with a BSW (basic sediments and water) of 35%. Simulations covering the BSW from 0% to 100% showed a “sui generis” behavior of the influence of CO2, coinciding with operational problems in many oil fields, and may help to explain their still unknown causes. An experimental prototype was designed and built to briefly perform this procedure. In addition, the unit will allow the research of several other phenomena related to flow assurance. In order to validate the equipment, some qualitative experiments were carried out, such as: scaling in gravel pack; formation of hydrates at 5 °C and 108 bar; precipitation of CaCO3 in the presence of CO2, CH4, salinity of 107,000 ppm, and Pre-Salt oil of 29 °API, at 95 °C and 104 bar, with the capture of “in situ” photomicrographs of crystals (calcite, aragonite, and vaterite); among others.
Estudo do comportamento mecânico em soldas do aço inoxidável lean duplex UNS S32304 utilizando modelos de encruamento
(Universidade Federal do Espírito Santo, 2023-01-27) Caetano, Gabriela Aksascki; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/0000000333721835; http://lattes.cnpq.br/6385356041873036; Bozzi, Antônio César; https://orcid.org/0000-0003-4857-0216; http://lattes.cnpq.br/3017292130810807; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; Mucsi, Cristiano Stefano; https://orcid.org/0000-0002-8637-4999; http://lattes.cnpq.br/2583729137737338; Bezzon, Vinicius Danilo Nonato; http://lattes.cnpq.br/8711723831656721; Vieira, Estefano Aparecido
Duplex stainless steels are characterized by their weldability, corrosion resistance, and good mechanical properties, the latter two properties being due to their biphasic microstructure of ferrite and austenite. The main focus of this research was to investigate the stress-strain behavior using work hardening models of the lean duplex stainless steel UNS S32304 with a thickness of 1.8 mm, welded by autogenous TIG process followed by heat treatment at different temperatures. In addition, initial investigations were carried out with laser beam welding using powder of duplex steel with TiB2 dispersion as a filler material. Microhardness tests, metallographic characterization with stereoscopy, optical and scanning electron microscopy, tensile test, and phase quantification by image processing were performed to evaluate the specimens welded by autogenous TIG process. The metallographic analysis showed that the heat treatments after TIG welding promoted an increase in the austenite phase content. An analysis of the stress-strain curves using work hardening models showed that the Voce and Hockett-Sherby models presented goodness-of-fit with the experimental data. In addition to the research, it was demonstrated that the parameters of both models are correlated with the volumetric content of austenitic phase in the fusion zone. Furthermore, laser beam welding with powder as filler material showed complete penetration, complete melting of the powder and the sheet, and no porosity was detected. It was verified through instrumented indentation measurements the dispersion of TiB2 and increased hardness and mechanical strength of the weld.
Síntese e caracterização dos compósitos metal-cerâmicos: AISI 316l/smba2cu3o7-δ e al/smba2cu3o7-δ
(Universidade Federal do Espírito Santo, 2023-03-02) Nunes, Lumena Glória de Souza; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; https://orcid.org/0000-0002-0927-8303; http://lattes.cnpq.br/7970077225500997; Rossi, Jesualdo Luiz; https://orcid.org/0000-0002-8304-9939; http://lattes.cnpq.br/0763948174052925; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; Mucsi, Cristiano Stefano; https://orcid.org/0000-0002-8637-4999; http://lattes.cnpq.br/2583729137737338; Vieira, Estefano Aparecido
The electrical, mechanical, and magnetic properties of superconducting ceramics have been investigated targeting technological applications. However, there are still technological challenges to be solved to enable its use on a large scale. Considering this scenario, in order to increase the mechanical properties of the bulk superconducting ceramic SmBa2Cu3O7- δ, a series of composites of stainless steel (100-x) AISI 316L + x SmBa2Cu3O7-δ and (100-x) SmBa2Cu3O7-δ + x Al were prepared by solid state reaction method. The (100-x) AISI 316L + x SmBa2Cu3O7-δ samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (MEV), hardness and magnetic susceptibility measurements. The microstructural analysis indicated the formation stainless steel with the presence of superconducting ceramics along their grain boundaries. Samples prepared without post-oxygenation, in the bulk form, presented ac magnetic susceptibility signal with superconducting transition at Tc ≈ 90K. Samples of (100-x) SmBa2Cu3O7-δ + x Al composites were also prepared by the solid-state reaction method. All samples were characterized by X-ray diffraction, magnetic susceptibility, scanning electron microscopy, relative density, and Vickers microhardness measurements. The results of microstructural analysis indicated that the addition of Al particles did not alter the crystal structure of the Sm-123 phase. Furthermore, ac magnetic susceptibility measurements of the samples revealed that the onset of the transition to the superconducting state of the composites are Tc ≈ 92K. However, the superconducting transitions of the composite samples showed a broadening as a result of the proximity and disorder effect. Energy dispersive spectrometry (EDS) analysis and elemental distribution maps of the composite samples indicated that Al nanoparticles precipitated at the grain boundaries of Sm123 ceramics. Finally, the Vickers microhardness values decreased with the addition of Al. These results demonstrate that the stainless steel and aluminum addition has improved the toughness of Sm-123 ceramic and it did not affect their superconducting properties.
Toward a safe and circular thermochemical process to sanitize human feces in resource-poor environments
(Universidade Federal do Espírito Santo, 2023-04-28) Bittencourt, Flavio Lopes Francisco; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; https://orcid.org/0000000182624762; http://lattes.cnpq.br/5146106444604968; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; Errera, Marcelo Risso; https://orcid.org/0000-0002-9394-2712; http://lattes.cnpq.br/1262935578021391; Magri, Maria Elisa; https://orcid.org/0000-0002-5911-4390; http://lattes.cnpq.br/2200887225218302; Pan, Ruming
Defecating in precarious facilities or even in the open environment is an undeniable reality in low-income countries. Despite the efforts made in recent years, unimproved facilities and the practice of open defecation are still generating around 70 wt% of the worldwide fecal matter. Smoldering combustion can be a fast, viable, and efficient mechanism to mitigate the impacts of fecal matter on the surrounding environment, using the energy potential of feces to transform them into solid and gaseous products without pathogens. Nevertheless, using human waste as a feedstock brings many challenges, especially regarding its hazardous aspect, rheologic properties, naturally moist state, and very-low permeability. In this thesis, a latrine-like device is conceptualized, constructed, and operated. The end products are safe for reuse from the perspective of circular economy and sustainability. A novel smoldering configuration driven by vacuum-induced airflow is studied to understand a series of thermal events that changes the aspects of propagating a combustion front in a smoldering reactor: the combination of a reactive porous bed shrinking with time and an open inlet increases the effects of free convection. Negligible free convection effects are observed when the shrinkage is meager; however, from the moment the thermal plume starts to grow, the boundary layer is squeezed into the reactor wall, gradually quenching the combustion front. A Nusselt number correlation expresses the energy available at the fluid-porous interface that can be recovered for secondary processes. After understanding and dominating the combustion process using the novel smoldering configuration, we present and launch the FeD-Latrine, reproducing in a laboratory-scale, real defecation scenarios to destroy fresh feces with an average dropping rate of 120 g/h. For the first time, fresh feces are destroyed in a smoldering reactor without decreasing their moisture content. To accomplish it, the arrangement of the FeD-Latrine uses out-of-bed heat to transform fecal matter into fecal chars and ashes. Even though the FeDLatrine emits pollutants at a controlled rate, reducing the global CO2-eq can make it even more sustainable. In such context, we present an integrated process for CO2 reduction and capture, using a gas looping to oxidize combustible gases and create favorable conditions to capture CO2 in bed. CaO used as a sorbent captures up to 8 mmol of CO2 per gram. Compared to kinetic-dominant processes for CO2 capture, we obtain an efficiency of around 52 %. Our findings show that using the FeD-Latrine to replace typical pit latrines reduces 60% of the CO2-eq emissions. Finally, a field trip to an Amazon community reveals that thermochemical processes are already part of the community member's routine, providing evidence of the potential application of thermochemical units for sanitation in resource-poor environments.
Tribological behavior of ZnO@GO core-shell nanoparticles as water-based lubricants additive and in composite cobalt-based coatings prepared via cathode plasma electrolysis deposition
(Universidade Federal do Espírito Santo, 2023-06-22) Romero, Manuelle Curbani; Scandian, Cherlio; https://orcid.org/8466752738430250; http://lattes.cnpq.br/8466752738430250; https://orcid.org/0000-0002-3578-8577; http://lattes.cnpq.br/2213541475559069; Tschiptschin, André Paulo; https://orcid.org/0000-0002-1806-2010; http://lattes.cnpq.br/2163698776105146; Mello, Valdicleide Silva e; https://orcid.org/0000-0001-6413-6650; http://lattes.cnpq.br/4147387781308845; Vieira, Lucia; Murray, Henara Lillian Costa; Strey, Nathan Fantecelle
Core-shell nanoparticles are hybrid nanostructure. This thesis addresses the electrostatic self-assembly of core-shell nanoparticles with hardcore of ZnO and soft graphene oxide (GO) shells. The assembled structures (ZnO@GO) were used as additive in water-based lubricants and in cobalt-based coatings. In the second chapter, the GO nanoparticles were synthesized and assembled with ZnO using a surface modifier, forming a ZnO@GO core-shell nanostructures. ZnO@GO, GO and ZnO were used as additives in water nanofluids which were wear tested in a ball-on-plate configuration using AISI 52100 as the ball and AISI 304 as the plate. ZnO@GO were efficient in reducing wear by the formation of a GO-rich protective tribolayer. The third chapter regards the production of cobalt coatings by cathodic plasma electrolytic deposition (CPED). The deposition mechanism and the effect of polyethylene glycol (PEG) on it are discussed. CPED was efficient in forming nanocrystalline and wear-resistant coatings. PEG decreased the current needed for deposition and affected the thickness and morphology of coatings, while not altering wear or friction. In the fourth chapter, the ZnO@GO nanoparticles were added to the electrolytic bath forming a composite cobalt-based coating. Coatings were tested against an AISI 52100 ball in sliding wear tests. Nanoparticles increased coatings hardness and decreased surface roughness. Composite coatings had a superior tribological performance when compared to pure Co-coatings due to the entrapment of exfoliated GO nanoparticles on the wear track, protecting the surface.
Modelagem termoeconômica generalizada e sistemática para o tratamento de resíduos e internalização de encargos ambientais em sistemas térmicos
(Universidade Federal do Espírito Santo, 2023-07-10) Faria, Pedro Rosseto de; Santos, José Joaquim Conceição Soares; https://orcid.org/0000-0003-3695-2014; http://lattes.cnpq.br/6666040476009642; https://orcid.org/0000000261503248; http://lattes.cnpq.br/5236112337927566; Reis Junior, Neyval Costa; https://orcid.org/0000000261594063; http://lattes.cnpq.br/4944106074149720; Palacio, José Carlos Escobar; https://orcid.org/0000-0001-8691-2737; http://lattes.cnpq.br/1472037977658347; Orozco, Dimas José Rúa; https://orcid.org/0000-0001-8153-989X; http://lattes.cnpq.br/3457569194994816; Ramos, Rogério; https://orcid.org/0000000344932435; http://lattes.cnpq.br/2975022316691139
Thermoeconomics originally combines Thermodynamics with Economics. Nevertheless, environmental issues can be incorporated. Despite the thermoeconomic modelling improvement and the quantity of methodologies available, topics such as waste cost allocation are still subject to criticism and can be considered important challenges to be solved for the rational and systematic inclusion of environmental charges. In many of the proposed methodologies there are subjective, incomplete, inconsistent or particular allocation criteria, which makes it difficult to define the waste cost formation process. Therefore, a generalized and systematic thermoeconomic methodology capable of treating waste and taking into account environmental issues in analyses of multiproduct systems is required. The main objective of this work is to consolidate the systematization of a methodology that is directly associated with the integration of a device that represents the environment with thermoeconomic diagrams. Models that already use this device have never been applied in thermal systems with more than one source of combustion to demonstrate the need for generalization and systematization. Still concerning the device that represents the environment, this work shows for the first time: i) how it is considered in closed-cycle thermal systems, such as steam cycles; ii) how it can be introduced in models that originally do not consider it explicitly, as in the E Model that uses exergy flows to define the thermoeconomic diagram; iii) the fundamental role it plays in the internalization of environmental charges, such as carbon credits and mitigation and environmental control devices cost; and iv) how it behaves and affects a thermoeconomic diagnosis assessment. The internalization of environmental cost exactly in the environment device systematically redistributes the costs to the other components of the system and the final products. Case studies, considering gas and steam cogeneration systems, show that the environmental device has a fundamental role in the generalized and systematic internalization of environmental charges, for instance, pollutant emissions, acquisition costs of mitigation and environmental control devices, and carbon pricing, among others. Through this internalization, it becomes feasible to assess the financial and environmental implications of emissions, foster the mitigation of greenhouse gases (GHG), and enhance the design and operation of systems.
A low-cost ERT system from a new perspective: performance improvement and film thickness measurements under fluid electrical conductivity variations
(Universidade Federal do Espírito Santo, 2023-08-18) Mata, Adriana Machado Malafaia da; Martins, Marcio Ferreira; https://orcid.org/000000023023222X; http://lattes.cnpq.br/7325983059020104; https://orcid.org/0000-0002-9076-456X; http://lattes.cnpq.br/2759329761747713; Guimaraes, Nubia Rosa da Silva; Demay, Miguel Burg; Moura, Bruno Furtado de; Junior, Arnaldo Gomes Leal; https://orcid.org/0000000290750619; http://lattes.cnpq.br/7246557168481527; Sepulveda, Francisco
Electrical tomography is a non-intrusive technique connecting electrodes around a system. Through voltage measurements, the conductivity in the region inside the electrodes is estimated through the Inverse Problem (IP). By utilizing advanced techniques in the calculation of PI, obtaining tomography images quickly has become a streamlined process. These features enable safety control and multiphase flow measurement with low flow interference, in multiphase flow. Eidors is consolidated software in this technique and provides real and imaginary part results. Considering only the real part (resistive effects), we can call it Electrical Resistance Tomography (ERT). Electrical tomography depends on a conductive medium and can distinguish oil and gas in water. Our line of research focused on identifying non-conductive objects in the continuous phase of water. Using a low-cost ERT acquisition system with varying conductivities, this thesis focused on data exploration and identification of variables with the most significant impact on reconstructed image quality. Most studies use tap water for testing, with conductivity up to 0.1 S/m. Oil extraction in deep waters brought the challenge of the presence of highly saline waters. Sea water can have high electrical conductivity, reaching up to 5.3 S/m, while formation water in oil extraction can have even higher values. The differential reconstruction is based on the measurement of the homogeneous tank compared with the tank with some non-conductive object. Therefore, the differential reconstruction reduces the effect of the background conductivity since the solution is the same in both measurements. However, it is possible to observe that when increasing the solution conductivity, the image reconstruction is affected. Therefore, the study of the influence of conductivity is relevant. The electrical tomography technique has the challenge of unrelated data. Because it is highly sensitive, small changes can result in unpredictable changes in the reconstructed image. Therefore, measured data may not be related to the applied tests. From the perspective of different conductivities, an analysis was proposed to assist in identifying critical variables. We identified the impact of the signal-to-noise ratio’s variance on the reconstructed image’s quality. In this way, it is possible to predict the final quality through the variance of the measurements and help in the adequate choice of techniques that propose the improvement of the images. Another challenge is that electrical tomography becomes unfeasible at high gas fractions. Alternatively, the film thickness calculation method allows using the same acquisition system. We then proposed improvements in modeling this technique with a dimensionless model to identify meaningful relationships. In this way, it was possible to validate the results using the strategy of varying the conductivity of the solution.
Estudo estrutural do compósito Fe-TiB2 obtido por spark plasma sintering
(Universidade Federal do Espírito Santo, 2023-08-21) Miranda, Mariane Gonçalves de; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; http://lattes.cnpq.br/2990952954091659; Rossi, Jesualdo Luiz; Passos, Carlos Augusto Cardoso; http://lattes.cnpq.br/2528679879816545; Oliveira, Marcelo Falcao de; Vieira, Estefano Aparecido
Metal matrix composites as Fe-TiB2 type have been widely investigated, since a great potential application has been identified, due to their physical and chemical properties, such as mass reduction and increased mechanical strength. Using a powder generated by the top-down technology of a microalloyed steel and a TiB2 ceramic powder, a composite with a mass ratio given by Steel (88%)/Ceramic (12%) was synthesized by the SPS (Spark Plasma Sintering) technique. The sintered samples were characterized by X-ray microtomography (μCT), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction, and transmission electron microscopy (MET). Thermodynamic simulation was also performed in order to calculate the phase transformation considering equilibrium. The high densification obtained by SPS was observed and the density reduction in relation to the matrix ρexp = 7.44(3) g/cm³. Results associated with microabrasion indicated that the presence of TiB2 promoted an increase in wear resistance of the composite in comparison to the steel. Detailed EBSD analysis revealed that the composite matrix consists of a submicrometric substructure, and combined with TEM analyses, it was possible to propose a model of the SPS sintering mechanism at the metal/ceramic interfaces.
Drop rise and interfacial coalescence initiation in complex materials
(Universidade Federal do Espírito Santo, 2023-11-10) Deoclecio, Lucas Henrique Pagoto; Soares, Edson José; http://lattes.cnpq.br/4485206584533650; https://orcid.org/0000000311368380; http://lattes.cnpq.br/7292913244820007; Cunha, Francisco Ricardo da; Siqueira, Renato do Nascimento; http://lattes.cnpq.br/9791817633014124; Thompson, Roney Leon; Ramos, Rogerio; https://orcid.org/0000000344932435; http://lattes.cnpq.br/2975022316691139
Drop rise and coalescence phenomena in complex materials hold significant relevance for various environmental and industrial processes. The intricate dynamics of the sequential steps of drop rise, collision, and film drainage are influenced by non-Newtonian behaviors such as plasticity and elasticity exhibited by the surrounding material. A comprehensive understanding of these processes is crucial for the efficient design and operation of industrial mixing and separating units. However, despite their importance, the underlying mechanisms governing these phenomena are not entirely comprehended. The primary objective of this thesis is to investigate the rise and interfacial coalescence initiation of a Newtonian drop in complex materials using time-dependent direct numerical simulations. The surrounding material is progressively modeled with formulations of increasing complexity, namely, Newtonian, inelastic viscoplastic, viscoelastic, and elasto-viscoplastic. To conduct the study, the elasto-viscoplastic Saramito model is implemented and validated. The investigation focuses on elucidating the influence of plastic, elastic, inertial, viscous, and surface tension effects, as well as their interaction on the dynamics of drop rise and coalescence initiation. Initially, the entrapment condition of spherical and non-spherical drops in inelastic viscoplastic materials is assessed in terms of the ratio of the force exerted by the yield stress and the buoyancy force. It is found that when determining the force exerted by the yield stress based on the radius of the maximum cross-sectional area of the drop (normal to buoyancy), this ratio remains constant for drops with low viscosity. However, for highly viscous drops, the ratio decreases asymptotically until it reaches the limit for solid spheres. For non-spherical drops, surface tension may yield the surrounding material to minimize the surface energy of the drop, making the drop to be permanently or only temporally mobile. For elasto-viscoplastic materials, elasticity increases the level of plasticity required for entrapment. Drop rise plays an important role in the initiation of the coalescence process. Inertial effects tend to increase the drop velocity and width, while an increase in the drop’s viscosity increases viscous dissipation and slows down the drop. The influence of surface tension on the droplet velocity and width depends on the dominant forces in the flow, which can cause both an increase or decrease in these quantities. Plastic effects result in a reduction of droplet velocity and width. Drop rise in viscoelastic materials is a dynamic process, influenced by the ratio of the relaxation time of the material to the characteristic rise time of the drop. Elastic effects also contribute to a reduction in drop width, facilitating its rise. In the case of elasto-viscoplastic materials, the interplay between elastic and plastic effects gives rise to intriguing behaviors. Plastic effects enhance the elastic behavior of the material, resulting in the appearance of the negative wake and teardrop shape (both characteristic of elastic behavior) for lower values of the elastic modulus when increasing the level of plasticity. Conversely, elastic effects suppress the plastic response of the material, leading to an expanded yielded region and reduced restriction on drop mobility by plasticity with increasing levels of elasticity. Regarding the coalescence phenomenon, plasticity manifests two main effects on the film drainage process. Firstly, it induces the formation of shorter and more spherical films, and secondly, it increases the resistance of the film to flow. The effect on the film shape facilitates the film drainage process, while the effect on the resistance of the film to flow hinders it. In regimes characterized by low surface tension, the influence of plasticity on the film geometry becomes more prominent than the resistance effect, resulting in a reduction in the drainage time. Conversely, in regimes characterized by high surface tension, where the interfaces between the fluids are less deformable, the resistance effect becomes more dominant compared to the effect of film shape, leading to an increase in the drainage time with the level of plasticity. Elastic effects also contribute to the formation of shorter films, thereby facilitating the drainage process. The partial or over activation of the viscosity of the elastic material further affects the rate of film drainage. Specifically, the partial activation of viscosity increases the drainage rate, while over-activation decreases it. In the case of elasto-viscoplastic materials, plastic effects enhance the partial activation of the material’s viscosity, facilitating the initial stage of the drainage process. Additionally, elastic deformation makes it more difficult for the drainage film to freeze due to yield stress.
Comportamento em desgaste por erosão-cavitação e em ensaios por esclerometria linear da liga Stellite 250 submetida a tratamentos térmicos e termoquímico de carbonitreção a plasma
(Universidade Federal do Espírito Santo, 2023-12-04) Oliveira, Daniela Bahiense de; Bozzi, Antonio Cesar; http://lattes.cnpq.br/3017292130810807; https://orcid.org/0000-0002-6173-6316; http://lattes.cnpq.br/6977424481086523; Franco Júnior, Adonias Ribeiro; Silva, Sidney Nicodemos da; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; Milan, Julio Cesar Giubilei
Cobalt superalloys are widely used due to their ability to maintain their mechanical, physical and chemical properties when used at high temperatures. However, concerns about the increasing demand for cobalt, unstable prices and few suppliers, make it essential to assess the efficiency of the materials applied. In this context, the present work investigated the effect of heat treatments (solution and aging treatments) and thermochemical plasma carbonitriding on the tribological behavior of the Stellite 250 alloy. The solution treatment was carried out at 1200°C for 1,5 hours and aging at 850°C for 4,5 hours. Thermochemical treatments were carried out at 360°C and 380°C for 9 hours. For tribological characterization, scratch tests were carried out with a progressive load (2 to 20N) and cavitation erosions tests were performed during 15 hours of exposure. The cross-sectional area of the scratches was verified by 3D profilometry. The wear mechanisms of the tribological tests were analyzed by scanning electron microscopy (SEM). The result of the microstructural characterization showed that for the cast alloy, the structure is formed by coarse grains, consisting of the α and ε phases. From the heat treatments, the structure remained mixed. Under all carbonitring conditions there was formation of a double layer of S-phase, composed of an N-enriched phase (SN) and another C-enriched layer (SC). The surface hardness values observed under carbonitrided conditions are in the order of 1100-1500 HV0.01. The scratch tests results showed that plasma carbonitriding condition enabled a considerable reduction in the coefficient of friction in relation to that observed for the Stellite 250 cast alloy. The wear mechanisms were tensile cracks in carbonitrided conditions; and in heat-treated conditions: formation of slip bands on the sides and cracks. The solution treated condition and subsequently carbonitrided at 380°C (SC380) showed greater resistance to cavitation erosion wear than the Stellite 250 cast alloy. Wear mechanisms include premature damage with formation and coalescence of pits, crater formation and brittle behavior of the material due to fatigue.

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