Papers by Alexandre Da Silva Rocha
Investigation on Different TiCn Duplex Treatments Applied to Cold Work Tool Steel for Surface Properties Improvement
Journal of Materials Engineering and Performance
In this work, different plasma nitriding and coating thickness combinations were tested to improv... more In this work, different plasma nitriding and coating thickness combinations were tested to improve surface proprieties of a cold work tool steel. A DIN X100CrMoV8-1-1 cold work tool steel was plasma nitrided, using a 5 vol-%. N2 + 95 vol-% H2 gas mixture, for 2.5- and 5.0-h nitriding times. Then, the non-nitrided and nitrided substrates were coated with titanium carbonitride (TiCN)-graded thin films produced by cathodic arc plasma-assisted physical vapor deposition. Different deposition parameters were used to produce coatings with thicknesses of 1.0 and 2.0 µm. The samples were characterized regarding the microstructure, surface hardness, coating adhesion, and friction coefficient, which were measured by ball-on-disc tests. In the plasma nitriding process, it was possible to generate a diffusion layer, without the formation of a compound layer, with depths of 58 µm and 68 µm for 2.5 and 5.0 h, respectively. Both plasma nitriding treatments avoided delamination of the TiCN coating when deposited on the cold work tool steel. The TiCN coatings significantly decreased the friction coefficient, regardless of substrate condition. The lowest friction values were found for the thinner coating. The deeper diffusion zone led to higher hardness value, and highest scratch crack propagation resistance of the coatings, meaning superior coating adhesion. The best surface properties were found when combining the deeper plasma nitriding diffusion layer with the thinner PVD coating.
Tecnologia em Metalurgia, Materiais e Mineração
The evaluation and control of residual stress states in manufacturing processes such as cold draw... more The evaluation and control of residual stress states in manufacturing processes such as cold drawing can be difficult, especially in multi-phase materials. Diffraction methods are ideal for characterizing residual stresses in individual phases provided these phases scatter neutrons or X-rays well enough to obtain a good signal. Residual stresses determination problems in drawn components have been reported. Main constraints are measurements in the primary ferrite phase only. The presence of cementite in carbon steel is often neglected. A problem that has not yet been extensively investigated is how residual stresses in the ferrite and cementite phases develop in subsequent steps of material processing such as cold drawing. In this work a combined straightening and bar drawing process of AISI 1045 round bars from coils of a hot-rolled material was investigated. A careful characterization of the material, including residual stress states in the ferrite (α−Fe) and cementite (Fe 3 C) phases, using neutron diffraction and synchrotron diffraction was performed for each of the different manufacturing steps. The drawing and polishing and straightening (P.S.) parameters by crossed rolls were changed to evaluate their influence on the α−Fe and Fe 3 C residual stress distributions. After the drawing process, residual stresses in the cementite phase are highly tensile, as already reported, however it can be shown that after polishing and straightening steps residual stresses in the cementite phase decrease and residual stress distributions also depend on the tool angle used.
Turning parameters effects in residual stresses of AISI 1045 steel
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2021
The main objective of this work was to evaluate the influence of turning parameters on the genera... more The main objective of this work was to evaluate the influence of turning parameters on the generation of residual stresses in AISI 1045 steel bars. Therefore, effects of four main parameters as feed rate, cutting velocity, tool nose radius, and rake angle were analyzed. Residual stresses investigation through X-ray diffraction (XRD) was carried out at different depths (surface, 5, 10, 20, 50, and 75 μm). As the samples showed distinct roughness patterns with variable amplitude and shape, and based in a previous work, samples were classified in two main groups accordingly with surface finishing (regular and irregular). The current results showed that feed rate and cutting speed played the major influence on residual stress distributions. Moreover, the tool nose radius affected surface residual stresses, whereas the rake angle did not significantly change it. Finally, samples could be divided in two residual stress groups, showing a direct relation of surface finishing quality and res...
Materials Research, 2021
In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma n... more In this study, the sliding wear of a DIN 18MnCrSiMo6-4 continuous cooling bainitic steel plasma nitrided with a nitrogen rich gas composition was investigated. To evaluate the influence of processing time and temperature on mechanical and microstructural characteristics of nitrided layer, the samples were nitrided at 400, 450, 500 and 550 °C for 3, 6 and 9 h. The produced nitrided layers were characterized concerning the microstructure, phase composition, microhardness and surface roughness. The samples were tested by ball-on-flat reciprocating dry sliding for friction coefficient and wear analysis. The tests were stopped after a given damage criteria involving the rapid growth of the friction coefficients and wear. The correlation of the different treatment parameters and resulting case depths and surface hardness with sliding distance at the time of microcracks formation or delamination of the surface layer was evaluated statistically by the analysis of variance (ANOVA). The plasma nitrided samples at 550 °C showed better wear performances in the ball-on-flat tests than the other groups investigated, since these samples have a thicker compound layer and diffusion zone higher than the other conditions investigated. In general, the beginning wear is slower because of the hardest region of the compound layer.
Materials Research, 2022
For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided ... more For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N 2-H 2 gas mixtures, containing 5, 24, and 76 vol.% N 2. Samples were characterized concerning the resulting roughness, microstructure, compound layer's phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe 2-3 (C)N content in the compound layer decreases. A γ'-Fe 4 N monophasic compound layer was achieved at 5 vol.% N 2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N 2 in the gas mixture as higher amounts of γ'-Fe 4 N were formed. The 76 vol.% N 2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ'-Fe 4 N and ε-Fe 2-3 (C)N) with a predominant content of ε-Fe 2-3 (C)N.
Materials Research, 2021
Thermo-mechanical treatments using continuous cooling after forging are an established method for... more Thermo-mechanical treatments using continuous cooling after forging are an established method for producing bainitic steels, mainly because of the elimination of energy intensive additional heat treatment processes. The cooling is usually employed in an uncontrolled manner in the industrial sector, which can be detrimental to the resulting microstructural morphology and, consequently, to the final product properties. In this study, a new controlled two-step cooling route based on the principles of bainitic displacive growth was designed and applied in a 0.18C (wt-%) steel. Inverse finite element method was used on the cooling data to obtain the evolution of temperatures for the samples during cooling, allowing to assess point to point cooling rates. Investigations via X-ray diffraction, optical microscopy analysis and hardness testing revealed a variation of bainitic morphology, namely, the transition from granular bainite to lath-like bainite with relatively high hardness and constituents/ phase boundaries than the pre-treated microstructure.
Devido a necessidade de obtencao de uma superficie resistente ao desg aste e a oxidacao, os cilin... more Devido a necessidade de obtencao de uma superficie resistente ao desg aste e a oxidacao, os cilindros hidraulicos sao tradicionalmente reve stidos com cromo duro eletrodepositado. Todavia, este tipo de revestimen- to apresenta uma ampliacao gradual da area de apoio aos elementos de vedacao e guias, interferindo diretamente na lubrificacao da haste, ocasionando danos aos elem entos de vedacao e promovendo consequentes vazamentos. Outro apelo contrario a utilizacao do processo de revestimento com cromo e a presenca, em elevados niveis, de cromo hexavalente Cr +6 , apresentando alto poder cancerigeno e de contaminacao ambiental. Atualmente, o pro- cesso de aspersao termica em alta velocidade (HVOF - High Velocity Oxi-Fuel ) se caracteriza como uma tecni- ca de revestimento alternativa ao cr omo duro, utilizando materiais composito s (metal-cerâmico), os quais propi- ciam baixas taxas de desgaste. Recentes pesquisas tem mostrado que algumas propriedades mecânicas favore- cem a utilizaca...
Tecnologia em Metalurgia, Materiais e Mineração, 2021
Publicado pela ABM. Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creat... more Publicado pela ABM. Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que o trabalho original seja corretamente citado. a Aços bainíticos de baixo carbono e baixa liga produzidos por resfriamento contínuo apresentam formidável combinação de resistência mecânica e tenacidade para uma série de aplicações. O ponto chave desta interessante combinação está relacionado à microestrutura multifásica, a qual é influenciada principalmente pela composição química e parâmetros de tratamentos térmicos ou termomecânicos. O modo e a velocidade de resfriamento são parâmetros essenciais nas transformações microestruturais, e impactam no tipo, proporção e refino da microestrutura, determinando o desempenho do material. O objetivo deste trabalho foi avaliar a influência de diferentes meios de resfriamento sobre a microestrutura do aço bainítico DIN 18MnCrSiMo6-4. Amostras do material na condição de recebimento foram submetidas à austenitização e posteriormente ao resfriamento em água e óleo (têmpera), ao ar (normalização), em forno (recozimento) e em banho aquecido (austêmpera). As amostras tratadas foram caracterizadas por microscopia óptica e medições de dureza Vickers. Os resultados mostraram que o resfriamento em forno favorece a formação de ferrita, reduzindo a dureza do material, enquanto que o resfriamento ao ar não modifica significativamente a microestrutura e dureza. Já o resfriamento em banho isotérmico produz bainita granular e bainita em ripas, aumentando ligeiramente a dureza. Os resfriamentos em água e óleo formam martensita com dureza de 436 e 424 HV, respectivamente.
Influência Da Deformação Por Trefilação Na Precipitação De Fase Delta, Mesotextura e Tamanho De Grão Na Superliga De Níquel 718
ABM Proceedings, 2019
Materials Research, 2019
Yield strength and toughness in steels are directly associated with hot forging processes, especi... more Yield strength and toughness in steels are directly associated with hot forging processes, especially by controlling austenitic grain size and cooling conditions. The phenomenological JMAK model in macroscale has been applied in different material classes to predict grain size after hot forming. However, on an industrial application, there is still a lack of understanding concerning the synergic effects of strain rate and temperature on recrystallization. This preliminary study aimed at investigating the applicability of coupled semi-empirical JMAK and visco-elastoplastic models in numerical simulation to predict austenitic grain size (PAGS). Hot forging of cylindrical samples of a ferritic-perlitic DIN 20MnCr5 steel was performed followed by water quenching. The main influences, such as temperature, strain and strain rate fields following the recrystallization model were investigated using the subroutine of FORGE NxT 2.1 software. The results were evaluated by comparing experimentally measured and simulated PAGS at process end. The forging process generates different strain and strain rate fields in the workpiece, which in turn lead to a variation in the PAGS and recrystallization fractions. The simulation was able to detect the PAGS variation showing a good agreement between the experimental forging results and the applied model.
Journal of Materials Research and Technology, 2018
The purpose of this paper is to investigate the correlation of strain and hardness parameters in ... more The purpose of this paper is to investigate the correlation of strain and hardness parameters in a drawing process chain of an SAE 1045 steel bar. The present work discusses the application of the experimental and numerical method of analysis, based on hardness measurements, which allows evaluation of the strain distribution and mechanical properties in drawn products. The influence on the strain, hardness and residual stress distributions of cold drawing parameter variations were investigated by numerical simulation. A misalignment between bar and drawing tool was evaluated in the models, as well as variation of friction at different regions of the bar. Compression tests were carried out at different reductions to determine the flow curve and analyze the material behavior during a cold hardening process. The microstructural analysis has shown a potential influence of material segregation in the characteristics of the final products. Simulation results validate the assumption of die misalignment and inhomogeneous lubrication influences on residual stresses profiles after wire drawing. Taking into account effects of misalignment and friction at the same time, in a so-called combination model, a better agreement between numerical simulation and experimental results for cold drawing process was achieved.
Metallurgical and Materials Transactions A, 2017
Shafts are usually manufactured from bars that are cold drawn, cut machined, induction hardened, ... more Shafts are usually manufactured from bars that are cold drawn, cut machined, induction hardened, straightened, and finally ground. The main distortion is characterized by bending that appears after induction hardening and is corrected by straightening and/or grinding. In this work, the consequence of the variation of manufacturing parameters on the distortion was analyzed for a complete manufacturing route for production of induction hardened shafts made of Grade 1045 steel. A DoE plan was implemented varying the drawing angle, cutting method, induction hardening layer depth, and grinding penetration depth. The distortion was determined by calculating curvature vectors from dimensional analysis by 3D coordinate measurements. Optical microscopy, microhardness testing, residual stress analysis, and FEM process simulation were used to evaluate and understand effects of the main carriers of distortion potential. The drawing process was identified as the most significant influence on the final distortion of the shafts.
Metallurgical and Materials Transactions A, 2015
In this study, the distortion of steel shafts was investigated before and after induction hardeni... more In this study, the distortion of steel shafts was investigated before and after induction hardening. Several essential influencing factors in the manufacturing process chain regarding cold drawing, cutting method, notches on the shafts, and induction hardening were analyzed by design of experiment (DoE). Further necessary examinations of microstructures, hardness profile, segregation of chemical composition, and residual stress state were conducted for understanding the distortion behavior. The results of the statistical analysis of the DoE showed that the drawing process is the most important factor influencing distortion. The surface hardening depth of induction hardening is the second main factor. The relationship between inhomogeneities in the work pieces and the distortion was finally discussed.
Surface and Coatings Technology, 2014
In this work DIN X100CrMoV8-1-1 cold work tool steel samples were plasma nitrided and coated with... more In this work DIN X100CrMoV8-1-1 cold work tool steel samples were plasma nitrided and coated with two different films TiCN and AlCrN by plasma-assisted physical vapor deposition with cathodic arc evaporation method. The samples were characterized concerning surface roughness, chemical composition profile by Glow Discharge Optical Emission Spectroscopy (GDOES), hardness profile, coating thickness, coating adhesion, present phases and residual stresses. Friction coefficient and wear rate were measured by carrying out pin-on-disk tests. Furthermore the developed surface treatments were applied to cutting punches and industrial tests were carried out. Surface conditions (nitrided or not) prior to PAPVD did not affect roughness after coating, but coating adhesion was improved. Compressive residual stresses were increased on the previously plasma nitrided substrates when compared to those on the non-treated ones, and plasma nitriding also resulted in better load bearing capacity. Results also showed that AlCrN and the duplex AlCrN didn't present the running-in behavior as seen for TiCN and duplex TiCN. It was also possible to assure that the combination of plasma nitriding and the TiCN hard coating on top gave the best coating adhesion and the lowest wear rate, what is reflected on the cutting punches analysis after real industrial use.
Nitrided layer embrittlement due to edge effect on duplex treated AISI M2 high-speed steel
Surface and Coatings Technology, 2004
... Acknowledgements. C. Kwietniewski gratefully acknowledges the financial support from CNPq and... more ... Acknowledgements. C. Kwietniewski gratefully acknowledges the financial support from CNPq and FAPERGS, Brazil. The authors also acknowledge the undergraduate students Giovanni Rocha and Julio Kwietniewski for specimens' metallographic preparation. References. ...
ABM Proceedings, Oct 1, 2018
Resumo Em determinadas rotas de manufatura de componentes automotivos, principalmente de produtos... more Resumo Em determinadas rotas de manufatura de componentes automotivos, principalmente de produtos do segmento rodoviário pesado, são muito comuns processos de desempeno a quente, assim como outros procedimentos como arqueamento e alinhamento de longarinas. O presente trabalho tem por objetivo traçar os principais impactos destes processos sobre o material de alta resistência e baixa liga norma DIN EN 10149 S700MC em uma rota de fabricação de produtos automotivos com interferência de um procedimento a quente. Esse material, quando submetido ao ciclo térmico para alinhamento a quente, através do aquecimento de algumas regiões pontuais e do posterior resfriamento ao ar calmo têm suas propriedades mecânicas alteradas. Para comprovar isso, foram reproduzidas as condições do processo atual para mapeamento de dados de temperatura para os subsequentes ensaios de laboratório. Comparando as amostras submetidas ao ciclo térmico, com as produzidas com a mesma matéria prima sem aquecimento, pode-se verificar o impacto causado pelo processo de alinhamento a quente utilizado sobre as propriedades mecânicas do material. Os resultados mostram que o aço DIN EN 10149 S700MC apresenta alterações expressivas em todos os ciclos realizados. Com isso, ocorrem modificações na microestrutura pelo ciclo térmico ocasionando a diminuição de algumas propriedades mecânicas importantes, como tensão de escoamento, dureza e a tensão limite de fadiga. Palavras-chave: Ciclo térmico de aquecimento; Propriedades mecânicas dos aços; Fadiga; Aços de alta resistência e baixa liga.
Materials Research
Controlling the recrystallization is an important way to reach grain size refinement and outstand... more Controlling the recrystallization is an important way to reach grain size refinement and outstanding strength and toughness on alloy metals. This study sets out the application and investigation of mathematical microstructure modeling of a newly designed bainitic steel for hot forging industrial applications. The macro-scale model was used to observe and predict the austenitic grain size behavior during the controlled forging of a gear. Arrhenius grain growth kinetic and recrystallization model for a new class of bainitic steel was established for the given strain rate ranges and temperatures. This model was calibrated through microscopic analysis and used to simulate the unpublished constants of low alloyed bainitic forging steel DIN 18MnCrSiMo6-4 microstructure module using DEFORM® commercial finite element code. The increased temperature due to the adiabatic effect was investigated by numerical analysis, demonstrating its influence on grain coarsening. Local tensile test and Charpy-V notch were compared at different industrial hot forging temperatures and local plastic strain. Changes in yield strength and ductility have demonstrated the grain size influence on the processing parameters. The employed numerical model was an efficient tool to predict and present an alternative path to develop robust industrial forging using semi-empirical models.
Anais do Congresso Anual da ABM, 2017
Resumo Este trabalho tem por objetivo avaliar a sinterização a plasma do alumínio com a utilizaçã... more Resumo Este trabalho tem por objetivo avaliar a sinterização a plasma do alumínio com a utilização da técnica Active Screen, em comparação com o processo em forno resistivo. Foi utilizado pó de alumínio atomizado, com granulometria entre 30 e 100µm, sendo misturado junto aos pós cerca de 1% em massa de estearato de zinco como agente lubrificante. Foram confeccionados corpos de prova com 13mm de diâmetro e 10mm de altura. A compressão dos pós se deu através de uma prensa hidráulica, de ação simples, utilizando pressão de compactação de 600MPa. O tempo te sinterização foi mantido em 60min a temperatura de 500ºC, utilizando atmosfera de nitrogênio. Foram realizadas medidas de densificação, antes e após a sinterização, medição de rugosidade e microdureza superficial, bem como análises em MEV da superfície das amostras. O processo a plasma se mostrou satisfatório, sendo capaz de produzir amostras com boa densificação. As medições de microdureza superficial evidenciaram valores semelhantes entre os processos, sendo a amostra sinterizada via plasma a apresentar menor variação de microdureza. Através da análise de EDS das imagens, foi identificada a presença de estearato de zinco em ambos os processos, evidenciado que a extração do lubrificante não foi totalmente eficaz. Ainda, houve uma leve redução da rugosidade no processo a plasma em relação ao convencional. Palavras-chave: Não ferrosos, gaiola catódica, metalurgia do pó.
Anais do Congresso Anual da ABM, 2017
Resumo A fabricação de componentes para conformação mecânica possui uma gama de exigências devido... more Resumo A fabricação de componentes para conformação mecânica possui uma gama de exigências devido aos esforços cíclicos, como por exemplo, fadiga térmica. Devido à capacidade de formar geometrias complexas e usinar metais de alta dureza, a eletroerosão (EDM-Eletrical Discharge Machining) possui eficiência na produção destas matrizes. O estudo da integridade superficial do material erodido torna-se importante para avaliarmos qual são as condições ideais para tratamentos termoquímicos que visam a otimização da superfície da matriz usinada. Neste trabalho, foi investigada a integridade superficial do AISI H13, utilizadas para a fabricação de matrizes de forjamento a quente. Foram avaliadas a rugosidade e camada afetada pela técnica de Perfilometria Mecânica,Microscopia Ótica (MO) e Microscopia Eletrônica de Varredura (MEV). Verificaram-se diferentes superfícies, em diferentes parâmetros de usinagem e profundidades estabelecidas, observandose a subsuperfície do material.
American Journal of Materials Science, 2018
In this study, coatings WC-10Co-4Cr and Cr3C2-25NiCr were deposited on the AISI H13 steel by oxy-... more In this study, coatings WC-10Co-4Cr and Cr3C2-25NiCr were deposited on the AISI H13 steel by oxy-fuel Thermal spraying (HVOF). This coating increases the wear resistance of surfaces subjected to severe conditions, such as: abrasive wear, thermal fatigue and plastic deformation. The coatings microstructure, hardness and wear resistance are investigated through friction and wear tests performed through a pin-on-disc type tribometer following the procedures defined in ASTM G99-04. It was verified that both materials used in the spraying have high resistance to wear, however, in the sample coated with Cr3C2-25NiCr there was a greater removal of material during the test.
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Papers by Alexandre Da Silva Rocha