Recobrimento Tribológico Cr-N e Nitretação a Plasma para Melhoria da Resistência à Erosão Cavitacional de um Aço Carbono ABNT 1045: uma Abordagem Topográfica
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Data
2005-09-01
Autores
Mancosu, Rafael Drumond
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Este trabalho visou desenvolver sistemas tribológicos recobertos com Cr-N para resistência ao desgaste provocado pela erosão cavitacional. Utilizou-se o aço ABNT 1045 como referência e foram desenvolvidos três sistemas que são: aço nitretado, conjugado monocamada e conjugado dúplex. A nitretação iônica e a deposição do recobrimento Cr-N, produzindo o sistema denominado dúplex, foi realizada em um único reator, utilizando parâmetros do processo PVD (Physical Vapour Deposition), desenvolvidos anteriormente pelo Grupo de Pesquisa inscrito no Diretório dos Grupos de Pesquisa do CNPq-UFMG como 'Modificação e Caracterização de Superfície'. A produção dos sistemas aço nitretado e monocamada foram realizadas a partir de parâmetros adotados comercialmente. A caracterização estrutural destes sistemas revelou que os recobrimentos de Cr-N, depositados nos sistemas monocamada e dúplex, apresentaram uma similaridade em termos de fases cristalinas (a-Cr, g-Cr1-zNz e b-Cr2N1-z), de composição química e de aderência ao substrato, tal que estas variáveis de caracterização não constituíram fontes prováveis de causas de desempenho diferenciados destes sistemas relativo à erosão por cavitação. No entanto, a realização da nitretação iônica anterior a deposi-ção do recobrimento modificou as propriedades mecânicas destes sistemas ao longo da profundidade, aferidas por testes de microdureza e por testes de nanodureza instrumentada, que levou os mesmos a apresentarem respostas diferenciadas quanto à resistência à erosão cavitacional. Análises estatísticas de regressão segmentada contínua, utilizadas para descrição dos dados experimentais obtidos pelos testes de erosão cavitacional, indicaram a presença de diferentes regimes de erosão ao longo do tempo de teste. O sistema conjugado dúplex de Cr-N apresentou o melhor desempenho para o uso em erosão cavitacional em água destilada, pois apresentou a menor perda de massa e um maior tempo de incubação. O sistema nitretado apresentou um desempenho similar ao sistema monocamada e superior ao aço. O monitoramento, por perfilometria tridimensional, da evolução da erosão cavitacional nos diferentes sistemas estudados foi capaz de determinar o início de formação dos vales, que são criadas por arrancamento de material da superfície por esta erosão. O tempo associado ao início deste fenômeno foi denominado de 't-cratera'. Este tempo se mostrou inferior ao de incubação, com exceção do sistema dúplex, que é o tempo onde não se há perda de massa detectável por balança. Imagens topográficas tridi-mensionais invertidas indicaram a profundidade obtida dos danos cavitacionais e constituiu uma ferramenta capaz de elucidar os mecanismos presentes no processo de erosão e permitiu confirmar a superioridade do sistema dúplex, que apresentou em um tempo de até 20 horas, danos com profundidade inferiores aos outros sistemas es-tudados. Este resultado foi atribuído não somente a uma elevada dureza superficial obtida pela deposição do recobrimento de Cr-N, mas também a uma maior profundidade de dureza, obtida pela nitretação iônica, que formou uma camada nitretada da ordem de 40mm.
This thesis sought to develop tribology systems covered with Cr-N for wear resistance against by cavitation erosion. The ABNT 1045 steel was used as a reference material, and three systems were develop: nitrided steel, single-layered coating, and duplex coating. The plasma nitriding and the deposition of the Cr-N coating, producing the system denominated duplex coating, were accomplished in a single reactor, using parameters of the PVD process (Physical Vapour Deposition), which had previously been developed by the Group of Research, enrolled in the Directory of the Groups of Research of CNPq-UFMG as "Modification and Characterization of Surface". The production of the nitrided steel and single-layered coating systems were carried out starting from parameters adopted commercially. The structural characterization of these systems revealed that the Cr-N coatings, deposited in the single-layered and duplex systems, presented similarities in terms of crystalline phases (α-Cr, γ-Cr 1-z N z and β-Cr 2 N 1-z ), chemical composition and substrate adherence. These variables of characterization, however, did not constitute the main source of reasons for the distinct performance of these co-related cavitation erosion systems. In the other hand, the results of this research showed that the mechanical properties of these systems were modified along the depth, by the accomplishment of the previous plasma nitriding the deposition of the coating, assured by micro-hardness and scored nano-hardness tests. As a result, the systems showed distinct performances in terms of cavitation erosion resistance. Statistical analyses of continuous segmented regression, used for description of the experimental data obtained by the tests of cavitation erosion, indicated the presence of different erosion regimes along the time of test. The Cr-N duplex system presented the best performance for the use in cavitation erosion in distilled water, as it presented the smallest mass loss and a larger incubation time. The nitrided system presented a similar performance to the single-layered system and superior to the steel. The control, carried out by three-dimensional profilometry tests, of the evolution of the cavitation erosion in the distinct researched systems was able to determine the beginning of formation of the valleys, created by the removing of materials of the surface by this erosion. The time associated to the beginning of this phenomenon was referred as "t-crater". Except for the duplex system this time was shown to be inferior to the incubation time, that it is the time where loss of mass there is not to be detected by balance. Three-dimensional topographical inverted images indicated the obtained depth of the damages and it constituted a tool capable to elucidate the present mechanisms in the erosion process and it allowed to confirm the superiority of the duplex system, that presented in a time of up to 20 hours, damages with depth inferior to the other researched systems. This result was attributed not only to a high superficial hardness obtained by the deposition of the Cr-N coating, but also to a larger hardness depth, obtained by the plasma nitriding, that it formed a nitrided layer in the order of 40μm
This thesis sought to develop tribology systems covered with Cr-N for wear resistance against by cavitation erosion. The ABNT 1045 steel was used as a reference material, and three systems were develop: nitrided steel, single-layered coating, and duplex coating. The plasma nitriding and the deposition of the Cr-N coating, producing the system denominated duplex coating, were accomplished in a single reactor, using parameters of the PVD process (Physical Vapour Deposition), which had previously been developed by the Group of Research, enrolled in the Directory of the Groups of Research of CNPq-UFMG as "Modification and Characterization of Surface". The production of the nitrided steel and single-layered coating systems were carried out starting from parameters adopted commercially. The structural characterization of these systems revealed that the Cr-N coatings, deposited in the single-layered and duplex systems, presented similarities in terms of crystalline phases (α-Cr, γ-Cr 1-z N z and β-Cr 2 N 1-z ), chemical composition and substrate adherence. These variables of characterization, however, did not constitute the main source of reasons for the distinct performance of these co-related cavitation erosion systems. In the other hand, the results of this research showed that the mechanical properties of these systems were modified along the depth, by the accomplishment of the previous plasma nitriding the deposition of the coating, assured by micro-hardness and scored nano-hardness tests. As a result, the systems showed distinct performances in terms of cavitation erosion resistance. Statistical analyses of continuous segmented regression, used for description of the experimental data obtained by the tests of cavitation erosion, indicated the presence of different erosion regimes along the time of test. The Cr-N duplex system presented the best performance for the use in cavitation erosion in distilled water, as it presented the smallest mass loss and a larger incubation time. The nitrided system presented a similar performance to the single-layered system and superior to the steel. The control, carried out by three-dimensional profilometry tests, of the evolution of the cavitation erosion in the distinct researched systems was able to determine the beginning of formation of the valleys, created by the removing of materials of the surface by this erosion. The time associated to the beginning of this phenomenon was referred as "t-crater". Except for the duplex system this time was shown to be inferior to the incubation time, that it is the time where loss of mass there is not to be detected by balance. Three-dimensional topographical inverted images indicated the obtained depth of the damages and it constituted a tool capable to elucidate the present mechanisms in the erosion process and it allowed to confirm the superiority of the duplex system, that presented in a time of up to 20 hours, damages with depth inferior to the other researched systems. This result was attributed not only to a high superficial hardness obtained by the deposition of the Cr-N coating, but also to a larger hardness depth, obtained by the plasma nitriding, that it formed a nitrided layer in the order of 40μm
Descrição
Tese de Doutorado apresentada ao Curso de
Pós-Graduação em Engenharia Metalúrgica e de
Minas da Universidade Federal de Minas Gerais.
Área de Concentração: Ciência e Engenharia de Materiais
Orientadora: Prof a Dr a . Geralda Cristina Durães de Godoy
Palavras-chave
Erosão Cavitacional, Tempo de Incubação, PAPVD, Perfilometria Tridimensional, Regressão Linear Segmentada Contínua
Citação
MANCOSU, Rafael Drumond. Recobrimento Tribológico Cr-N e Nitretação a Plasma para Melhoria da Resistência à Erosão Cavitacional de um Aço Carbono ABNT 1045: uma Abordagem Topográfica. 2005. 334 p. Tese de Doutorado (Pós-Graduação em Engenharia Metalúrgica e de
Minas) - Universidade Federal de Minas Gerais, Belo Horizonte, 2005