Recobrimento tribológico Cr-N e nitretação a plasma para melhoria da resistência à erosão cavitacional de um aço carbono ABNT 1045: uma abordagem topográfica

• Ano de defesa: 2005
• Autor(a) principal: Rafael Drumond Mancosu
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Regressão Linear Segmentada Contínua; PAPVD; Erosão Cavitacional; Tempo de Incubação; Perfilome-tria Tridimensional; Engenharia metalúrgica; Metais Erosão; Aço-carbono; Ciência dos materiais
• Link de acesso: http://hdl.handle.net/1843/BUOS-8DUHER

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 (-Cr, -Cr1-zNz and -Cr2N1-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 40m.