Made available in DSpace on 2014-06-11T19:34:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T18:45:51Z : No. of bitstreams: 1 rodrigues_hl_dr_guara.pdf: 9863359 bytes, checksum: 8b410bae9d6a8516cca10d9c51e2625b (MD5) / Universidade Estadual Paulista (UNESP) / As necessidades do mercado mundial têm motivado a pesquisa de novos materiais para a fabricação de ferramentas e, apesar da evolução no projeto e manufatura de máquinas ferramenta, da otimização constante dos processos de fabricação e da tendência de crescimento da automação industrial, estes materiais continuam como um dos fatores limitantes no processo de usinagem. A deposição de finas camadas de carbetos sobre um substrato de metal duro, ao final da década de 60, resultou em um aumento da velocidade de corte e da vida da ferramenta. Atualmente os revestimentos mais aplicados são o nitreto de titânio (TiN), o óxido de alumínio (Al2O3), o carbeto de titânio (TiC), o carbonitreto de titânio (TiCN) e o nitreto de alumínio titânio (TiNAl). Neste trabalho, com o objetivo de avaliar e relacionar os valores do desgaste de flanco e da rugosidade da peça usinada, foram realizados testes de usinagem em aço ABNT-1050 com ferramentas de metal duro revestido por carbeto de titânio (TiC), óxido de alumínio (Al2O3) e nitreto de titânio (TiN). Sob uma velocidade de corte de 297 m/min, profundidade de usinagem de 0,5 mm e avanço de 0,15 mm/rot, tornearam-se percursos de corte correspondentes aos seguintes tempos: 2,2 min, 4,1 min, 6,14 min, 7,9 min, 14,2 min e 18,6 min. Verificou-se que os mecanismos de desgaste por difusão, adesão e delaminação, atuantes nas superfícies de folga das ferramentas, influenciaram o acabamento superficial das peças usinadas, enquanto que a influência principal no crescimento do desgaste de flanco (VB) resultou da ação do mecanismo de desgaste por difusão. / The needs of the world market have improved the research of new materials for tools production. Besides the design and manufacturing of tool-machines, the constant optimization of production process and the growth tendency of industrial automation, these materials continue being one of the limiters factors in a machining process. The deposition of fine carbide layers on hard metal substrates, at the end of 60 s, resulted in a increase of the cutting speed and tool life. Now, the main coating materials are titanium nitride (TiN), aluminum oxide (Al2O3), titanium carbide (TiC), titanium carbon nitride (TiCN) and titanium aluminum nitride (TiNAl). In this work, several machining tests in a ABNT-1050 steel with hard metal tools coated by TiC, Al2O3 and TiN were been realized in order to evaluate the tool flank wear and the workpiece roughness. Cutting speed of 297 m/min, cutting depth of 0.5 mm and feed of 0.15 mm/rot were applied to machine cutting paths corresponding 2.2 min, 4.1 min, 6.14 min, 7.9 min, 14.2 min and 18.6 min. Diffusion, adhesion and delamination wear mechanisms were verified in the tool flank surface, having influence in the surface roughness of the machined workpieces, while the flank wear growth (VB) were resulted by the action of diffusion wear mechanism.

Orientador: Sérgio João Crnkovic / Banca: Marcelo dos Santos Pereira / Banca: Marcos Valério Ribeiro / Banca: Olivério Moreira de Macado Silva / Resumo: As necessidades do mercado mundial têm motivado a pesquisa de novos materiais para a fabricação de ferramentas e, apesar da evolução no projeto e manufatura de máquinas ferramenta, da otimização constante dos processos de fabricação e da tendência de crescimento da automação industrial, estes materiais continuam como um dos fatores limitantes no processo de usinagem. A deposição de finas camadas de carbetos sobre um substrato de metal duro, ao final da década de 60, resultou em um aumento da velocidade de corte e da vida da ferramenta. Atualmente os revestimentos mais aplicados são o nitreto de titânio (TiN), o óxido de alumínio (Al2O3), o carbeto de titânio (TiC), o carbonitreto de titânio (TiCN) e o nitreto de alumínio titânio (TiNAl). Neste trabalho, com o objetivo de avaliar e relacionar os valores do desgaste de flanco e da rugosidade da peça usinada, foram realizados testes de usinagem em aço ABNT-1050 com ferramentas de metal duro revestido por carbeto de titânio (TiC), óxido de alumínio (Al2O3) e nitreto de titânio (TiN). Sob uma velocidade de corte de 297 m/min, profundidade de usinagem de 0,5 mm e avanço de 0,15 mm/rot, tornearam-se percursos de corte correspondentes aos seguintes tempos: 2,2 min, 4,1 min, 6,14 min, 7,9 min, 14,2 min e 18,6 min. Verificou-se que os mecanismos de desgaste por difusão, adesão e delaminação, atuantes nas superfícies de folga das ferramentas, influenciaram o acabamento superficial das peças usinadas, enquanto que a influência principal no crescimento do desgaste de flanco (VB) resultou da ação do mecanismo de desgaste por difusão. / Abstract: The needs of the world market have improved the research of new materials for tools production. Besides the design and manufacturing of tool-machines, the constant optimization of production process and the growth tendency of industrial automation, these materials continue being one of the limiters factors in a machining process. The deposition of fine carbide layers on hard metal substrates, at the end of 60’s, resulted in a increase of the cutting speed and tool life. Now, the main coating materials are titanium nitride (TiN), aluminum oxide (Al2O3), titanium carbide (TiC), titanium carbon nitride (TiCN) and titanium aluminum nitride (TiNAl). In this work, several machining tests in a ABNT-1050 steel with hard metal tools coated by TiC, Al2O3 and TiN were been realized in order to evaluate the tool flank wear and the workpiece roughness. Cutting speed of 297 m/min, cutting depth of 0.5 mm and feed of 0.15 mm/rot were applied to machine cutting paths corresponding 2.2 min, 4.1 min, 6.14 min, 7.9 min, 14.2 min and 18.6 min. Diffusion, adhesion and delamination wear mechanisms were verified in the tool flank surface, having influence in the surface roughness of the machined workpieces, while the flank wear growth (VB) were resulted by the action of diffusion wear mechanism. / Doutor

Fretting wear occurs when two bodies in contact are subject to small oscillatory displacements. This wear phenomenon is common in many industrial applications, such as gears, couplings, bearings, screws, valves and joints where vibrations occur. It has been shown that many factors affect the fretting wear rate, e.g. the normal load, sliding distance, geometry of the bodies, surface roughness, material properties, lubrication status, temperature and presence of third bodies. Fatigue has also been the subject of much investigation over the past century. Fatigue damage is observed in the form of microcracks, debonding, etc. in the vicinity of stress risers (e.g. inclusions, voids etc.) within the materials. The stress component causing fatigue failure can be normal, shear, or a combination due to a compound state of loading. In order to investigate the shear mode of fatigue failure, torsional fatigue testing has been the subject of many studies. Shear mode of failure is of significant importance in triaxial state of stress present for ball and rolling element bearings and machine component which are subject to fretting fatigue. A number of different experimental and numerical techniques have developed to study the torsion fatigue and fretting wear of materials at different conditions. An in-situ fretting wear measurement technique was developed to investigate the effects of temperature on the coefficient of friction and wear rate of Inconel 617 in fretting wear in air and helium environments. Due to the importance of the shear mode of stress in fretting fatigue phenomenon, another set of experiments were designed to measure high cycle torsional fatigue properties of Inconel 617 at elevated temperatures. An MTS torsional fatigue test rig was modified with customized mechanical grips and cooling fins. In order to achieve the objectives of analytical aspects of this investigation, a 3D elastic-plastic finite element model was developed to examine the torsional fatigue damage in Inconel 617 material at high temperatures. Then, a 3D finite element model was developed to study fretting wear of similar materials in Hertzian line and circular contacts. The wear law incorporated in this model is based on the accumulated dissipated energy law. The FEM was used to investigate partial slip regime. Then, the model was verified by performing several experimental tests for the circular contact configuration. During fretting wear, the generated wear debris is of significant importance. A finite element model was created to study the third body effects on fretting wear of Hertzian contacts in the partial slip regime. Both first bodies and third bodies were modeled as elastic-plastic materials. The effect of the third body particles on contact stresses and stick-slip behavior was investigated. The influence of the number of third body particles and material properties including modulus of elasticity, hardening modulus, and yield strength were analyzed. Finally, A new thermally cured polymer-graphene-zinc oxide-based solid lubricant was developed that reduced friction and wear significantly during the sliding wear of bearing steel under extreme contact pressure and long duration. The dry solid coating composite was made from a mixture of graphene, zinc oxide, and a specific industrial binder and then laminated on the surface of 52100 steel disks using the spin-coating technique. After ∼3000 cycles, the 15 μm thick coating created a significant reduction in the steel's coefficient of friction (approximately 82%) and wear loss compared to the uncoated surfaces. Following the tribological<a></a> examination, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy were conducted to determine the topography and morphology of the composite coating and resultant wear scars.

Os aços Hardox possuem microestrutura de martensita revenida e são caracterizados pelas elevadas dureza e resistência à tração, sendo empregados em situações que requerem alta resistência ao desgaste. Entretanto, os processos de soldagem alteram significativamente a sua microestrutura e propriedades. Assim, o objetivo deste estudo foi avaliar a resistência ao desgaste de juntas soldadas de um aço Hardox 500 produzidas através do processo MAG convencional e, juntamente, com o Hardox sem soldagem (metal base), para comparação. A soldagem ocorreu utilizando dois consumíveis, um recomendado pela empresa fabricante do aço, o AWS ER80S-G, e outro de maior resistência mecânica, o consumível AWS ER120SG. As propriedades mecânicas das juntas soldadas foram avaliadas através de perfis de microdureza, ensaios de tração e dobramento. Ainda, foi realizada uma análise da superfície de fratura dos corpos de prova do ensaio de tração, em microscópio eletrônico de varredura. Foram executados ensaios de desgaste por um abrasômetro do tipo roda de borracha. Análises através de microscopia óptica e microscopia eletrônica de varredura foram utilizadas para verificar os mecanismos de desgaste nas superfícies submetidas à abrasão Nos ensaios de dobramento, constatou-se que a condição soldada com o arame de menor resistência apresentou maior ductilidade. Verificou-se, também, que com a soldagem houve uma diminuição da resistência mecânica das juntas em comparação ao metal sem soldagem. Em relação aos ensaios de desgaste, com o uso do arame de maior resistência foi atingido um melhor desempenho no desgaste abrasivo em comparação ao de menor resistência, pois as taxas de desgaste foram de 0,058 e 0,083 mm³/m, respectivamente, mas o comportamento foi ainda inferior ao exibido pelo aço Hardox 500 sem soldagem, que apresentou uma taxa de desgaste de 0,031 mm³/m. Constatou-se, também, que os mecanismos de desgaste foram dúcteis em todas as condições estudadas, pois as superfícies desgastadas mostravam predominantemente micro sulcamento e regiões com micro fadiga; essa última parece ter aumentado de tamanho à medida que a dureza do material testado aumentava. / The Hardox steels have a martensite microstructure and are characterized by high hardness and tensile strength. This steel has been used in situations that require high resistance to wear. However, the welding processes significantly alter their microstructures and properties. Thus, the purpose of this study was to evaluate the wear resistance of welded joints of Hardox 500 steel produced by the conventional MAG process and with Hardox without welding (base metal), for comparison. The welding took place using two consumables, one recommended by the steel manufacturer, the AWS ER80S-G and another with higher resistance, the consumable AWS ER120S-G. The mechanical properties of welded joints were evaluated through micro hardness profiles, tensile and bending tests. In addition an analysis of the fracture surface of the tensile test specimen was carried out by scanning electron microscopy. Wear tests were performed by a rubber wheel type abrasometer. Analyses by optical microscopy and scanning electron microscopy were used to verify the mechanisms of wear on surfaces subjected to abrasion In the bending tests, it was verified that the welded condition with the filler metal of lower resistance presented greater ductility. It was also verified that with the welding, there was a decrease in the mechanical strength of the joints in comparison with the base metal. In relation to the wear tests, with the use of the higher strength wire, a better performance was obtained when compared to the lower one, since the wear rates were 0.058 and 0.083 mm³/m respectively, but the behavior was lower in the Hardox 500 steel without welding, which presented a wear rate of 0.031 mm³/m. It was also observed that the wear mechanisms were ductile in all the studied conditions, since the worn surfaces showed predominantly micro plowing and regions with micro fatigue, the latter seem to have increased in size as the hardness of the tested material increased.

As superligas à base de cobalto são bem conhecidas por sua excelente resistência ao desgaste. Muitas pesquisas reportadas na literatura abordam o comportamento do desgaste destas ligas, seja no desgaste por deslizamento, erosivo ou abrasivo. Não obstante, o desgaste microabrasivo destas ligas não tem sido muito investigado, apesar dos danos causados por este tipo de solicitação. O comportamento do desgaste microabrasivo de três superligas à base de cobalto: a) 48% Co, 29 %Cr, 19 % Fe; b) uma liga com composição química próxima à da liga comercial Tribaloy T400 (Co 56 %, Cr 8.5%, Mo 29% Si 3.3 %) e c) uma liga com composição próxima à da liga comercial Stellite 6 (Co 64%, Cr 24 %, W 4.2 %, C 2,3%) foram investigadas. Os ensaios de microabrasão foram conduzidos com três abrasivos SiO2, Al2O3, e SiC em suspensão em água destilada, com concentração de 0,1 g/cm3. A carga aplicada foi de 0,3 N, a velocidade angular 20 rpm e a distância total de deslizamento, 48 metros. A análise das superfícies desgastadas por microscopia óptica, eletrônica de varredura e por perfilometria de contato mostraram que o tamanho, forma e dureza dos abrasivos podem influenciar significativamente os coeficientes de desgaste. Os ensaios conduzidos com partículas abrasivas de SiC e Al2O3 apresentaram maiores coeficientes de desgaste que os conduzidos com partículas de SiO2. A Liga Co-Cr-Fe mostrou os maiores coeficientes de desgaste quando comparada com as demais ligas, devido à baixa fração volumétrica de partículas de segunda fase, duras, precipitadas em sua microestrutura. Durante os ensaios, as três ligas, ensaiadas com os três diferentes abrasivos, apresentaram coeficientes de desgaste crescentes com o aumento da dureza do abrasivo; observou-se uma variação linear dos coeficientes de desgaste com a razão entre a dureza do abrasivo (Ha) e a dureza composta da liga (Hs), com R2 = 0.74. O micromecanismo dominante em todos os ensaios foi o desgaste abrasivo a dois corpos (grooving wear). A liga com composição próxima à da liga comercial Tribaloy T400, contendo fases de Laves dispersas em sua microestrutura, apresentou uma transição de micromecanismo de desgaste dúctil para frágil, quando submetida a ensaios com partículas abrasivas de Al2O3. Assim sendo, o volume de material removido nesta liga foi ligeiramente maior que o observado no ensaio com partículas de SiC. Na liga contendo baixa fração volumétrica de partículas de segunda fase, com matriz constituída por Co (CFC), observou-se uma camada subsuperficial nanocristalina de aproximadamente 1 µm de espessura, severamente deformada, imediatamente abaixo da superfície desgastada. Concluiu-se que o desgaste microabrasivo induziu a recristalização a frio do material encruado, com formação de grãos equiaxiais de dimensões nanométricas. / Cobalt alloys are well known for their excellent wear resistance. Many investigations are reported in literature related to the behavior of erosive, abrasive or sliding wear of these alloys. Nevertheless, the micro-abrasive wear of these alloys has not been thoroughly investigated, despite the damage caused by this type of wear. The microabrasive wear behavior of three cobalt alloys: a) 48 wt.% Co, 29 wt.% Cr, 19 wt.% Fe; b) an alloy with chemical composition close to Tribaloy T400 (56 wt.% Co, 8.5 wt.% Cr, 29% wt. Mo, 3.3 wt. %Si) and c) an alloy with chemical composition close to Stellite 6 (64wt.% Co 24 wt.% Cr, 4.2 wt.% W, 2,3 wt.% C were investigated. The tests were carried out using three 0,1 g/cm3 slurries composed by SiO2, Al2O3, and SiC particles, in suspension in distilled water. The applied load was 0.3 N, the rotational speed 20 rpm and the total sliding distance 48 m. Analysis of the worn surfaces of the tested alloys by Optical Microscopy, Scanning Electron Microscopy and Contact Stylus Profilometry showed that abrasive size, shape and hardness could significantly influence the wear coefficients. The tests carried out with SiC and Al2O3 slurries resulted in greater wear rates than those carried out in SiO2 slurry. Stellite 250, showed the greatest wear coefficient, compared to the two other experimental alloys, due to a very low volume fraction of hard second phase particles in the microstructure. Wear coefficients decreased with increasing abrasive particles hardness. An approximate linear correlation with the ratio between the hardness of the abrasives (Ha) and the compound hardness of the alloys (Ha) with a correlation factor R2= 0.74. The dominant wear micromechanism observed in all tests was two-body abrasion (grooving wear). The modified T400 alloy, containing Laves phase showed a transition from ductile to brittle wear mechanisms when testing with alumina slurries. The worn volume was slightly greater than the one observed with SiC. A severely deformed nanocrystalline layer was identified, immediately below the worn surface. It was concluded that cold recrystallization of the work-hardened material occurred, with the formation of nano sized equiaxed grains.

Wear transitions in the wheel–rail contact are of increasing interest since the general trend in railway traffic is toward increased velocities and axle loads. Curving increases the risk of flanging, causing the contact to change from an almost pure rolling wheel tread–rail head contact to more of a sliding wheel flange–rail gauge contact on the high rail in curves. Under wheel flange–rail gauge contact conditions, wear transitions to severe or catastrophic wear will occur if the contact is improperly lubricated. Such a transition is the most undesirable transition in the wheel–rail contact, as it represents a very expensive operating condition for railway companies. The contact conditions responsible for this transition are very severe as regards sliding velocity and contact pressure, and thus place high demands on both the lubricant and the wheel and rail materials. The focus of this thesis is on the transitions between different wear regimes in a wheel–rail contact. Wear is discussed both in traditional tribological terms and in terms of the categories used in the railway business, namely mild, severe and catastrophic wear. Most of the work was experimental and was performed at the Royal Institute of Technology (KTH), Department of Machine Design. The effects of contact pressure, sliding velocity, and type of lubricant have been investigated, producing results that resemble those of other studies presented in the literature. The absence of research relating to the wheel flange–rail gauge contact is addressed, and it is concluded that a lubricant film must be present on rails in curves to prevent severe or catastrophic wear. The formulation of this lubricant can further increase its wear- and seizure-preventing properties. To obtain a deeper understanding of wear transitions, methods such as airborne particle measurement and electron microscopy have been used. Paper A presents the test methodology used to detect seizure and discusses the wear-reducing influence of free carbon in highly loaded contacts. Paper B presents the testing of seizure-initiating conditions for a range of environmentally adapted lubricants applied to wheel and rail materials; a transient pin-on-disc test methodology was used for the testing. Paper C presents the use of pin-on-disc methodology to study the wear-reducing effects of a wide range of lubricants. The best performing lubricant was a mineral oil containing EP and AW additives. Paper D relates wear rates and transitions to airborne particles generated by an experimentally simulated wheel–rail contact. The airborne particles generated varied in size distribution and amount with wear rate and mechanism. Paper E relates additional analysis techniques, such as FIB sectioning, ESCA analysis, airborne particle measurements, and SEM imaging of airborne wear particles, to the contact temperature. / QC 20100721 / Samba 6

Os aços Hardox possuem microestrutura de martensita revenida e são caracterizados pelas elevadas dureza e resistência à tração, sendo empregados em situações que requerem alta resistência ao desgaste. Entretanto, os processos de soldagem alteram significativamente a sua microestrutura e propriedades. Assim, o objetivo deste estudo foi avaliar a resistência ao desgaste de juntas soldadas de um aço Hardox 500 produzidas através do processo MAG convencional e, juntamente, com o Hardox sem soldagem (metal base), para comparação. A soldagem ocorreu utilizando dois consumíveis, um recomendado pela empresa fabricante do aço, o AWS ER80S-G, e outro de maior resistência mecânica, o consumível AWS ER120SG. As propriedades mecânicas das juntas soldadas foram avaliadas através de perfis de microdureza, ensaios de tração e dobramento. Ainda, foi realizada uma análise da superfície de fratura dos corpos de prova do ensaio de tração, em microscópio eletrônico de varredura. Foram executados ensaios de desgaste por um abrasômetro do tipo roda de borracha. Análises através de microscopia óptica e microscopia eletrônica de varredura foram utilizadas para verificar os mecanismos de desgaste nas superfícies submetidas à abrasão Nos ensaios de dobramento, constatou-se que a condição soldada com o arame de menor resistência apresentou maior ductilidade. Verificou-se, também, que com a soldagem houve uma diminuição da resistência mecânica das juntas em comparação ao metal sem soldagem. Em relação aos ensaios de desgaste, com o uso do arame de maior resistência foi atingido um melhor desempenho no desgaste abrasivo em comparação ao de menor resistência, pois as taxas de desgaste foram de 0,058 e 0,083 mm³/m, respectivamente, mas o comportamento foi ainda inferior ao exibido pelo aço Hardox 500 sem soldagem, que apresentou uma taxa de desgaste de 0,031 mm³/m. Constatou-se, também, que os mecanismos de desgaste foram dúcteis em todas as condições estudadas, pois as superfícies desgastadas mostravam predominantemente micro sulcamento e regiões com micro fadiga; essa última parece ter aumentado de tamanho à medida que a dureza do material testado aumentava. / The Hardox steels have a martensite microstructure and are characterized by high hardness and tensile strength. This steel has been used in situations that require high resistance to wear. However, the welding processes significantly alter their microstructures and properties. Thus, the purpose of this study was to evaluate the wear resistance of welded joints of Hardox 500 steel produced by the conventional MAG process and with Hardox without welding (base metal), for comparison. The welding took place using two consumables, one recommended by the steel manufacturer, the AWS ER80S-G and another with higher resistance, the consumable AWS ER120S-G. The mechanical properties of welded joints were evaluated through micro hardness profiles, tensile and bending tests. In addition an analysis of the fracture surface of the tensile test specimen was carried out by scanning electron microscopy. Wear tests were performed by a rubber wheel type abrasometer. Analyses by optical microscopy and scanning electron microscopy were used to verify the mechanisms of wear on surfaces subjected to abrasion In the bending tests, it was verified that the welded condition with the filler metal of lower resistance presented greater ductility. It was also verified that with the welding, there was a decrease in the mechanical strength of the joints in comparison with the base metal. In relation to the wear tests, with the use of the higher strength wire, a better performance was obtained when compared to the lower one, since the wear rates were 0.058 and 0.083 mm³/m respectively, but the behavior was lower in the Hardox 500 steel without welding, which presented a wear rate of 0.031 mm³/m. It was also observed that the wear mechanisms were ductile in all the studied conditions, since the worn surfaces showed predominantly micro plowing and regions with micro fatigue, the latter seem to have increased in size as the hardness of the tested material increased.

Made available in DSpace on 2014-12-17T14:57:49Z (GMT). No. of bitstreams: 1 RuthileneCL _TESE.pdf: 6178470 bytes, checksum: b0cae8fac326f39bc2fe0d49e1a7bcc5 (MD5) Previous issue date: 2010-04-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Present work proposed to map and features the wear mechanisms of structural polymers of engineering derived of the sliding contact with a metallic cylindrical spindle submitted to eccentricity due to fluctuations in it is mass and geometric centers. For this it was projected and makes an experimental apparatus from balancing machine where the cylindrical counterbody was supported in two bearings and the polymeric coupon was situated in a holder with freedom of displacement along counterbody. Thus, the experimental tests were standardized using two position of the two bearings (Fixed or Free) and seven different positions along the counterbody, that permit print different conditions to the stiffness from system. Others parameters as applied normal load, sliding velocity and distance were fixed. In this investigation it was used as coupon two structural polymers of wide quotidian use, PTFE (polytetrafluroethylene) and PEEK (poly-ether-ether-ketone) and the AISI 4140 alloy steel as counterbody. Polymeric materials were characterized by thermal analysis (thermogravimetric, differential scanning calorimetry and dynamic-mechanical), hardness and rays-X diffractometry. While the metallic material was submitted at hardness, mechanical resistance tests and metallographic analysis. During the tribological tests were recorded the heating response with thermometers, yonder overall velocity vibration (VGV) and the acceleration using accelerometers. After tests the wear surface of the coupons were analyzed using a Scanning Electronic Microscopy (SEM) to morphological analysis and spectroscopy EDS to microanalysis. Moreover the roughness of the counterbody was characterized before and after the tribological tests. It was observed that the tribological response of the polymers were different in function of their distinct molecular structure. It were identified the predominant wear mechanisms in each polymer. The VGV of the PTFE was smaller than PEEK, in the condition of minimum stiffness, in function of the higher loss coefficient of that polymer. Wear rate of the PTFE was more of a magnitude order higher than PEEK. With the results was possible developed a correlation between the wear rate and parameter (E/&#961;)1/2 (Young modulus, E, density, &#961;), proportional at longitudinal elastic wave velocity in the material. / O presente trabalho prop?s-se a mapear e caracterizar os mecanismos de desgaste de pol?meros estruturais de engenharia oriundos do contato de deslizamento com um eixo-?rvore cil?ndrico rotativo met?lico submetido a excentricidades decorrentes de flutua??es em seu centro de massa e centro geom?trico. Para isso projetou-se e confeccionou-se uma bancada experimental a partir de uma m?quina balanceadora, onde o contracorpo cil?ndrico era apoiado em dois mancais e o corpo-de-prova polim?rico era posicionado em um portaamostra com liberdade de deslocamento ao longo do contracorpo. Desta forma, os ensaios experimentais foram parametrizados utilizando duas posi??es dos mancais (Fixos ou livres) e sete posi??es distintas ao longo do contracorpo, o que permitiu imprimir condi??es diferentes para a rigidez do sistema. Demais par?metros como carga normal aplicada, velocidade e dist?ncia de deslizamento foram mantidas constantes. Nesta investiga??o utilizou-se como corpos-de-prova dois pol?meros estruturais de engenharia de largo uso cotidiano, PTFE (politetrafluoretileno) e PEEK (poli-?ter-?ter-cetona) e o a?o liga AISI 4140 comocontracorpo. Caracterizou-se os materiais polim?ricos atrav?s de an?lises t?rmicas (termogravim?trica, calorimetria explorat?ria diferencial e din?mico-mec?nica), dureza e difra??o de raios-X. J? o met?lico foi submetido a ensaios de dureza, resist?ncia mec?nica e an?lise metalogr?fica. Durante os ensaios tribol?gicos eram coletadas as respostas de aquecimento com o aux?lio de termopares, al?m da velocidade global de vibra??o (VGV) e a acelera??o utilizando aceler?metros. Ap?s os ensaios, as superf?cies de desgaste dos corposde- prova foram analisadas utilizando um Microsc?pio Eletr?nico de Varredura (MEV) para an?lise morfol?gica e espectroscopia EDS para microan?lise, juntamente com a rugosidade do contracorpo, caracterizada antes e ap?s os ensaios tribol?gicos. Observou-se que as respostas tribol?gicas dos pol?meros foram diferentes e que eram fun??o de suas estruturas moleculares e capacidades de amortecimento distintas. Foram identificados mecanismos de desgaste predominantes em cada pol?mero. A VGV do PTFE foi menor que a do PEEK, na condi??o de m?nima rigidez e atribu?do ao maior coeficiente de perda daquele pol?mero. A taxa de desgaste do PTFE foi mais de uma ordem de grandeza maior que a do PEEK. Os resultados permitiram desenvolver uma correla??o entre a taxa de desgaste e o par?metro (E/&#961;)1/2 (m?dulo de elasticidade, E, massa espec?fica, &#961;), proporcional ? velocidade de propaga??o de uma onda el?stica longitudinal no material.

Os aços Hardox possuem microestrutura de martensita revenida e são caracterizados pelas elevadas dureza e resistência à tração, sendo empregados em situações que requerem alta resistência ao desgaste. Entretanto, os processos de soldagem alteram significativamente a sua microestrutura e propriedades. Assim, o objetivo deste estudo foi avaliar a resistência ao desgaste de juntas soldadas de um aço Hardox 500 produzidas através do processo MAG convencional e, juntamente, com o Hardox sem soldagem (metal base), para comparação. A soldagem ocorreu utilizando dois consumíveis, um recomendado pela empresa fabricante do aço, o AWS ER80S-G, e outro de maior resistência mecânica, o consumível AWS ER120SG. As propriedades mecânicas das juntas soldadas foram avaliadas através de perfis de microdureza, ensaios de tração e dobramento. Ainda, foi realizada uma análise da superfície de fratura dos corpos de prova do ensaio de tração, em microscópio eletrônico de varredura. Foram executados ensaios de desgaste por um abrasômetro do tipo roda de borracha. Análises através de microscopia óptica e microscopia eletrônica de varredura foram utilizadas para verificar os mecanismos de desgaste nas superfícies submetidas à abrasão Nos ensaios de dobramento, constatou-se que a condição soldada com o arame de menor resistência apresentou maior ductilidade. Verificou-se, também, que com a soldagem houve uma diminuição da resistência mecânica das juntas em comparação ao metal sem soldagem. Em relação aos ensaios de desgaste, com o uso do arame de maior resistência foi atingido um melhor desempenho no desgaste abrasivo em comparação ao de menor resistência, pois as taxas de desgaste foram de 0,058 e 0,083 mm³/m, respectivamente, mas o comportamento foi ainda inferior ao exibido pelo aço Hardox 500 sem soldagem, que apresentou uma taxa de desgaste de 0,031 mm³/m. Constatou-se, também, que os mecanismos de desgaste foram dúcteis em todas as condições estudadas, pois as superfícies desgastadas mostravam predominantemente micro sulcamento e regiões com micro fadiga; essa última parece ter aumentado de tamanho à medida que a dureza do material testado aumentava. / The Hardox steels have a martensite microstructure and are characterized by high hardness and tensile strength. This steel has been used in situations that require high resistance to wear. However, the welding processes significantly alter their microstructures and properties. Thus, the purpose of this study was to evaluate the wear resistance of welded joints of Hardox 500 steel produced by the conventional MAG process and with Hardox without welding (base metal), for comparison. The welding took place using two consumables, one recommended by the steel manufacturer, the AWS ER80S-G and another with higher resistance, the consumable AWS ER120S-G. The mechanical properties of welded joints were evaluated through micro hardness profiles, tensile and bending tests. In addition an analysis of the fracture surface of the tensile test specimen was carried out by scanning electron microscopy. Wear tests were performed by a rubber wheel type abrasometer. Analyses by optical microscopy and scanning electron microscopy were used to verify the mechanisms of wear on surfaces subjected to abrasion In the bending tests, it was verified that the welded condition with the filler metal of lower resistance presented greater ductility. It was also verified that with the welding, there was a decrease in the mechanical strength of the joints in comparison with the base metal. In relation to the wear tests, with the use of the higher strength wire, a better performance was obtained when compared to the lower one, since the wear rates were 0.058 and 0.083 mm³/m respectively, but the behavior was lower in the Hardox 500 steel without welding, which presented a wear rate of 0.031 mm³/m. It was also observed that the wear mechanisms were ductile in all the studied conditions, since the worn surfaces showed predominantly micro plowing and regions with micro fatigue, the latter seem to have increased in size as the hardness of the tested material increased.

As superligas à base de cobalto são bem conhecidas por sua excelente resistência ao desgaste. Muitas pesquisas reportadas na literatura abordam o comportamento do desgaste destas ligas, seja no desgaste por deslizamento, erosivo ou abrasivo. Não obstante, o desgaste microabrasivo destas ligas não tem sido muito investigado, apesar dos danos causados por este tipo de solicitação. O comportamento do desgaste microabrasivo de três superligas à base de cobalto: a) 48% Co, 29 %Cr, 19 % Fe; b) uma liga com composição química próxima à da liga comercial Tribaloy T400 (Co 56 %, Cr 8.5%, Mo 29% Si 3.3 %) e c) uma liga com composição próxima à da liga comercial Stellite 6 (Co 64%, Cr 24 %, W 4.2 %, C 2,3%) foram investigadas. Os ensaios de microabrasão foram conduzidos com três abrasivos SiO2, Al2O3, e SiC em suspensão em água destilada, com concentração de 0,1 g/cm3. A carga aplicada foi de 0,3 N, a velocidade angular 20 rpm e a distância total de deslizamento, 48 metros. A análise das superfícies desgastadas por microscopia óptica, eletrônica de varredura e por perfilometria de contato mostraram que o tamanho, forma e dureza dos abrasivos podem influenciar significativamente os coeficientes de desgaste. Os ensaios conduzidos com partículas abrasivas de SiC e Al2O3 apresentaram maiores coeficientes de desgaste que os conduzidos com partículas de SiO2. A Liga Co-Cr-Fe mostrou os maiores coeficientes de desgaste quando comparada com as demais ligas, devido à baixa fração volumétrica de partículas de segunda fase, duras, precipitadas em sua microestrutura. Durante os ensaios, as três ligas, ensaiadas com os três diferentes abrasivos, apresentaram coeficientes de desgaste crescentes com o aumento da dureza do abrasivo; observou-se uma variação linear dos coeficientes de desgaste com a razão entre a dureza do abrasivo (Ha) e a dureza composta da liga (Hs), com R2 = 0.74. O micromecanismo dominante em todos os ensaios foi o desgaste abrasivo a dois corpos (grooving wear). A liga com composição próxima à da liga comercial Tribaloy T400, contendo fases de Laves dispersas em sua microestrutura, apresentou uma transição de micromecanismo de desgaste dúctil para frágil, quando submetida a ensaios com partículas abrasivas de Al2O3. Assim sendo, o volume de material removido nesta liga foi ligeiramente maior que o observado no ensaio com partículas de SiC. Na liga contendo baixa fração volumétrica de partículas de segunda fase, com matriz constituída por Co (CFC), observou-se uma camada subsuperficial nanocristalina de aproximadamente 1 µm de espessura, severamente deformada, imediatamente abaixo da superfície desgastada. Concluiu-se que o desgaste microabrasivo induziu a recristalização a frio do material encruado, com formação de grãos equiaxiais de dimensões nanométricas. / Cobalt alloys are well known for their excellent wear resistance. Many investigations are reported in literature related to the behavior of erosive, abrasive or sliding wear of these alloys. Nevertheless, the micro-abrasive wear of these alloys has not been thoroughly investigated, despite the damage caused by this type of wear. The microabrasive wear behavior of three cobalt alloys: a) 48 wt.% Co, 29 wt.% Cr, 19 wt.% Fe; b) an alloy with chemical composition close to Tribaloy T400 (56 wt.% Co, 8.5 wt.% Cr, 29% wt. Mo, 3.3 wt. %Si) and c) an alloy with chemical composition close to Stellite 6 (64wt.% Co 24 wt.% Cr, 4.2 wt.% W, 2,3 wt.% C were investigated. The tests were carried out using three 0,1 g/cm3 slurries composed by SiO2, Al2O3, and SiC particles, in suspension in distilled water. The applied load was 0.3 N, the rotational speed 20 rpm and the total sliding distance 48 m. Analysis of the worn surfaces of the tested alloys by Optical Microscopy, Scanning Electron Microscopy and Contact Stylus Profilometry showed that abrasive size, shape and hardness could significantly influence the wear coefficients. The tests carried out with SiC and Al2O3 slurries resulted in greater wear rates than those carried out in SiO2 slurry. Stellite 250, showed the greatest wear coefficient, compared to the two other experimental alloys, due to a very low volume fraction of hard second phase particles in the microstructure. Wear coefficients decreased with increasing abrasive particles hardness. An approximate linear correlation with the ratio between the hardness of the abrasives (Ha) and the compound hardness of the alloys (Ha) with a correlation factor R2= 0.74. The dominant wear micromechanism observed in all tests was two-body abrasion (grooving wear). The modified T400 alloy, containing Laves phase showed a transition from ductile to brittle wear mechanisms when testing with alumina slurries. The worn volume was slightly greater than the one observed with SiC. A severely deformed nanocrystalline layer was identified, immediately below the worn surface. It was concluded that cold recrystallization of the work-hardened material occurred, with the formation of nano sized equiaxed grains.