Biblioteca Digital

The addition of ceramic reinforced material, SiC particles, to resin matrices, results in the improvement of the overall performance of the composite, allowing the application of these materials as tribo-materials in industries such as: automotive, aeronautical and medical. Particle-reinforced polymeric composites are widely used as biomaterials, for example as dental filler materials and bone cements. These reinforced composites have improved mechanical and tribological performance and have higher values of elastic modulus and hardness, and also reduce the shrinkage during the polymerisation compared with resin matrices. However, the effect of the filler level in mechanical and tribological behaviour is not quite understood. The aim of this work is to determine the influence of the particle volume fraction and particle size in the wear loss of the composites and their antagonists. Reciprocating wear tests were conducted using a glass sphere against resin polyester silica reinforced composite in a controlled medium, with an abrasive slurry or distilled water. For 6 μm average particle dimension, seven particles contents were studied ranging from 0% to 46% of filler volume fraction (FVF). Afterwards, filler volume fractions of 10% and 30% were selected; and...

AISI H13 tool steel discs were pulsed plasma minded during different times at a constant temperature of 400 degrees C Wear tests were performed in order to study the acting wear mechanisms The samples were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20 +/- 0 05 for all tested conditions and depends strongly on the presence of debris After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue These mechanisms were correlated to the microstructure and hardness of the nitrided layer (C) 2010 Elsevier B V All rights reserved; CNPq[142812/2006-4]; CNPq[550316/2007-8]; CNPq[573628/2008-4]

This paper presents the results obtained in pin-on-disk test apparatus using glass and alumina as abrasive materials, showing the rates and mechanisms of abrasive wear of 1070 and 52100 steels, and ductile and white cast irons. The test conditions were selected in order to obtain wear rates that correspond to mild and severe abrasion, using different metal hardness-to-abrasive hardness ratios(H/H(A)) and 0.2 or 0.06 mm abrasive grains. The use of bulk Vickers hardness, instead of microhardness, allows a better description of the different abrasion regions. Under severe abrasion, the microcutting mechanism of wear prevailed together with friction coefficients larger than 0.4. On the other hand, when relatively soft abrasives are tested, indentation of abrasive particles followed by its fragmentation, and a creation of a thin deformed layer were the main damage mechanisms, with the friction coefficient lying below 0.4. The abrasive particle size under mild regime is able to change the wear rates in an order of magnitude. (C) 2009 Elsevier B.V. All rights reserved.

In this work, multi-component white cast iron was applied by HVOF thermal spray process as alternative to other manufacture processes. Effects of substrate type, substrate pre-heating and heat treatment of coating on mass loss have been determined by rubber wheel apparatus in accordance with ASTM G-65. Furthermore, influence of heat treatment of coating on wear mechanisms was also determined by scanning electron microscopy analysis. Heat-treated coatings presented mass loss three times lower than as-sprayed coatings. Furthermore, wear mechanisms of as-sprayed coating are micro-cutting associated with cracks close to unmelted particles and pores. In heat-treated coating, lesser mass loss is due to sintering. (C) 2011 Elsevier B.V. All rights reserved.

Neste trabalho estudaram-se os mecanismos de desgaste predominantes no riscamento circular em materiais metálicos quando de uma transição do tipo de desgaste por deslizamento para o desgaste por abrasão. A técnica utilizada foi a esclerometria circular. Para fazer a função de elementos abrasivos, utilizou-se indentadores de rubi e diamante com geometrias semi-esféricas e em troncos de cone (essas para simular partículas abrasivas desgastadas). O principal material de contra-corpo analisado foi o aço 0,4 % C de baixa liga, com dureza de 48 HRc (temperado e revenido). Foram investigados também os comportamentos de desgaste do cobre eletrolítico, latão 360 (ASTM B-16), ligas de alumínio 2011-T3, 6061-T8, 6262-T8 e ferro fundido cinzento e vermicular. Os carregamentos normais utilizados foram reduzidos e dependentes da geometria dos indentadores utilizados, de forma a se iniciar o ensaio sempre em uma condição de deslizamento. As mudanças nos comportamentos de desgaste foram acompanhadas por alterações nas curvas de força de atrito em relação ao número de voltas do disco (ciclos). Identificaram-se três estágios bem distintos do comportamento de desgaste: Estágio I ou Desgaste ¨Zero¨, Transição e Estágio II ou Desgaste em Regime Permanente. Apenas a partir da Transição é que ocorrem desprendimentos sensíveis de material na forma de partículas de desgaste. No Estágio II...

O esmalte dental é o tecido mineralizado mais duro do corpo humano; apesar disto, seu desgaste é um problema muito comum. Este pode estar associado aos processos de envelhecimento, ou ainda, ser encontrado em indivíduos jovens, como consequência de atividades parafuncionais, por exemplo, atrição dental. Este tipo de dano pode resultar em prejuízo da função mastigatória e em diminuição da qualidade de vida. Por isto, o desgaste do esmalte dental tem sido objeto de muitos estudos, embora poucos tenham utilizado conceitos tribológicos. Não foi encontrado nenhum estudo que explorasse o desgaste de esmalte e seus micromecanismos oriundos do deslizamento alternado de incisivo contra incisivo, configuração que mais se aproxima do tribossistema real de atrição. O presente estudo tem por objeto investigar o desgaste e seus mecanismos em pares deslizantes de esmalte incisal (configuração pino-plano), selecionados por seus similares valores de dureza e de tenacidade à fratura, submetidos a diferentes cargas normais e lubrificações do meio. Incisivos bovinos foram ensaiados em deslizamento alternado sob duas cargas normais (8 N e 16 N) e quatro modos de lubrificação: saliva natural; saliva artificial; gel lubrificante oral (Oralbalance!...

Nesse trabalho, procurou-se estudar os mecanismos de desgaste de diversas geometrias de ferramentas cerâmicas (Al2O3 + SiCw e Al2O3 + TiC) e ferramentas de PCBN. Para isto foram realizados ensaios de torneamento com alta velocidade de corte em uma superliga à base de níquel (Waspaloy) com dureza de aproximadamente 40 HRC sob condição de corte a seco. As superligas são conhecidas como materiais de difícil usinabilidade devido à alta dureza, alta resistência mecânica em alta temperatura, afinidade para reagir com materiais da ferramenta e baixa condutividade térmica. Os resultados mostraram que o material da ferramenta e a geometria influenciaram o comportamento dos mecanismos de desgaste. de uma maneira geral, o tipo de desgaste dominante foi o de entalhe e os mecanismos foram abrasão, attrition (aderência com arrastamento) e provável difusão na maioria das ferramentas utilizadas.; The purpose of this work is to study the wear mechanisms in several geometries of ceramic tools (Al2O3 + SiCw and Al2O3 + TiC) and PCBN tools. Several high speed turning experiments were accomplished in nickel-base superalloy (Waspaloy) with hardness of approximately 40 HRC under dry cutting condition. The nickel based superalloys are known as difficult to cut materials due to their high hardness...

Although titanium and its alloys own good mechanical properties and excellent corrosion resistance, these materials present poor tribological properties for specific applications that require wear resistance. In order to produce wear-resistant surfaces, this work is aimed at achieving improvement of wear characteristics in Ti-Si-B alloys by means of high temperature nitrogen plasma immersion ion implantation (PIII). These alloys were produced by powder metallurgy using high energy ball milling and hot pressing. Scanning electron microscopy (SEM) and X-ray diffraction identified the presence of α-titanium, Ti6Si2B, Ti5Si3, TiB and Ti3Si phases. Wear tests were carried out with a ball-on-disk tribometer to evaluate the friction coefficient and wear rate in treated and untreated samples. The worn profiles were measured by visible light microscopy and examined by SEM in order to determine the wear rates and wear mechanisms. Ti-7.5Si-22.5B alloy presented the highest wear resistance amongst the untreated alloys produced in this work. High temperature PIII was effective to reduce the wear rate and friction coefficient of all the Ti-Si-B sintered alloys. © 2013 Elsevier B.V.

AISI H13 tool steel discs were pulsed plasma minded during different times at a constant temperature of 400 degrees C Wear tests were performed in order to study the acting wear mechanisms The samples were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20 +/- 0 05 for all tested conditions and depends strongly on the presence of debris After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue These mechanisms were correlated to the microstructure and hardness of the nitrided layer (C) 2010 Elsevier B V All rights reserved; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Abstract. Functionally graded aluminium matrix composites reinforced with SiC particles are attractive materials for a broad range of engineering applications in the automotive, aircraft, sports, military and aerospace industries, whenever a superior combination of surface and bulk mechanical properties are required. In general, these materials are developed for the production of high wear resistant components. Also, often this kind of mechanical part operates in the presence of aggressive environments, such as marine atmospheres. In this work, aluminium composites with functionally graded properties, obtained by centrifugal cast, are characterised by reciprocating pin-on-plate sliding wear tests against nodular cast iron. Three different volume fractions of SiC reinforcing particles in each functionally graded material were considered. Sliding experiments were performed with and without the presence of a lubricant (3% NaCl aqueous solution). All tests were carried out at room temperature, under a normal load of 10N and constant frequency (1 Hz) and stroke (6 mm). In the case of the lubricated tests, electrochemical parameters (corrosion potential) were monitored during sliding. The worn surfaces as well as the wear debris were characterised by SEM/EDS. Friction values were in the order of 0.42 for unlubricated conditions...

Prova Tipográfica (In Press); Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on various materials are gaining more attention by scientists and engineers due to its practical and economical significances in a wide range of applications. The main objective of the present work were to investigate the tribocorrosion behaviour of single layered titanium oxycarbide, TiCxOy, thin filmso on a reciprocating sliding tribometer, and in the presence of artificial sweat solution at room temperature, by considering the practical usage of such films as a decorative coating on various components. The films were produced by DC reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O2 was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, electrochemical impedance spectroscopy (EIS) tests were performed before and after sliding process. The modifications on the ‘‘native’’ coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear–corrosion mechanisms occurring in each system. The corrosion studies...

Recently, tribocorrosion is widely accepted as an interdisciplinary area of research and such studies on the various materials is gaining more attention by the scientist and engineers due to its practical and economical significances. Hence the main objective of present work was to investigate the tribocorrosion behavior of single layered titanium oxycarbide, TiCxOy, thin films on a reciprocating sliding tribo-meter, and in the presence of artificial sweat solution at room temperature. Such films can be used as a decorative coating on various components. The films were produced by dc reactive magnetron sputtering, using C pellets incrusted in the Ti target erosion area. A gas atmosphere composed of Ar and O2 was used. The Ar flow was kept constant, and the oxygen gas flow varied from 0 to 10 sccm. During the wear tests both the open circuit potential and the corrosion current were monitored. Also, Electrochemical Impedance Spectroscopy (EIS) tests were performed before and after sliding in order to evaluate, in detail, the modification of the protective character of the coating introduced by the joint action of wear and corrosion. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the wear-corrosion mechanisms occurring in each system. The effect of hardness...

In this work two very simple apparatuses, namely the ball crater (or ball-on-plate) and the linear reciprocating (or pin-on-plate) tests, were used in order to investigate the wear mechanisms of TPH Spectrum® and Resilab Master® dental composite resins. Loads in the range of 100 g to 1 kg and a total number of up to 24000 cycles were employed. During some of these tests, aqueous aluminum oxide suspensions were used as abrasive agent either diluted or not in distilled water. In case of the ball-on-plate test wear is dominated by abrasive and/or adhesive mechanisms, and is characterized by scratches which are composed of wear defects comprising particle detachment, wear of the polymer matrix and ceramic particle abrasion. However, the relative contributions of the two wear mechanisms could not be determined separately. In case of the pin-on-plate test wear is governed by the fatigue mechanism, although abrasive and adhesive wear mechanism are also present. After a certain number of cycles fatigue wear dominates the wear behavior and results in severe material loss. This mechanism seems to be more important in case of more brittle materials and when higher loads are employed. Qualitative analysis of the results suggests that the combination of these two very simple methods under appropriate conditions can yield sound results which may be representative of a number of clinical situations.

Durante o processo de beneficiamento da pirita e arsenopirita, minérios do qual se extrai o Ouro, são necessários equipamentos para a cominuição, classificação, concentração, entre outros, de um minério contendo elevados teores de óxidos altamente abrasivos, em especial, o óxido de Silício. Os componentes destes equipamentos apresentam, por esta razão, elevadas taxas de desgaste abrasivo e erosivo, gerando altos custos com reposição de peças. Como exemplo destes, citam-se: Ferramentas de penetração no solo, caçambas, barras de britadores, carcaça e rotores de bombas e revestimentos de moinhos. Os ferros fundidos brancos de alto Cromo (FFBAC) têm sido empregados na confecção de componentes de bombas de polpa. Neste trabalho foram identificados os mecanismos de desgaste atuantes nestes componentes, com o objetivo de selecionar os ensaios de desgaste mais adequados para a seleção de materiais usados na fabricação de rotores e revestimentos de bombas de polpa. Foram avaliadas ligas ferrosas com diferentes teores de Cromo e Molibdênio no estado temperado e revenido a 200ºC. São apresentados também, os resultados obtidos no desenvolvimento dos FFBAC contendo de 0,0 até 1,5% em peso de Nb. O comportamento foi analisado utilizando ensaios de laboratório feitos para reproduzir condições de campo. Foi utilizado um jato erosivo para avaliação do desgaste de componentes de bombas...

Ligas de níquel apresentam elevada resistência mecânica a elevadas temperaturas, alta resistência à fluência e à fadiga, além de ótima resistência à oxidação, sendo por isso utilizadas na fabricação de componentes mecânicos para a indústria aeroespacial. Este trabalho consistiu na investigação dos tipos de desgastes e suas evoluções nas ferramentas de corte durante a usinagem das superligas à base de níquel: Inconel® 751 e Inconel® 718. Também foram objeto de estudo os mecanismos de desgaste das ferramentas associados, assim como as avarias nestas decorrentes do processo de corte. Utilizando-se a metodologia de planejamento de experimentos foram construídas matrizes para os testes com três tipos de ferramentas cerâmicas: SiAlON, Preta, Whisker e três tipos ou classes de metais duros: WC/Co, WC/Co 6% com revestimento TiAlN e WC/Co 10% com revestimento TiAlN para os insertos, tendo sido variadas a velocidade de corte, geometria da ferramenta de corte e atmosfera envolvente. Durante estes testes, medidas de rugosidade da peça e das componentes da força de usinagem foram realizadas. A análise dos resultados mostrou que todas as variáveis estudadas apresentaram influência sobre os tipos de desgaste. O desgaste de entalhe foi observado...

High chromium white irons are used extensively for wear resistance applications and owing to their high chromium content are often used in erosive-corrosive environments such as alumina processing plants using the Bayer refining process. The first stages of the Bayer refining processes (the red side) involve the transfer of hot slurries containing a high proportion of erosive quartz particles suspended in a pH 14 caustic solution. The solution contains varying amounts of dissolved alumina making the environment erosive and corrosive. High chromium white irons are often used to prolong service life and reduce operating costs. Pump components are often cast high chromium white irons and piping is often weld overlayed with high chromium white iron. To date there has been very little information reported in the literature on the wear of high chromium white irons in alumina processing environments. Furthermore, very limited work has been reported on the corrosion behaviour of high chromium white irons in caustic environments. This thesis investigates the development of microstructure in high chromium white irons typically used in the Australian Alumina Industry and how variables such as the bulk chemical composition, cooling rate and heat treatment can be used to vary the microstructure. Microstructural characteristics that influence wear and corrosion were investigated by undertaking corrosion and erosion-corrosion wear tests in a sodium aluminate solution representative of what is found in the alumina processing industry. The corrosion of high chromium white irons in sodium hydroxide solution was compared with their corrosion in sodium aluminate solution to investigate the influence aluminate ions have on corrosion. A range of ex-service alumina processing plant high chromium white irons castings and weld overlays were investigated. This not only provided materials for further testing but from the examination of the wear surface allowed the results of laboratory wear tests to be compared with those of the plant samples and test methods validated. A total of four different commercially produced casting materials ranging from hypoeutectic to hypereutectic compositions were compared with an experimental high chromium white iron casting...

peer-reviewed; The formation and development of wear is now widely accepted as one of the major concerns in the long-term survivorship of contemporary knee prostheses in vivo. This review examines the role of surface topography, third-body debris, load, contact mechanics and material quality in the wear process. Some of the kinematic and physiological issues that need to be modelled in the development of wear testing regimes for evaluation of material combinations and geometrical combinations in total knee implant designs are considered. Wear testing procedures and some of the results from wear tests are discussed and the need to consider the impact of rolling and sliding in the study of wear in total knee components is highlighted. The dominant wear mechanisms that occur in vivo are identified and the role of these mechanisms is currently being examined experimentally at the University of Limerick wear testing machine.

This article presents the results of an experimental study on the Ti17 titanium alloy, which was carried out to analyze tool wear and the degradation mechanisms of an uncoated tungsten carbide tool insert. Two machining conditions, roughing and finishing, have been studied under different lubrication conditions. The experimental procedure included measurement of the cutting forces and the surface roughness. Different techniques have been used to explain the tool wear mechanisms. Distribution maps of the elemental composition of the titanium alloy and the tool inserts have been created using Energy Dispersive X-ray Spectroscopy (EDS). An area of material deposition on the tool rake face, characterized by a high titanium concentration has been observed. The width of this area and the concentration of titanium, decrease when increasing water jet pressure. The study shows that wear mechanisms, with and without high-pressure water jet assistance (HPWJA) are not the same. For example, for the roughing condition using conventional lubrication, the temperature in the cutting area becomes very high, this causes plastic deformation of the cutting edge which results in its rapid collapse. By contrast, this problem disappears when machining with HPWJA. In addition...

The authors whish to thank J. Geraud and D. Gehin for their help in the experimental part. Part of this work has been funded by the French Department of Education and Science through the contract no. 02K0538 (MEDOC Project); The aim of this study is to improve the general understanding of tungsten carbide (WC–Co) tool wear under dry machining of the hard-to-cut titanium alloy Ti6Al4V. The chosen approach includes experimental and numerical tests. The experimental part is designed to identify wear mechanisms using cutting force measurements, scanning electron microscope observations and optical profilometer analysis. Machining tests were conducted in the orthogonal cutting framework and showed a strong evolution of the cutting forces and the chip profiles with tool wear. Then, a numerical method has been used in order to model the machining process with both new and worn tools. The use of smoothed particle hydrodynamics model (SPH model) as a numerical tool for a better understanding of the chip formation with worn tools is a key aspect of this work. The predicted chip morphology and the cutting force evolution with respect to the tool wear are qualitatively compared with experimental trends. The chip formation mechanisms during dry cutting process are shown to be quite dependent from the worn tool geometry. These mechanisms explain the high variation of the experimental and numerical feed force between new and worn tools.

The demand for increasing productivity when machining heat resistant alloys has resulted in the use of new tool materials such as cubic boron nitride (CBN) or ceramics. However, CBN tools are mostly used by the automotive industry in hard turning, and the wear of those tools is not sufficiently known in aerospace materials. In addition, the grade of these tools is not optimized for superalloys due to these being a small part of the market, although expanding (at 20% a year). So this investigation has been conducted to show which grade is optimal and what the wear mechanisms are during finishing operations of Inconel 718. It is shown that a low CBN content with a ceramic binder and small grains gives the best results. The wear mechanisms on the rake and flank faces were investigated. Through SEM observations and chemical analysis of the tested inserts, it is shown that the dominant wear mechanisms are adhesion and diffusion due to chemical affinity between elements from workpiece and insert.