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Utilizou-se o aço SAE 1045 para receber o revestimento eletrolítico de cobre na superfície, formando assim um filme superficial. A rugosidade superficial do aço influencia diretamente na espessura e adesão do filme. O processo apresentou maiores quantidades depositadas em superfícies com maior rugosidade, porém com a formação de filmes irregulares e heterogêneos. As evidências coletadas via metalografias e ensaio de rugosidade comprovaram o resultado, e simultaneamente realizou-se ensaios de microdesgaste abrasivo entre amostras revestidas e amostras sem deposição, sendo que a presença do cobre e o efeito lubrificante aliado a característica dúctil do metal promoveu a formação de calota com diâmetros menores, indicando maior resistência ao desgaste. Concluiu-se que a preparação superfícial influenciou na deposição do cobre sobre a superfície do aço SAE 1045 adquire resistência mecânica relevante após a deposição do filme de cobre sobre sua superfície.

TiN granular thin films were deposited on SiO2 substrates using cathodic cage plasma nitriding (CCPN) and SEM images, roughness analysis, contact angle measurements, and X-ray diffraction (XRD) were employed to characterize the structure of these films varying time and temperature of the process. Results have shown an inverse relationship between roughness and contact angle. Thin films with low roughness have presented higher contact angle values, and the opposite was observed in the films with more prominent or more grains per area. TiN is a hydrophobic material, and the decrease of contact angle value presented in some films produced occur due to modification of the morphological characteristics, which the roughness measurements and hysteresis of contact angle confirmed it, specifically, for samples synthesized at 2h and 350°C, the roughness is the smallest, and the contact angle is the largest [(111.23±8.87)°]. This connection between roughness and contact angle is essential, and it can be used to describe and characterize the most types of thin films produced by plasma deposition and to infer the surface modifications with different atmospheres of treatment.

The purpose of the plasma oxidation process is to increase the hardness, corrosion resistance and to improve the biocompatibility properties of Ti6Al4V alloys by thickening the natural oxide in the material, which is produced by this treatment. The aim of this work is to verify the effect of temperature on the thickness, hardness and wear resistance of the Ti6Al4V alloy treated with plasma oxidation. The treatment was performed using a Pulsed DC vacuum reactor, with a gas ratio of 60% Ar and 40% O2and 1.65 torr pressure for 1 hour of treatment, at temperatures of 480°C, 520°C, 670°C and 705°C. In regards to the multilayer formation of anatase and rutile, it was observed that the layer thickness increased as the treatment temperature increased. The increase of surface hardness provided by the treatment caused a considerable increase in the wear resistance of the studied material. The greatest layer thickness and surface hardness were obtained for the material treated at 705°C, but the lowest wear volume was obtained for the material treated at 520°C.

Resumo: Ao analisar a norma ABNT NBR 8800-2008, foi constatado que não há consideração sobre a tensão ou compressão exercida nas regiões soldadas por filetes. O cálculo para dimensionamento de perna só leva em referência o cisalhamento da seção. Utilizando recursos como a simulação e o ensaio mecânico de tração, foi possível comparar as dimensões mínimas das pernas com a estipulada pela norma NBR. Realizou-se o processo de soldagem com eletrodo revestido, utilizando o aço estrutural ASTM A36, e para realização da soldagem foi empregado o eletrodo AWS A5.1 E7018. As soldagens focaram com tamanho de filetes com perna entre 3,5 mm e 7 mm que posteriormente estas juntas soldadas foram submetidas a ensaios de tração. Para a comparação dos resultados, foi empregado simulação numérica estática em tração pelo método dos elementos finitos com auxílio do software Abaqus®. Assim com os dados gerados através da simulação e o ensaio mecânico de tração pode-se legitimar as especificações da norma em relação ao tamanho mínimo de perna em relação à espessura da chapa. Abstract: It was found that there is no consideration of the tensile or compression stresses applied in the regions of fillet weld when analyzing the ABNT NBR 8800-2008 standard. The calculation for dimensioning the leg only takes into account the section shear. Using resources such as simulation and mechanical traction test, it was possible to compare the minimum dimensions of the legs with that stipulated by the NBR standard. The welding process was carried out with a coated electrode, using structural steel ASTM A36, and the welding was performed using the AWS A5.1 E7018 electrode. Tensile testing were performed on fillet welding samples with lengths between 4 mm and 8 mm. It was used a numerical simulation in traction by the finite element method was used with the aid of the Abaqus® software. Thus, with the data generated through the simulation and the mechanical tensile test, the specifications of the standard can be assured in relation to the minimum leg size in relation to the plate thickness.

The aim of this work was to study the influence of thermochemical treatment of ionic plasma nitriding on the resistance to micro-abrasive wear and to the corrosion process of AISI 316L and AISI 470 stainless steels. The thermochemical treatment was performed at different times and temperatures with a gas mixture of 25% H2 and 75% N2. The treated materials were characterized by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tests, micro-abrasive wear tests (MAWTs) and corrosion tests. The results show an increase in the thickness of the layer formed by increasing treatment time and in the wear resistance of the materials studied. Temperatures exceeding 450 °C favor the formation chromium nitrides, which, for being very hard broke making the formed layer brittle decreasing the wear resistance of the material. In addition, the formation of these phases substantially decrease the corrosion resistance of stainless steels. Keywords: Corrosion, Wear tests, Expanded ferrite, Expanded austenite

The 2524-T3 aluminium (Al) alloy produced by ALCOA may be used as skin material by the aircraft industry. Some studies are available in the literature about fatigue and fatigue - corrosion behaviour of 2524-T3 Al alloy. However, the corrosion mechanisms are not yet fully understood since the material has a very complex microstructure due to impurities and the addition of alloying elements which lead to an increase in the localized corrosion process. It is known that the corrosion process in Al alloys, most of the time, is due to the galvanic coupling of the intermetallic particles (IMs) and the Al matrix. Thus, the use of protective coatings appears as a possible alternative against the advancement of the corrosion process of the 2524-T3 alloy. In this way, a set of DLC films was obtained by using physical vapor deposition (PVD) method and characterized by various techniques including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic force microscopy (AFM) and Raman spectroscopy. The deposited films on the surface of the 2524-T3 Al alloy were characterized electrochemically by using potentiodynamic polarization curves (PPc), electrochemical impedance spectroscopy (EIS) and mechanically by using micro-abrasive wear tests (MAWTs). The results show an advantage in using the PVD method to produce thin films on the 2525-T3 Al alloy surfaces, as the wear resistance of the Al alloy coated by DLC film is higher than for the bare material and the corrosion resistance of the material is not compromised. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1321

Tratamentos a plasma vem sendo amplamente utilizados com o objetivo de melhorar as caracteristicas em desgaste, corrosao e fadiga dos materiais metalicos. Porem, para producao da camada ou adesao de revestimento, a etapa de limpeza a plasma deve ser efetiva. O objetivo deste trabalho e demonstrar o efeito dos parâmetros do processo de ablacao a plasma na limpeza da superficie e adesao de filmes diamond-like carbon (DLC) em liga Ti6Al4V. As superficies foram limpas pelo processo de ablacao a plasma utilizando fonte DC-pulsada, variando a pressao de trabalho (0,39 a 2,00 Torr), tipo (Ar e H2) e proporcao (100 a 50% de Ar e 0 a 50% de H2) dos gases. Avaliou-se a adesao e a resistencia ao desgaste do filme DLC depositado na superficie da liga Ti6Al4V apos cada etapa do processo de ablacao estudado. Observou-se reducao dos oxidos presentes na superficie da liga em pressoes maiores de tratamento utilizando mistura gasosa (Ar e H2), evidenciando que esses parâmetros sao fatores determinantes para se obter menor volume de desgaste e maior adesao do filme DLC na superficie tratada.

Duplex treatments are performed to promote an additional property to a previous surface treatment to improve wear and corrosion resistance of the material, like the DLC film (diamond-like carbon) deposited on nitriding or nitrocarburizing surfaces on the AISI 4340 steel. The purpose of this work is to study the effect of the duplex treatment (nitriding + DLC and nitrocarburizing + DLC film deposition) on the wear and corrosion resistance of AISI 4340 steel. The nitrocarburizing treatments by plasma were performed with 80% N2 + 17% H2 + 3% CH4 at 400, 450, 500, 525 and 550 °C for 5 h. The nitriding treatment by plasma at 450 °C was performed with 80% N2 + 20% H2 for 5 h. The interlayer deposition was performed using hexamethyldisiloxane as a precursor. The deposition of DLC film was performed by DC-PECVD method using 90% CH4 + 10% Ar at 200 °C for 2 h. The duplex treatment was performed at the optimum temperature of the nitrocarburizing process. Micro-abrasive wear tests by fixed ball, and corrosion tests showed that all material treated presented lower wear volume and higher corrosion resistance than untreated material, but the duplex treatments provided greater wear and corrosion resistance than that observed on materials treated with only one type of treatment, showing that duplex treatment improves surface resistance of the AISI 4340 steel. The nitrocarburizing + DLC duplex treatment presented greater wear and corrosion resistance than nitriding + DLC duplex treatment, evidencing the great positive effect of carbon added to the treatment.

Corrosion and fatigue of aluminum alloys are major issues for the in-service life assessment of aircraft structures and for the management of aging air fleets. The aim of this work was to evaluate the effect of localized corrosion on fatigue crack growth (FCG) resistance of the AA2198-T851 Al-Li alloy (Solution Heat Treated, Cold Worked, and Artificially Aged), comparing it with the FCG resistance of AA2524-T3 (Solution Heat Treated and Cold Worked), considering the effect of seawater fog environment. Before fatigue tests, the corrosion behavior of 2198-T851 and 2524-T3 aluminum alloys was verified using open circuit potential and potentiodynamic polarization techniques. Fatigue in air and corrosion fatigue tests were performed applying a stress ratio (R) of 0.1, 15 Hz (air) and 0.1 Hz (seawater fog) frequencies, using a sinusoidal waveform in all cases. The results showed that the localized characteristics of the 2198-T851 and 2524-T3 aluminum alloys are essentially related to the existence of intermetallic compounds, which, due to their different nature, may be cathodic or anodic in relation to the aluminum matrix. The corrosive medium has affected the FCG rate of both aluminum alloys, in a quite similar way.

Super duplex stainless steels are widely used in harsh environments due to their high corrosion resistance. However, the improvement of their tribological properties can contribute to a better performance of these materials in service. In this regard, this study aimed to evaluate the application influence of duplex treatment on the tribological properties of the UNS S32760 super duplex stainless steel. Two treatment times, 2 h and 4 h, were studied for both the nitriding step and the cathodic cage plasma deposition step. The results showed that the combination of the nitrided layer and the TiN film, confirmed with the application of Rietveld refinement on the XRD data, contributes to the wear volume decrease by up to 9.41 times. This behaviour was associated with the increase in surface microhardness and the excellent adhesion conditions (HF1) presented by the film deposited over the nitrided layer. The film provided a change in the wear mechanism, evidenced by the reduction in the tendency to wear by scratches. Additionally, was observed the presence of lower oxygen content in the wear region of the treated samples, that can be associated a lower heating of the samples during the test. Thus, the duplex treatment has a great application potential for improving the wear resistance of UNS S32760 steel.

The use of herbicides is important to eliminate losses of weed interference on crops. However, excessive and inappropriate employment of these substances can cause serious consequences to the environment. In this way, the release system is very attractive for the weed control in the agriculture area. The aim of this work was to study a new delivery system for sulfentrazone herbicide encapsulated into the calcium alginate (Ca-ALG) microparticles for the weed control. The alginate microparticles were prepared via ionotropic gelation method and characterized by using optical microscopy, scanning electron microscopy, and thermogravimetric and differential thermal analysis. The controlled release (M t /M ∞ vs. time) of the sulfentrazone herbicide was also analyzed using UV–Vis spectroscopy where we proposed different mathematical models to understand the mechanisms of controlled release of the herbicide. Furthermore, the release tests in field trial weed control were conducted using bioindicator species (Cucumis Sativus—Cucumber) to study the phytotoxicity evaluation caused by the Ca-ALG microparticles at different concentrations and their relationship with leaching depth. The results showed that the Ca-ALG microparticles exhibited good encapsulation efficiency (%EE): 76.11, 78.62, and 80.42% for the 4, 5 and 6 g L−1 concentration of herbicide. The release rates in the region I were 39.2, 46.5, and 35.5 mg s−1 for the 4, 5, and 6 g L−1 of herbicide concentration, respectively. The Ca-ALG microparticles containing sulfentrazone herbicide demonstrated potential application in controlled release platforms in agricultural as well as for controlling of weeds and minimization of leaching processes.

As ligas de Alumínio (Al) são largamente utilizadas pela indústria aeronáutica, devido à sua baixa densidade, alta resistência mecânica e boa resistência à corrosão. A sua resistência à corrosão é atribuída à película de óxido (Al2O3) que se forma espontaneamente na superfície do material. No entanto, na presença de íons agressivos, as ligas de Al estão sujeitas ao processo de corrosão localizada.O comportamento eletroquímico das ligas AA7050 - T7451 e AA7081 - T73511 utilizadas pela indústria aeronáutica foi investigado sob as condições de transporte de massa controlado através de um eletrodo cilíndrico rotatório em meio de uma solução de 0,6M NaCl. Os eletrodos foram usinados em forma cilíndrica com 6 mm de diâmetro e embutidos em resina epóxi. Todos os testes foram realizados utilizando um eletrodo de calomelano saturado com taxas de rotação de 0, 100, 400, 800 e 1200 rpm. A densidade de corrente teórica foi determinada através da equação de Kouteki – Levich. Os resultados confirmam que o intermetálico Al7Cu2Fe atua como cátodo preferencial causando o acoplamento galvânico e a dissolução da matriz de Al em torno dele.

In this paper, we present an alternative method to obtain thin films for coating protection on the surface of the AA2524-T3 Al-alloy by using the Layer-by-Layer (LbL) technique. The LbL films were fabricated by alternated immersion of the Al-alloy into a poly(styrene sulfonate) (PSS) and polyaniline nanoparticles (PAni-NPs) solutions, obtaining a PAni-NPs/PSS bilayer architecture. The LbL films were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), electrochemical and micro-abrasive wear tests. The results show that the number of bilayers promotes shifts to less negative potentials, indicating an optimized system, in which the best performance was observed for a 15-bilayer PAni/PSS LbL film. The pitting potential (Epit) values shifted 130 mV (from -610 mV to -480 mV) in comparing a bare Al-alloy. The predominantly wear mechanism for AA2524-T3 with PAni-NPs/PSS bilayers was scratching whereas for the bare material there was an equivalence between scratching and rolling mechanisms. The results proved that the incorporation of PAni-NPS by the LbL method may be propitious as protective coating against corrosion in AA2524-T3 alloy.

The aim of this work was to study the corrosion process of new aluminium alloy AA2524-T3 (Solution Heat Treated and Cold Worked), which is a promising substitute of the base line AA2024-T3 for aircrafts fabrication, by global and localised techniques in sodium chloride medium (0.05 mol L-1 NaCl). The open circuit potential results revealed a stochastic evolution of pitting events and to the resulting variations in the ratio of passive/active areas and/or cathode/anode, which may be related to the presence of different types of intermetallics. The cyclicvoltammetry showed that the corrosion potential (Ecorr) and the pit nucleation potential (E pit) values are quite similar (approximately -0.525 V). The results of EIS show that the corrosion rate is quite stable, with no tendency to increase or decrease for longer immersion periods. The results of SVET were in agreement with the results obtained by EIS technique, showing strong anodic activity on the surface with no repassivation along the whole immersion time. Besides, corrosion process led to significant surface degradation after 24h.

Super duplex stainless steels (SDSS) have high corrosion resistance because of their high contents of chromium, nickel, molybdenum and nitrogen but low wear resistance. To improve the wear resistance of these steels without affecting their corrosion resistance, samples of SDSS were treated by plasma ion nitriding at temperatures ranging from 350 °C to 570 °C for two hours. This thermochemical treatment resulted in the formation of different types of nitrides that affected the microhardness, the microwear behaviour and the corrosion resistance of the metal surface. The microwear resistance decreased at 400 °C because different nitrides formed on the surface, thereby increasing the hardness and volume wear resistance of the steel. The test results showed that the alloys that were nitrided at 400 °C and 450 °C exhibited the highest corrosion resistance to a solution medium containing chloride ions.

Made available in DSpace on 2018-12-11T17:28:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-05-01. Added 1 bitstream(s) on 2021-07-15T15:04:02Z : No. of bitstreams: 1 S1516-14392016000300686.pdf: 1708787 bytes, checksum: caccd20f90901b04b4a1395a349daf8e (MD5) P20 steel, which is mainly used in plastic molds, was thermochemically treated by ion plasma nitriding and solid and gas carburization. In this work, the solid and gas carburization were performed at 925 °C for four different durations. The ion plasma nitriding was performed at 520 °C for four different durations. The thermochemical treatment increased the micro abrasive wear resistance of the studied material. The gas carburizing treatment resulted in a greater surface microhardness. Longer treatment times increased the effectiveness of the thickness layer in all cases. The solid carburization produced a larger thickness layer than the gas carburization and ion nitriding. Sorocaba Technological College FATEC, Av. Engenheiro Carlos Reinaldo Mendes, 2015 Federal Institute Goiano-IF Goiano, Rodovia Sul Goiana, Km 01, Zona Rural Paulista State University-UNESP, Av. 3 de Março Federal University of São Carlos-UFSCar, Rodovia João Leme dos Santos, Km 110 Paulista State University-UNESP, Av. 3 de Março

The friction and wear properties of AISI 1045 steel, nylon 6.6 composites with different types and percentages of reinforcement and a nitrile rubber, Alpha 66, were submitted to sliding wear tests. The five types of nylon 6.6 composites tested generated matching, low values for the coefficient of friction. This may be due to the greater influence of the nylon 6.6 matrix on the coefficient of friction. However, the wear in nylon composites showed wide variation, determined by the type of reinforcement added to the composite. The other two materials tested, nitrile rubber and 1045 steel, showed behavior different from that of the composites. The NBR (signifying a norm established by the Brazilian Association of Technical Norms) rubber showed a superior coefficient of friction and greater wear. On the other hand, the steel showed a high coefficient of friction and low wear, suggesting that the coefficient of friction has no direct connection to the wear resistance of the materials studied here.

An investigation was made to determine the causes of surface contact fatigue failure of a case hardened driver pinion located in the intermediate shaft of a reducer gearbox used in a sugar and alcohol mill. The examination of the component revealed the presence of a cemented layer substantially thicker than that generally specified for pinions devised for this application. This, associated with the massive presence of brittle threadlike carbon-rich cementite phase (Fe 3 C) in prior austenite grain boundaries of the pinion teeth, favored surface crack nucleation and propagation during cyclic loading, leading to spallation of the contact surface with the counterpart gear, which impaired the system's operation. Poor carburization practice was discovered as the root cause of the mechanical failure, thus demanding the implementation of a new manufacturing route to avoid problems in similar load-bearing rotating components.

The development of controlled delivery system formulations has received increasing interest in the agriculture area. Tebuthiuron (TBH) is the most commonly used herbicide for weed control in sugar cane and cotton crops. The TBH and some of its metabolites are detected in surface water by leaching process, evidencing contamination and the need for an efficient process to decrease pesticide residues. The development of a controlled system release appears as a good solution. The present investigation aimed to study the development and evaluation of alginate microparticles as a delivery system for the TBH. The calcium alginate microparticles were prepared from the crosslinking of sodium alginate by Ca++ containing varied amounts of TBH supplied in CaCl2 aqueous solution. The particle size and morphological analysis of microparticles were determined by optical microscopy (OM) and by field emission gun scanning electron microscopy (FEG-SEM). The encapsulation efficiency and release of TBH studies was accessed by UV-vis spectroscopy. The results show that the polymeric microparticles containing TBH can be obtained successfully through a simple method and is suitable as a controlled release carrier system for herbicides and can be effective for controlling weeds.

O objetivo deste trabalho foi desenvolver um dispositivo para tratamento a plasma e verificar sua eficiencia no aco P20. A influencia dos principais parâmetros de tratamento na camada formada foi verificada por meio de testes de comissionamento. Os tratamentos de nitretacao ionica a plasma foram realizados na superficie do aco P20 com 80% de N2 e 20% de H2, utilizando fonte de tensao DC corrente continua e fonte de tensao DC corrente pulsada. Observou-se a formacao de camada heterogenea com efeito de borda ao se realizar o tratamento com fonte de tensao DC corrente continua; o efeito oposto foi observado para o tratamento utilizando fonte de tensao DC corrente pulsada. Os resultados mostram que a tensao influencia diretamente na temperatura de tratamento, enquanto a pressao determina a formacao da bainha catodica, atuando na uniformidade da luminescencia catodica e na uniformidade da camada produzida. Foi possivel observar a relacao da temperatura com a dureza, enquanto o tempo foi significativo na espessura da camada formada. Conclui-se que o equipamento construido mostrou eficacia para os fins a que foi designado, e seu melhor desempenho deu-se com o uso da fonte de tensao DC corrente pulsada.

The influence of annealing on the mechanical properties of high-silicon cast iron for three alloys with distinct chromium levels was investigated. Each alloy was melted either with or without the addition of Ti and Mg. These changes in the chemical composition and heat treatment aimed to improve the material’s mechanical properties by inhibiting the formation of large columnar crystals, netlike laminae, precipitation of coarse packs of graphite, changing the length and morphology of graphite, and rounding the extremities of the flakes to minimize the stress concentration. For alloys with 0.07 wt.% Cr, the annealing reduced the impact resistance and tensile strength due to an enhanced precipitation of refined carbides and the formation of interdendritic complex nets. Annealing the alloys containing Ti and Mg led to a decrease in the mechanical strength and an increase in the toughness. Alloys containing approximately 2 wt.% Cr achieved better mechanical properties as compared to the original alloy. However, with the addition of Ti and Mg to alloys containing 2% Cr, the chromium carbide formation was inhibited, impairing the mechanical properties. In the third alloy, with 3.5 wt.% of Cr additions, the mechanical strength improved. The annealing promoted a decrease in both hardness and amount of iron and silicon complex carbides. However, it led to a chromium carbide formation, which influenced the mechanical characteristics of the matrix of the studied material.

Fretting fatigue tests were performed in an AA7050-T7451 alloy, with both contact load and fatigue alternate stresses kept constants. Only the applied mean stress, responsible for the maximum and minimum cyclic stresses are varied for each test condition. Such results are compared with the ones from the conventional fatigue tests obtained for the studied material. Similarly to the conventional fatigue results, it was observed that increasing the mean stress, lead to a reduced fretting fatigue life. There were cases that, crack nucleation took place due to the severity of the fretting loads, and they were propagated due to the applied fatigue stress, even with the maximum cyclic stress close to zero, which is considered too low to initiate a crack, leading the specimens to fracture. For cyclic loading totally compressive, again crack nucleation took place, due to the fretting loading, and the cracks did not propagated, leading the specimen to infinite life. The fretting effect in conjunction with fatigue loads significantly reduces the specimen life.

The aims of this work are: (i) to produce new experimental data for fretting fatigue considering the presence of a mean bulk stress and (ii) to assess two design methodologies against failure by fretting fatigue. Tests on a cylinder–flat contact configuration were conducted using a fretting apparatus mounted on a servo-hydraulic machine. The material used for both the pads and fatigue specimen was an aeronautical 7050-T7451 Al alloy. The experimental program was designed with all relevant parameters, apart from the mean bulk load (always applied before the contact loads), kept constant. The mean bulk stress varied from compressive to tensile values while maintaining a high peak pressure in order to encourage crack initiation. Two methodologies against fretting fatigue are proposed and confronted against the experimental data. The non-local stress-based methodology considers the evaluation of a critical plane fatigue criterion at the center of a process zone located beneath the contacting surfaces. The results showed that it correctly predicts crack initiation, but was not capable to provide successful prediction of the integrity of the specimens. Alternatively, we considered a crack arrest criterion which has the potential to provide a more complete description about the integrity of the specimens.

The aim of this work was to design a fretting apparatus and to carry out a series of tests to evaluate the effect of a mean bulk load on the fretting fatigue life of an aeronautical Al 7050-T7451 alloy. The device was mounted on a servohydralic test system. The configuration chosen to carry out the experimental program was of cylindrical pads pressed against flat tensile specimens. A model was proposed to compute the apparatus equivalent stiffness, which controls the magnitude of the fretting load. The tests were designed so that all relevant parameters, apart from the mean bulk load (always applied before the contact loads), were kept constant. This essentially means that the equivalent shear stress amplitude computed at a material point, as defined in many multiaxial stress based high cycle fatigue models, was identical from test to test although the registered fretting lives varied greatly. These results pose a great challenge to a number of fretting lifing methodologies available in the liter...

O ensaio de micro desgaste abrasivo tem sido objeto de uma quantidade significativa de pesquisas nos últimos anos, quando o seu potencial para avaliar o comportamento de recobrimentos finos se tornou relevante. O objetivo deste trabalho é a construção de um dispositivo para a realização de ensaios de micro desgaste abrasivo por esfera fixa. O contato abrasivo é realizado por uma esfera de aço AISI 52100, a qual é presa num eixo que gira com grande precisão, com ajuda de um motor, em relação a uma amostra plana que se manterá estacionária. A carga normal de ensaio é aplicada através de ajustes de peso no suporte pivotado do corpo de prova, a qual pode ser variada a cada ensaio realizado. Este dispositivo foi utilizado para a determinação da resistência ao desgaste abrasivo e da eficácia de tratamentos de superfície utilizados em peças que sofrem este tipo de solicitação em serviço, além de utilizá-lo para estudar novos produtos desenvolvidos para o aumento de resistência ao desgaste de superfícies. Foi avaliada a resistência ao microdesgaste abrasivo de aço AISI 420 temperado e revenido. Observou-se que o aumento da dureza do material tratado aumentou a resistência ao desgaste abrasivo quando comparado com o material sem tratamento térmico.

The P20 steel, mainly used in plastic molds, was thermochemical treated by ion plasma nitriding, solid and gas carburization. In this work, the solid and gas carburization were carried out at 925oC in four different times. The ion plasma nitriding was performed at 520oC in three different times. It was observed that the thermochemical treatment increases the microwear resistance of the studied material. The gas carburizing treatment produced a bigger surface microhardness. Longer times of treatment increase effectiveness of thickness layer in all cases. The solid carburization produced larger thickness layer than gas carburization and ion nitriding.

In an attempt to improve a surface of super-duplex stainless steel was carried out ion plasma nitriding. The super-duplex stainless steel was nitriding by plasma process during 2 hours at the 350 – 570 o C. As can be seen, the thermochemical treatment influenced the microhardness superficial due to kind of nitride formed. The microwear resistance decreased at 400 o C due to formation different nitrides in surface, causing an increase in hardness and wear volume resistance.

This chapter describes cast steel features that may be identified or attributed to component failure during heat treatment or subsequent processing or service, namely porosity (generated by the presence of gas as well as by shrinkage pores), decarburization, cold joint, and inclusions.