Organic coatings are frequently applied to metals, often in circumstances where there is a need to protect the substrate from corrosion or to improve the aesthetic quality of a product. Increasingly, coatings are also expected to provide additional functionality, such as anti-bacterial properties. Concurrent with the need to satisfy ever more demanding specifications, coating formulators are being obliged to comply with stringent environmental legislation. A research area which may benefit the development of coating formulations is that of nanocomposite synthesis, in which the composite additives have at least one dimension in the nanometre size range. The current research has sought to modify a waterborne organic coating primer with two types of nano-sized additives: layered clays and titanium dioxide nanoparticles. Dispersion of the particles at loadings up to 5% w/w was achieved by ball milling and the modified coatings were subjected to numerous tests to ascertain the effect of the additives. Titanium dioxide was found to improve the tribological properties and corrosion resistance of the coatings, while the addition of magnesium aluminium hydroxycarbonate (hydrotalcite) layered clay had a deleterious effect. Some coatings exhibited a cracked morphology, although no correlation between particle loading and the presence of cracks could be determined. A preliminary investigation into substrate preparation was also conducted. This ensured that the degree of cleanliness of the hot-dip galvanized substrates was both satisfactory and consistent.

Zinc and its alloys are among the most widely utilised metallic coatings for the sacrificial protection of steel. Although excellent in this mode of protection, these coatings are often less durable when subjected to environments of combined wear and corrosion due to their intrinsic relative softness and ductility. A possible and fast growing way of improving the durability of these coating is by the codeposition of inert particles into the zinc and zinc-alloy matrix. The main aim of this research was therefore to improve the durability of zinc and zinc-nickel coatings by the incorporation of inert particles via electrolytic codeposition methods. The first five chapters of this thesis comprise literature review on the electrodeposition of zinc, its alloys and composite electrodeposition in general. A major part of which was dedicated to the review of various conventional methods and parameters such as current density, agitation, temperature, solution composition, bath additives and pH usually investigated in electrodeposition. The experimental work was principally based on DC electrodeposition and was aimed at understanding the deposition behaviour of zinc and zinc-nickel electrodeposition baths, conditions which influence them and solution compatibility to the introduction of silica particles. A systematic study on the deposition behaviour of both zinc/silica and zinc-nickel/silica composite baths was carried out with particular interest on the rate of particle incorporation and the influence of particles on zinc-nickel alloy deposition. The complimentary codeposition behaviour of the nickel and silica particles was observed. The influence of bath additives such as N,N Dimethyldodecylamine (NND) and sodium nitrate on the rate of silica incorporation was also studied. Both additives were found to improve the rate of particle incorporation for the zinc/silica. The morphologies and compositions of the coatings were analysed with the use of SEM and FEGSEM. Corrosion performance studies were carried out in a neutral salt spray chamber and linear polarisation resistance methods used to determine barrier corrosion properties of the coatings. Anodic polarisation studies were also carried out. The results show an improvement in the corrosion performance of these coatings with the addition of silica particles Reciprocating wear tests were used to determine the wear behaviour of the coatings in terms of weight loss. Improvement in wear resistance was not observed in the zinc/silica coatings probably due to the high content of silica in the coatings. Lower silica contents may be required for the desired improvements. However, there were obvious improvements in the wear behaviour of the zinc-nickel/silica coatings due to the presence of the silica particles.

Um dos principais problemas dos materiais restauradores (incluindo a resina composta) é o desgaste por abrasão. Portanto, o objetivo neste trabalho foi avaliar in vitro o desgaste abrasivo por escovação da resina composta 4Seasons, de duas cores diferentes (A3 e C4) e com fotopolimerização por dois diferentes tempos (20 e 40 s), utilizando escova Sorriso, da Colgate, e creme dentifrício Colgate Tripla Ação; também foi usado, como material de referência, o polimetil metacrilato. Assim, foram confeccionados dez corpos-de-prova, para cada um dos cinco grupos formados (PMMA, A3 20s, A3 40s, C4 20s, C4 40s). Cada espécime consistia basicamente num cilindro de cerca de 1,8 mm de altura e 8 mm de diâmetro. Cada espécime, após sua confecção, era imerso em água deionizada, a 37 ± 2 ºC, por 24 horas, quando então eram regularizados com lixa (granulação # 600 e # 1.000); após lavagem com ultrassom, voltavam a ser armazenados nas mesmas condições, até completar-se um período de uma semana. A escovação foi então efetuada numa máquina própria, que comportava dez espécimes simultaneamente, sendo de 3 N a carga de cada escova sobre o respectivo espécime; a velocidade de cada escova era de 18 cm/s, com a freqüência (ida e volta, num percurso total de 4 cm) de 4,5 ciclos/s; o período de escovação de um espécime compreendia 150. 000 ciclos. Foram efetuados cinco períodos (ou lotes) de escovação, de modo que um espécime do material de cada grupo tivesse sido submetido à ação de cada uma das posições ocupadas pelas dez escovas. A quantidade de massa perdida, para cada espécime, foi calculada por meio de pesagem (pré e pós escovação), numa balança com acuidade de milionésimo de grama. O trabalho foi também ilustrado com gráficos de rugosidade e com fotomicrografias tomadas ao MEV. A taxa média de desgaste foi de 2,8 mg para o PMMA, de 5,5 mg para o A3-20s, 4,7 mg para o A3-40 s, 5,4 para o C4-20s e 4,2 mg para o C4-40s; a respectiva análise de variância mostrou não existir diferença significante entre os grupos, para p=0,166; o coeficiente de variação entre os grupos foi bastante semelhante. Foi possível concluir que não existiu diferença da resistência ao desgaste abrasivo entre os grupos estudados. / One of the main problems of dental restorative materials (including the resin composites) is the abrasion wear. Therefore, the aim of this work was to evaluate in vitro the abrasive wear by toothbrushing of the resin composite 4Seasons, of two different colors (A3 and C4), cured by two different times (20 and 40 s), using a toothbrush (Sorriso - Colgate), and a dentifrice (Tripla Ação Colgate). Polimetil meth-acrylate was used as reference material. Ten cylindric samples (approximately 1.8 mm height and 8 mm diameter) had been prepared for each one of the five evaluated groups (PMMA, A3 20s, A3 40s, C4 20s, C4 40s). After confection, samples were immersed in deionized water, at 37 ± 2ºC, for 24 h, and then regularized by abrasive gritting with sandpaper (from #600 to # 1 000); after that, were cleaned in ultrasound bath, and restored to the same described conditions, until completing the period of one week. The toothbrushing was then conducted in a proper machine that holds 10 specimens simultaneously, with a 3 N load of each toothbrush on the respective sample. The speed of each toothbrush was of 18 cm/s, at a frequency of 4.5 cycles/s (each cycle consisting of 2 cm forward and 2 cm backward). 150. 000 cycles were applied per sample. Five periods (or lots) of toothbrushing had been performed, in a way that one sample of each group had been submitted to the brushing action at one position in the machine. The amount of weight loss for each sample was calculated by means of weighting (before and after toothbrushing), in an analytical balance with accuracy of millionth of gram. Roughness and MEV photomicrographies were also evaluated. The average rate of wear was of 2.8 mg for PMMA, 5.5 mg for A3-20s, 4.7 mg for A3-40 s, 5.4 for C4-20s, and 4,2 mg for C4-40s. One-way ANOVA showed no significant difference between groups (p = 0.166). The coefficient of variation between the groups was sufficiently similar. It was possible to conclude that difference of the resistance to the abrasive wear between the studied groups did not exist.

<div>Magnesium alloys are regarded as the most promising structure materials in transportation and aerospace fields because of their low densities and high specific strengths. However, the unsatisfactory mechanical performance and corrosion resistance restrict their applications. Grain refinement is an effective way to improve the mechanical properties and widen the applications. Among which, ultrasonic shot peening shows a great potential in producing refined grains or even nanocrystalline. A nanocrystalline forms at the surface after ultrasonic shot peening treatment. The formed nanocrystalline has been proved to dramatically affect the mechanical properties, such as hardness, mechanical stress, wear resistance and fatigue life. </div><div><br></div><div> </div><div>In this dissertation, the microstructure evolution of AZ31 Mg alloy after the ultrasonic shot peening as well as its effect on the mechanical properties are investigated. The grain size, the twin structure, the surface roughness and the residual stress distribution after ultrasonic shot peening are characterized. A gradient nanostructure is achieved through ultrasonic shot peening and the thickness of this gradient nanostructure increases with prolonging the treated time. The grains at the top surface after 5 min treatment is refined to 45 nm and further refined to 42 nm for 10 min and 37nm for 15 min treatment from the XRD result. A lamellar nanocrystaline is below the top surface and a lot of tensile twins are found at the heavily deformed grains below the nanocrystalline layer. Below the twinned layer, a residual stress is distributed as deep as 400 $\mu$m in the matrix. A rough surface is obtained and the surface roughness of the 5 min treated sample was 5.934 $\mu$m, increased to 6.161 $\mu$m for10 min and 6.236 $\mu$m for 15 min. The nanocrystalline leads to the improvement of the microhardness, from 65 HV of the as-received to 123 HV, 127 HV and 145 HV for 5 min, 10 min and 15 min treatment, respectively. The tensile stress and compression stress are also improved remarkably. The yield stress is increased from 127.7 MPa of as-received to 198 MPa of 10 min treated sample and the compression stress is improved from 73 MPa to 100 MPa. The improved yield stress is attributed to the grain refinement and the work hardening of the nanocrystalline. </div><div><br></div><div> </div><div> </div><div>The wear resistance of AZ31 Mg alloy is improved greatly after ultrasonic shot peening process. The coefficient of friction and the wear rate of the ultrasonic shot peening treated sample are both lower than that of as-received. The width of the wear track of ultrasonic shot peening treated is also narrower than that of as-received, and the worn surface has a lower surface roughness. In as-received samples, abrasion and oxidation dominate the wear mechanism at low sliding speed and low applied load. The increase of sliding speed or applied load resulted in the delamination. Severe wear such as thermal softening happens with the further increase of load value or sliding speed. In ultrasonic shot peening treated samples, oxidation, the abrasion and delamination are also existing while no severe wear is found. The improved wear resistance of the ultrasonic shot peened sample is due to the improved hardness and a higher activity of oxidation during wear process. The nanocrystalline on the top surface leads to the the transition boundary between the mild wear and severe wear to a higher sliding speed and higher applied load. </div><div><br></div><div><br></div><div>The corrosion resistance of AZ31 Mg alloy before and after ultrasonic shot peening is tested in 3.5 $\%$ NaCl solution. The corrosion resistance after ultrasonic shot peening is reduced greatly because of the Fe particles at the top surface, which was exfoliated from the shot during the treating process. After a 40 $\mu$m thick polishing, Fe particles are removed totally and the corrosion resistance is improved, compared with that of as-received. The anodic current density of the nanocrystallized surface after polishing is reduced because of the compression residual stress and a rapid formation of protective layer. Meanwhile, the grain boundary acts as a physical barrier for corrosion and reduces the corrosion rate. </div><div><br></div><div><br></div><div>The bending behavior of AZ31 Mg alloy before and after ultrasonic shot peening is studied by a V-bending test. The ultrasonic shot peening treated sample has a similar bending performance even though the ductility has been reduced after ultrasonic shot peening. A single side ultrasonic shot peening (either at the inner side or the outer side) changed the bending behavior because of its asymmetric structure. The ultrasonic shot peening at the inner side for 5 min improves the bendability and longer treated, such as 10 min and 15 min degenerates the bendability to as-received. The improved bendability of 5 min treated sample is due to the drawing back of the neutral layer. The ultrasonic shot peening at the outer side for 5 min also improves the bending performance and a longer treatment of 15 min further enhanced the bendability. The improved bendability after outer side treatment is due to the high yield stress of nanocrystalline at the convex, resulting in the smaller strain here. </div>

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.

The objective of this project is to find which type of coating has the best performance characteristics for finishing firearms. This is accomplished by measuring and comparing several performance characteristics, such as: adhesion, hardness, wear resistance, friction control, and corrosion resistance. Appearance is not a factor since any exterior coating that is flashy can be subdued or camouflaged with special purpose paints, which have proven durable enough for such purposes. Cost will not be a limiting factor for this experiment, but will be discussed in the conclusion as a secondary concern. This data will be used to identify the best coating for steel and aluminum firearm parts. The goal is to lengthen a firearm’s life cycle while increasing performance and reliability by applying the best coating.

In this study, by considering different mechanical properties such as wear resistance and toughness of two different metal alloys in design and production stages, bi-metal casting technique was used for producing composite material which will be a solution for the cracking and wear problem in coal crushing hammer heads. The failure analysis of the classical hammer heads which are made from Hadfield steels (austenitic steel) showed that there are crack formations through austenitic grains and also the phase transformation from austenite to martensite is not completed until the material consumed its life. Thermal analysis is the basic technique in this study to determine the solidification conditions. By using thermocouples with a suitable set-up, the cooling curves of the materials which were used in bi-metal casting had been taken and analysed. By using these cooling curve data with a written software program which is based on Newton Thermal Analysis, the solid fraction values by time and by temperate were obtained. According to these values, the interface was investigated by changing experimental conditions and solid fractions. At the last part of the study, a new approach was tried in white cast iron production.

Made available in DSpace on 2014-06-11T19:23:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-28Bitstream added on 2014-06-13T20:30:13Z : No. of bitstreams: 1 antonio_ca_me_bauru.pdf: 1720399 bytes, checksum: 396bef6efc3f71eb7d1f9f3cad7c2279 (MD5) / Apesar da excelente relação resitência/peso das ligas de alumínio, a aplicação tecnológica destas ligas é limitada pela baixa resistência ao desgaste. Neste trabalho, amostras de uma liga de alumínio (AA 5052) foram tratadas pelo processo de oxidação por plasma eletrolítico, com tempo de exposição variando de 150 a 900 s. A composição e a estrutura química dos revestimentos assim produzidos foram analisadas por espectroscopia de absorção no infravermelho. Um método baseado na medida de correntes parasitas e a perfilometria foram usados, respectivamente, na determinação da espessura e da rugosidade das camadas depositadas. O revestimento formado porssui espessura de até 9,2um. Análises da morfologia dos revestimentos foram feitas com microscopia eletrônica de varredura enquanto a resistência a desgastte das superfícies foi avaliada com um sistema pino-sobre-disco. Os resultados revelaram a deposição de um revestimento cerâmico, que conferiu expressivo aumento à resistência a desgaste da liga, o qual mostrou que as amostras tratadas suportaram uma carga aplicada de 13,44 vezes em comparação com amostras sem tratamento / Despiste the excellent strengh/weight ratio, technological applications of aluminum aloys are limited by their low wear resistance. In this work, samples of AA 5052 aluminum alloy have been modified by plasma electrolytic oxidation, with exposure time ranging from 150 s to 900 soconds. Compositional characterization has been performed by fourier transform infrared spectroscopy. Eddy current and profilometry have been used, respectively, to evaluate thickness and roughness of the deposited layers. The coating formed has a thickness of up to 9,2 micrometers. Morphological investigations have been performed with scanning electron microscopy while wear resitance has been assessed using a pin-on-disk devide. The results have revealed the deposition of ceramic layers with significant enhancement of wear resistance, which showed that the treated samples resistance, which showed that the treated samples resist an applied load 13.44 times more compared with untreated samples

Made available in DSpace on 2014-10-09T12:53:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:29Z (GMT). No. of bitstreams: 1 12220.pdf: 3040591 bytes, checksum: cf07d18c47b6b9bc7f1a361b3a6fe286 (MD5) / Dissertação (Mestrado) / IPEN/D / Universidade Mackenzie. Departamento de Engenharia de Materiais, São Paulo

Made available in DSpace on 2014-10-09T12:55:31Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:01Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP