No / This study investigates the effect of heat treatment on changes in microstructure and wear behaviour of WC-NiCr coatings. Two feedstock powders with a similar chemical composition and different particle sizes (near nano-structured WC-17NiCr and microstructured WC-15NiCr) were used. High-velocity oxyfuel spraying technique was used to deposit coatings on to a mild steel substrate using identical spraying parameters. Coated samples were then heat treated in a nitrogen atmosphere at 500 and 700°C. The effect of heat treatment on changes in hardness and wear performance of the coatings was studied using microstructural analysis, micro-hardness indentation and abrasive wear tests. The results showed that the heat treatment increased the hardness of both coatings and a corresponding increase in wear resistance was recorded. The formation of a brittle CrWO4 phase in the microstructured coating resulted in brittle fracture of the coating and this gave lower wear resistance compared to the nanostructured coatings.

Abrasive blasting is a common process for cleaning or roughening the surface of a material prior to the application of a coating. Although the process has been in practice for over 100 years, the lack of a comprehensive understanding of the complex interactions that exist with the process can still yield an inferior surface quality. Subsequently, parts can be rejected at one of many stages of the manufacturing process and/or fail unexpectedly upon deployment. The objective of this work is to evaluate the effect of selected input parameters on the characteristics of the blasted surface characteristics so that a more useful control strategy can be implemented. To characterize surface roughness, mechanical profilometry was used to collect average roughness parameter, Ra. Decreasing blast distance from 6” to 4” gave ΔRa = +0.22 µm and from 8” to 6” gave ΔRa = +0.22 µm. Increasing blast pressure from 42 psi to 60 psi decreased the Ra by 0.33 µm. Media pulsation reduced Ra by 0.56 µm and the use of new media reduced Ra by 0.47 µm. Although blasting under the same conditions and operator on different days led to ΔRa due to shorter blast times, there was no statistically significant variance in Ra attributed to blasting on different days. Conversely, a ΔRa = +0.46 µm was observed upon blasting samples with different cabinets. No significant ΔRa was found when switching between straight and Venturi nozzles or when using different operators. Furthermore, the feasibility of fiber optic sensing technologies was investigated as potential tools to provide real time feedback to the blast machine operator in terms of substrate temperature. Decreasing the blast distance from 6” to 4” led to ΔT = +9.2 °C, while decreasing the blast angle to 45° gave ΔT= -11.6 °C for 304 stainless steel substrates. Furthermore, increasing the blast pressure from 40 psi to 50 psi gave ΔT= +15.3 °C and changing from 50 psi to 60 psi gave ΔT= +9.9 °C. The blast distance change from 8” to 6” resulted in ΔT = +9.8 °C in thin stainless steel substrate temperature. The effects of substrate thickness or shape were evaluated, giving ΔT= +7.4 °C at 8” distance, ΔT= +20.2 °C at 60 psi pressure, and ΔT= -15.2 °C at 45° blasting when comparing thin stainless steel against 304 stainless steel (thick) temperatures. No significant ΔT in means was found when going from 6” to 8” distance on 304 stainless steel, 40 psi and 60 psi blasting of thin SS, as well as angled and perpendicular blasting of thin SS. Comparing thick 304 and thin stainless steel substrates at a 6” blast distance gave no significant ΔT. / Master of Science

Abrasive waterjet (AWJ) cutting is one of the most recently developed nontraditional manufacturing technologies. It has been increasingly used in industry owing to its various distinct advantages over the other cutting technologies. However, many aspects of this technology require to be fully understood in order to increase its capability and cutting performance as well as to optimize the cutting process. This thesis contains an extensive literature review on the investigations of the various aspects in AWJ machining. It shows that while considerable work has been carried out, very little reported research has been found on the AWJ contouring process although it is a common AWJ cutting application. Because of the very nature of the AWJ cutting process, the changing nozzle traverse direction involved in AWJ contouring results in kerf geometrical or shape errors. A thorough understanding of the AWJ contouring process is essential for the reduction or elimination of these shape errors. It also shows that a lack of understanding of the AWJ hydrodynamic characteristics has limited the development of cutting performance models that are required for process control and optimization. Accordingly, a detailed experimental investigation is presented in this thesis to study the various cutting performance measures in AWJ contouring of an 87% alumina ceramic over a wide range of process parameters. For a comparison purpose, the study also considers AWJ straight-slit cutting. The effects of process parameters on the major cutting performance measures in AWJ contouring have been comprehensively discussed and plausible trends are amply analysed. It finds that the taper angles on the two kerf walls are in different magnitudes in AWJ contouring. The kerf taper on the outer kerf wall increases with the arc radius (or profile curvature), while that on the inner kerf wall decreases. Moreover, the depth of cut increases with an increase in arc radius and approaches the maximum in straight cutting for a given combination of parameters. The other process variables affect the AWJ contouring process in a way similar to that in straight cutting. The analysis has provided a guideline for the selection of process parameters in the AWJ contouring of alumina ceramics. In order to predict the cutting performance in process planning and ultimately optimize the cutting process, mathematical models for the major cutting performance measures in both straight-slit cutting and contouring are developed using a dimensional analysis technique. The models are then verified by assessing both qualitatively and quantitatively the model predictions with respect to the corresponding experimental data. It shows that the models can adequately predict the cutting performance measures and form the essential basis for developing strategies for selecting the optimum process parameters in AWJ cutting. To achieve an in-depth understanding of the jet dynamic characteristics such as the velocity and pressure distributions inside a jet, a Computational Fluid Dynamics (CFD) simulation is carried out using a Fluent6 flow solver and the simulation results are validated by an experimental investigation. The water and particle velocities in the jet are obtained under different input and boundary conditions to provide an insight into the jet characteristics and a good understanding of the kerf formation process in AWJ cutting. Various plausible trends and characteristics of the water and particle velocities are analysed and discussed, which provides the essential knowledge for optimizing the jet performance through optimizing the jetting and abrasive parameters. Mathematical models for the water and particle velocity distributions in an AWJ are finally developed and verified by comparing the predicted jet characteristics with the corresponding CFD simulation data. It shows that the jet characteristics models can yield good predictions for both water and particle velocity distributions in an AWJ. The successful development of these jet dynamic characteristics models is an essential step towards developing more comprehensive mathematical cutting performance models for AWJ cutting and eventually developing the optimization strategies for the effective and efficient use of this advanced manufacturing technology.

The formulated study is focused on the analysis and quantification of the accuracy–parameters related to the abrasive process. The scope of the mentioned study deals with the identification of the abrasive process, technological influence and accuracy–parameters of abrading surfaces. In the final part of this study, there is a practical sample described with respect to the technological influence on the resulting accuracy–parameters of the abrasive process.

Orientador: Eduardo Carlos Bianchi / Resumo: Aços-rápidos são materiais que exibem elevada resistência ao desgaste abrasivo, aliada a uma tenacidade relativamente alta, propriedades estas que os tornam adequados para se fabricar ferramentas de corte. Grande parte de suas propriedades se deve a presença de carbonetos na microestrutura. Ao mesmo tempo que estas propriedades mecânicas são favoráveis para a utilização como ferramentas, tornam-se desafios na sua fabricação. O processo de retificação é empregado nas últimas etapas de fabricação de ferramentas de corte como machos e brocas e a presença dos carbonetos afetam a eficiência dos rebolos. Neste contexto, este trabalho visa investigar o quanto a diferença de microestrutura de aços-rápidos classe AISI M3:2, obtidos de diferentes fornecedores, influencia na retificação, levando em consideração a integridade superficial. Os materiais, aqui nomeados como M-A, M-B e M-C, foram avaliados sob três aspectos: características da microestrutura, resistência à abrasão e integridade da superfície após a retificação. Da microestrutura os carbonetos tipo MC e M6C, foram descritos quanto à forma e a distribuição, utilizando para isso MEV e EDS. A resistência à abrasão dos materiais foi medida recorrendo ao método de ensaio tribológico pino-lixa. Após esta caracterização, foram realizados ensaios de retificação tangencial plana com rebolo de Carboneto de Silício (SiC) em várias penetrações de trabalho (entre 10 µm e 30 µm). As superfícies das amostras foram avaliadas mensurando a rug... (Resumo completo, clicar acesso eletrônico abaixo) / High-Speed Steels are materials that exhibit high abrasive wear resistance coupled withrelatively high toughness, properties that make them suitable for making cutting tools. Much ofits properties are due to the presence of carbides in the microstructure. While these mechanicalproperties are favorable for use as tools, they impose challenges in their manufacture. Thegrinding process is employed in the final stages of the cutting tools manufacturing, such as tapsand drills and the presence of carbides affects the efficiency of the grinding wheels. In thiscontext, this work aims to investigate how the microstructure difference of class AISI M3: 2steel, obtained from different suppliers, influences the grinding, taking into consideration thesurface integrity. The materials, here named M-A, M-B, and M-C, were evaluated under threeaspects: microstructure characteristics, abrasion resistance, and surface integrity after grinding.From the microstructure, carbides type MC and M6C were described regarding the shape anddistribution, using for this purpose SEM and EDS. The abrasive wear resistance of the materialswas measured using the pin-abrasive tribological test. After this characterization, flat tangentialgrinding tests were performed, using silicon carbide grinding wheel (SiC), in various workdepths (between 10 μm and 30 μm). The ground samples surfaces were evaluated by measuringthe roughness parameters, evaluated by SEM, and the microhardness profil / Doutor

The basic objective of this study was to evaluate the environmental performance of two abrasives Copper Slag and Barshot in terms of productivity (in terms of area cleaned- ft2/hr), consumption and or used-abrasive generation rate (of the abrasive- ton/2000ft2; lb/ft2) and particulate emissions (mg/ft2; mg/lb; lb/lb; lb/kg; lb/ton). This would help in evaluating the clean technologies for dry abrasive blasting and would help shipyards to optimize the productivity and minimize the emissions by choosing the best combinations reported in this study to their conditions appropriately. This project is a joint effort between the Gulf Coast Region Maritime technology Center (GCRMTC) and USEPA. It was undertaken to simulate actual blasting operations conducted at shipyards under enclosed, un-controlled conditions on plates similar to steel plates commonly blasted at shipyards.

Neste trabalho, foi investigado o efeito do tamanho do abrasivo e do pH do meio na resistência ao desgaste abrasivo do aço H-13 com matriz martensítica e do aço Hadfield com matriz austenítica. Ensaios de abrasão foram realizados utilizando o equipamento roda de borracha a úmido, variando o tamanho do abrasivo entre 0,15 e 2,40 mm e o pH do meio entre 5,5 e 12,8. As microestruturas dos materiais estudados foram analisadas utilizando microscopia óptica, as superfícies de desgaste e as partículas de desgaste foram analisadas em microscópio eletrônico de varredura. A macrodureza e a microdureza, antes e após os ensaios, foram obtidas utilizando durômetro Vickers. A topografia da região central da superfície de desgaste foi obtida utilizando Perfilometria 3D, visando obter valores de profundidade de penetração do abrasivo. Os resultados mostraram que o aço Hadfield é mais resistente do que o aço H-13 em todos os valores de pH e tamanhos de abrasivo utilizados. Para os dois materiais, a perda de massa aumenta linearmente até um tamanho crítico de abrasivo (TCA) e, após este, a mesma continua a aumentar, mas com uma intensidade menor. Para os dois materiais e para todos os tamanhos de abrasivo, o aumento do pH do meio resultou em menores perdas de massa, sendo este efeito maior para os dois menores tamanhos de abrasivo. Para maiores valores de pH, foram observadas menores profundidades de penetração do abrasivo. A microdureza da superfície de desgaste do aço H-13 sofreu um pequeno aumento com o aumento do tamanho do abrasivo enquanto que para o aço Hadfield esse aumento foi mais intenso. A análise das partículas de desgaste mostraram que, para todas as condições ensaiadas, os debris do aço H-13 tinham duas morfologias, contínuas e descontínuas enquanto que os cavacos do aço Hadfield foram sempre descontínuos. Para os dois materiais, foram observados dois micromecanismos de desgaste, sendo eles microcorte e microsulcamento. Por fim, os resultados apresentados neste trabalho sugerem que a análise de desempenho do aço Hadfield em serviço deve considerar o pH do meio bem como a granulometria do abrasivo em contato. / In this work, the effects of abrasive particle size and pH value of the aqueous solution on abrasive wear resistance of the H-13 steel with martensitic matrix and the Hadfield steel with austenitic matrix were investigated. Abrasive wear tests, using a wet rubber wheel abrasion tester, were carried out using abrasive sizes between 0.15 and 2.40 mm and pH values of the aqueous solution between 5.5 and 12.8. The microstructures of the materials studied were analyzed by optical microscopy and the wear surfaces and wear particles were analyzed by scanning electron microscopy. The hardness and microhardness before and after the tests were measured using a Vickers hardness tester. The topography of the middle of wear scars, were obtained by a noncontact 3D profiler in order to measure the depth of abrasive penetrations.The results show that the Hadfield steel is more wear resistant than the H-13 steel at all pH values and abrasive sizes conditions tested. For both materials, mass loss increases linearly up to a critical abrasive size, and after this the mass loss continues to increase, but with a lower intensity. Moreover, for both materials and all the abrasive sizes, increases in the pH values of the aqueous solution resulted in lower mass losses, and this effect is greater for the two smaller grain sizes. For higher pH values, lower depths of penetration of abrasive were observed. The microhardness in the wear scar surface of the H-13 steel presented a slight increase with the abrasive size, while for the Hadfield steel, this microhardness increases in a more intense form with the abrasive size. The analysis of the wear particles showed that, for all test conditions, the chips of H-13 steel has two types of morphologies, continuous or discontinuous, and for Hadfield steel only discontinuous. For both materials, two abrasive wear micromechanisms were observed, microcutting and microploughing. Finally, the results presented in this work suggest that the wear performance analysis of the Hadfield steel, to be used in an abrasive environment, must consider the effects of pH of the aqueous solution and particle size.

Made available in DSpace on 2016-12-23T14:08:10Z (GMT). No. of bitstreams: 1 Karla Dubberstein Tozetti.pdf: 2038739 bytes, checksum: f6618f8c3d4a6be204f5f15fc187f5a1 (MD5) Previous issue date: 2013-04-01 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / No trabalho foi investigado o efeito da carga e do tamanho da partícula abrasiva na resistência ao desgaste da liga de ferro fundido branco alto cromo (FFBAC) com composição química de 2,9% de carbono e 19,9% de cromo em massa. A microestrutura da liga é composta por uma matriz de martensita revenida a 200 ºC com carboneto eutético. No ensaio abrasivo pino sobre lixa foram utilizadas lixas de sílica e de granada como abrasivo, com três granulometrias distintas: 63 μm, 149 μm e 177 μm, sob a aplicação de duas cargas: 5 N e 10 N. Em abrasão no roda-deborracha utilizou-se como abrasivo a areia normal brasileira (ANB) com três tamanhos médios: 87 μm, 115 μm e 170 μm e três cargas: 44 N, 80 N e 130 N. As superfícies de desgaste foram analisadas com um analisador tridimensional de superfícies e os micromecanismos de desgaste foram caracterizados usando microscopia eletrônica de varredura. Os resultados obtidos nos ensaios mostraram, de maneira geral, um aumento no volume perdido no desgaste com o aumento da carga e do tamanho da partícula abrasiva e permitiram, para a roda-de-borracha, a observação de um tamanho crítico do abrasivo. No ensaio pino sobre lixa de sílica, para o maior tamanho de abrasivo, o volume perdido no desgaste triplicou com o aumento da carga de 5 N para 10 N / In this research, the effects of different applied load and abrasive size on the martensitic high-chromium write cast iron (with a chemical composition: 2,9% carbon and 19,9% chromium) abrasive wear was investigated. The alloy s microstructure consists of: a matrix martensite tempered at 200 ° C with eutectic carbide. Abrasive wear tests using a pin test on silica and garnet paper were carried out using three different abrasives sizes: 63 μm, 149 μm e 177 μm and two applied load: 5 N e 10 N. And the rubber wheel abrasion test (ASTM standard G-65) was carried out using three abrasives sizes: 87 μm, 115 μm e 170 μm and three distinct applied loads: 44 N, 80 N e 130 N. The specimens wear surface was examined by scanning electron microscopy (SEM) for identifying the wear mechanism. The rubbers wheel abrasion test results show that: the mass loss of the write cast iron alloy increases linearly with the increase of particle size until the critical particle size is reached. In pin test on silica paper, to the largest abrasive size, the lost volume in abrasion tripled with applied load increasing of 5 N to10 N. In general, the mass loss increases with the increase of the load applied and the abrasive size

Neste trabalho, foi investigado o efeito do tamanho do abrasivo e do pH do meio na resistência ao desgaste abrasivo do aço H-13 com matriz martensítica e do aço Hadfield com matriz austenítica. Ensaios de abrasão foram realizados utilizando o equipamento roda de borracha a úmido, variando o tamanho do abrasivo entre 0,15 e 2,40 mm e o pH do meio entre 5,5 e 12,8. As microestruturas dos materiais estudados foram analisadas utilizando microscopia óptica, as superfícies de desgaste e as partículas de desgaste foram analisadas em microscópio eletrônico de varredura. A macrodureza e a microdureza, antes e após os ensaios, foram obtidas utilizando durômetro Vickers. A topografia da região central da superfície de desgaste foi obtida utilizando Perfilometria 3D, visando obter valores de profundidade de penetração do abrasivo. Os resultados mostraram que o aço Hadfield é mais resistente do que o aço H-13 em todos os valores de pH e tamanhos de abrasivo utilizados. Para os dois materiais, a perda de massa aumenta linearmente até um tamanho crítico de abrasivo (TCA) e, após este, a mesma continua a aumentar, mas com uma intensidade menor. Para os dois materiais e para todos os tamanhos de abrasivo, o aumento do pH do meio resultou em menores perdas de massa, sendo este efeito maior para os dois menores tamanhos de abrasivo. Para maiores valores de pH, foram observadas menores profundidades de penetração do abrasivo. A microdureza da superfície de desgaste do aço H-13 sofreu um pequeno aumento com o aumento do tamanho do abrasivo enquanto que para o aço Hadfield esse aumento foi mais intenso. A análise das partículas de desgaste mostraram que, para todas as condições ensaiadas, os debris do aço H-13 tinham duas morfologias, contínuas e descontínuas enquanto que os cavacos do aço Hadfield foram sempre descontínuos. Para os dois materiais, foram observados dois micromecanismos de desgaste, sendo eles microcorte e microsulcamento. Por fim, os resultados apresentados neste trabalho sugerem que a análise de desempenho do aço Hadfield em serviço deve considerar o pH do meio bem como a granulometria do abrasivo em contato. / In this work, the effects of abrasive particle size and pH value of the aqueous solution on abrasive wear resistance of the H-13 steel with martensitic matrix and the Hadfield steel with austenitic matrix were investigated. Abrasive wear tests, using a wet rubber wheel abrasion tester, were carried out using abrasive sizes between 0.15 and 2.40 mm and pH values of the aqueous solution between 5.5 and 12.8. The microstructures of the materials studied were analyzed by optical microscopy and the wear surfaces and wear particles were analyzed by scanning electron microscopy. The hardness and microhardness before and after the tests were measured using a Vickers hardness tester. The topography of the middle of wear scars, were obtained by a noncontact 3D profiler in order to measure the depth of abrasive penetrations.The results show that the Hadfield steel is more wear resistant than the H-13 steel at all pH values and abrasive sizes conditions tested. For both materials, mass loss increases linearly up to a critical abrasive size, and after this the mass loss continues to increase, but with a lower intensity. Moreover, for both materials and all the abrasive sizes, increases in the pH values of the aqueous solution resulted in lower mass losses, and this effect is greater for the two smaller grain sizes. For higher pH values, lower depths of penetration of abrasive were observed. The microhardness in the wear scar surface of the H-13 steel presented a slight increase with the abrasive size, while for the Hadfield steel, this microhardness increases in a more intense form with the abrasive size. The analysis of the wear particles showed that, for all test conditions, the chips of H-13 steel has two types of morphologies, continuous or discontinuous, and for Hadfield steel only discontinuous. For both materials, two abrasive wear micromechanisms were observed, microcutting and microploughing. Finally, the results presented in this work suggest that the wear performance analysis of the Hadfield steel, to be used in an abrasive environment, must consider the effects of pH of the aqueous solution and particle size.

This contribution describes the investigation of flow channels which are designed to be directly integrated into an aerospike engine by means of additive manufacturing with laser powder bed fusion (LPBF). During the experimental testing of a previous aerospike engine in 2019, it was observed that high surface roughness of such additively manufactured integrated channels caused a significant reduction in the mass flow rates of the propellants ethanol and liquid oxygen as well as the coolant due to increased pressure drop. In an extensive study within the CFDmikroSAT project, various factors influencing this surface roughness are, therefore, being investigated, which include the geometry of the channels as well as selected manufacturing parameters of the LPBF process, such as layer thickness and component orientation. To further reduce the roughness after manufacturing, suitable post-processing methods are also being investigated for internal cavities, initially analysing the abrasive flow machining process. Within the paper, the overall investigation approach is presented, such as the overview of the considered specimens, and the initial results of a various studies with selected specimens are discussed. These studies consist of the examination of surface roughness reduction, shape accuracy and flow behaviour of post-processed cooling channel specimens. Finally, a brief overview of the already manufactured aerospike demonstrator is presented.