Correlação entre microestrutura, resistências mecânica e à corrosão da liga de soldagem livre de chumbo sn-0,7%cu

Ligas do sistema Sn-Cu consistem alternativa promissora na substituição das ligas de soldagem contendo chumbo. Entretanto, pouco se conhece dos efeitos da taxa de resfriamento sobre a microestrutura de solidificação dessas ligas, bem como das alterações provocadas nas resistências mecânicas e à corrosão. No presente trabalho, a técnica de solidificação unidirecional transitória foi empregada para obtenção de um lingote de Sn-0,7%Cu (em peso). Os resultados experimentais incluem: parâmetros térmicos de solidificação (taxa de resfriamento, Ṫ, velocidade de solidificação, v, e coeficiente de transferência de calor metal/substrato, hi), espaçamentos celular, λc, e dendrítico primário, λ1, taxa de corrosão, potencial de corrosão e resistência à polarização, além de resistência mecânica e ductilidade. Os resultados mostram uma transição microestrutural do tipo celular/dendritica com prevalência de células eutéticas para Ṫ< 0,9°C/s. Menores niveis de resistência à corrosão foram associados às regiões de morfologia dendrítica em comparação com regiões de células eutéticas. Nas regiões dendríticas foi observada a presença de intermetálico Cu6Sn5 extremamente fino e de morfologia fibrosa114277286CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/13030-

Correlation between unsteady-state solidification microstructure and wear behavior

Ciclo de Seminarios del CENIMIn the past, many studies have been performed on the improvement of mechanical properties of alloys by refining grain size. Nonetheless, there is considerable uncertainty regarding the mechanism of the grain size effect. In this talk, it will be shown that the influence of microstructural features, located inside the grain, such as the matrix morphology (cell, dendrite) and second-phase particles, can be particularly important from the point of view of mechanical behavior. The influence can often be quantified in a constitutive relation that is an appropriate variant on the familiar Hall-Petch relation: the quantitative improvement in properties varies with d-1/2 , where d is the microstructural feature spacing. Since microstructural features can be tailored by processing the molten metal, it is important to understand how they evolve during solidification, being controlled by cooling and solidification rates. This talk aims to present some of the results from the work developed during his stage at CENIM, referring to the correlation between unsteady-state solidification microstructure of Zn-Al-Bi alloys and wear behavior.N

Interação entre uma base de conhecimento e um modelo matematico de solidificação na analise da qualidade no lingotamento continuo de aços

Orientador: Amauri GarciaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Neste trabalho foi desenvolvido um modelo numérico baseado na técnica de diferenças finitas que permite o mapeamento térmico durante a solidificação ao longo do processo de lingotamento contínuo. Aferiu-se o respectivo modelo com resultados experimentais e de outros modelos constantes na literatura. Realizou-se a interação entre uma base de conhecimento e este modelo matemático de solidificação para a análise da qualidade no lingotamento contínuo de tarugos de aços. A base de conhecimento foi estruturada com informações que correlacionam problemas de qualidade com parâmetros do processo, a partir da literatura especializada e da interação com siderúrgica envolvida com a prática do lingotamento contínuo. A comunicação do modelo numérico com a base de conhecimento foi efetuada através de um programa computacional desenvolvido neste trabalho, permitindo uma interação autônoma na busca de soluções ótimas. O modelo foi aplicado na análise de situações de operações reais de um equipamento de lingotamento contínuo de uma siderúrgica e também foi utilizado para projetar um sistema otimizado de lingotamento contínuo de tarugos empregando tendências atuais de maior comprimento de molde e velocidades de produção mais elevadasAbstract: In this work, a nunerical mode! based on the finite difference technique was developed permitting to determine the a thermal field evolution during solidification along the continuous casting process. The model predictions were compared to experimental results as well as to those furnished by other models found in literature. An interaction between a knowledge base and the mathematical model was carried out in order to analyse steel billet quality. As a result of literature search and interaction with knowledge provided by a continuous casting industry, the knowledge base was structured with information that correlate quality problems with process parameters. The numerical model communication with the knowledge base was established by employinga computer program in order to permit automatic solutions of optimized operating conditions to be attained. The model was applied to analyse real casting operation of a steel plant equipment as well as to designan optimized continuous billet casting system by employing recent trends of larger mould lenght and higher production speedsMestradoMateriais e Processos de FabricaçãoMestre em Engenharia Mecânic

Simulação numerica de tratamento superficial por refusão a laser : interação radiação laser-materia e solidificação

Orientador: Amauri GarciaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: Neste trabalho, é desenvolvido um modelo numérico bidimensional em coordenadas cilíndricas baseado na técnica de diferenças finitas, que permite o mapeamento térmico durante o aquecimento, fusão, solidificação e resmamento ao longo do processo de tratamento superficial a laser. O respectivo modelo é aferido com resultados experimentais e de outros modelos constantes na literatura para os casos de têmpera e refusão superficial a laser. Ensaios experimentais em amostras de aço AIS! 1045 e Al-15%Cu foram realizados no Laboratório Nacional de Luz Síncrotron, utilizandoum laser de C02 CW com potência máxima disponível de I kW. Para efeito comparativo, as trilhas foram feitas variando-se valores de velocidade para um mesmo valor de potência estabelecidos para cada tipo de tratamento. Para as amostras do aço AIS! 1045, os ensaios visaram o estudo do processo de têmpera superficial a laser assim como da resolidificação. Amostras de Al-15%Cu foram submetidas ao tratamento de refusão a laser relação ao aço. Analisou-se as microestruturas resultantes dos tratamentos a laser através de microscopia óptica e eletrônica de varredura, sendo observadas microestruturas refinadas na área tratada a laser refletindo no aumento significativo da dureza confirmado pelos ensaios de microdureza Vickers. Realizou-se a interação entre uma base de conhecimento e o modelo matemático de têmpera superficial a laser através de uma busca heurística de Inteligência Artificial para sugestão de parâmetros operacionais otimizados para a obtenção da máxima profimdidade de martensita a partir da superficieAbstract: In this work, a two dimensional numerical modei in cylindrical coordinates based on the finite difference technique is developed pennitting the description of the thermal field evolution during heating, fusion, solidification and cooling along the laser surface treatment processo The model predictions are compared to experimental results as well as to those fumished by other models found in literature for the surface quenching and remelting process by laser. AISI 1045 steel and Al-15%wtCu samples were used for the surface treatment by using a 1000W C02 CW laser of the Laboratório Nacional de Luz Síncrotron. For a comparative effect, the laser tracks were performed with different velocities for a fixed value of power established for each treatment type. AISI 1045 steel samples were used for studying the surface quenching and remelting process by laser and the Al-15%wtCu samples were submitted to the laser surface remelting treatment in order to simulate the process with a material of higher therma1 diffusivity than the steel. The microstructures resulting from the laser treatment are analyzed by using optical and electron scanning microscope and a very refined microstructure is observed which reflects significant hardness increase confirmed by the Vickers microhardness tests. An interaction between a knowledge base and the mathematical model is carried out by using a heuristic search of Artificial Intelligence in order to optimize operational parameters which permit to attain the highest martensite depth from the surfaceDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

The use of a directional solidification technique to investigate the interrelationship of thermal parameters, microstructure and microhardness of Bi–Ag solder alloys

Bi–Ag alloys have been stressed as possible alternatives to replace Pb-based solder alloys. Although acceptable melting temperatures and suitable mechanical properties may characterize such alloys, as referenced in literature, there is a lack of comprehension regarding their microstructures (morphologies and sizes of the phases) considering a composition range from 1.5 to 4.0 wt.%Ag. In order to better comprehend such aspects and their correlations with solidification thermal parameters (growth rate, v and cooling rate, Ṫ), directional solidification experiments were carried out under transient heat flow conditions. The effects of Ag content on both cooling rate and growth rate during solidification are examined. Microstructure parameters such as eutectic/dendritic spacing, interphase spacing and diameter of the Ag-rich phase were determined by optical microscopy and scanning electron microscopy. The competition between eutectic cells and dendrites in the range from 1.5 to 4.0 wt.%Ag is explained by the coupled zone concept. Microhardness was determined for different microstructures and alloy Ag contents with a view to permitting correlations with microstructure parameters to be established. Hardness is shown to be directly affected by both solute macrosegregation and morphologies of the phases forming the Bi–Ag alloys, with higher hardness being associated with the cellular morphology of the Bi-2.5 and 4.0 wt.%Ag alloys96115125CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/13030-5; 2013/08259-

Sn–0.7 wt%Cu–(xNi) alloys : microstructure–mechanical properties correlations with solder/substrate interfacial heat transfer coefficient

In spite of being barely studied, the prediction of mechanical properties by controlling and monitoring solidification thermal parameters (growth rate – v; cooling rate – ; solder/substrate interfacial heat transfer coefficient – hi) may be a powerful tool in the pre-programming of optimized final properties in solder alloys. The management of these parameters is fundamental to determine the final as-soldered microstructure, including the morphologies and sizes of phases. Within this scope, the aim of the present investigation is to determine interrelations of thermal parameters (v, , hi), microstructure and tensile properties for Sn–0.7 wt%Cu–xNi (0–0.1 wt%Ni) solders solidified under steady-state conditions against a copper water-cooled substrate. It is demonstrated that the ultimate tensile strength can be linearly correlated with hi for Sn–Cu–Ni alloys. The final microstructures are shown to be very responsive to the changes in v as well as in Cu and Ni contents632274285CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/08259-3; 2013/13030-

SEM Characterization of Al₃Ni Intermetallics and its Influence on Mechanical Properties of Directionally Solidified Hypoeutectic Al-Ni Alloys

International audienceRod-like Al3Ni intermetallic structures have been widely studied by Bridgman techniques of solidification. However, there is a lack of experiments conducted under unsteady-state solidification conditions. Such conditions are very close to the industrial reality since the thermal solidification variables (tip cooling rate, tip growth rate and thermal gradient) are freely changing as solidification progresses. In this research, Al3Ni structures found in hypoeutectic Al-Ni alloys were characterized under transient solidification conditions. Two Al-Ni alloys (1.0 and 5.0 wt%Ni) were directionally solidified. SEM (Scanning Electron Microscope) micrographs were obtained along the casting length (P). It was possible to observe with adequate magnifications the distribution of rod like Al3Ni particles along the interdendritic regions. In order to emphasize the examination ofmorphology and distribution of such particles, the aluminum-rich matrix was dissolved by immersion of the sample in a fluoride acid solution (0.5%HF + 99.5% H2O). The effects of nickel content, dendritic arrangement and Al3Ni distribution on mechanical properties were investigated by tensile tests

Microstructural Refinement and Improvement of Microhardness of a Hypoeutectic Al–Fe Alloy Treated by Laser Surface Remelting

In laser surface remelting (LSR) treatment, only a small region is affected by heat, surpassing the melting temperature, followed by rapid cooling at 103–108 K/s, thus producing an extremely refined microstructure. The treated region shows a more homogeneous microstructure and better mechanical properties as compared to the substrate. Iron is a common impurity found in Al-based alloys but in the 2618 commercial alloy, around 1 wt.% of Fe is intentionally added to improve the high temperature strength and the corrosion resistance. In this work, LSR experiments were performed, by using a CO2 laser operating in a continuous-wave mode, to investigate the influence of process parameters on the treated surface of an as-cast Al-1 wt.% Fe alloy. These parameters encompass work distance (z), laser beam speed (v) and laser average power (P), setting a total of 18 combinations. The configuration of z = 6 mm, v = 500 mm/s and P = 800 W resulted in a molten pool with 710 µm of width for 242 µm of length without major porosities, therefore being the largest stable pool amongst all parameter combinations. The resulting cellular microstructure is shown to have an average interphase spacing of 0.93 ± 0.17 µm, a decrease of about 14 times in relation to that of the substrate. The effects of LSR on microhardness were remarkable, with the remelted track presenting Vickers microhardness of 50.1 ± 2 HV, which corresponds to increase of about 43% as compared to that of the original substrate21CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESNão temNão te