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Agradecimentos: A.R., A.G., P.P. contributed equally to this work. E.F.O. would like to thank the Brazilian agency FAPESP (grants 2016/18499-0 and 2019/07157-9) for financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID grant no. 2013/08293-7 is also acknowledged. D.S.G. also acknowledges support from CAPES and CNPq. Some of the authors would like to thank the Board of Research in Nuclear Sciences (BRNS) (project no.: 57/14/05/2019-BRNS) for the financial support. C.S.T. was thankful for the support by AOARD grant no. FA2386-19-1-4039. CST acknowledges Ramanujan fellowship Abstract: Composites have played a key role in revolutionizing the automobile, marine, and aerospace industries. There is a constant attempt for the development of low-density composite materials with superior mechanical and corrosion-resistant properties for elevated temperature applications. Herein, an attempt is made to develop a nature-inspired unique aluminum-based composite with low-density polymer (polyethylene terephthalate, i.e., soft material) reinforcement, which shows an enhancement in strength and toughness. The composite is processed using the easily scalable and simple friction stir processing technique. Mechanical properties of the uniformly reinforced aluminum composite show double ultimate strength and fivefold improvement in plasticity. The ultimate strength of the composite increases at elevated temperatures. The experimental observations are further supported by theoretical calculations and molecular dynamics simulations FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Orientador: Ambrósio Florêncio de Almeida Neto Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química Resumo: O processo de corrosão está constantemente transformando os materiais metálicos de modo que em alguns casos a durabilidade e o desempenho dos mesmos ficam comprometidos. Uma forma de minimizar os efeitos da corrosão em materiais metálicos é revesti-los com outros materiais. A eletrodeposição é um método muito utilizado na obtenção de revestimentos metálicos resistentes à corrosão. Esse método também pode ser utilizado como técnica de tratamento de efluentes contaminados com metais tóxicos. A eletrodeposição promove a reação de redução de íons, presentes em soluções, em sua espécie metálica, a qual se deposita em um eletrodo, recuperando os metais, e em muitos casos possibilitando a reutilização da água. Este trabalho visa à obtenção de ligas metálicas de tungstênio e apresenta um apelo ambiental referente à recuperação de metais tóxicos de efluentes, que podem ser utilizados como metais indutores na formação das ligas de tungstênio. Os depósitos binários estudados foram Fe-W, Ni-W e Co-W, sendo estes considerados como uma codeposição do tipo induzida, pois a eletrodeposição do tungstênio a partir dos seus sais dissolvidos em solução aquosa não é possível. A otimização do processo de eletrodeposição das ligas de tungstênio com o ferro, o cobalto e o níquel, foi desenvolvida por meio de um estudo sobre a influência dos parâmetros de operação (concentração do sal fonte do metal, temperatura do banho e densidade de corrente) na eficiência de deposição e na resistência à corrosão. Para o estudo do processo de eletrodeposição foi realizado um planejamento fatorial 23 para cada liga metálica. As ligas binárias Fe-W, Ni-W e Co-W foram eletrodepositadas sobre um substrato de cobre com área superficial de oito cm2 e caracterizadas quanto a morfologia e composição química. As ligas obtidas que apresentaram boa aderência foram analisadas por meio das curvas de polarização e diagramas de impedância eletroquímica como forma de avaliar os revestimentos em relação à resistência à corrosão Abstract: The corrosion process is constantly changing the metal material in a way that its durability and performance are compromised. One way to minimize the effects of corrosion in metallic materials is coating them with other materials. Electroplating is a widely used method to obtain metal coatings that are resistant to corrosion. This method can also be used as a treatment technique for the wastewater which is contaminated with toxic metals. The electrodeposition ions promote the reduction reaction, present in solution, in its metallic state, which is deposited on an electrode, therefore recovering metals, and in many cases allowing the reuse of water. This study aims at developing and obtaining alloys of tungsten and presents an environmental call related to the recovery of toxic metals from effluent that can be used to induce the formation of metal tungsten alloys. The binary deposits studied were Fe-W, Ni-Co-W and W, being these considered as a codeposition of induced type because tungsten electrodeposition from salts dissolved in the aqueous solution is not possible. The optimization of the electrodeposition process of the tungsten alloys with iron, cobalt and nickel, has been developed through a study on the influence of the operating parameters (concentration of the source of the metal salt, bath temperature and current density) the deposition efficiency and corrosion resistance. For the study of the electrodeposition process a 23 factorial planning was conducted for each metallic alloy. The binary Fe-W, Ni-Co-W and W were electrodeposited on a copper substrate with a surface area of eight cm2 and characterized according to its morphology and chemical composition. The alloys obtained with good grip were analyzed using linear potentiodynamic polarization curves and electrochemical impedance diagrams for to evaluate the coatings for resistance to corrosion Mestrado Engenharia Química Mestra em Engenharia Química FAEPEX FAPESP

In electrical contacts, thin films of nickel and gold or silver are traditionally plated on top of a copper base plate to provide corrosion resistance and wear protection. Most recently, the rising cost of noble metals and intensified competition in manufacturing technology has driven the industry towards thinner plating layers, which gives rise to questions regarding how interfacial contact and wear is affected by plating thickness and material characteristics. This study uses a combination of finite element analysis and ex-situ wear measurement to determine the effect of gold plating thickness on wear performance under linear reciprocating sliding contact. Correlations between predicted and measured results lead to insight into the stress state within the multi-layer system under contact conditions as well as a wear map for gold platings that can be used to inform future connector designs. The middle layer material, Ni, is relatedly inexpensive, but takes a relatively long time to deposit. Because this deposition time has a direct influence on the cost of manufacturing, it is important to reduce the Ni thickness as well. This project thus determines how different combinations of Ni and Au properties influence wear and subsurface layer exposure, which is critical for determining the makeup of future, low-cost, connector designs.

Aluminium smelting is a high temperature electrometallurgical process, which suffers considerable inefficiencies in power utilization and equipment maintenance. Aluminium smelting cell works in the extreme environments that contain extraordinarily aggressive gases, such as HF, CO and SO2. Mild steel used as a structural material in the aluminium industry, can be catastrophically corroded or oxidized in these conditions. This project was mainly concerned with extending the lifetime of metal structures installed immediately above the aluminium smelting cells. An aluminium-rich coating was developed on low carbon steel A06 using pack cementation technique. Yttria (Y2O3) was also used to improve the corrosion resistance of coating. Kinetics of the coating formation were studied. XRD, FESEM and FIB were employed to investigate the phase constitution and the surface morphology. Together with other potentially competitive materials, aluminium-rich coating was evaluated in simulated plant environments. Results from the long time (up to 2500h) isothermal oxidation of materials at high temperature (800ºC) in air showed that the oxidation resistance of coated A06 is close to that of stainless steel 304 and even better than SS304 in cyclic oxidation tests. Coated A06 was also found to have the best sulfidation resistance among the materials tested in the gas mixture contains SO2 at 800ºC. Related kinetics and mechanisms were also studied. The superior corrosion resistance of the coated A06 is attributed to the slow growing alpha-Al2O3 formed. Low temperature corrosion tests were undertaken in the gas mixtures containing air, H2O, HCl and SO2 at 400ºC. Together with SS304 and 253MA, coated A06 showed excellent corrosion resistance in all the conditions. The ranking of the top three materials for corrosion resistance is: 253MA, coated A06 and SS304. It is believed that aluminised A06 is an ideal and economical replacement material in the severe corrosive aluminium smelting cell environment.