Atualmente o ramo industrial tem voltado grande parte de suas atenções para situações ambientais. Um dos grandes problemas mundiais encontra-se no uso de cromo hexavalente, prejudicial à saúde humana, além de contaminar leitos e rios por ser solúvel em água e a fosfatização que é responsável pela eutrofização das águas. Novos processos sustentáveis têm sido estudados para reduzir os impactos ambientais causados por esses tratamentos, dentre os quais podemos citar os revestimentos chamados de nanocerâmicos, por formarem camadas nanoestruturadas de óxido de zircônio na superfície do substrato. Vários parâmetros influenciam na formação da camada (substrato, pH, concentração, tempo). O trabalho teve como objetivo o estudo da influência dos parâmetros no desempenho contra a corrosão do revestimento formado por camadas de conversão obtidas a base de ácido hexafluorzircônio em aço galvanizado. O comportamento eletroquímico foi analisado através dos ensaios de potencial de circuito aberto, espectroscopia de impedância eletroquímica e polarização potenciodinâmica. Também foram realizados ensaios de avaliação anticorrosiva com adição de um revestimento final (tinta comercial) sobre a camada de conversão para avaliar o comportamento como revestimento. A partir dos ensaios realizados chega-se a parâmetros que foram considerados ideais e com melhor desempenho. Com isso obtém-se um pré-tratamento capaz de fazer frente a processos convencionais de cromatização e fosfatização. / Currently, the industrial sector has turned much of their attention to environmental situations. One of the great global problems is the use of hexavalent chromium, harmful to human health and pollute rivers and beds being soluble in water and phosphate which is responsible for water eutrophication. New sustainable processes have been studied to reduce the environmental impacts caused by these treatments, among which we can mention the nanoceramic coatings called for forming nanostructured layers of zirconium oxide on the substrate surface. Several parameters influence the layer formation (substrate, pH, concentration, time). The work aims to study the influence of parameters on the performance against corrosion coating formed by conversion layers obtained acid based hexafluorzirconic on galvanized steel. The electrochemical behavior was analyzed through the trials of open circuit potential data, electrochemical impedance spectroscopy and polarization. Also evaluation trials were performed with addition of an anti-corrosive top coat (commercial ink) on the layer of conversion coating painted as to evaluate the corrosion resistance. From the tests to parameters that were considered ideal and best performance. Thus is obtained a pretreatment able to cope with the conventional processes chromate and phosphate.

Atualmente o ramo industrial tem voltado grande parte de suas atenções para situações ambientais. Um dos grandes problemas mundiais encontra-se no uso de cromo hexavalente, prejudicial à saúde humana, além de contaminar leitos e rios por ser solúvel em água e a fosfatização que é responsável pela eutrofização das águas. Novos processos sustentáveis têm sido estudados para reduzir os impactos ambientais causados por esses tratamentos, dentre os quais podemos citar os revestimentos chamados de nanocerâmicos, por formarem camadas nanoestruturadas de óxido de zircônio na superfície do substrato. Vários parâmetros influenciam na formação da camada (substrato, pH, concentração, tempo). O trabalho teve como objetivo o estudo da influência dos parâmetros no desempenho contra a corrosão do revestimento formado por camadas de conversão obtidas a base de ácido hexafluorzircônio em aço galvanizado. O comportamento eletroquímico foi analisado através dos ensaios de potencial de circuito aberto, espectroscopia de impedância eletroquímica e polarização potenciodinâmica. Também foram realizados ensaios de avaliação anticorrosiva com adição de um revestimento final (tinta comercial) sobre a camada de conversão para avaliar o comportamento como revestimento. A partir dos ensaios realizados chega-se a parâmetros que foram considerados ideais e com melhor desempenho. Com isso obtém-se um pré-tratamento capaz de fazer frente a processos convencionais de cromatização e fosfatização. / Currently, the industrial sector has turned much of their attention to environmental situations. One of the great global problems is the use of hexavalent chromium, harmful to human health and pollute rivers and beds being soluble in water and phosphate which is responsible for water eutrophication. New sustainable processes have been studied to reduce the environmental impacts caused by these treatments, among which we can mention the nanoceramic coatings called for forming nanostructured layers of zirconium oxide on the substrate surface. Several parameters influence the layer formation (substrate, pH, concentration, time). The work aims to study the influence of parameters on the performance against corrosion coating formed by conversion layers obtained acid based hexafluorzirconic on galvanized steel. The electrochemical behavior was analyzed through the trials of open circuit potential data, electrochemical impedance spectroscopy and polarization. Also evaluation trials were performed with addition of an anti-corrosive top coat (commercial ink) on the layer of conversion coating painted as to evaluate the corrosion resistance. From the tests to parameters that were considered ideal and best performance. Thus is obtained a pretreatment able to cope with the conventional processes chromate and phosphate.

Atualmente o ramo industrial tem voltado grande parte de suas atenções para situações ambientais. Um dos grandes problemas mundiais encontra-se no uso de cromo hexavalente, prejudicial à saúde humana, além de contaminar leitos e rios por ser solúvel em água e a fosfatização que é responsável pela eutrofização das águas. Novos processos sustentáveis têm sido estudados para reduzir os impactos ambientais causados por esses tratamentos, dentre os quais podemos citar os revestimentos chamados de nanocerâmicos, por formarem camadas nanoestruturadas de óxido de zircônio na superfície do substrato. Vários parâmetros influenciam na formação da camada (substrato, pH, concentração, tempo). O trabalho teve como objetivo o estudo da influência dos parâmetros no desempenho contra a corrosão do revestimento formado por camadas de conversão obtidas a base de ácido hexafluorzircônio em aço galvanizado. O comportamento eletroquímico foi analisado através dos ensaios de potencial de circuito aberto, espectroscopia de impedância eletroquímica e polarização potenciodinâmica. Também foram realizados ensaios de avaliação anticorrosiva com adição de um revestimento final (tinta comercial) sobre a camada de conversão para avaliar o comportamento como revestimento. A partir dos ensaios realizados chega-se a parâmetros que foram considerados ideais e com melhor desempenho. Com isso obtém-se um pré-tratamento capaz de fazer frente a processos convencionais de cromatização e fosfatização. / Currently, the industrial sector has turned much of their attention to environmental situations. One of the great global problems is the use of hexavalent chromium, harmful to human health and pollute rivers and beds being soluble in water and phosphate which is responsible for water eutrophication. New sustainable processes have been studied to reduce the environmental impacts caused by these treatments, among which we can mention the nanoceramic coatings called for forming nanostructured layers of zirconium oxide on the substrate surface. Several parameters influence the layer formation (substrate, pH, concentration, time). The work aims to study the influence of parameters on the performance against corrosion coating formed by conversion layers obtained acid based hexafluorzirconic on galvanized steel. The electrochemical behavior was analyzed through the trials of open circuit potential data, electrochemical impedance spectroscopy and polarization. Also evaluation trials were performed with addition of an anti-corrosive top coat (commercial ink) on the layer of conversion coating painted as to evaluate the corrosion resistance. From the tests to parameters that were considered ideal and best performance. Thus is obtained a pretreatment able to cope with the conventional processes chromate and phosphate.

In this thesis, a novel in-situ method for incorporating nanoscale ceramic particles into metal has been developed. The ceramic phase is introduced as an organic-polymer precursor that pyrolyzes in-situ to produce a ceramic phase within the metal melt. The environment used to shield the melt from burning also protects the organic precursor from oxidation. The evolution of volatiles (predominantly hydrogen) as well as the mechanical stirring causes the polymer particles to fragment into nanoscale dispersions of a ceramic phase. These “Polymer-based In-situ Process-Metal Matrix Composites” (PIP-MMCs) are likely to have great generality, because many different kinds of organic precursors are commercially available, for producing oxides, carbides, nitrides, and borides. Also, the process would permit the addition of large volume fractions of a ceramic phase, enabling nanostructural design, and production of MMCs with a wide range of mechanical properties, meant especially for high temperature applications. An important and noteworthy feature of the present process, which distinguishes it from other methods, is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal is not required to produce the dispersion of the refractory phase. The polymer precursor powder, with a mean particle size of 31.5 µm, was added equivalent to 5 and 10 weight % of the melt (pure magnesium) by a liquid metal stir-casting technique. SEM and OM microstructural observations show that in the cast structure the pyrolysis products are present in the dendrite boundary region in the form of rod/platelets having a thickness of 100 to 200 nm. After extrusion the particles are broken down into fine particles, having a size that is comparable to the thickness of the platelets, in the 100 to 200 nm range, and are distributed more uniformly. In addition, limited TEM studies revealed the formation of even finer particles of 10-50 nm. X-ray diffraction analysis shows the presence of a small quantity of an intermetallic phase (Mg2Si) in the matrix, which is unintended in this process. There was a significant improvement in mechanical properties of the PIP-MMCs compared to the pure Mg. These composites showed higher macro-and micro-hardness. The composite exhibited better compressive strength at both room temperature and at elevated temperatures. The increase in the density of PIP-composites is less than 1% of Mg. Five weight percent of the precursor produced a two-fold increase in the room-temperature yield strength and reduced the steady state creep rate at 723 K by one to two orders of magnitude. PIP-MMCs showed higher damping capacity and modulus compared to pure Mg, with the damping capacity increasing by about 1.6 times and the dynamic modulus by 11%-16%. PIP-composites showed an increase in the sliding wear resistance by more than 25% compared to pure Mg.

Ceramic metal matrix composites (CMMCs) are materials generally created by mixing of hard ceramic particles in a metal matrix. They were expected to combine the ductility and toughness of the metal with the high strength and elastic modulus of the ceramic. MMCs have potential applications in automotive, aeronautical and aerospace industries. Hence, a simple and economical method for fabricating MMCs is an area of intense research. In MMCs, damage evolution starts preferentially at particle matrix interface or at particle clusters in the matrix. This is due to the different physical and mechanical properties of the particle and matrix. Higher local particle volume content leads to higher stress triaxiality making it a preferential site for damage nucleation. Problems with lowering of ductility, fatigue, fracture and impact resistance, agglomeration of ceramic phase and issues related to the predictability of properties of MMCs have been the major issues that have limited their use. In order to overcome some of these shortcomings, the use of nano particles has been attracting increasing attention. The reason is their capability in improving the mechanical and physical properties of traditional MMCs. The dispersion of a nanoscale ceramic phase is needed in order to overcome the problems related to fatigue, fracture toughness, and creep behaviour at high temperatures. However, manufacturing costs, preparation of nano composites and environmental concerns have to be addressed. Agglomeration of nano particles, when produced by the melt stir casting route, the primary route to produce MMCs, is a serious issue that limits the use of nano-particles to produce MMCs with good properties. To avoid agglomeration of the ceramic phase MMCs/nano MMCs have been produced through the powder metallurgy route. Agglomeration is avoided as this is a solid state process. Secondary processing, such as extrusion and rolling are often needed to fully consolidate materials produced in this manner. A high extrusion ratio is often required to get MMCs without porosity. A new method of making nano-ceramic MMC using a polymer derived ceramics (PDC) has been reported. A polymer derived ceramic is a material that converts itself into a ceramic when heated above a particular temperature. In the PDC method a polymer precursor is dispersed in the metal and then converted in-situ to a ceramic phase. A feature of this process is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal or air is not required to produce the ceramic phase. The polymer can be introduced through casting or powder metallurgy route. In the casting route, the polymer powder is directly added to molten metal and pyrolyzed in-situ to create castings of metal-matrix composites. These composites have shown better properties at elevated temperatures but the problem of agglomeration of particles due to Van der Waal's forces and porosity still remains. In the powder method, the organic precursor was milled with copper powder and then plasma sprayed to produce a metal matrix composite. It is reported that these composites retains its mechanical strength close to the melting point of the copper. However, getting a nano sized distribution is difficult through this route as the plasma spray route is a melting and solidification method. Solid state processing by powder metallurgy is possibly a better method to produce well dispersed nano-MMCs. However, powder metallurgy routes are much more expensive and only parts of limited sizes can be produced by this method. Another solid state process Friction Stir Processing (FSP) has successfully evolved as an alternative technique to fabricating metal matrix composites. FSP is based on the principles of Friction Stir Welding (FSW). In FSW, a rotating tool with a pin and a shoulder is inserted into the material to be joined, and traversed along the line of the joint. The friction between the tool and the work piece result in localized heating that softens and plasticizes the material. During production of MMCs using FSP method, the material undergoes intense plastic deformation resulting in mixing of ceramic particles and the metal. FSP also results in significant grain refinement of the metal and has also been used to homogenize the microstructure. FSP technology has also been used to fabricate surface/bulk composites of Al-SiC, friction stir surfacing of cast aluminum silicon alloy with boron carbide and molybdenum disulphide powders and to produce ultra-fine grained Cu-SiC composites. A major problem in the FSP of MMCs is severe tool wear that results from abrasion with hard ceramic particles. The progressive wear of the tool has been reported to increase the likelihood of void or defect development. This change in geometry has been reported in the friction stir welding of several MMCs. The problems concerning the tool life has become a serious issue in the application of FSP for producing MMCs. In the present work the advantages of the PDC method and FSP have been combined to produce polymer derived nano ceramic MMCs. This method mainly consists of three steps. In the first step, a polymer, which pyrolysis to form a PDC at temperatures lower than the melting point of the metal, is dispersed in the metal by FSP. This step is different from the melt route where the PDC forms at temperatures above the melting point of the metal. In the second step, external pyrolysis of the polymer dispersed material is carried out. Since this is a solid state process at stresses much higher than the shear or fracture of the polymer is expected to get evenly and finely distribution in the metal. This is done by heating the polymer dispersed material to a temperature above the pyrolysation temperature of the ceramic but lower than the melting point of the metal matrix. It should be mentioned that some pyrolysis of the polymer is possible during the FSP process itself. In the third step FSP is carried out on the pyrolised material for removing porosity that would form due to gas evolution during pyrolysis and to get a more uniform dispersion of polymer derived ceramic particles in the matrix. This method will produce nano-scale metal matrix composites with a relatively high volume fraction of the ceramic phase. This method can be extended to big sheets or a particular region in a sheet with no or low wear of tools. The material selected for the present study were pure Copper (99.9%) and Nickel Aluminum Bronze (NAB) copper alloy. The polymer precursor was poly (urea methyl vinyl) silazane, which is available commercially as CERASET. The polymer consists of silicon, carbon, nitrogen, oxygen and hydrogen atoms. The liquid precursor was thermally cross-linked into a rigid polymer, which was milled into a powder. This powder, having angular shaped particles of an average size of 10 µm, was used as the reinforcement. The polysilazanes convert into a highly refractory and amorphous ceramic upon pyrolysis and is known as polymer-derived silicon carbonitride which consists principally of silicon, carbon and nitrogen. The in-situ process is feasible because copper melts above the temperature at which the organic phase begins to pyrolise. The polysilazanes pyrolise in the temperature range of 973 to 1273 K, which lie below the melting temperature of copper, 1356K.The precursor has a density of approximately 1 gcm-3 in the organic phase and approximately 2 gcm-3 in the ceramic state. In the present work, we seek to introduce approximately 20 vol% of the ceramic phase into copper. The microstructure and mechanical properties of the developed copper-based in-situ polymer derived nano MMCs have been characterized in detail to understand the distribution of particles. The microstructure of the as received, processed as well as the FSP composite material was characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and Transmission Electron Microscope (TEM). OM and SEM microstructural observations show that PDC particles are distributed uniformly with a bimodal (submicron+micron) distribution. In addition, TEM micrographs reveal the formation of very fine PDC particles of diameter 10-30 nm. X-ray diffraction and Thermo-gravimetric analysis confirms the presence of ceramic phase (Si3N4/SiC) in the matrix. Significant improvement in mechanical properties of the FSP PD-MMCs has been observed. This in-situ formed Cu/PDC composites show five times increase in micro-hardness (260Hv - 2.5GPa) compared to processed copper base metal and in-situ NAB/PDC composite shows two times increase in micro-hardness (325Hv- 3.2GPa) compared to NAB matrix. The Cu-PDC composites exhibited better tensile strength at room temperature. In-situ formed Cu-PDC composite’s yield strength increased from 110MPa to 235MPa as compared to processed base metal, where as ultimate tensile strength increases from 246MPa to 312MPa compared to processed base metal at room temperature. This strengthening could be attributed to the presence of in-situ formed hard phases and the concomitant changes in the microstructure of the matrix material such as reduction in grain size and contribution from Orowan strengthening. In the present work, we have observed tool wear by observing tool after each FSP pass and apart from producing a significantly harder material with higher elastic modulus, possibly for the first time, the issue of tool wear has been overcome. This is due to the fact that the composite is made by the polymer route and that the ceramic fractures easily till it reaches the nano-size. Wear studies of this composite was carried out in a pin-on-disc machine by sliding a pin made from the composite against an alumina disc. The wear rate of the FSP PD-MMC composites increased from 1.63×10-5 to 5.72×10-6 mm3/Nm. Improved wear resistance could be attributed to the presence of the in-situ formed hard nano-phase.

Solution combustion synthesis (SCS) with its origin at IPC department of IISc has been widely practiced for synthesis of oxide materials. It is simple and low cost process, with energy and time savings that can be used to produce homogeneous, high purity, uniformly doped, nano crystalline ceramic powders. The powders characteristics such as crystallite size and surface area are primarily governed by enthalpy, flame temperature of combustion, fuel and fuel to oxidizer ratio ( F/O). In the present work an attempt has been made to investigate the process in order to exercise a control over the phase formation and nature of the product. Initial part of the work deals with the effect of fuel to oxidizer ratio on the powder properties of binary oxides with urea as fuel. The variation of adiabatic flame temperatures are calculated theoretically for different F/O ratios according to thermodynamic concept and correlated with the observed flame temperatures. Difference in the measured flame temperature and theoretical flame temperature in the fuel rich region is explained on the basis of incomplete combustion model. The effect of decomposition temperature difference of fuel and oxidizer, solubility of reactants on exothermicity of combustion reaction taking aluminiumnitrate system for various fuels is investigated. The effect of mixed fuel approach is studied by using the urea-glycine mixed fuel system using aluminium nitrate as oxidizer and employed for successful synthesis of the gamma alumina. Further Compaction behavior of SCS nano ceramic powders is studied by using Universal testing machine and the effect of F/O ratio, on agglomeration strength, aggregation strength of powder is investigated. Very few reports can be found on usage of SCS ceramic powder for biomaterial applications. By using these investigations a pyroxene series Diopside (CaMgSi2O6) silicate material is synthesized by SCS. Effect of different fuels on Diopside (DP) phase formation is investigated. Finally the DP and DP-ZnO composites, made by using Uniaxial hot pressing are investigated for their antibacterial, cytocompatibility properties. Antibacterial activity of E.Coli bacterium of Diopside powders was dose dependent type. Results of the bioactivity investigations shown flattened MC3T3 mouse osteoblast cells and MC C2C12 Myoblast cells and linkage bridges formed between them on Diopside and DP-ZnO surfaces show cyto compatibility and MTT results showed that percentage of ZnO needs to be tailored between 0-10 in order to achieve maximum cytocompatibility coupled with antibacterial property.