Estudo da sinterização e evolução microestrutural de misturas de Fe-MoS2

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 201

Strong macroscale supercrystalline structures by 3D printing combined with self-assembly of ceramic functionalized nanoparticles

To translate the exceptional properties of colloidal nanoparticles (NPs) to macroscale geometries, assembly techniques must bridge a 106-fold range of length. Moreover, for successfully attaining a final mechanically robust nanocomposite macroscale material, some of the intrinsic NPs’ properties have to be maintained while minimizing the density of strength-limiting defects. However, the assembly of nanoscale building blocks into macroscopic dimensions, and their effective macroscale properties, are inherently affected by the precision of the conditions required for assembly and emergent flaws including point defects, dislocations, grain boundaries, and cracks. Herein, a direct-write self-assembly technique is used to construct free-standing, millimeter-scale columns comprising spherical iron oxide NPs (15 nm diameter) surface functionalized with oleic acid (OA), which self-assemble into face-centered cubic (FCC) supercrystals in minutes during the direct-writing process. The subsequent crosslinking of OA molecules results in nanocomposites with a maximum strength of 110 MPa and elastic modulus up to 58 GPa. These mechanical properties are interpreted according to the flaw size distribution and are as high as newly engineered platelet-based nanocomposites. The findings indicate a broad potential to create mechanically robust, multifunctional 3D structures by combining additive manufacturing with colloidal assembly.Financial support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Projektnummer 192346071, SFB 986 -, the National Science Foundation CAREER Award (CMMI-1346638, to A.J.H.), and from the MIT-Skoltech Next Generation Program. A.T.L.T. was supported by a postgraduate fellowship from DSO National Laboratories, Singapore. XRM at the University of Bremen was funded within the CO 1043 12-1 (Call for Major Equipment, XRM)

Desenvolvimento de compósito autolubrificante de matriz ferrosa contendo MoS2

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2016.Esta tese visou o desenvolvimento de um material autolubrificante volumétrico de matriz ferrosa contendo MoS2 como elemento lubrificante majoritário. Estudos demonstram a dificuldade em se produzir este tipo de compósito, devido a reação do MoS2 com a matriz ferrosa durante a sinterização. Desta forma, a pesquisa desenvolvida nesta tese buscou soluções para evitar ou reduzir esta reação, avaliando a influência de parâmetros da matéria-prima da matriz e da fase lubrificante (tamanho de partícula, adição de outros elementos e teor de lubrificantes), bem como parâmetros de processamento (taxa de aquecimento, temperatura, formação de fase líquida, tempo de patamar e atmosfera de sinterização). Os resultados mostraram que a temperatura influiu de forma preponderante na reação, mas não a taxa de aquecimento e que o uso de um pó de Fe de menor tamanho de partícula acelera-a; o melhor desempenho está associado ao MoS2 de maior tamanho de partícula (d50=32µm) e 9% em volume é o teor limite; a adição de grafite ou h-BN retarda a reação, porém apenas compósitos com MoS2+grafite apresentaram coeficiente de atrito abaixo de 0,2 associado a um baixo desgaste. A adição de elementos de liga modificou a forma como o MoS2 reagiu com a matriz ferrosa e o desempenho tribológico do compósito, sendo que alguns apresentaram resultados similares ao Fe puro (Ni misturado e P pré-misturado), outros possuem caráter deletério (Cr e Mo misturados e Mo pré-ligado) e alguns apresentaram caráter benéfico (C e P misturados e Cr pré-ligado). É viável sinterização de amostras em temperaturas entre 800 e 850 °C, porém as abordagens visando a intensificação da densificação e propriedades mecânicas não foram bem sucedidas. Através da definição e controle da matéria prima inicial (nomeadamente tamanho de partícula da matriz e do MoS2), composição do compósito e parâmetros de processamento (temperatura, tempo e atmosfera de sinterização) foi possível a produção de materiais autolubrificantes de matriz ferrosa contendo MoS2 como elemento lubrificante majoritário que apresentam baixo coeficiente de atrito a seco (0,06-0,08) associado a uma baixa taxa de desgaste (2,0-3,5 x 10-6 mm³.N-1.m-1).<br>Abstract : This thesis aimed the development of a self-lubricating composite containing MoS2 dispersed in an iron matrix produced by powder metallurgy. Previous studies demonstrate that MoS2 reacts with iron matrices during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore the research developed within this thesis focused on the possible solutions to avoid or reduce this reaction, evaluating the influence of raw material (particle size, amount and type of lubricants) and processing (heating rate, temperature, dwell time, liquid phase formation and atmosphere) parameters. The results have shown that temperature has a major influence on the reaction, but not the heating rate; the use of a small Fe particle size accelerates the reaction; better performance was achieved by using the d50=32µm MoS2 and 9% in volume is the limit amount; the addition of graphite or h-BN slows the reaction, but only MoS2+graphite composites presents friction coefficient below 0,2 associated with low wear rate. The addition of alloying elements modified how MoS2 interacts with the iron matrix and the composite friction coefficient, some of which had a beneficial effect (admixed C and P, and pre-alloyed Cr alloy), while others (admixed Cr and Mo, and pre-alloyed Mo alloy) are harmful. It is possible to produce iron samples by low temperature sintering (800-850 °C), however the approaches to improve densification and mechanical properties were not successful. By means of defining and adequate control of the raw material (namely particle size of matrix and lubricants), composition and processing parameters (sintering temperature, time and atmosphere) it was possible to produce self-lubricating iron based composites containing MoS2, which presented low dry friction coefficient (0,06-0,08) and low wear rate (2,0-3,5 x 10-6 mm³.N-1.m-1)

Controlling the Solid-State Reaction in Fe-MoS₂ Self-Lubricating Composites for Optimized Tribological Properties

In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron and that the combination of MoS2 + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant’s particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 × 10−6 mm3·N−1·m−1) were achieved

Controlling the Solid-State Reaction in Fe-MoS2 Self-Lubricating Composites for Optimized Tribological Properties

In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron and that the combination of MoS2 + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant&rsquo;s particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 &times; 10&minus;6 mm3&middot;N&minus;1&middot;m&minus;1) were achieved

Influence of pores arrangement on stability of photonic structures during sintering

Discrete Element Method (DEM) has been used for numerical investigation of sintering-induced structural deformations occurring in inverse opal photonic structures. The influence of the initial arrangement of template particles on the stability of highly porous inverse opal α-Al2O3 structures has been analyzed. The material transport, densification, as well as formation of defects and cracks have been compared for various case studies. Three different stages of defects formation have been distinguished starting with local defects ending with intrapore cracks. The results show that the packing of the template particles defined during the template self-assembly process play a crucial role in the later structural deformation upon thermal exposure. The simulation results are in very good agreement with experimental data obtained from SEM images and previous studies by ptychographic X-ray tomography.Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number 192346071 – SFB 986 (projects A3 and C5)

Effects of processing parameters on 3D structural ordering and optical properties of inverse opal photonic crystals produced by atomic layer deposition

Vertical convective self‐assembly has been extensively used for the preparation of direct photonic crystals, which can be later infiltrated with a more stable material, such as oxide ceramics, by atomic layer deposition. However, the relationship between the self‐assembly parameters of the direct photonic crystals and the optical properties of the inverse opal photonic crystals remains elusive. In this work, the effect of different experimental parameters on the 3D structure and the density of defects of polystyrene direct photonic crystals produced by vertical convective selfassembly was assessed. Self‐assembly was investigated using deionized water as media with polymer particles’ concentrations up to 2 mg/mL; temperatures of 40, 50, and 80°C; and relative humidity of 45%, 70%, and 90%. The 3D structure of the resultant direct photonic materials was characterized by the combination of scanning electron microscopy and image analysis, and their optical properties were assessed by reflectance measurements. These results were correlated with the performance of oxide‐based inverse opal photonic crystals produced by the controlled infiltration of the former direct photonic crystals by atomic layer deposition (ALD). It was found that the thickness increased with the concentration of polystyrene particles, while the photonic structure ordering is dependent on the synergy between humidity and temperature. Results also showed higher defects population with increasing evaporation temperature and decreasing relative humidity.Financial support from the German Research Foundation (DFG) via SFB 986 “M3,” projects UA‐UHH and C5. The authors also acknowledge financial support from the PROBRAL program, a partnership between the German Academic Exchange Service (DAAD) and the Brazilian Federal Agency for Post‐graduate Education (CAPES) through the project 23038.006803/2014‐50

Nanotomography of Inverse Photonic Crystals Using Zernike Phase Contrast – CORRIGENDUM

X-ray full field microscopy usingsynchrotron radiation is afrequently used tool inmaterial science. In particular for low absorbing samples,however,the contrast is often not sufficient for tomography. To enhance the contrast of this type of materialsthe established technique of Zernike Phase Contrast(ZPC) [1,2,3]has been implementedat the Nanotomography endstationof the Imaging Beamline P05 at PETRA III storage ring, located at DESY (Hamburg, Germany).Using an energy of 11 keV, a spatial resolution of 100nm wasachieved and the obtainedhigh contrast made 3D investigation of low absorbing materials possible. Inverse photonic crystals consisting of hollow spheres absorbvery littledue to their high air content and are therefore an ideal test system for the ZPC tomography setup