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Seltzer R.,IMDEA Madrid Institute for Advanced Studies | de la Escalera F.M.,Aernnova Engineering Solutions Iberica | Segurado J.,IMDEA Madrid Institute for Advanced Studies
Materials Science and Engineering A | Year: 2011

This study aims to elucidate the combined effects of reinforcing particles and water on PA12 processed by selective laser sintering (SLS). PA12 is one of the toughest polyamides. However, PA12 processed by SLS is rather brittle due to the presence of voids and the relative low molecular weight of the polymers used in SLS. It is demonstrated that humidity impoverishes the mechanical properties of neat PA12, including ductility and toughness. A ductile/brittle transition was detected, which was attributed to the competition between the plasticizing effect and the hydrolization of PA12 molecules plus the increase in crystallinity which counteracted this mechanism. It has been found that addition of hard particles, such as glass spheres and ceramic fibers, prevents the ductile/brittle transition by water conditioning at high temperature to happen. © 2011 Elsevier B.V. Source

Garcia E.,CSIC - Institute of Ceramics and Glass | Nistal A.,CSIC - Institute of Ceramics and Glass | Martin de la Escalera F.,Aernnova Engineering Solutions Iberica | Khalifa A.,Aernnova Engineering Solutions Iberica | And 3 more authors.
Journal of Thermal Spray Technology | Year: 2014

The suitability of certain glass compositions in the Y2O3-Al2O3-SiO2 (YAS) system as protecting coatings for silicon carbide components has been prospected. One particular YAS composition was formulated considering its glass formation ability and subsequent crystallization during service. Round-shaped and homogeneous granules of the selected composition were prepared by spray drying the corresponding homogeneous oxide powder mixture. Glassy coatings (197 µm thick) were obtained by oxyacetylene flame spraying the YAS granules over SiC substrates, previously grit blasted and coated with a Si bond layer (56 µm thick). Bulk glass of the same composition was produced by the conventional glass casting method and used as reference material for comparative evaluation of the characteristic glass transition temperatures, crystallization behavior, mechanical, and thermal coating properties. The mechanical properties and thermal conductivity of the coating were lower than those of the bulk glass owing to its lower density, higher porosity, and characteristic lamellar structure. The crystallization of both bulk glass and coating occurred during isothermal treatments in air at 1100-1350 °C. Preliminary data on ablation tests at 900 °C using the oxyacetylene gun indicated that the YAS glassy coating was a viable protective shield for the SiC substrate during 150 s. © 2014, ASM International. Source

Garcia E.,CSIC - Institute of Ceramics and Glass | Nistal A.,CSIC - Institute of Ceramics and Glass | Khalifa A.,Aernnova Engineering Solutions Iberica | Essa Y.,Aernnova Engineering Solutions Iberica | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2015

Hybrid coatings consisting of a heat resistant Y2O3-Al2O3-SiO2 (YAS) glass containing 2.3 wt % of graphene nanoplatelets (GNPs) were developed by flame spraying homogeneous ceramic powders-GNP granules. Around 40% of the GNPs survived the high spraying temperatures and were distributed along the splat-interfaces, forming a percolated network. These YAS-GNP coatings are potentially interesting in thermal protection systems and electromagnetic interference shields for aerospace applications; therefore silicon carbide (SiC) materials at the forefront of those applications were employed as substrates. Whereas the YAS coatings are nonconductive, the YAS-GNP coatings showed in-plane electrical conductivity (∼102 S·m-1) for which a low percolation limit (below 3.6 vol %) is inferred. Indentation tests revealed the formation of a highly damaged indentation zone showing multiple shear displacements between adjacent splats probably favored by the graphene sheets location. The indentation radial cracks typically found in brittle glass coatings are not detected in the hybrid coatings that are also more compliant. © 2015 American Chemical Society. Source

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