P. Poza

Confinement-Induced One-Dimensional Ferroelectric Polymer Arrays

This work demonstrates the use of wetting nanoporous alumina template with polymer solution to produce arrays of isolated poly(vinylidene fluoride) (PVDF) ferroelectric gamma-type nanorods supported within a nonpolar alpha-structure film. The method is based upon a crystal phase transition which occurs due to PVDF confinement within alumina nanoporous. The system was studied using scanning X-ray microdiffraction (micro-XRD) that allows the solid-solid phase transition from the alpha-nonpolar crystal form (bulk) to the gamma polar ferroelectric form (nanorod array) to be spatially resolved, as well as providing crystallinity and orientation information. The results reveal that the interaction between polymer chains and the porous membranes walls imposes a flat-on lamella growth along the nanorrods long axis, while improving crystal orientation.

Cold-Sprayed Ni-Al2O3 Coatings for Applications in Power Generation Industry

Cermets coatings are extensively used in energy applications both because of their high wear resistance as required, for example, in components like gas turbine sealants, and because of their specific functionality as required in solar absorbers. So far, high-temperature thermal spraying and physical vapor deposition have traditionally been used to deposit this kind of coatings. In this study, Ni-Al2O3 coatings have been deposited using a Kinetic®3000 cold-spray system starting from Ni and Al2O3 powders blend; five blends have been prepared setting the alumina content in the feedstock to 10, 25, 50, 75, and 90xa0wt.%. The embedded alumina ranges between a few percent weight up to 16 and 31xa0wt.%, while the microhardness shows a deep increase from 175 Vickers in the case of pure Ni coatings up to 338xa0Vickers. The spray and coating growth mechanism have been discussed, with special attention to the fragmentation of the ceramic particles during the impact. Finally, the coating behavior at high temperature was analyzed by oxidation tests performed in air at 520xa0°C emphasizing a good oxidation resistance that could represent a very promising basis for application in power generation systems.

Evaluation of mechanical properties of Ti6Al4V cold sprayed coatings

ABSTRACT The majority of the mechanical components in aeronautical applications show a reduction of their performance during their service life. Sometimes the component replacement is necessary, with the consequent cost of material and time. An alternative is to repair the component depositing a coating onto the metallic alloy. In this work, a cold spray technique was used to generate Ti6Al4V coatings onto a bulk of the same material. The mechanical response of these coatings was investigated by instrumented indentation tests. Additionally, instrumented indentation tests were also conducted on the particles used for the spraying process and on the substrate. The Young’s modulus and the hardness of the coatings were compared to those obtained on the particles and on the substrate. The mechanical properties obtained on the coatings presented values similar to those obtained on the substrate. Also, the sprayed particles showed a hardness significantly lower than that obtained on the coatings.

Wear resistance of cold sprayed Al alloys for aeronautical repairs

ABSTRACT Al–Cu alloys, like Al 2024, and Al–Si alloys, like Al F357 and Al C355, are used in aeronautic gearboxes and fuselage parts operating in severe conditions. It is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) could be an alternative as it is real solid-state processing technique. However, the repaired component should exhibit similar properties as the original substrate. This paper evaluates the wear performance of Al coatings CS onto the same Al substrates in sliding and oscillating conditions. The results were compared with the corresponding substrates. The wear rate of coatings processed using new conditions, developed to enhance the coatings performance, was similar or smaller than that measured in the substrate bulk alloys. For Al 2024 and Al C355 CS could be used for repairing, from the tribological point of view.

Microstructure and High-Temperature Oxidation Behavior of Cold Gas-sprayed Ni-Al2O3 Coatings

Cermet coatings are widely used for high-temperature industrial applications. This study investigates the effect of high-temperature oxidation on cold gas dynamic-sprayed Ni-Al2O3 coatings. For this purpose, high-temperature oxidation tests were performed at 520 and 640xa0°C. The selected exposure times were 24, 48, 72, 168, and 336xa0h. The microstructural evolution during exposure at high temperature was analyzed by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD). The oxidation kinetics was estimated by thickness measurements. The results show that the coatings protect the substrates against oxidation. In order to study possible changes in the mechanical properties of the system, Vickers microhardness experiments on the coatings and on the 10CrMo9-10 steel substrates were conducted. It was observed that hardness decreased by exposing the specimens to high temperature.

Microstructural Evolution of Thermal Barrier Coatings during Isothermal Oxidation

This paper analyses the degradation of a ceramic top coating 70%ZrO2 – 30%CaO deposited onto a stainless steel AISI 304 by thermal spray, using Ni-6%Al-5%Mo as overlay coating. These thermal barrier coatings were heat treated for 48, 120 and 288 h at 800 °C to evaluate the degradation of these materials by isothermal oxidation. The microstructure evolution during oxidation was analysed by environmental scanning electron microscopy, transmission electron microscopy and X ray microanalysis. A thermally grown oxide layer was observed between the overlay coating and the ceramic top coating after oxidation. This layer was formed by a mixed Al, Ni and Mo oxides.