J.M.K. Assis

Bio: J.M.K. Assis is an academic researcher from Aeronáutica. The author has contributed to research in topics: Materials science & Cubic zirconia. The author has an hindex of 2, co-authored 4 publications receiving 6 citations. Previous affiliations of J.M.K. Assis include National Institute for Space Research.

Sintering Study of NiCrAlY

Abstract: In ceramics TBC s (thermal barrier coating) the MCrAlY layer is used like a bond coat between nickel superalloys and zirconia ceramics used in aeronautical turbine blades. However the oxidation of this layer is an important step to obtain an Al2O3 as TGO (thermally grown oxide), on which the zirconia ceramics is placed on to protect the turbine blades from high temperatures and oxidizers and corrosive gases generated during the burning of the fuel. To understand the oxidation process, parallel and flat surface samples are required. These surfaces will allow characterization, especially the tribologic ones. The samples were prepared through different process and sintering routes. Powders of NiCrAlY with and without binder were uniaxially pressed from 100 MPa to 250 MPa. Isostatically pressed samples at 300 MPA were also prepared. The samples were sintered in the air, at 10-7 Torr and hot uniaxially pressed at 10 MPa. The sintering temperature started at 800 °C up to 1200 °C during one hour. The best result was from the hot pressed samples between 1000 °C and 1150 °C. Above this temperature the process became complicated and started melting at 1200 oC. Mainly due to the spherical shape of NiCrAlY particles, it was not possible to get good samples when sintering in the air.

Thermal conductivity study of ZrO2-YO1.5-NbO2.5 TBC

Abstract: The reduction of thermal conductivity provided by the zirconia ceramic for TBC application improves protection of turbine blades during the thermal cycles and the high temperature operations. The TBC is a complex system composed of different layers: a metal substrate, a metallic bond coat, thermally grown oxide (TGO), and ceramic top coat. The present study determined thermal conductivity properties by theoretical calculation of the thermal diffusivity, measured by laser flash technique, at 800 °C and 1250 °C for ZrO2-YO1.5-NbO2.5 (TC) with 14.5, 16.0, and 17.5 mol% equimolar yttria and niobia in zirconia, by CO2 laser on the substrate of titanium. Although microscopy and EDS showed that specific parameters of the laser parameters must be defined to lager thickness of the TBC layers, zirconia co-doped with yttria and niobia promoted a significant reduction of the thermal conductivity by approximately 52 % when compared to zirconia with 7.6 % molar with yttria, currently used in gas turbine engine industry. That TC composition with laser processing could be explored as a candidate thermal insulation material for TBC application.

Kollicoat MAE® 100P as a film former polymer for nanoparticles preparation

Abstract: Introduction: Until now, few research works have reported the usefulness of Kollicoat MAE® 100P as a film-former polymer for coating nanocapsules and as a matrix former for nanospheres. Aim: To update the current knowledge about the use of Kollicoat MAE® 100P as a film-former polymeric to prepare gastro-resistant nanoparticles. Physicochemical characteristics and functionality of nanoparticles coated with Kollicoat MAE® 100P were reported. Methodology: An exhaustive review was performed (from 1980 to 2021) in various scientific databases like Medline, Scopus, EBSCO and Cambridge. Results: Kollicoat MAE® 100P is a versatile polymer that can be used to prepare gastro-resistant nanoparticles with actives of natural and synthetic origin. This polymer allows producing homogeneous nanoparticles with sizes smaller than 130 nm, and high z-potential, which confers a great stability to nanoparticle systems. On the other side, nanoparticles coated with Kollicoat MAE® 100P combined with plasticizer exhibit a hard and flexible shell, with excellent thermal stability up to 60 °C that dissolve at pH above 5.5. Conclusion: Kollicoat MAE® 100P ris a viable, low-cost, and multifunctional alternative for nanoparticle preparation, however, more studies are needed to develop enhanced nanoparticles with better performances.

Study of Non-Transformable T’-Ysz by Addition of Niobia

Abstract: Materials containing tetragonal zirconia are promising for structural applications because of their stress assisted tetragonal-to-monoclinic transformation near room temperature allied with their potential for ferroelastic domain switching at high temperatures. The target of this work was the obtainment of tetragonal zirconia polycrystalline (TZP) with high density, from mixtures of high purity powders of zirconia, yttria and niobia. Samples were produced by mixing of initial powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering in air. The samples were characterized for phase composition, microstructure and mechanical properties by X-ray diffraction, scanning and transmission electron microscopy and nanoindentation measurements, respectively. The results presented evidences of ferroelasticity mechanism. This mechanism would justify the high toughness of these zirconias, paving the way for the development of new materials for application in TBC for gas turbine blades.

Investigation on the microstructure and creep behavior of laser remelted thermal barrier coating

Abstract: Laser surface modification of the thermal barrier coating was investigated with the aim of increasing creep resistance. Yttria-stabilized-zirconia (YSZ) with a CoNiCrAlY bond coat was deposited by air plasma spraying on equiaxed Ti–6Al–4V substrates. Analysis was carried out comparing uncoated samples with as-sprayed and laser remelted ones. A cross section and detailed characterization of coating surface was carried out by scanning electron microscopy and X-ray diffraction techniques. Mechanical properties in terms of microhardness and creep resistance were evaluated. Constant load creep tests were conducted at stress levels of 125 to 319 MPa at 500 °C and 600 °C. A dense ceramic layer of thickness about 40 μm was formed by laser remelted treatment and its microhardness surface was higher than the other layers. As-sprayed YSZ had higher creep resistance than other samples. Analysis of creep behavior showed that the steady-state creep rate of laser remelted samples had about 42% reduction in 600 °C condition, evidencing a higher creep resistance than uncoated material. SEM images revealed a ductile fracture with presence of equiaxed dimples.

High-Sensitive Thin Film Heat Flux Gauge With ITO/In2O3 Thermopile on Nickel Alloys for Turbine Blade Applications

Abstract: Heat flux is key parameter for evaluating the heat dissipation of turbine blade. The accurate measurement of heat flux is vital for the optimizing cooling system and fabrication of turbine blade. The thin film heat flux gauge is usually fabricated on insulated substrate and located away from the measured area of turbine blade. As a result, the changes of heat flux on the surface of turbine blade cannot be reflected quickly and accurately. This paper innovatively designs membrane structure of thin film heat flux gauge on nickel alloys. The sensor is fabricated on the surface of the nickel alloys by thin-film depositing technology to realize in-situ surface heat flux measurement, and ITO/In₂O₃ thermopile is used to replace precious thermopile to improve sensitivity. The results show that the sensitivity and response frequency of the sensor respectively are measured to be $61.93~\mu \text{V}$ /(kW/m²) and over 14400Hz respectively, which can measure heat flux of 236.4kW/m² at $888^\circ \text{C}$ . Besides, the thin film heat flux gauge is fabricated on the surface of turbine blade to verify functional feasibility with same preparation process of that on nickel alloys, and can obtain reproducible results. This work suggest that the thin film sensor based on ITO/In₂O₃ thermopile has great potential in applications used as optimizing cooling system of components in aeronautics and astronautics.