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Phase transformations in air plasma-sprayed thermal barrier coatings composed of ZrO2 – 8 wt.% Y2O3 zirconia - 8 wt.% yttria are studied using X-Ray diffraction and Rietveld refinement measurements. Samples of TBC deposited onto Inconel 625 substrate were fabricated and heat treated at two different conditions: exposition to 1100ºC up to 1000 hours and exposition to temperatures between 700ºC and 1100ºC during 50 hours. According to Rietveld refinement measurements, the content of the cubic phase in the top coat increases with time and temperature; it starts at 7.3 wt.% and reaches 15.7 wt.% after 1000 hours at 1100ºC. The presence of a cubic phase in high amounts is undesirable due its lower mechanical properties compared with the tetragonal phase. After 800 hours of exposure to high temperature, the amount of Y2O3 in the tetragonal phase reduces to 6.6 wt.% and a fraction of this phase transforms to a monoclinic structure during cooling. The monoclinic phase reached 18.0 wt.% after 1000 hours. This phase is also undesirable, not only due to its higher thermal conductivity, but also because the tetragonal-to-monoclinic transformation implies a volume change of circa 5%, which favors crack formation and propagation and compromises the coating integrity.

Tipo de documento: Artículo - Article

Información adicional: Derechos de autor reservados

Palabras clave: Thermal Barrier Coating TBC, Heat Treatment, Phase Transformation, Rietveld Analysis





Fuente: http://www.bdigital.unal.edu.co


Introducción



DYNA http:--dyna.medellin.unal.edu.co- Phase transformations in air plasma-sprayed yttria-stabilized zirconia thermal barrier coatings Transformaciones de fase en recubrimientos de barrera térmica de zirconia estabilizada con yttria depositados mediante aspersión por plasma atmosférico Julián D.
Osorio a, Adrián Lopera-Valle b, Alejandro Toro c and Juan P.
Hernández-Ortiz d a Materials and Minerals Department, National University of Colombia, Medellín, Colombia, jdosorio@unal.edu.co b Mechanical Engineering, National University of Colombia, Medellín, Colombia, adloperav@unal.edu.co c Tribology and Surfaces Group, National University of Colombia, Medellín, Colombia, aotoro@unal.edu.co d Materials and Minerals Department, National University of Colombia, Medellín, Colombia, jphernandezo@unal.edu.co Received: September 24th, 2012.
Received in revised form: January 23th, 2014.
Accepted: January 27th, 2014 Abstract Phase transformations in air plasma-sprayed thermal barrier coatings composed of ZrO2 – 8 wt.% Y2O3 (zirconia - 8 wt.% yttria) are studied using X-Ray diffraction and Rietveld refinement measurements.
Samples of TBC deposited onto Inconel 625 substrate were fabricated and heat treated at two different conditions: exposition to 1100ºC up to 1000 hours and exposition to temperatures between 700ºC and 1100ºC during 50 hours.
According to Rietveld refinement measurements, the content of the cubic phase in the top coat increases with time and temperature; it starts at 7.3 wt.% and reaches 15.7 wt.% after 1000 hours at 1100ºC.
The presence of a cubic phase in high amounts is undesirable due its lower mechanical properties compared with the tetragonal phase.
After 800 hours of exposure to high temperature, the amount of Y2O3 in the tetragonal phase reduces to 6.6 wt.% and a fraction of this phase transforms to a monoclinic structure during cooling.
The monoclinic phase reached 18.0 wt.% after 1000 hours.
This phase is also undesirable, not only due t...






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