Dense t′ ZrO 2-8 mol.% YbO 1.5 candidate thermal barrier material was aged for 192 h at 1150 and 1250 °C. The high initial indentation toughness (∼87 J m -2) reduced by ∼56% in early-stage aging at both temperatures. The toughness increased gradually with aging at 1150 °C and more rapidly at 1250 °C. Precipitation of the cubic phase and its transformation to t″ during cooling was observed. Transformation toughening was activated by 192 h at 1250 °C. Ferroelastic toughening was dominant in the absence of transformation toughening. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ashutosh S. Gandhi

Cubic phase

Ferroelastic toughening

HIGH TEMPERATURE AGING

Indentation toughness

Thermal barrier materials

Transformation toughening

Coatings

Phase Transitions

Spark plasma sintering

Toughness

Zirconia

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Scripta Materialia

The effect of high-temperature exposure on the t′ phase transformation and indentation toughness in zirconia with 8 mol% REO1.5 (RE = Gd and Y) was studied. Dense compacts prepared by spark plasma sintering were subjected to thermal exposure at 1150 °C up to 96 h. As-processed materials comprising of the t′ phase exhibited high indentation toughness: GdSZ 117 ± 8 Jm−2 and YSZ 98 ± 9 Jm−2. Upon thermal exposure, toughness decreased initially and then increased gradually. After 96 h, GdSZ showed a higher toughness compared to YSZ. Ferroelasticity remains the dominant mechanism, although onset of transformation toughening was observed in GdSZ by 96 h. Two tetragonal phases appeared in GdSZ. The minor tetragonal phase is likely an artifact of coherency strains between the cubic precipitates and tetragonal matrix. The matrix tetragonal was depleted in GdO1.5 with time. Consequent increase in tetragonality led to enhanced ferroelastic toughening. The transformations in YSZ occurred much slower than in GdSZ; hence, the toughness recovery was slower as well. © 2017, Springer Science+Business Media New York.

Journal of Materials Science

Toughness evolution in Gd- and Y-stabilized zirconia thermal barrier materials upon high-temperature exposure

Dense pellet of rare-earth oxide (5YbO1.5+1.5GdO1.5+1.5NdO1.5) stabilized zirconia, a candidate thermal barrier composition, was prepared by spark plasma sintering. Isothermal annealing was carried out at 1250°C up to 192h. X-ray diffraction and Raman spectroscopy were used to characterize the phases. Cubic precipitates formed in the initial tetragonal phase from 6h, with volume fraction of 22.31% after 192h. 15.35vol.% of monoclinic phase was observed in XRD at 192h along with cubic and two tetragonal phases. Indentation toughness increased by 49% from 155±24Jm-2 at 0h to 231±71Jm-2 at 6h of annealing and it decreased towards the initial value upon further annealing to 192h. Ferroelastic toughening dominates until transformation toughening ensues at 192h. The toughness is consistently higher than for singly doped, sintered t' zirconia pellets that are reported in the literature. © 2015 Elsevier Ltd.

Journal of the European Ceramic Society

Phase and fracture toughness evolution during isothermal annealing of spark plasma sintered zirconia co-doped with Yb, Gd and Nd oxides

Effect of high-temperature aging on the fracture toughness of ytterbia-stabilized t′ zirconia

Journal	Scripta Materialia
ISSN	13596462
Open Access	No