Ferroelastic domain identification and toughening mechanism for yttrium tantalate–zirconium oxide
Yttrium tantalate (YTaO 4 ) is the next generation of higher service temperature thermal barrier coatings (TBCs) materials due to its smaller volume effect in phase change, lower thermal conductivity and unique ferroelastic domain structure. However, the low fracture toughness limits its application. We first characterized the diffraction patterns of variants, and two variants (M 1 and M 2 ) observed in transmission electron microscopy (TEM) results were determined from four possible variants by mechanical derivation. The role of Zr 4+ doping in ferroelastic toughening was explained in detail. With the increase of Zr 4+ doping concentration, the monoclinic angle β and the domain rotation angle α decrease, respectively. The spontaneous strain component and the principal strain in the main space also have a similar decreasing trend. The decrease of the ferroelastic domain inversion energy barrier is beneficial to the improvement of fracture toughness . Combining the results of Vickers indentation, we found that Zr 4+ could be enriched at the domain boundary to inhibit the generation of cracks. An appropriate amount of Zr 4+ is conducive to the improvement of fracture toughness, and the excessive Zr 4+ will reduce the fracture toughness due to the generation of by-product t -ZrO 2 . So, the optimal composition is Y 0.44 Ta 0.44 Zr 0.12 O 2 and the best fracture toughness (2.9–3.8MPa m 1/2 ) is equivalent to the commercial 8YSZ. This result will promote the application of a new generation of TBCs.
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