Huge local elastic strains in bulk nanostructured pure zirconia materials

Abstract

From the liquid state to room temperature, two successive solid-state phase transitions occur in pure zirconia. It is well-known that the last one (tetragonal to monoclinic) is martensitic and induces large volume variations and shear strains. Elastic and inelastic behaviors of zirconia-based materials are strongly influenced by this transition and the associated strain fields that it induces. Knowledge of strain and stress at the crystal scale is thus a crucial point. Using fully dense pure zirconia polycrystals obtained by a fuse casting process, we have determined at a sub-micrometric scale, by X-ray Laue microdiffraction, the strains map at room temperature in as-cast specimens and after a post elaboration high temperature thermal treatment. We observed that the fluctuation of deviatoric elastic strain is huge, the standard deviation of normal component being in the range of 1-2%. The heat treatment tends to even further increase this range of fluctuation, despite the development of a multiscale crack network formed during the cooling. Correspondingly, the associated stress level is also huge. It lies in the 5 GPa range with stress gradient amounting 1 GPa μm − 1 .

Coupling between elastic strains and phase transition in dense pure zirconia polycrystals

“…c → t and t → m, occurring during the cooling of the sample. All the 24 theoretically possible variants are present [26], and the size of the coherent domains is typically a few tens of nanometers [27]. The two SPTs are associated with an intensive twinning process that is illustrated in Fig.…”

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials

“…This case study demonstrates the capability of the LaueNN model to resolve complex Laue images acquired on lowsymmetry monoclinic zirconia polycrystalline material that has undergone the solid-state martensitic phase transition (from tetragonal to monoclinic) and thus exhibits a very subdivided and complex microstructure with microcracks (Ors et al, 2021;Guinebretie `re et al, 2022). Low-symmetry crystal Laue patterns are often difficult to index using the conventional approach described in Section 2.1, as screening of a large number of spots is necessary to ensure a result.…”

“…Prior knowledge of the unit-cell lattice parameters helps to restrict the tolerance angle to consider a valid recognition. We briefly explain the different elements of classical analysis here; interested readers will find more details in the literature (Petit et al, 2015;O ¨rs et al, 2018).…”

Tetragonal reconstruction and monoclinic variants rearrangement during heat treatment in zirconia

“…The tetragonal ( t ) to monoclinic ( m ) martensitic transformation toughening, combing with high strength, superior corrosion resistance, and low thermal conductivity have made zirconia‐based ceramics highly attractive for applications in biomedicine implant fabrication, the chemical industry, shape‐memory, and thermal barrier coatings 1–3 . The martensitic transformation is reversible and always accompanied with a volume expansion or contraction of ∼4%, which leads to micro‐cracks and degradation 4 . Although zirconia is generally alloyed with other oxides, such as Y 2 O 3 and CeO 2 , to obtain the fully tetragonal phase, the transformation can also be triggered by low‐temperature treatments within steam 5 .…”

“…[1][2][3] The martensitic transformation is reversible and always accompanied with a volume expansion or contraction of ∼4%, which leads to micro-cracks and degradation. 4 Although zirconia is generally alloyed with other oxides, such as Y 2 O 3 and CeO 2 , to obtain the fully tetragonal phase, the transformation can also be triggered by lowtemperature treatments within steam. 5 Consequently, for its both positive and negative effects, martensitic transformation has been one of the most investigated phase transformations in ceramics.…”