Phase Transformation and Microstructure of Partially-Stabilized Zirconia

Abstract

Phase transformations and the resultant microstructures of partially-stabilized zirconia (PSZ) are briefly reviewed with a special interest in the nature of phase transformations. The martensitic tetragonal-to-monoclinic transformation, which plays a principal role in toughening of PSZ, accompanies lattice defects such as twins or dislocations in the product phase m-ZrO2. The diffusionless cubicto-tetragonal (c-t) transformation is characterized by two different microstructures; one with the domain structure whose boundaries have curvilinear features showing the contrast of anti-phase domain boundaries in ordered alloys, and the other with thin-plates or 1enticular features. It seems that the diffusionless c-t transformation is always completed by an initial development of domain structure over the entire region of samples. The thin plates or lenticular features may be subsequently formed by the strain accommodation. The nature of the diffusionless c-t transformation is the second order phase transition. The precipitation of t-ZrO2 in the c-ZrO2 matrix is commonly found in alloys heat-treated in the cubic/tetragonal two-phase region. Together with the usual precipitation structures, the modulated or tweed structure is also formed at an early stage of aging. The origin of these microstructures, and the nature of the diffusional reaction or precipitation is discussed in this paper.

Effect of variant strain accommodation on the three-dimensional microstructure formation during martensitic transformation: Application to zirconia

“…T ! M transformation takes place by a displacive mechanism [55]. An important type of displacive phase transformation, which is very common in both metals and ceramics, is martensitic transformation.…”

Isothermal Tetragonal-to-Monoclinic Phase Transformation in a Zirconia–Yttria System

“…These properties are also known to be strongly related to the stress-induced transformation from the metastable tetragonal (T) to the stable monoclinic (M) phases. [1][2][3][4][5] This transformation is usually called a martensitic transformation and is affected by many factors, e.g., yttria content, grain size, water environment, thermal history, third oxide addition and so on. [6][7][8][9][10][11][12][13][14] The nature of this transformation is thus so complex that no clear view has been obtained.…”

Laser melted ZrO2–Y2O3 thermal barrier obtained by plasma spraying method

“…The obtained data have been verified with the density of coatings separated from substrate determined by piknometric method and theoretical density of ceramic calculated while taking into account Y2O3 concentration, atomic weights to the volume of phases elementary cells and their volume fraction in coatings [3,14].…”

“…The maximum operating temperature of monocrystalline gas turbine blades produced nowadays from nickel base alloys is close to 1100 • C, and the application of ceramic thermal barriers helps increase it by about 100 • C [1,2]. ZrO 2 plus 8 wt.% Y 2 O 3 which stabilizes the modification of this ceramic material with a cubic lattice up to the melting temperature over 2700 • C generates considerable interest [3,4]. Ensuring greater structural stability makes it possible to avoid stresses which appear between metal substrate and ceramic coating.…”