Structural Study on the Cubic to Tetragonal Transformation in Arc-melted ZrO<SUB>2</SUB>-3 mol%Y<SUB>2</SUB>O<SUB>3</SUB>

Abstract

A herringbone structure observed in an as arc-melted specimen was investigated using XRD, TEM and surface relief study. The specimen was cooled on a water cooled copper hearth and the grain size was approximately 1mm. The results confirmed the crystal structure to be tetragonal (at=0.5100 and ct=0.5166nm, c/a=1.0129). The orientation relation among the different variants of the tetragonal lattice and their arrangement in the herring bone structure were determined; the structure was shown to be suited for accommodation to the cubic (fluorite structure) to tetragonal transformation strain. Surface relief associated with the transformation was also observed and correlated to the transformation strain. From these results, the transformation was suggested to be of diffusionless type (martensitic).

Transformation Toughening in Zirconia‐Containing Ceramics

“…[52][53][54]57,58 In the latter case, the t 3 m transformation has been observed to occur spontaneously in samples rapidly cooled from the melt 52,53,57 and isothermally in specimens aged at ϳ550 K following rapid cooling. 53,58 In rapidly cooled samples, the parent t phase itself has a multiply twinned, herringbone microstructure, 70,71 and it undergoes partial t 3 m transformation to thin plates of the m phase. The ability of the crystallographic theory to account for all features of the transformation in this complex microstructure 54 is further strong evidence that the theory can be used to make reliable quantitative predictions for the martensitic transformation in ZrO 2 .…”

PAC Characterization of Nontransformable Tetragonal t′ Phase in Arc‐Melted Zirconia–2.8 mol% Yttria Ceramics

“…The reported observation that the tЈ phase slowly decomposes into the equilibrium (t) and (c) phases of respectively lower and higher yttria contents, determined by the phase diagram during hightemperature exposures, 16 is not always confirmed. 17 188 journal unambiguously by transmission optical microscopy and transmission electron microscopy experiments performed on single crystals or relatively coarse specimens, 14,19,20 the tЈ phase exhibits twins and antiphase domain boundaries, which are the consequence of a displacive, diffusionless phase transformation from the cubic phase or the liquid when the material is cooled abruptly.…”

“…6 -10,12 The Y 2 O 3 -ZrO 2 phase diagram 13 shows the existence of the technologically relevant, metastable tetragonal tЈ phase, which is obtained by heating given Y 2 O 3 -ZrO 2 alloys and rapidly cooling them from the stability range of the cubic phase 14,15 or by plasma-spray 16 or arc-melting, followed by quenching. [17][18][19] This structure reluctantly transforms martensitically to m-ZrO 2 , 16 thus improving the mechanical properties of the ceramic. The reported observation that the tЈ phase slowly decomposes into the equilibrium (t) and (c) phases of respectively lower and higher yttria contents, determined by the phase diagram during hightemperature exposures, 16 is not always confirmed.…”