Fracture toughness and mechanical strength of Y-TZP/PSZ ceramics

• Published in: Scripta materialia Vol. 45; no. 2; pp. 213 - 220
• Main Authors: Casellas, Daniel, Feder, Adrian, Llanes, Luis, Anglada, Marc
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Ltd 31.07.2001; Elsevier Science
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Creep; Exact sciences and technology; Fracture strength; Fracture toughness; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Microstructure; Physics; Y-TZP; Y-TZP/PSZ; Y-TZP/PSZ; Fracture strength; Microstructure; Y-TZP; Fracture toughness; Zirconia; Fracture mechanics; Mechanical strength; Thermal ageing; Mechanical properties; SEM; Stabilized zirconia; Ceramics; Experimental study; Rupture strength; Heat treatments; Tenacity
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(01)01020-X

Within the framework of this investigation, two different zirconia ceramics can be distinguished from a microstructural viewpoint: yttria-tetragonal zirconia polycrystals (Y-TZPs) and partially-stabilized zirconias (PSZs) (Green et al. 1989). In Y-TZP ceramics, the tetragonal phase is stabilized by adding a small amount of yttria (about 2-3 mol percent), resulting in a microstructure formed by fine tetragonal grains (0.2-0.5 micron of average grain diameter). Consequently, their mechanical strength is considerably elevated ( > 1 GPa), combined with a moderate to low fracture toughness (4-5 MPa x sq rt m) due to their limited transformability (Green et al., 1989). On the other hand, PSZ materials contain 6-10 mol percent of stabilizer, usually magnesia or calcia, and here the tetragonal phase is present as fine precipitates embedded in a coarse cubic matrix. These materials exhibit markedly larger fracture toughness (more than 10 MPa x sq rt m) and smaller flexural strength (about 500 MPa) than Y-TZPs, which is related to a high transformability of the tetragonal precipitates and to the coarseness of the cubic matrix, respectively (Green et al., 1989). Although the aforementioned inverse correlation between fracture toughness and flexural strength is typical for zirconia ceramics, recent studies have pointed out that zirconia-based materials with an optimum degree of fracture resistance may be developed by heat treating Y-TZP materials at high temperatures (1550-1650 C) (Ruiz and Readey, 1996; Casellas et al., 2001). Since such materials have a microstructure with features close to PSZ and Y-TZP, they are referred to as Y-TZP/PSZ. The interest on Y-TZP/PSZ materials lies in the combination of high fracture toughness and mechanical strength, which is not common in other zirconia ceramics. The purpose of this paper is to document and discuss the fracture characteristics of Y-TZP/PSZs developed through annealing, at different temperatures and times, of a conventional Y-TZP. (CSA)