Thermal shock resistance of composites of alumina and partially stabilized zirconia

Abstract

The ZrO 2 martensitic transformation (tetragonal-tomonoclinic) and the attendant volume expansion and the related microcracking effects can be used to improve substantially the fracture energy and/or strength in alumina composites and the resistance of the materials to thermal stresses by rapid cooling and heating [1]. The thermal shock resistance of ceramics is of particular importance in a variety of applications. To meet the needs of these various applications, a number of thermal shock (R) parameters based on material properties have been generated. The basis of this approach is to analyse thermal stress failure in terms of the relationship between the usual thermomechanical properties of materials. This has led to the generation of a series of thermal shock parameters: R, R', R", R'", R'' and ATe. Of these, R, R' and R" are thermal shock fracture resistance parameters and R'" and R .... are thermal shock damage resistance parameters. The fracture resistance parameters apply to crack initiation problems, whereas the damage resistance parameters apply to crack propagation problems. ATe is called the critical temperature difference, at which the remaining strength of the material suddenly drops considerably [2-5]. The physical and mechanical properties of the composites of 20wt% alumina and remainder zirconia-3 mol% yttria (TZ-3Y20A; Tosoh Corporation, Tokyo, Japan) for both the as-sintered condition (sintered at 1500 °C for 2 h) and the sintered + hot isostatically pressed (HIPed) condition (sintered at 1500 °C for 2 h and subsequently HIPed at 1450 °C and 190 MPa for 1 h) are summarized in Table I.