High strength materials : alumina-zirconia composite using low cost raw powder

Abstract

Most of high performance ceramics are not single-phase materials. The addition of Yttria-Tetragonal Zirconia Polycrystals (Y-TZP) to alumina can improve strength and toughness of the composites through a phenomenon known as transformation toughening. Moreover, their superior mechanical properties are achieved by special process such as hot isostatically pressed (HIP), and using fine particle material. This research focuses on using low cost raw powders and non-special process. In order to know the effect of ZrO[subscript 2]/Al[subscript 2]O[subscript 3] ratio on the mechanical properties, Al[subscript 2]O[subscript 3] A21 and ZrO[subscript 2] GTYS-5 were used as raw powders and the attrition mill was used to reduce the particle size of these powders. The compositions of Al[subscript 2]O[subscript 3] (A)-ZrO[subscript 2] (Z) specimens were 100A, 80A20Z, 60A40Z, 40A60Z, 20A80Z, and 100Z. They were prepared by ball mill mixing and sintered at a temperature ranging from 1350-1650 ?C for 2 hours. The particle sizes of A-21 and GTYS-5 at 50wt% cumulative (D[subscript 50]) were 0.73 and 0.57 micrometre, respectively. The tendency of particle size distribution change corresponded to the increment of specific surface area. Those milled powders could be sintered to nearly theoretical density (96-98%). The average grain size of A-21 decreased with increasing GTYS-5 content. The ZrO[subscript 2]predominantly at the grain boundary of Al[subscript 2]O[subscript 3] effectively pinned the grain growth of Al[subscript 2]O[subscript 3] and limited the Al[subscript 2]O[subscript 3] grain size. Therefore, Vickers hardness (H[subscript v]) of the composite increased with increasing A-21 content. Fracture toughness (K[subscript 1c]) of 80A20Z and 20A80Z was maximum at 6.0 MPa.m[superscript 1/2]. The flexural strength of 20A80Z (632 MPa) was higher than 80A20Z (525 MPa). The t vector m transformation was thought to be the main mechanism to increase K[subscript 1c]and the transgranular fracture found in the composites containing high GTYS-5 content suggested the high strength