An investigation on fracture toughness of traditional and technical ceramics

Ceramics have very high melting point, corrosion resistance, strength and they insulate electric and heat. However, ceramics are very brittle and this property limits their use. Intensified studies have been performed for years regarding enhancing the fracture toughness of ceramic materials. In this study the fracture toughness of some traditional and technical ceramics were determined by ASTM E399 Standard. Experimental studies consists of three steps; in the first step t-ZrO2 was produced and then alumina powder mixtures were prepared containing different amount of tetragonal, monoclinic zirconia and zircon. Zircon and zirconia toughened mullite, floor and wall tile recipes were also prepared. In the second step, these powder mixtures were shaped by slip casting technique according to the dimensions of ASTM E399 Standard and then sintered at different temperatures. In the third step; water absorption, hardness, three point bending strength tests, XRD and SEM-EDX analysis were applied to the sintered samples. Fracture toughness increased with the increasing sintering temperature. Monoclinic and tetragonal zirconia addition increased the fracture toughness of alumina. Fracture toughness of alumina samples containing 0 %, 5 % m-ZrO2 and 20 % t-ZrO2 and sintered at 1600 ºC were determined as 5.9, 7.0 and 11.5 MPa?m respectively. Fracture toughness of zirconia toughned mullite was found lower than alumina. Fracture toughness of the floor and wall tiles was found as 2.7 and 0.9 MPa?m respectively.