Evaluation of Fracture Toughness and R-Curve Behaviour of Y-TZP Ceramics

Abstract

The fracture toughness of tetragonal zirconia polycrystals containing 2 and 3 mol% Yttria (Y-TZP) were evaluated by 4 measuring techniques which included (1) Double Cantilever Beam (DCB), (2) Vickers indentation technique by direct measurement of radial cracks or Single Indentation Technique (SIT), (3) from the strength dependence of the Vickers indentation load and crack length or the so called Modified Indentation Technique (MIT), and (4) Single Edge Pre-crack Beam (SEPB). There were considerable differences of K_1c value between the different techniques with these being exaggerated for 2 mol% Y-TZP material. It was found that SEPB and DCB techniques gave the most conservative and consistent estimates of K_1c. The SIT technique was very sensitive to the indentation load for 2Y-TZP, estimates of K_1c decreasing with increasing load. It was found that K_1c increased with the ratio of transformation zone size to crack length. Recommendations for determination of K_1c of TZP materials are made. R-Curve behaviour and K_1c in various environments were determined by the DCB technique. The monoclinic content of different specimen surfaces including as-sintered, as-polished and fracture surface have also been analysed by X-ray diffraction.