Development of an optical, non-destructive technique for inspection of Zirconia ceramic parts

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) as a high toughness, high strength and biocompatible material can be found in many medical applications where customized part manufacturing is required. Current machining techniques, including mechanical grinding and (developed within our group) laser processing, may introduce cracking, resulting in reduced strength. Uncertainty of the exact shape, size and distribution of flaws introduced during manufacturing or machining require a reliable testing technique. In this paper we present a novel mid-infrared transmission technique for flaw detection in zirconia. This technique is an imaging method using optical transmission through the sample which is possible due to the reduced scattering that occurs at these wavelengths. Dark regions appearing in the images indicate the presence of features within the bulk material. The samples contain laser machined holes and between these holes cracks have developed due to the high thermal gradients occurring during the laser process. ESEM images of the sample after sectioning confirm the detected cracks.