Ageing, Shocks and Wear Mechanisms in ZTA and the Long‐Term Performance of Hip Joint Materials

International audienceThe surface morphologies and microstructures of Zirconia Toughened Alumina (ZTA)femoral heads were analyzed followingin vitrotests aiming to simulatein vivodegradation. Threephenomena potentially leading to degradation were investigated: shocks, friction and hydrothermalageing. Shocks due to micro-separation created the main damage with the formation of wear stripeson the femoral head surfaces. Atomic Force Microscopy (AFM) images suggested the release of weardebris of various shapes and sizes through inter- and intra-granular cracks; some debris may have asize lower than 100 nm. A decrease in hardness and Young’s modulus was measured within the wearstripes by nanoindentation technique and was attributed to the presence of surface and sub-surfacemicro-cracks. Such micro-cracks mechanically triggered the zirconia phase transformation in thoseworn areas, which in return presumably reduced further crack propagation. In comparison withshocks, friction caused little wear degradation as observed from AFM images by scarce pullout ofgrains. The long-term resistance of the ZTA composite material against hydrothermal ageing isconfirmed by the present observation