Sliding wear behaviour of surface nitrided zirconia

Abstract

Tetragonal polycrystalline zirconia stabilised with 3% molar yttria (3Y-TZP) has found wide applications in orthopaedics and dentistry because of its excellent mechanical properties (flexural strength above 1000 MPa, fracture toughness about 5 MPa·m1/2, hardness above 12 GPa) and biocompatibility. However, 3Y-TZP has a strong drawback: poor resistance to hydrothermal ageing also referred to as low temperature degradation (LTD). Nitriding of 3Y-TZP can make the surface resistance to LTD, but surface mechanical properties are also affected. In this work, the sliding wear resistances of as sintered and nitrided 3Y-TZP have been studied and compared. Nitriding has been carried out by embedding 3Y-TZP in a powder of ZrN and posterior heat treatment at 1400, 1500 and 1600 °C in a nitrogen atmosphere. The sliding wear behaviour of as sintered and nitrided surfaces was studied by means of ball on disc tests. The results show that by nitriding at 1400 °C the nitrided surface is resistance to LTD without any significant drop in the surface mechanical properties, so that it has similar sliding wear behaviour and surface mechanical properties as those of the starting 3Y-TZP. The results are discussed in terms of the change in the microstructure induced by nitriding.