Corrosion fatigue of bio-ceramic sapphire in isotonic sodium chloride solution

Alumina (sapphire) is considered as a candidate material for bio-ceramics, because of its superior strength characteristics, corrosion resistance and bio-inert properties. These biomaterials are used in aggressive corrosive environments such as the human body under severe mechanical conditions superposing cyclic loading on constant load. Therefore, it is necessary to evaluate the static and cyclic fatigue characteristics in an environment as severe as the human body. In this paper, the effects of human body environment corrosion upon cyclic fatigue characteristics of single crystal sapphire and polycrystalline alumina have been investigated using in vitro testing in isotonic sodium chloride solution, whose composition is closely similar to body fluid. Also, degraded corrosion morphologies and fracture surfaces of single crystal sapphire specimens were examined in detail by SEM and AFM. The fatigue limit of single crystal sapphire was found to be extremely degraded in the isotonic sodium chloride solution compared with that in air. The importance of environment assisted slip deformation is indicated.