Toughening of calcium hydroxyapatite with silver particles

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Calcium hydroxyapatite bioceramic was toughened by preparing composites with silver particles as reinforcements. The composites were fabricated from hydroxyapatite and silver oxide raw powders. The sintering behaviour was investigated using dilatometry. An optimized sintering programme was designed to promote densification and to suppress the decomposition of the hydroxyapatite matrix and the evaporation of silver. High density was achieved on both small cylinder samples and large block samples by pressureless sintering. The density of the composites is over 92.4% theoretical with silver inclusions up to 30 vol%. The strength of the composites is greater than 80 MPa as tested by four-point bending. Silver inclusions improve the toughness consistently, from 0.70 MPa m½ for the monolithic hydroxyapatite to 2.45 MPa m½ at 30 vol% silver. Studies on the toughening mechanism indicate that crack bridging and subsequent plastic work of silver are mostly responsible for the toughening, whereas crack deflection also makes some contribution.

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