TOUGHENING OF CALCIUM HYDROXYAPATITE WITH SILVER PARTICLES

Calcium hydroxyapatite bioceramic was toughened by preparing composite s with silver particles as reinforcements. The composites were fabrica ted from hydroxyapatite and silver oxide raw powders. The sintering be haviour was investigated using dilatometry. An optimized sintering pro gramme was designed to promote densification and to suppress the decom position of the hydroxyapatite matrix and the evaporation of silver. H igh density was achieved on both small cylinder samples and large bloc k samples by pressureless sintering. The density of the composites is over 92.4% theoretical with silver inclusions up to 30 vol%. The stren gth of the composites is greater than 80 M Pa as tested by four-point bending. Silver inclusions improve the toughness consistently, from 0. 70 MPa m(1/2) for the monolithic hydroxyapatite to 2.45 MPa m(1/2) at 30 vol% silver. Studies on the toughening mechanism indicate that crac k bridging and subsequent plastic work of silver are mostly responsibl e for the toughening, whereas crack deflection also makes some contrib ution.