Structural Transformations in Hydroxyapatite Ceramics Resulted from Severe Plastic Deformation

The aim of the present work is to reveal the structural transformations in the dense microcrystalline hydroxyapatite (HA, Ca10(PO4)6(OH)2) ceramics resulting from severe plastic deformation. The substructure and hardness of ceramics have been studied using the nanoindentation method and transmission electron microscopy. The severe plastic deformation of microcrystalline HA ceramics in the bulk leads to the nanocrystalline structure with the inclusions of tricalcium phosphate (?-TCP) and amorphous calcium phosphate (ACP). The results are in agreement with the model of the cluster mechanism of the HA structure (Ca9(PO4)6, Ca3(PO4)2 and PO43-) representing the plastic deformation of HA by the processes of cluster fragmentation and cluster-boundary "sliding".