Modulus and hardness evaluations of sintered bioceramic powders and functionally graded bioactive composites by nano-indentation technique

Nano-indentation experiments on various sintered bioceramic powders and bioceramic functionally graded coatings, were performed with a berkovich indenter to establish an improved method for determining hardness and elastic modulus from load and displacement data. The materials included, spherical hydroxyapatite, SHA (Taihei chemicals, Japan), hydroxyapatite powders of different batches namely, P81B, P88 and P120 (Plasma Biotal, UK), in-house hydroxyapatite, HA and alpha tri-calcium phosphate, αTCP (Merck, Germany), functionally graded coatings (FGCʹs) of HA–G–Ti and HA–αTCP–Ti. The elastic modulus and hardness values of all the materials were obtained by nano-indentation with the corresponding load–displacement curves confirming the characteristic properties of the sintered materials and functionally graded coatings. The results showed that the SHA powder yielded the highest modulus and hardness value and P88 (HA) showed the least value confirming that its relatively softer than other bioactive powders. Furthermore, the continuous stiffness measurement also showed that SHA yielded the best mechanical property. In case of the FGCʹs, HA–G–Ti yielded higher values of modulus and hardness in comparison with HA–αTCP–Ti.