REINFORCEMENT OF HYDROXYAPATITE BIOCERAMIC BY ADDITION OF NI3AL AND AL2O3

The effects of Ni3Al and Al2O3 additions on the mechanical properties of hydroxyapatite (HAp) were investigated. The addition of Ni(3)AI par ticles increased the strength as well as the fracture toughness of HAp . However, the improvements in the properties were limited because of the formation of microcracks around the metal particles. The microcrac ks were formed because of the large difference in the coefficients of thermal expansion between HAp and Ni(3)AI, and because of the relative ly large size of Ni(3)AI particles (similar to 20 mu m). The addition of submicrometer Al2O3 powder was also effective in increasing the mec hanical properties. The flexural strength and the fracture toughness w ere increased from about 100 MPa and 0.7 MPa.m(1/2), respectively, to 200 MPa and 1.5 MPa.m(1/2) by the addition of 20 vol% Al2O3. When Ni3A l and Al2O3 were added together, the fracture toughness was further in creased to 2.3 MPa.m(1/2). This increase in the fracture toughness was attributed to the synergistic effect of matrix strengthening and crac k interactions with the metal particles.