Mechanical properties and corrosion behavior of powder metallurgy iron-hydroxyapatite composites for biodegradable implant applications

Nine Fe-HA composites were fabricated via powder metallurgy method by varying the amount (2.5, 5, 10 wt%) and particle size (<1 mu m, 1-10 mu m, 100-200 mu m) of hydroxyapatite (HA) as a bioactive phase in the iron (Fe) matrix. X-ray diffraction did not detect any phase changes in HA after the sintering process. Uniaxial tensile tests measured the strengths of the composites. Polarization and immersion tests estimated the corrosion rates (CR). Yield strength, tensile strength, and ductility of the composites decreased with increasing HA content and decreasing HA particle size, whereas their corrosion rates increased. The strongest composite was Fe-2.5 wt% HA (100-200 mu m) with sigma(y) = 81.7 MPa, sigma(u) = 130.1 MPa, fracture strain of 4.87%, and CR = 0.23 mmpy. The weakest composite was Fe-10 wt% HA (<1 mu m) which did not exhibit plastic deformation, fractured at sigma(u) = 16.1 MPa with 0.11% strain, and showed the highest CR of 1.07 mmpy. This study demonstrates how the relative particle size between Fe and HA determines the mechanical and corrosion properties of Fe-HA composites, thereby aiding in enhancing future resorbable implant designs. The model can also be used when designing other bioactive composites (i.e. Ti-HA, Mg-HA) via powder metallurgy. (C) 2016 Elsevier Ltd. All rights reserved.