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

• Hydroxyapatite (HA) powders in three particle size groups (< 1 μm, 1–10 μm, 100–200 μm) were synthesized.
• Nine iron-hydroxyapatite composites (HA content = 2.5, 5, 10 wt%) were fabricated via the powder metallurgy process.
• Tensile strength and ductility of the composites decreased with increasing HA content and decreasing HA particle size.
• In vitro corrosion rates of the composites increased with increasing HA content and decreasing HA particle size.

Nine Fe–HA composites were fabricated via powder metallurgy method by varying the amount (2.5, 5, 10 wt%) and particle size (< 1 μm, 1–10 μm, 100–200 μm) 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 μm) with σy = 81.7 MPa, σu = 130.1 MPa, fracture strain of 4.87%, and CR = 0.23 mmpy. The weakest composite was Fe–10 wt% HA (< 1 μm) which did not exhibit plastic deformation, fractured at σu = 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.

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