Microstructure and corrosion resistance of AZ91- Hydroxyapatite composites processed via deformation-driven metallurgy

This study explores the microstructural evolution, mechanical properties, and corrosion behavior of AZ91 composites reinforced with hydroxyapatite (HA) particles, processed at varying rotational speeds (600, 1000, and 1400 rpm) using a deformation-driven metallurgy process. Microstructural analysis revealed that plastic deformation and heat generation during processing resulted in complete bonding between AZ91 powder particles and reinforcements, forming a fine equiaxed microstructure through dynamic recrystallization. The average grain size increased with rotational speed, measuring 54.2 ± 1.3 µm, 67.1 ± 1.5 µm, and 74.5 ± 1.9 µm for samples processed at 600, 1000, and 1400 rpm, respectively, highlighting the dominant role of temperature in grain growth. Mechanical testing demonstrated a decreasing trend in hardness and tensile strength with increasing rotational speed. The hardness dropped from 85.2 ± 2.9 HV0.1 at 600 rpm to 71.2 ± 6.8 HV0.1 at 1400 rpm, while ultimate tensile strength declined from 334.2 ± 6.3 MPa to 265.3 ± 4.9 MPa. Corrosion resistance was significantly influenced by processing parameters. The lowest corrosion current density (40.901 µA/cm²) and highest polarization resistance (Rp = 239.996 Ω·cm²) were observed in samples processed at 600 rpm, demonstrating enhanced corrosion resistance due to finer grains and uniform HA dispersion. In contrast, at 1400 rpm, increased grain size and uneven HA distribution contributed to a higher corrosion rate and reduced Rp (186.194 Ω·cm²).