Fabrication and evaluation of bulk nanostructured cobalt intended for dental and orthopedic implants

Bulk nanostructured cobalt (Co) was fabricated by a combination of high energy ball milling and warm pressing. The obtained cobalt has an average grain size of 35 nm with measured hardness and elastic modulus of 7.32 GPa and 211.4 GPa, respectively. Dry sliding wear testing shows such bulk nanostructured Co has high sliding wear resistance. However, electrochemical study shows that such Co has a relatively high corrosion rate and no passive behavior in the artificial saliva solution. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis further reveal that the corrosion product is composed of insoluble cobalt (II) phosphate and cobalt hydroxide. The evaluation results suggest that bulk nanostructured cobalt can be a promising wear resistant material but may not be suitable for dental/orthopedic implants.