Structure and tribological behavior of Ni-B and Co-B galvanic coatings

The structure and tribological properties of Ni-B and Co-B galvanic coatings with boron concentration from 4 to 20 at % are investigated. The coatings containing over 8 at % B are shown to have amorphous structures. Ni-B and Co-B coatings with boron concentrations preceding the onset of amorphization (6–7.5 at %) possess optimal tribological properties under dry sliding. Coatings with metastable amorphous structure demonstrate the worst tribological behavior. An increase in boron concentration up to 20 at % stabilizes the amorphous structure and improves the wear resistance, microhardness, and thermal stability of the galvanic coatings in question.