Effect of electrodeposition conditions on hardness of Ni–B/diamond composite films

Ni–B/diamond composite films were prepared via electrodeposition. Ni–B matrix and co-deposited diamond particles have very high hardness, so the Ni–B/diamond composite films also showed high hardness. The film hardness of the Ni–B/diamond composite film was ca. 3000 Hv at the most, which is approximately the same hardness as for previously reported super-hard films. The film hardness depended on the diamond content in the films and the size of co-deposited diamond particles. The diamond content can be controlled by electrodeposition conditions such as the concentration of diamond in baths and the current density. The composite films with higher diamond content and larger diamond particles showed higher hardness. Moreover, thermal-treatment at 573 K in air hardened the Ni–B/diamond composite films. In this paper, the co-deposition process of diamond particles is discussed based on the classical mechanism for composite plating.