Effect of boron content and crystalline structure on hardness in electrodeposited Ni–B alloy films

Ni–B alloy films were electrodeposited using a conventional Ni plating bath containing dimethylamine borane (DMAB) or trimethylamine borane (TMAB) as boron sources. Properties (hardness, boron content, and crystalline structure) of the electrodeposited Ni–B alloy films were significantly affected by electrodeposition conditions (current density, pH, and the amount of boron sources in plating bath). X-ray amorphous Ni–B alloy films showed high hardness, whereas hardness of Ni–B alloy films that consisted of large crystallites was low. In TMAB bath, the crystalline structure of Ni–B alloy films was controlled by the amount of co-deposited boron atoms; however in DMAB bath, clear relationship between film hardness and boron content was not confirmed. The crystalline structure of Ni–B films was drastically changed by heat-treatment and the effect of structural changes on hardness was discussed.