Electrodeposited Ni–Co–B coatings: Preparation and evaluation of its wear resistance

Ni-Co-B coating was electrodeposited in sulfate bath with dimethylamine borane (DMAB) as reducing agent. The experiment explored the effect of DMAB concentration (CDMAB, 1∼10 g/L), current density (Jk, 2∼8 A/dm2), bath temperature (Tbath, 30∼60 °C) on the coating morphology and hardness, and determined the best parameters: CDMAB= 8 g/L, Tbath=60 °C, Jk=4 A/dm2. The average hardness of the crack-free coating is 818 HV, and the B content is about 2 wt.%. In order to develop a stress-relieving heat treatment scheme, the effects of heat treatment temperatures (100∼500 °C) and holding times (1.5 h and 3 h) on the hardness of Ni-Co-B coating were studied. The highest hardness (1130 HV) is obtained at 350 °C for 1.5 h. The heat-treated Ni-Co-B coating was characterized by XRD, SEM and EPMA, and the second phase Ni3B was detected. In addition, the wear resistance and wear mechanism of the coating at room temperature and high temperature (300 °C) were studied. The results show that the wear volume of Ni-Co-B coating is reduced by more than 55% compared with Ni-Co coating. In general, Ni-Co-B coating can be used as an alternative to Ni-Co wear-resistant coating.