Microhardness Improvement of Ni-W/SiC Composite Coatings by High Frequency Induction Heat Treatment

Electrodeposited Ni-W alloy coating is considered as one of the most suitable candidate to replace the environmentally hazardous hexavalent hard chromium coatings. However, it is necessary to carry out heat-treatment at a high temperature to improve its microhardness and refine its grain. In the present work, an alternative high frequency induction heat-treatment (HFI-HT) technology was used to improve surface microhardness of Ni-W/SiC composite coatings, which were electrodeposited from an ammonium-citrate bath, containing suspended green SiC particles. Transformation of amorphous to crystalline structure can be observed after HFI-HT. The precipitation of a Ni6W6C phase rather than a Ni4W phase occurs by prolonging induction time to 64 s at a power density of 21 W mm(-2) or turning power density up to 42 W mm(-2) for 4 s. While the two phases of Ni6W6C and Ni4W can be precipitated at 900 degrees C. The microhardness of Ni-W/SiC composite coatings can be improved up to 1100 HV with HFI-HT at 21 W mm(-2) for 8 s, which is comparable to that of hard chrome coatings. (C) 2019 The Electrochemical Society.