Novel conversion annealing pretreatment for improved deposition of diamond coatings onto WC-Co cemented carbide

To maintain the substrate strength and toughness of WC-Co cemented carbide as well as improve its adhesion with a diamond coating deposited by hot filament chemical vapor deposition (HFCVD), a novel conversion annealing pretreatment was studied. The pretreated substrates, as-nucleated, and as-grown diamond coating specimens were characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and Rockwell hardness tests. It was found that conversion treatment could effectively convert the Co in the surface layer into intermetallic (Co3W, Co7W) and/or Co-rich compound (M6C, M12C) phases. The conversion layer underwent a re-carburization process during the nucleation stage of HFCVD. The intermetallic phases returned to the gamma-Co (W) phase which will be encapsulated by the freshly formed WC layer. This is beneficial for seeding growth and new diamond nuclei formation. However, those Co-rich carbides consumed much carbon atoms to decompose and react to form a lot of free gamma-Co phase during the nucleation stage, which promoted severe graphitization at the growth interface during HFCVD, and caused the film to peel off. A high-quality microscale diamond coating with an adhesion of the HF 2-3 level could be deposited onto the conversion layer with only the WC and Co3W phases. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

By converting the surface layer of WC-Co cemented carbide into intermetallic and Co-rich compound phases through a novel conversion annealing pretreatment, the adhesion of diamond coating can be improved and a high-quality microscale diamond coating can be deposited onto the conversion layer.