Brittle-ductile transition in compliant finishing of HVOF sprayed hard WC-Co coating

Abstract WC-Co coating with nanolevel surface finish is required in some special components in aviation, automobile and forming industries. In this study, compliant finishing of WC based coating is carried out using an in-house fabricated wheel based SAG tool. Theory of contact mechanics and the interactions of active abrasive particles with the workpiece surface are considered to develop a material removal rate (MRR) model. The brittle-to-ductile transition of WC-Co coating is investigated during compliant finishing with diamond abrasive pads having different particle size. It is observed that the material is purely removed through ductile mode when 6 μm polishing pad is used and the critical chip thickness for brittle to ductile transition lies in the range of 60–100 nm. Moreover, the lower wheel compression and higher wheel speed can slightly enhance the possibility of ductile machining. A low surface roughness of 21 nm is achieved using multistep compliant finishing operations with decreasing abrasive particle size in a sequence. The residual stress of the finished coating is found to be −78 ± 8 MPa which is almost 28% of the ground surface. The cross-section of the finished coating is analysed and no appreciable sub-surface damage is detected.