Influence of the WC grain size on the properties of PVD/HVOF duplex coatings

Abstract

Duplex coatings are an innovative approach to further improve cemented carbide surfaces in terms of tribo-mechanical properties by depositing a thin Physical Vapor Deposition (PVD) layer on top of the High Velocity Oxygen Fuel (HVOF) sprayed coating. Within this investigation, AISI M3 steel substrates were primarily coated with three different WC-12Co feedstock powders by means of HVOF spraying. The agglomerate size of all powders was constant (−45+15μm), the WC grain size was varied from conventional (carbide size 2.5μm) over fine (carbide size 1μm) to nanosized (carbide size 0.1μm) carbides. Subsequently, the samples were polished prior to the deposition of a CrAlN PVD coating by means of magnetron sputtering. The aim is to evaluate the influence of the WC grain size on the CrAlN/WC-12Co duplex coating properties.It was shown that a smaller carbide grain size influences the microstructure of the CrAlN coating and causes a finer crystalline structure. Furthermore, higher compressive residual stresses occur in the duplex interlayer and the top layer when using nanosized carbides. Moreover, nanosized carbides in the HVOF coating are favorable in terms of layer adhesion, which was analyzed by means of HRC indent test and scratch test. Further enhancements are the increase in hardness and the reduction in roughness which was directly influenced by the WC grain size. Considering the obtained results, it is to conclude that a reduction of the interlayer WC grain size improves the performance of CrAlN/WC-12Co duplex coatings.