Indentation and sliding contact testing of three laser-textured and PVD-coated cemented carbide tools

Abstract

A new concept for cemented carbide tools was presented with laser-generated abrasive-like protrusions on their machining surfaces that mimic the surface features of diamond or cubic boron nitride abrasives commonly used on honing tools. In this study, the surface structure on the new tools were protected by three different PVD ceramic hard coatings. All three nitride-based coatings, i.e., TiSiN-AlTiN, TiSiN-AlTiN-CrN and AlTiN-CrN, differed in the adhesion layer and coating structure. The coating-substrate systems were assessed by means of indenting and sliding contact testing in order to find out an appropriate one for the textured tools. Experimental methodology included (1) ‘passive’ Vickers indentation hardness tests, and (2) ‘active’ machining tests. In both cases, the resulting surface integrity was inspected by using FIB/SEM/EDS. It is found that both laser texturing and coating deposition changed the hardness. The tool coated by the two-layer film (TiSiN-AlTiN) achieved the best performance, in terms of both hardness enhancement and damage prevention experienced under both tests. Meanwhile, improvement was much less pronounced by the two-layer (AlTiN-CrN) coated tool. Here, cracks appeared under the Vickers indentations and the film was completely or partially spalled-off at some protrusion tops (cutting fronts), due to the concentrated stress during the machining. Finally, the three-layer coating with the TiSiN on the top (TiSiN-AlTiN-CrN) exhibited an intermediate response, where moderate hardness increase was combined with some wear – although less severe than for AlTiN-CrN film - taking place at critical points, such as cutting fronts.