Improvement of coating adhesion on cemented carbide tools by plasma etching

Abstract

Surface treatments are one of the main factors to control adhesion between coating and substrate on a cutting tool. Poor coating adhesion on the substrate accelerates the wear progress and decreases tool lifetime due to the pull-out and release of hard abrasive particles between the tool rake or flank face and the workpiece. Mechanical and chemical substrate treatments are used in order to improve the coating adhesion. This study evaluated and compared the chemical and plasma etching effectiveness in the improvement of substrate-coating adhesion, and consequently, tool life of PVD-coated cemented carbide tools. The plasma etching was performed in plasma reactors in which the cations produced collide with the samples and remove from the surface atoms or molecules modifying the topography. In the chemical etching, acid and alkaline solutions were used to remove tool surface material, changing its initial roughness and chemical composition. After these surface treatments, the samples were PVD coated with (Ti,Al)N. To ascertain the effectiveness of the surface treatment, Rockwell B indentation and machining experiments were performed on treated and untreated tools. Tool topographies were analyzed by atomic force microscopy (AFM) and flank wear lands were evaluated by scanning electronic microscopy (SEM). The plasma-treated tool showed better performance in the indentation and turning tests. Therefore, the chemical etching-treated tool showed the highest roughness, but the coating adhesion was poor due to chemical changes on substrate surface. Furthermore, good anchoring is not influenced only by roughness, it also depends on the substrate surface chemical nature.