Multilayer Systems for Cutting Tools: On the Relationship between Coating Design, Surface Processing, and Residual Stress

Abstract

AbstractCutting tools made of cemented carbide (WC/Co) are coated by chemical vapor deposition with Al2O3 and TiC1−xNx (x = 0 … 1) or combinations of these materials to improve wear resistance. Due to the high deposition temperature > 800 °C and the differences in the thermal expansion coefficients the as grown coating systems show unfavorable tensile residual stresses. To generate beneficial compressive residual stresses which improve the toughness behavior of the tools, mechanical post‐treatment processing like dry or wet blasting is introduced after coating deposition. By variation of the blasting parameters as well as of the coating design and the structural coating properties, it is possible to tailor the residual stresses with respect to both amount and depth distribution. In the present study we demonstrate by the example of Al2O3/TiCN coating systems on WC cutting inserts that an efficient assessment of this “residual stress engineering” step is possible by employing X‐ray methods which allow for nondestructive, phase selective, and depth resolved materials characterization. In order to be sensitive in different depth zones below the surface, low energy angle‐dispersive diffraction and high energy white beam synchrotron diffraction were applied to analyze the residual stress state within the coatings and in the interfacial substrate region, respectively.