High-resolution depth profiling of mechanical properties of thick cubic boron nitride coatings

The small-angle cross-section nanoindentation method (SACS) allows a depth profiling of mechanical properties on the nanometer scale. The high resolution of the SACS will be demonstrated on nanoscale, multi-functional, superhard, thick cubic boron nitride coatings with low residual stresses. These coatings recently have been successfully deposited by r.f. magnetron sputtering using a tailored coating constitution and an innovative growth concept. This novel concept allowed 2-μm-thick c-BN to be grown on top of a coating system initiated by a B-rich base layer followed by a nucleation layer with gradient chemical composition. A small amount of oxygen was incorporated in the coatings to reduce the very high stress usually appearing in c-BN coatings. The SACS permitted a high-resolution depth profiling to distinguish between the different layers used in this concept and to measure their different mechanical properties like hardness and elastic modulus as well as interface widths and revealed a maximum hardness of 59 GPa and an elastic modulus of 463 GPa of the thick c-BN:O top layer. In addition, surface topography and crack development have been studied by atomic force microscopy (AFM) and microindentation.