The microstructure of the affected zone of a worn PCBN cutting tool characterised with SEM and TEM

The results show an adherent layer smearing the crater on the rake face of the PCBN tool cutting edge. Closer investigation of this layer reveals an inner layered structure with some characteristic features. This layer consists of elements from the workpiece material. The tool-adherent layer interface is smooth, showing rounded, concave wear surfaces of micron-sized cBN instead of the original flat grain surfaces. Larger Fe-rich areas are found which are oxidised on the surface, sometimes containing smaller amounts of Cr and Ni. Mn and S are found as larger, often elongated areas primarily close to the tool-adherent layer interface. The dominating degrading mechanism appears to be chemical degradation. The detailed microstructure of the tool-adherent layer interface and the adherent layer is presented.