Coatings strength evaluation of cutting inserts using advanced multi-pass scratch method

Abstract

The strength of the cutting inserts coating significantly determines the tool wear and the quality of the machined surface. To determine the inserts coating strength, a new method of micromechanical evaluation was developed and tested. The method is based on multi-pass progressive sclerometry with a stepwise maximum indenter load increasing with each subsequent pass. On the first pass, the indenter load increased from zero to 300 mN in the middle of the scratch distance and decreased to zero at the end of the scratch distance. On each subsequent pass, the maximum load on the indenter was increased by a further 100 mN. The indenter loading and unloading rate were 13.4 mN/s. Coating failure criterion is defined as a significant change in the correlation tightness between successive scratches profilograms. The accuracy of determining the load at which coatings starts to fail depends on the step of increasing the indenter load. The developed method has been tested on various PVD coatings of inserts. Surface topography measurements of formed scratches confirms the coatings failure in area of maximum loads on the indenter.