In metal cutting applications, coatings are often applied onto cemented carbide inserts as wear and heat resistant protection layers extending the tool life. A commonly used coating on inserts is Al₂O₃ which provides chemical stability, thermal and wear protection for the cemented carbide insert. The crater wear and plastic deformation behavior in certain applications can be improved by altering the phase and/or texture of the wear protective coating.  Worn (0001)-textured α-Al₂O₃ and κ-Al₂O₃-TiN multilayer coatings on inserts which had been used in cutting applications have been investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), XRD, electron backscatter diffraction (EBSD) in the SEM and (scanning) transmission electron microscopy ((S)TEM) techniques. The microstructure of the α-Al₂O₃ coating can be seen in the SE-SEM image and its (0001)-texture is shown in the EBSD orientation map, see Fig. 1a and b. The specimens for (S)TEM characterization were prepared in a Helios NanoLab 650 instrument (FEI Company) equipped with an EBSD detector (NordlysMax², Oxford Instruments), EDXS detector (X-Max^N, Oxford Instruments) and AZtec software package (Oxford Instruments). (S)TEM characterization was performed using a Titan³ 60-300 equipped with ChemiSTEM (FEI Companay). (S)TEM characterization of the worn α-Al₂O₃ coating revealed a modified region and EDXS elemental maps showed that this region contains Mg, Ca and Si beside the Al and O, see Fig. 2. Also, small grains of Fe were observed below this modified region.  For comparison, (S)TEM characterization was performed on the worn κ-Al₂O₃-TiN multilayer coating. By determining the elemental distribution and formed phases the chemical wear mechanisms can be described.

Figures:

Fig. 1: a) SE-SEM image of the α-Al2O3 coated cemented carbide insert. b) EBSD orientation map with α-Al2O3 grains coloured according to the c-axis orientation, where yellow denotes that the c-axis of the α-Al2O3 grains is parallel to the out-of-plane direction.

Fig. 2: ADF-STEM image (on top) and EDXS elemantal maps (below) of the worn α-Al2O3 coating.

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EMC Abstracts - https://emc-proceedings.com/abstract/electron-microscopy-characterization-of-the-wear-of-textured-%ce%b1-al2o3-and-%ce%ba-al2o3-tin-multilayer-coatings-for-cutting-tool-applications/