Studying Tungsten Carbide Coatings for Metal Cutting Tools

Metal cutting tools use cemented carbides like WC-Co (tungsten carbide in cobalt-rich matrix) with different CVD and PVD based coatings to improve the surface hardness, rigidity and wear resistance. These coatings are mainly transition metal nitrides and carbides like TiN, TiC, ZrN, VN, TiCN, TiAlN. SEM-EDS is a fantastic tool with which to study tungsten carbide coatings.

In this application example, TiC/N, and Al₂O₃ layers on WC-Co layers are mapped with EDS. Fig. 1 shows the focused ion beam (FIB) cross section of the cutting tool edge. Top TiN coating layer is followed by Al₂O₃/TiN/TiCN/TiN and WC-Co as substrate. With EDS, we could differentiate changes in N composition between TiN, TiCN and TiN layers (Fig. 2). Additionally, ESPRIT analytical software from Bruker is able to deconvolute strongly overlapping Ti and N (Fig. 4) automatically.

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Fig. 1: EDS map and SE image of different coating layers on tungsten carbide cutting tools, the surface is polished using focused ion beam milling (FIB).

Fig. 2: EDS map showing Ti, C and N distribution, from left: TiN/TiCN/TiN and TiC. EDS can easily distinguish the compositional change between light elements like C and N.

Fig. 3: EDS map of WC substrate and Co binder in super hard cutting tools.

Fig. 4: Automated deconvolution and quantification of Ti and N using the ESPRIT analytical software.