CVD diamond coating on WC-Co substrate with Al-based interlayer

Diamond coating with sufficient adhesion on WC-Co cutting tools is expected to significantly increase their cutting performance. In order to enhance the coating-substrate interfacial adhesion, Al2O3 and Ta mono-interlayer, Al-Al2O3, Al-AlN and Al-Ta duplex interlayer systems have been developed in this study. These interlayer materials were prepared using a magnetron sputtering method, and diamond coating were deposited on them using microwave plasma enhanced chemical vapor deposition. Grazing incident X-ray diffraction was carried out to determine the phase components in the Al-Al2O3 and Al-AlN interlayers. Raman spectroscopy and scanning electron microscopy were used to evaluate the quality, morphology and microstructure of the deposited diamond coatings. Rockwell C indentation testing was performed to evaluate the adhesion of the coatings. To elucidate the coating failure mechanism, the compositions around the delaminated spots of diamond coatings after indentation were identified by Energy-dispersive X-ray spectroscopy. The results show that continuous diamond coatings were achieved on Al2O3, Al-Al2O3, Al-AlN and Al-Ta interlayered substrates, whereas a graphite layer was still formed with the Ta monolayer accompanied by an easy spallation of diamond coatings. The Al interlayer has played an important role in obtaining high purity diamond by in-situ forming an alumina barrier layer. Especially, the diamond coating deposited with an Al-AlN interlayer demonstrates superior interfacial adhesion in comparison with all the other interlayers.