Carbide tools are hard, wear-resistant, heat-resistant and have a long tool life. The prerequisite for this is the optimum combination of substrate, geometry and coating. The composition of a carbide is decisive for its coatability with diamond coatings. Carbide for cutting tools mainly consists of tungsten carbide (WC) as the hard material and a binder metal, usually cobalt (Co). The tungsten carbide provides the hardness and the cobalt provides the toughness. "In the past, the adhesion of the diamond coating to the carbide was not as good as it is today. That's why we - CemeCon and Extramet - worked closely together back in the 1990s to adapt the composition of the carbide," says Bruno Süess, Member of the Board of Directors of Extramet AG.
Diamond coatings for carbide tools
For good coatability, it is important that the grain is not too fine and that the carbide does not contain too much cobalt. The cobalt content is particularly important when it comes to coating with diamond, as the cobalt is dissolved from the surface of the carbide during the coating process. If its content is too low, the WC grains no longer hold together. If the proportion is too high, a graphitic phase is formed instead of the hard diamond coating. For this reason, CemeCon carries out suitability tests in which the carbide is tested for its coatability.
Premium coatings thanks to high-quality carbide
The homogeneity and therefore the quality of a carbide has a significant influence on the coating result and therefore also on the performance of the precision tool. High-quality carbides achieve both good adhesion and a uniformly coated surface. "The powder should be exposed to an oxygen atmosphere for as short a time as possible to prevent oxidation," explains Bruno Süess.
The carbon concentration in the sintering process is important
Another factor for the quality - even within a batch - is the sintering process. If one part of the green compacts is exposed to a higher carbon concentration than the other, the carbon content of the carbide blanks and ultimately also of the ground tool varies. These differences can lead to poor or uneven adhesion of the diamond coating.
REACH as a challenge for the future
REACH is one of the major challenges facing the carbide industry. The regulation forces manufacturers to minimize cobalt and nickel in the composition of hard metals. Research has achieved encouraging results in recent years, but the new carbides do not yet meet the desired mechanical requirements, especially when it comes to solutions for cutting tools.