CVD diamond coatings for cutting tools

Modern Machine Shop, Jan, 1991

Diamond coated cutting tools have been around for some time. But the coating is known as polycrystalline, and it is composed of small diamond crystals fused to a cutting tool surface.

A new technology that uses CVD (chemical vapor deposition) to develop a homogeneous diamond layer on cutting tools has been announced by Norton Company, 1 New Bond St., Worcester, MA 01606. They are working in conjunction with Sandvik Coromant of Fairlawn, New Jersey, to coat a variety of cutting tools and indexable inserts.

The CVD process uses a plasma of hydrogen in methane gas under carefully controlled conditions to generate a diamond deposition. Norton points out that it is the control of the diamond formation and deposition that their research, in conjunction with coating specialists, has solved.

Most cutting tools today are either cemented carbides or high-speed steel. In both cases they can be formulated to have a tough substrate that can take shock.

Because diamond is the hardest known material-twice as hard as cubic boron nitride and four times as hard as silicon carbide--it is said to be the ultimate material for many wear-resistant and cutting applications.

Diamond film in the range of ten microns (0.0004 inch) can be coated onto all kinds of cutting tools. Such tools can be expected to last 10 to 100 times longer than conventional tools. Diamond is also one of the best substances for heat dissipation. Therefore, it can work with higher rates of material removal.

Because diamond will not adhere to other materials, and because galling is reduced during cutting operations, parts machined with diamond usually have an excellent finish.

Diamond is excellent for machining many different materials. It will very effectively cut glass, ceramics, refractory materials, carbides, silicon, composites, graphite, aluminum, copper, and others.

It is claimed that diamond cannot be used with any of the iron family. During the machining process, the pure carbon of diamond tends to chemically react with iron to form iron carbides.

Both Norton and Sandvik plan to market CVD coated cutting tools through their respective sales channels.