Physical vapor deposition tool coatings

Physical vapor deposition (PVD) of hard coatings such as titanium nitride have been an industrial reality since the beginning of the 1980s. Two PVD processes, low voltage electron beam and cathodic arc deposition, were responsible for the early commercial success of hard coatings on high speed steel tooling. Since that time, two other PVD processes have also been prosperous in the industrial world—high voltage triode electron beam and unbalanced magnetron sputtering. There are many similarities and differences between these four PVD hard coating processes, but not all of the commonly used PVD hard coatings can be deposited well in the four systems. Titanium nitride and titanium carbonitride are the two most widely used PVD tool coatings, and they can be deposited in all four PVD systems. Titanium aluminum nitride can be deposited easily with the unbalanced magnetron process and also with the cathodic arc processes as long as cast targets are used. Uniform composition cannot be maintained with the electron beam processes because of the different vapor pressures of titanium and aluminum. New PVD hard coatings are being developed and applied. Diamond-like carbon is now being tried for some non-ferrous cutting applications, and metal-carbon films are showing promise. Polycrystalline nitride superlattice coatings made of thin alternating layers of two hard coatings such as titanium nitride and niobium nitride are showing potential for abrasive cutting situations because of the very high hardness (up to 5200 HV) of these coatings. The search continues for potentially even better tool coatings. An intense effort is underway to produce the superhard crystalline carbon nitride, which is predicted to have a hardness as hard or even harder than diamond. Similarly, cubic boron nitride (CBN) coatings are still very much in the development stage. Thin CBN coatings can now be deposited up to approximately 2000 Å in thickness, but stress in the films prevents thicker films from being made. Aluminum oxide, which has been very difficult to make by PVD techniques, except in the very slow r.f. sputtering mode, can now be deposited in the d.c. magnetron mode when pulsed power is used.