One PVD coating technique with certain advantages

When you think about PVD coating, you probably think about the type of coating on your cutting tools, but do you consider how it gets there?

Most PVD coaters use cathodic-arc evaporation, in which an electric arc vaporizes the coating material from a cathode. The vaporized material condenses on the tool, resulting in a wear-resistant coating imbued with whatever qualities the coater is looking to impart to the tool.

A sputtering cathode lights up under high voltage. Image courtesy Angstrom Sciences.

But there’s another, less-common physical-vapor-deposition method called high-power impulse magnetron sputtering, or HIPIMS, that combines the advantages of high ionization from cathodic-arc techniques with the superior adhesion of magnetron sputtering.

Smooth, Dense

HIPIMS is a derivative of a process called magnetron sputtering, in which a high voltage is applied to a sputtering cathode that deposits a plasma coating on the target surface while accelerating argon ions toward the target. The argon ions project the sputtering material onto the surface, depositing the coating.

When you coat a tool using a cathodic arc, “you have a high-energy electrical arc that basically rasters on the substrate,” said Mark Bernick, president of cathode and magnetron manufacturer Angstrom Sciences Inc., Duquesne, Pa. “When you do that, you are basically vaporizing the surface layer, resulting in both microparticles and macroparticles, which means the distribution of the coating material varies.”

Both cathodic arc and HIPIMS take place in a vacuum chamber, and both use electricity to vaporize the coating material. The advantage of cathodic arc is that it’s a quick process and its power supplies are relatively inexpensive, and if surface finish is not a major consideration, the uneven distribution may not be an issue.

However, sputtering provides a more homogenous particular distribution. HIPIMS, as the name states, relies on high-power pulses rather than constant power, meaning the sputterant approaches the substrate perpendicularly and with higher impinging energy than in the cathodic-arc process. The result is an extremely smooth, dense coating that effectively adheres to the substrate.

On the Pulse

“HIPIMS is basically the embodiment of a new type of power supply,” said Gary Lake, president of coating service provider CemeCon Inc., Horseheads, N.Y. “Conventional sputtering uses constant power; with HIPIMS, you need a power supply that is capable of storing energy and then pulsing that energy at a very high level, using something like a 10-kilowatt supply to generate 1-megawatt pulses. We’ve addressed many of the physical problems associated with that process, and the resulting power supplies are much more reliable.”

Compared to arc evaporation, a HIPIMS+ coating allows for equivalent cutting performance with about a 1µm-less coating thickness. Images courtesy CemeCon.

Along with power-supply-related differences from conventional sputtering, HIPIMS is further differentiated into two variants, yielding slightly different results.

“One version uses relatively short, very-high-power pulses, and the other is lower power but gives the ability to program the pulse shape,” explained Michiel Eerden, tooling product manager at IHI Hauzer Techno Coating B.V., Venlo, Netherlands, which offers both variants, as well as arc evaporation. “The results are functionally very similar, but we decided to adopt both in order to offer our customers what is most useful for their application.”

Usually, the lower power-supply costs and shorter turnaround associated with arc evaporation win, he continued, but whenever the job involves a soft or sticky substrate that tends to adhere to the cutting tool, the additional cost of HIPIMS is worth considering.

Barrier to Entry

“People are still looking for commercial applications for HIPIMS, but nobody’s hit ‘the big one’ yet,” said Frank Papa, U.S. business and technology manager for Liverpool, U.K.-based sputtering technology developer Gencoa Ltd. “HIPIMS systems are still quite expensive, and there isn’t widespread demand in the tool coating industry at this point. We need to reach the point where power supply costs come down significantly in order for it to be attractive to the industry as a whole.