Almost thirty years ago, my initial exposure to aerospace coatings in racing was in the application of an aluminum oxide plasma spray applied to clutch friction surfaces. The results were so outstanding that it quickly appeared viable to apply the same material to the crowns of pistons, largely to improve power. In this case, the results were disastrous, enabling small flakes of aluminum oxide (at a Rockwell hardness of about 70C) to wipe out the rings and score cylinder walls. However, before the damage, it became apparent that the anticipated power gain had occurred, albeit with problematic side effects. Essentially, the difficulty lay in maintaining proper bond strength, largely because the technology had not yet embraced specific automotive requirements.
Shortly thereafter, I met and came to know another person with a strong desire to explore the potential benefits of thermal coatings. He had a broader vision of the notion that included the application of materials for friction reduction and corrosion prevention. Also on his mental landscape were ways to improve valve spring life through friction reduction and temperature control. His name was Leonard Warren. But Leonard wasn't the first to contemplate the transition of aerospace coatings techniques into the motorsports environment. VHT paints had been around for a time (largely applicable to exhaust headers) and Smokey had previously showed me dyno results from some "heat paint" he'd been using on the underside of piston crowns. I'd also had the pleasure of meeting and working with Jeff Holm, founder of High Performance Coatings, in particular with respect to his ceramic coatings for headers. While all this technology had begun to evolve in the high performance sector, it was quickly gaining a foothold in the general automotive and racing communities.
This is a "break-in" coating...
This is a "break-in" coating applied to the skirt of the piston only, designed to show wear. This coating is a .0003-inch to .0005-inch thick spray-on dry film that will help reduce friction and inhibit galling. No manufacturing allowance is required as this application is made to wear in to the cylinder wall. Courtesy of JE Pistons
Actually, there had been high-temperature paint before then, but Leonard's and Jeff's visions were instrumental in spawning what is today a continually growing industry on the motorsports landscape. Literally sold from out of the back of his car (when we first met), his Tech Line Coatings are now prominent among companies who either coat parts or make the materials to do so. Also included in the story are some thoughts and experiences from an engine builder well known to the CT audience, Dennis Wells. But first, let's examine some of the basic coatings and their applications. Overall, the message here is that the variety and range of coatings for motorsports use is so vast that you need to conduct your own research to make certain choices are correct for your application. A little time spent in this effort can pay large dividends when the parts are put into service.
Essentially, this continues to be an expanding frontier. However, it's probably safe to identify the more fundamental applications. These include coatings that provide a thermal barrier, those aiding the containment or dissipation of heat and others that address corrosion or chemical invasion. It is interesting that you can also find these various methods to combine for more than one purpose. For example, it's possible for a coating that is a so-called "thermal dispersant" to also combat corrosion.
Perhaps the best approach here would be to categorize coatings into four groups; (1) thermal barriers, (2) thermal dispersants, (3) dry film lubricants and (4) those addressing chemical or corrosion resistance. By first discussing these categories, we can then move to specific parts application.
Smokey Yunick discovered that...
Smokey Yunick discovered that valve springs raise the operating temperature of engine oil more than combustion heat with his own version of today's "Spintron" spin fixture. From the Circle Track Archives
Thermal Barriers - The transfer of heat (differences in temperature) is a time-based process. Stated another way, it is the conductivity path that resides between two different temperatures that affects the rate of heat transfer in a given period of time. For example, some materials are virtually non-conductive. Such insulators can be used to maintain the heat of combustion both inside an engine's cylinders and along its exhaust path, reducing power loss by the retention of heat (energy) within the system. Ceramics are commonly found in this group.
Thermal Dispersants - These materials aid in the control or rate of heat dissipation. Bringing materials with high rates of thermal conductivity into areas where you'd like to disperse heat has been a traditional method that aids accelerating heat release. So-called "heat sinks" and black paint have been commonly used. However, it's now possible to select specific coating materials that do the job as well or better. It is in this area that combinations of such materials enable a more precise control of how fast and where excessive heat is directed away from critical areas.