- 06 December 2005 -
Nanotechnology is on the Verge of Revolutionizing Surface Finishing

Nanotechnology--the manipulation and control of materials on an extremely small scale (a human hair is steel-cable-thick by nanotechnology standards)--offers so many benefits to the metal-finishing industry that its growing number of enthusiastic proponents predict nothing short of a revolution of plating and finishing technology.

Nano-coatings have already been applied to a diverse but specialized array of objects, from parts for nuclear steam generators and barrels of field artillery to expensive golf clubs.

Experts say the exciting thing for the metal finishing industry, which grew from the experiments of ancient and medieval alchemists, is that nanotechnology represents something completely new. Indeed, the first application of an electrodeposited nano-coating occurred in 1994, yet already there are nano-coated golf clubs. Air Canada recently announced it will experiment next year with a commercial jet stripped entirely of its traditional paint job. The weight reduction will be about 350 pounds and the resultant savings in fuel could total more than $25,000 per year, but protected with a nano-coating. Other such cost-saving experiments and applications are expected to follow.

Some surface finishers expect to see such coatings applied on more common items once costs come down. “I think nanotechnology is going to be widespread fairly soon,” comments Danielle Miousse, a plating process specialist with Heroux Devtek in Montreal who works in the company’s Landing Gear Division. “This is a long-term technology for the industry, though not that many companies are using it yet. But it’s very interesting in many ways.” Miousse also serves as president of the local American Electroplaters and Surface Finishers (AESF) branch.

In essence, nanotechnology has the ability to bring order to chaos. Under a microscope, even the smoothest crystalline coatings--such as polished chrome--show irregular gaps between the crystals. Over time, this causes these materials to weaken, crack and creep, especially when the structure is under stress. In general, experts say these gaps can be controlled in one of two ways: by reordering the gaps into a uniform pattern, or by reducing crystal size.

The weaknesses caused by the gaps aren’t a big problem for, say, chrome automobile bumpers. Automotive chrome coatings usually outlast the life of a typically driven car. But in applications where both strength and weight are of paramount importance, crystalline and molecular weakness can become troubling issues, industry members note.

The irregular gaps can be exploited and made worse by outside forces such as water, temperature, and ultra-violet light from the sun. Air pressure, weight, and g-forces will also stress coatings and can lead to metal failure, observers say. This can have disastrous effects in certain specialty applications, such as aircraft landing gear.

Miousse’s division at Heroux Devtek uses nanotechnology to plate and coat landing gear for Canada’s fighter jets and other aircraft, greatly improving the strength of these structures which come under extreme stress during take-offs and landings. Nanotechnology in metal plating and coating can also reduce friction on the striking surfaces of golf clubs, thus creating a larger “sweet spot” and reducing club weight. For example, PowerMetal Technologies ( Carlsbad, Calif.) offers high-end nano-coated woods and drivers; the super-thin face coatings on these clubs help move some of the weight to the meatier portion of the club, encouraging longer, more accurate shots. Some of PowerMetal’s coated clubs are being used on the PGA tour, and the firm said it is also working on nano-coated baseball bats, skis, and super-lightweight high-performance bicycle components.

Moreover, nanotechnology offers an effective way to address environmental issues, industry watchers say. Nano cobalt-phosphorus, for instance, is compatible with most existing electroplating equipment and positioned as an effective replacement for hexavalent chromium. Nan crystalline material is considered stronger and longer-lasting than hex chrome. Electroplated nano-aluminum coatings offer potential as a cadmium replacement and are environmentally safe.

To be sure, nano-coatings have not been cheap to apply to date, and the expertise required to develop and use the technology is highly specialized and therefore expensive. However, costs are coming down; PowerMetal claims to have significantly reduced the processing expenses of nano-coating golf clubs and other sporting equipment, bringing these items into a relatively affordable range. In addition, where cost is secondary to certain other factors, such as strength and safety, nano-coating technology is growing from a niche into a category for the metal finishing industry.

Francisco “Paco” Gonzalez, vice president of process and product development at Integran Technologies (Toronto), reports that nanotechnology is used by platers and finishers of mechanical optical and analytical equipment, biomaterials and drug packaging, electronics and computer-chip manufacture, and in automotive applications such as antireflection coatings, in addition to the applications mentioned earlier. Integran uses two approaches to manipulate grain boundaries in various materials.

According to the company, the “top down” approach, which Integran trademarked under the name Grain Boundary Engineering (GBE), is just as it seems: it works down from the surface into the inside of a material. The “bottom up” approach, called Nanoplate at Integran, improves coating strength through electroplating.

The approaches were developed with the help of Uwe Erb, a professor in the Department of Materials Science and Engineering at the University of Toronto who specializes in nanomaterials. The GBE process is designed to control disorderly gaps between the crystals in crystalline materials. The Nanoplate process reduces grain size to create a larger overall grain surface area. According to Erb’s research, in conventional plating, unavoidable impurities in metal alloys spread throughout a coating, migrating naturally to grain boundaries and precipitating there, causing weaknesses that stress and other factors can exploit.

By comparison, nano-coatings the size of the grains is much, much smaller, and their number is increased exponentially. The result is impurities are super-diffused, which is called “homogenization by segregation.” Such a coating is said to be stronger and more resistant to stress and corrosion cracking. So when a fighter pilot touches down on the wet landing surface of an aircraft carrier rocking in heavy seas, nano-coating technology can mean the difference between success and failure—or life and death, in other words.

Integran’s GBE process can be applied to bulk metals but also as a surface treatment to pre-finished and semi-finished metals. Erb refers to a “heating and beating” system; a finished or semi-finished surface is exposed to shot-peening (“beating”), then induction-heated to create a kind of coating from the substrate layers of the original surface. Research has shown that as much as 70% of this “coating” is orderly grain-boundary material, or an ideal nano-coating. For pre- and semi-finished metals, weldability, corrosion resistance, sulfidation resistance, fatigue resistance, and resistance to high-temperature creep are all improved. Tests on Allow 800, which is particularly vulnerable to intergranular corrosion, Erb says, show a corrosion reduction rate from 2.2 to 0.22 mm per year.

The Nanoplate process uses electrodeposition, and is, Gonzalez says, a low-cost repeatable process for producing nano-crystalline metals and alloys. Other plating methods, including vapor deposition and chemical synthesis, can produce very small grains in a coating. But Integran claims the Nanoplate process is applicable to a wider range of work pieces, including strips, plates, wires, and rods, than either the vapor or chemical processes.

Nanoplate will also coat items with complex shapes, including micro components for electronic equipment, the company says. Batch and continuous processing are possible.

Indeed, in any application where strength, durability and long-term cost are of concern, she points out, nanotechnology has an application. “We who are already using it, so obviously we see the benefits of nanotechnology,” says Heroux Devtek’s Miousse. “It’s only a matter of time before these benefits are widely understood throughout the industry.”—Steve Bjerklie