TechArchive

This article was originally written in the period 1995-2000

Researchers have been entranced by diamond for decades. It has all the features of a perfect material: harder than any other known substance, essentially transparent, highly ordered crystallinity, intriguing electrical properties. Until the 1950s, only naturally obtained diamonds could be studied – diamond seemed to be beyond human fabrication. This changed dramatically in the middle of that decade, when researchers developed a high-pressure, high temperature (HPHT) method to fabricate diamond from graphite.

Diamond offers a tantalising set of properties for a wide variety of applications. Its hardness is 5700 to 19,400 kg/mm2 (Knoop hardness), some three to five times that of commercial carbides. Its thermal conductivity is 20 W/cm.K, four times that of beryllium oxide. Its coefficient of friction is on a par with Teflon fluoropolymer. Unlike silicon and other common semiconductors, it has a negative electron affinity, enabling its use as a display medium operating efficiently and with superb light control.

Diamond undertook another dramatic swing in the mid-1980s, when, ironically, diamond fabrication methods that had been tried and abandoned in the mid-1950s were re-evaluated. The benefit of years of semiconductor research and manufacturing, along with some insightful research breakthroughs in the former Soviet Union and in Japan resulted in a new type of diamond: diamond film. Suddenly, it seemed as if any common material – metal, ceramic, glass, even plastic – could be effortlessly coated with a layer that retained all the properties of this most perfect crystal. Moreover, the equipment needed to produce diamond films were rather simple, the raw materials relatively cheap, and significant work could be performed on a tabletop. A near-stampede of companies and research programs was undertaken, reaching some 500 companies and consuming $100 million at its peak, according to some sources.

In the intervening 10 years, a perhaps predictable reassessment has set in. The most commonly used method of producing diamond film, chemical vapour deposition, needs relatively high temperatures (about 1000degC), takes hours to produce measurable amounts of film, and wastes both energy and raw materials. Nagging problems of producing ordered crystal layers over more than a small area appeared. And while diamond is hard, it is not touch (resistant to shock). Diamond layers on cutting tools broke off, and in some cases, literally bounced off as the layer thickened during growth and internal stresses built up.

The vision of effortless production, as insignificant cost, has vanished, but much remains. A handful of the companies started during the stampede have survived, and have identified opportunities that may enable them to prosper. Enhancements to the basic diamond deposition process, including plasmas, electric fields, radio frequency and microwave energy, and new reactive chemistry, ranging from halogens to fullerenes, have appeared.

Along the way, an equally exciting field has arisen: diamond-like coatings (DLCs). DLCs are usually based on the same carbon chemistry used to produce diamond films, but can be processed at lower energy levels and at a more affordable cost. DLCs do not equal diamond in overall properties, but numerous applications have been found where they exceed conventional coating chemistry by a significant margin.

All this is occurring in a context of rapidly expanding technical expertise in surface treatments. Researchers have been taking fairly standard technology, such as thermal spraying and ion implantation, and ramping up their properties to new levels. Existing refractory compounds, such as carbides and nitrides, are being produced in new forms such as cubic boron nitride and carbon nitride. Hard metals – tungsten and titanium carbide, cobalt-chrome, among others – are being processed in new ways. Materials scientists have a growing range of material selections to solve difficult problems in wear, chemical resistance and protection from atmospheric damage.

Moreover, a number of truly revolutionary changes may evolve out of the current diamond and DLC research. Although beyond the scope of this report, there is significant progress in the development of diamond as a semiconductor component, which could lead to new levels of high-speed computing. Diamond films may be the key to the hotly pursued field of ‘cold’ cathodes, which can be used to produce flat-panel displays for digital video and computer screens. These applications could be worth tens of billions of dollars in the first decade of the next century. Should such a bonanza be attained, intense R&D will be devoted to the technology of diamond film production, which in turn could overcome all the current limitations of this material.

The current scene

Initial estimate of the diamond market made in the late 1980s were for a $2-billion scale, with growth rates rising rapidly through the remainder of this decade. Technical Insights estimates that the current world-wide market is a much more modest $150 million, with a slower growth rate that should double it by the end of the century. If funds being spent on contract R&D (coming from government support, private investment and internal investment) are added in, the total rises by about $50 to 100 million, to a total of $200 million to $250 million. (The indeterminacy is present because it is hard to distinguish many types of research as to their relevance to diamonds and other supertough coatings.)

On the one hand, this estimate can be viewed with some cynicism, as another example of a high-tech gold mine that didn’t pan out. On the other, it can be verified that diamond file (including DLCs) technology has emphatically crossed the line from research to commercial products. It has even entered the consumer market, which usually offers much greater revenue volume than the industrial market. Moreover, for the most part it is not dependent, as are many other high-tech materials, on military spending. (Exceptions are noted below.)

This $200 to 250 million should be put in the context of broader markets for diamonds and thermal-spray surface treatments. The current world-wide market for synthetic HPHT diamond is about $1 billion. And the current surface treatment market is about the same, including both materials and equipment and the value of treatment services by job shops.

Existing commercial applications

The biggest successes for diamond technology are cutting tools, high-performance optical windows and heat spreaders for microelectronics. For cutting tools and inserts for machine tools and other cutting equipment, Crystallume, Norton Diamond Films, General Electric and several Japanese firms all have commercial production going on. Optical windows for infrared or X-ray instruments are another successful application; these are used both in laboratory settings and as components for aerospace equipment, where the delicate nature of conventional window materials demands some type of tough surface treatment.

Heat sinks or heat-spreading components are important on certain types of high-power microelectronics, where the excellent thermal conductivity and electrical insulating properties allow for higher performance. Crystallume, for example, has recently acquired an electronics packaging company with an eye toward speeding its technology into the commercial realm.

DLCs have won commercial status as a coating for consumer eyewear, and as optical windows for, among other applications, laser barcode readers. These can be characterised as low-performance optical coatings (as distinguished from the diamond films mentioned above), or as wear-resistant coatings. Other successful wear-resistant coatings are being used on computer hard disks, read/write heads for videocassette recorders, audio recorders and disk drives. A key performance limitation of DLCs is that they are generally susceptible to oxidation and graphitization above 300oC. A number of composite DLCs, containing silicon or other components, are under development that may extend this range.

Thermal spraying, which has been in commercial use for at least two decades, continues to see steady improvement in capabilities. The newest technologies, high velocity oxyfuel (HVPF) spraying, which uses a combustion flame in combination with powdered metals or ceramics, and detonation bonding, which uses an explosive propulsion through a long nozzle, are winning new applications in machining and process applications.

Ion implantation, another long-standing commercial product, finds several new areas of application in the current surface treatment scene. ‘Ion assisted beam deposition’ is being used, by Diamonex among others, to build up DLC coatings and in some diamond film work. The traditional limitation of ion implantation as a line-of-sight process unsuitable for complex shapes is being challenged by plasma ion-source implantation, which uses a cloud of plasma that is attracted by a voltage bias to the workpiece, rather than by the momentum of a beam impinging a surface.

Future applications

The most prominent application which has yet to be reduced to commercial practice is the use of diamond files as a ‘cold’ cathode for digital display screens. As envisioned by numerous researchers, diamond film could enable the commercialisation of flat-panel displays that are cost-competitive with the bulky, short-lived cathode-ray tube display. This market (using liquid crystal displays and active matrix designs) is already worth some $5 billion, and could easily jump to $10 billion or more early in the 21st century. The entire structure of the nascent diamond film industry could change radically if this technology comes to fruition.

You can expect diamond film and DLCs to drop in price as more industrial experience is gained. The market for wear-resistant coatings could expand greatly at lower prices, to include such areas as seals and gaskets, chemical-resistant vessels, heat-exchange equipment and scratch-resistant, touch architectural glass. Medical implants, optical applications and low-friction bearings could also be near-term applications.

Key players

The leading US firms in diamond technology are Advanced Technology Materials, Crystallume, Diamonex, a division of Monsanto Co., General Electric Co., Kennametal, Norton Diamond Films, a division of Compagnie de Saint-Gobain, and SI Diamond Technology. Advanced Technology Materials, Crystallume, Diamonex and SI Diamond were started in the 1980s to commercialise diamond technology. Norton, General Electric and Kennametal are major corporations. Likewise in Japan, major conglomerates such as Sumitomo, Mitsubishi, Idemitsu Petrochemical are key players.

Major US research centres are at Los Alamos National Laboratory, the Jet Propulsion Laboratory, Argonne National Laboratory, the Basic Industrial Research Laboratory at North-western University, Rice University, and Pennsylvania State University. AEA Technology in the United Kingdom is a leading European centre, as are the Max Planck Institutes in Germany.

More information: Supertough Coatings. expanding the Performance of Conventional Materials. A report published byTechnical Insights Inc. Contact Peter Savage on +1 201 568 4744