Manufactured diamonds have been commercially available for more than 50 years, but were not used extensively by diamond blade manufacturers until about the mid-1970s. The main reasons was suppliers of natural (mined) diamonds convinced manufacturers for many years that their natural material was better, and simply because manufactured diamonds were more expensive.
From a technical viewpoint, it was easy to see that the manufactured variety may prove to be better than the natural alternative, because the former were block-shaped, single crystals with far fewer internal flaws than the natural type. However, this remained undemonstrated on a large scale until the mid-1970s when, due to political upheaval in Africa, natural diamonds were in short supply and their price skyrocketed. Now, manufactured diamonds were not only less expensive, but were almost the only type of diamonds.
Diamond blade manufacturers launched fast-track development projects to learn how to use the manufactured variety in their saw blade segments. These projects required changes to process parameters to minimize exposure of the diamonds to high temperatures and, in some cases, changes in metal bond chemistry. Overall, manufacturers found the conversion was easier than expected. Once the changes were made, results were astonishing. Suddenly, hard materials were easier to cut, cutting rates went up, and blade life improved in many cases.
Today, manufactured diamonds are used almost exclusively in metal-bond diamond saw blades. It is well-known that man manufactures diamonds in a similar way as Mother Nature: by subjecting carbon to high temperatures and ultra-high pressures. At the temperatures and pressures used, the carbon atoms are squeezed so closely together that new atomic bonding occurs and the atoms are locked into the diamond crystal structure. The transformation from carbon to diamond occurs within a molten metal matrix of either cobalt or iron-nickel alloy.
The product recovered from the press is an odd-shaped nugget of metal with diamond particles protruding all over. The metal is then leached away with acids and the diamond particles are recovered and sorted by size, shape, and purity. Particle toughness is directly related to purity—the higher the purity, the higher the toughness.
Diamonds manufactured by the cobalt matrix method generally have inclusions called dendrites, which resemble tree branches. These inclusions have an effect on crystal friability or resistance to fracture. Friability is determined by subjecting the crystals to a crushing action using standard loads for standard time periods, then measuring the weight loss. Diamonds manufactured by the iron-nickel matrix method also have inclusions, but usually not the dendritic variety. However, these inclusions also affect friability of the diamond.
Over the years, diamond makers have been working on ways to increase the yield of high-purity particles in every batch of diamonds produced, with relative success. This has given diamond blade manufacturers another direction to take when the need to alter blade performance arises.
Another important development in manufactured diamond technology is the recent progress being made in coated diamonds. Using coated diamonds improves diamond retention in the metal bonds so that diamonds are not lost before they can be fully used.
In the past, single layer coatings on diamonds were not effective due to incompatibility with either the diamond particles or the metal bond. The newer coatings now available are multi-layered, having one material in contact with the diamond particles and another material in contact with the metal bond. These new coatings are being used successfully in many applications.
Today's synthetic diamonds are harder, stronger, and less expensive than those produced 50 years ago. They are designed more for cutting concrete, including increased blade life and more aggressive cutting techniques. Synthetic diamonds are more than capable of standing up to the growing needs of the concrete sawing and drilling industry.
Robert Hodson is the research director of Sanders Saws Inc., a division of Multiquip. Reprinted courtesy of the Concrete Sawing & Drilling Association, Concrete Openings magazine, March 2009.