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Although there have been a number of advances in metal composite materials, much excitement has been focused on the application of microwave sintering of “green bodies” associated with powder metal technology. These microwave-processed (MWP) metals are stronger and their potential applications are still being explored.
Microwave-processed (MWP) materials
Powder metal technology is not new, but the sintering, or densifying, of the green body through microwave heating is a novel concept made possible only recently. The microwave energy heats relatively quickly and evenly from within the green body. This allows a process time that is a fraction of that for conventional sintering (hours vs. days). In addition, as noted in Fig. 1, the finished product is typically 30% stronger with improved impact resistance and corrosion resistance. Fig. 1 also shows that MWP is applicable to a number of materials, notably:
- Tungsten carbide
- Diamond composite
A research program is under way at Pennsylvania State U. (with its commercialization partner, Dennis Tool Co.) to investigate the potential use of MWP for the manufacture of ceramics and hard transparent polycrystalline materials. The latter involves a Defense Advanced Research Agency-funded project to investigate the potential for using MWP to manufacture “transparent armor.” If successful, such materials could find their way into hardened subsystems for measurement while drilling (MWD).
It should be noted that the ability to form diamond composite with tungsten carbide was a significant leap forward in materials development. In conventional processing/sintering, the diamond composite is turned to graphite, because of the high temperatures required for sintering the tungsten carbide and the long heating and cooling times required. With microwave processing, the entire sintering process can be accomplished before the diamond composite is affected. In addition, the boundary between the diamond composite and tungsten carbide is not well defined, because of a diffusion bonding process. This process is being investigated for its potential to make “functionally graded” materials. Such materials would allow entire bits and/or cutter assemblies to be manufactured in a single process in which diamond composite is bonded to tungsten carbide that is bonded to drill steel. It might even be possible to form thread into the green body before sintering to eliminate machining.
MWP for coiled tubing
An extension of this technology has been in the investigation of the potential for MWP to be applied to the manufacture of coiled tubing. If use of MWP technology results in a tubular that is 30% stronger, and retains the same ductile character of competing steels used for coiled tubing, another leap in coiled-tubing drilling capability will be a reality. This should be known within the next 3 years.
In a related development, the above-mentioned “supermaterials” will allow even more aggressive cutting structures and drilling machines. One such drilling tool is already being evaluated by Dennis Tool Co. It is a drilling motor that uses high-speed milling concepts to abrade rock. A pilot bit is rotated counter to the direction of three high-speed cones that follow the bit and open the hole to the required diameter. The result of this action is zero torque transferred to the drillstring, a significant benefit to coiled-tubing operations. The drill appears to be capable of drilling on the order of 80 ft/hr in almost any type of rock. A final commercial version of this high-potential drilling machine could depend on proper application of the new supermaterials.