When moving parts of a machine are subject to friction, more energy is required to move them, the machine does not operate as efficiently, and the parts have a tendency to wear over time.
But if parts could be manufactured with tough, 'slippery' surfaces, there would be less friction, requiring less input energy and the parts would last longer.
Researchers at the USA Department of Energy's (DOE) Ames Laboratory are collaborating with other research laboratories, universities, and industrial partners to develop just such a coating.
Bruce Cook, an Ames Laboratory scientist and co-principal investigator on the four-year, $3million project, says: "If you consider a pump, like a water pump or a hydraulic pump, it has a turbine that moves the fluid. When the rotor spins, there is friction generated at the contacting surface between the vanes and the housing, or stator. This friction translates into additional torque needed to operate the pump, particularly at start-up. In addition, the friction results in a degradation of the surfaces, which reduces efficiency and the life of the pump. It takes extra energy to get the pump started, and you cannot run it at its optimum (higher speed) efficiency because it would wear out more quickly."
Applying a coating to the blades to reduce friction and increase wear resistance could have a significant effect in boosting the efficiency of pumps, which are used in numerous industrial and commercial applications. According to Cook, government calculations show that a modest increase in pump efficiency resulting from use of these nanocoatings could reduce USA industrial energy usage by 31 trillion BTUs annually by 2030, equivalent to savings of $179million a year.
The coating Cook is investigating is a boron-aluminium-magnesium ceramic alloy he discovered with fellow Ames Laboratory researcher and Iowa State University professor of Materials Science and Engineering Alan Russell about eight years ago. Nicknamed BAM, the material exhibited exceptional hardness, and the research has expanded to include titanium-diboride alloys as well.
In many applications it is far more cost-effective to apply the wear-resistant materials as a coating than to manufacture an entire part out of the ceramic. Fortunately the BAM material is amenable to application as a hard, wear-resistant coating. Working with ISU materials scientist Alan Constant, the team is using a technique called pulsed laser deposition to deposit a thin layer of the alloy on hydraulic pump vanes and tungsten carbide cutting tools. Cook is working with Eaton Corporation, a leading manufacturer of fluid power equipment, using another, more commercial-scale technique known as magnetron sputtering to lay down a wear-resistant coating.
Pumps are not the only applications for the boride nanocoatings. The group is also working with Greenleaf Corporation, a leading industrial cutting tool maker, to put a long-lasting coating on cutting tools. If a tool cuts with reduced friction, less applied force is needed, which directly translates to a reduction in the energy required for the machining operation.
To test the coatings, the project team includes Peter J Blau and Jun Qu at one of the USA's leading friction and wear research facilities at DOE's Oak Ridge National Laboratory, or ORNL, in Tennessee. Initial tests show a decrease in friction relative to an uncoated surface of at least an order of magnitude with the AlMgB14-based coating. In preliminary tests, the coating also appears to outperform other coatings such as diamond-like carbon and TiB2.
The photograph shows an AlMgB14 coating on a steel substrate. The substrate is the mottled region on the left-hand side of the photo and the coating is the thin (2-3micron), darker strip running along the edge of the steel.
For more information, visit www.external.ameslab.gov
