Super Hard Steel forms a tough, low cost, wear and corrosion resistant coating that outperforms traditional high-performance coatings. Developed at the Department of Energy's Idaho National Engineering and Environmental Laboratory, this coating offers a wealth of possibilities for new industrial applications.
One of the hardest metallic materials known, Super Hard Steel has been recognized as one of the 100 most significant technological achievements for the year 2001 by R&D Magazine. Super Hard Steel can be sprayed onto a wide variety of metal surfaces using conventionally available thermal spray technologies, and surpasses the existing commercial coatings in wear, corrosion and impact resistance.
Researchers create the Super Hard Steel coating by transforming steel alloy into a non-crystalline metallic glass. "We essentially coach mother nature to frustrate the atoms in the alloy, and capture a snapshot in time when the atoms have a liquid structure in order to form a very hard and strong solid," said INEEL materials scientist Daniel Branagan. Because metallic glass has an extremely low density of defects such as tiny cracks or holes, Super Hard Steel responds differently to external stresses such as physical loads than metals with a high density of defects. This property of metallic glass makes the material both hard and tough-perfect for use as a impact resistant coating.
Alternatively, for specific applications researchers can heat the coating to create a stable structure made up of crystal grains from 2 to 75 nanometers in size, only slightly larger than a single atom. "This approach is a much more robust route to forming nanoscale crystalline structure when compared with other approaches that try to maintain the nanoscale features during the production process," said Branagan.
Once sprayed on, the Super Hard Steel coating cannot be removed-even with a hammer and chisel. Because the material is sprayed on under high-pressure conditions, the material remains in a compressed state even after it cools, which makes it stronger. The coating was tested using high velocity (170 mph), high intensity grit blasting for four times longer than the normal testing standard, and showed no evidence of cracking or wear.
Super Hard Steel has hardness properties among the highest ever reported for any metallic structure or alloy-up to 16 giga Pascals. In comparison to existing high performance coatings, Super Hard Steel is significantly harder than electrolytic hard chrome and approaches the best tungsten carbide. In an independent, standard abrasion test, Super Hard Steel actually wore down the hardest commercially available pin material, silicon nitride, which is used to develop wear scars on hard coatings. The extreme hardness of Super Hard Steel in conjunction with its metallic bonds gives the material abrasion wear resistance properties that Branagan believes will significantly improve the lifetime of coated machine parts. The unlubricated material also exhibits a low coefficient of friction in the range of lubricated steel, another property that can be exploited for a range of applications.
The properties of Branagan's metal coatings are such an improvement over current products and technologies, that he has had a hard time convincing people to believe what they're seeing. "Industry just doesn't believe our data at first," he said. In one instance, a skeptical company president handed a coated sample to a technician for testing while Branagan was giving his presentation. "I was a little nervous," Branagan said, "but I just kept going with my presentation." Not long later the technician returned and reported that the sample had survived the testing completely unscathed. "The room went silent," he said. "Then I really had their attention."
Developed during several years of research funded by both INEEL discretionary research funding and the Defense Advanced Research Projects Agency, this technology has the potential for tremendous impact to the manufacturing industry. "I'm proud of the award-winning work done at the department's Idaho National Engineering and Environmental Laboratory. This accomplishment demonstrates the value of government-funded research to the Nation," Energy Secretary Spencer Abraham said.
Branagan sees the possibilities for coatings like his to be nearly endless because all areas of industry experience wear and corrosion problems. The product is also extremely affordable because it is only a steel which has exotic structures. It costs only a fraction of what hard ceramics such as tungsten carbide. He feels that the biggest cost savings will occur over the lifetime of a coated part since the machine will simply last much longer, and require significantly less maintenance. From the beginning, Branagan's goal was to develop a coating that would have real-world applicability. "We purposely used off-the shelf technology to apply the coatings with the idea of increasing the ease of getting this technology out to industry," Branagan said.
Over the next year, Branagan will work with a range of industrial partners to conduct proof-of-concept tests, putting his coating through extensive erosion, corrosion, and fatigue testing. More than 15 companies are reviewing Super Hard Steel for licensing or testing, in such applications as varied as self-sharpening knives and mining rock crushers. Additionally, the technology will soon be applied to key military devices for extensive testing in tough applications with challenging environments.
Super Hard Steel represents one of the first fruits from of the emerging field of nanoscale science. "What really spawned the development of this technology was the development of a new material in combination with sustained advances in the science of thermal spray," Branagan said. "It's interesting to see how development in one area of research spawns advancements in another."
The research team includes INEEL materials scientists Daniel Branagan, Elizabeth Taylor and Joseph Burch, and thermal spray researchers James Fincke, David Swank and DeLon C. Haggard. Also included is former INEEL laboratory director Bart Krawetz, now retired from Lockheed Martin Missile and Space Systems.
R&D Magazine has sponsored the international R&D 100 Awards program since 1963. This is the 27th such award for the INEEL and the second for Branagan and Fincke, who won awards in 1999 and 1997 respectively. The research team from the Department of Energy's Idaho National Engineering and Environmental Laboratory will receive its award at the Museum of Science and Industry in Chicago in October 2001