Vol. 53, No. 8        April 20, 2001

Industry warms to Cold Spray™ • Extreme Ultraviolet lithography celebration • ALEGRA software code released

Industry warms up to promises of Cold Spray™

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By John German

Sandia is studying the science of splat.

Working with a consortium of eight US companies that includes automakers and aircraft engine manufacturers, researchers at Sandia's Thermal Spray Research Laboratory are using experimental and computer-modeling capabilities to improve the world's fundamental scientific understanding of an emerging

manufacturing technique called Cold Spray™ (Lab News, Jan. 26, 2001).

Cold Spray involves injecting microscopic powdered particles of metal or other solids into a supersonic jet of rapidly expanding gas and shooting them at a target surface. When these 10- to 50-micron-wide particles hit the substrate, they splat so hard they stick -- like a bug to a windshield.

Building a reputation

Consortium members want to use new Cold Spray processes refined at Sandia to create wear-resistant coatings on car- or aircraft-engine components, for instance, or to deposit layers of reactive metals such as aluminum or copper onto substrates for use as heat-tolerant circuits.

The Sandians ultimately want to employ successfully commercialized Cold Spray processes, which originated, ironically, at a Soviet-era research lab in Siberia, to improve US nuclear weapons components. (See "The promise of Cold Spray processes" below right.)

"Cold Spray has some significant advantages as a coating and fabrication tool," says Mark Smith, Manager of Joining and Coating Dept. 1833. "We think the best way to legitimize Cold Spray for use in the nuclear weapons program is to have its use proven in US industry, and to support the development of a commercial supplier base."

Members of the consortium -- Alcoa, DaimlerChrysler, Ford Motor Co., The Jacobs Chuck Manufacturing Co., Ktech Corp., Pratt & Whitney, Praxair, and Siemens/Westinghouse -- met at Sandia recently to discuss progress they've made toward readying the Cold Spray processes for widespread commercial use.

Cold Spray 101

Cold Spray more appropriately might be called "room-temperature spray."

Conventional "thermal spray" processes require preheating the sprayed materials so the particles are in a semi-molten state when they reach the substrate, allowing them to splash across the surface. But as the "splats" cool, they contract slightly, creating residual (stored) stresses or flaws at the interface that can cause defects later.

Cold-sprayed materials typically remain at or near room temperature until impact, slamming into the substrate so hard (travelling at 500 to 1,500 meters per second) that a tight bond is formed without the undesirable chemistry changes and stresses associated with conventional processes.

Although the science behind this bonding process is not yet well understood, the researchers think the high-velocity impact disrupts thin metal-oxide films on the particle and substrate surfaces, pressing their atomic structures into intimate contact with one another under momentarily high interfacial pressures and temperatures.

Understanding splat

Unlike thermal-sprayed materials, cold-sprayed particles experience little to no defect-causing oxidation during flight and exhibit remarkably high densities and conductivities once fabricated, the researchers have found. In addition, deposition rates comparable to traditional thermal spray processes can be achieved with Cold Spray.

"This is the logical conclusion of research thrusts in thermal spray technology during the last two decades toward faster-and-faster and cooler-and-cooler methods," says Richard Neiser (1833).

To advance the state of fundamental understanding and improve the usefulness of Cold Spray, the Sandians are combining modeling expertise in Engineering Sciences Center 9100 with experimentation in Materials and Process Sciences Center 1800.

The team has examined gas dynamics, aerosol physics, and plastic deformation during splat-to-substrate impact. Current efforts focus on avoiding fouling of nozzles with powder residue; experimenting with varying materials, particle sizes, and impact velocities; and characterizing splat patterns and Cold Spray-fabricated bulk materials.

The researchers also want to design better aerodynamic lenses that focus or spread out the spray pattern like a thumb held over the end of a garden hose.

A variety of metals have been deposited, including copper and aluminum, as well as several types of steel and nickel-based alloys. Even a few metal-ceramic composites have been successfully cold sprayed.

Revolutionary changes

The Cold Spray consortium supplies $400,000 a year for three years toward Sandia's R&D efforts, plus in-kind contributions by each member. Sandia also is collaborating with several individual member companies on proprietary Cold Spray R and D.

Cold Spray technology came to the US in 1994, ten years after its Russian inventors first recognized its potential significance while conducting high-velocity wind tunnel tests at the Institute of Theoretical and Applied Mechanics of the Russian Academy of Sciences in Novosibirsk.

One of its discoverers, Prof. Anatolii Papyrin, who holds the US patent for Cold Spray, now works for Ktech in Albuquerque, which hopes to supply fabrication equipment to a broadened Cold Spray market.

Sandia is among just a few R&D institutions in the world successfully turning improved understanding of Cold Spray science into marketable technology, says Mark.

"We think Cold Spray provides capabilities not previously possible," he says. "It's a new enough technology that we don't yet know all the possible applications, but it has the potential to make truly revolutionary changes in the way some products are manufactured."

-- John German

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Extreme excitement: Celebration marks EUVL microchip milestone

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By Nancy Garcia

"It seems that EUV is winning out," Craig Barrett, president and CEO of Intel Corp., observed at a big celebration event at Sandia's California site last week.

EUV, extreme ultraviolet lithography, is being developed through an industry-funded consortium by Sandia, Lawrence Livermore, and Lawrence Berkeley national laboratories as a way to create ever-finer features on microchips. (See April 6 Lab News for a four-page retrospective on the entire research project and partnership.)

When it was first made feasible in the 1990s, Barrett said at the April 11 event held in the Combustion Research Facility auditorium, EUV lithography "was perhaps one of the dark horses" among competing potential approaches under consideration for next-generation chip-making lithography. Now, he said, "it has become more the leading horse in the race."

A new approach is needed because the current chip-printing technique, traditional optical lithography, is hitting a physical limit around 2005 and won't be able to continue increasing functionality by doubling the number of transistors that can be etched on a sliver of silicon every 18 months or so -- a pace the semiconductor industry has enjoyed since the 1960s.

In the last four years, an industry consortium that is funding research at the three labs has grown to six members, and now includes Intel, AMD, Motorola, Micron Technology, Infineon, and IBM.

Huge step, leading choice

Sunlin Chou, an Intel senior vice president and manager of technology and manufacturing -- who heads the industrial consortium, the EUV Limited Liability Company -- called EUV lithography a promising "huge step" that won't require the ordinary, slow, and expensive development of new materials for each successive generation of microchip manufacture.

Instead, he said, EUV would allow "many, many" generations of microchip manufacture. He considers it the leading choice for use in the second half of this decade and beyond, saying it will meet industry needs for more than a decade. In a process similar to photographic printing, it uses a wavelength an order of magnitude smaller than those in use today to inscribe features that could be as small as 20-25 nanometers. This breakthrough required many developments to achieve, so the light, invisible to the eye, could be used to create smaller and faster circuits for memory chips, microprocessors, and application-specific integrated circuits.

'Wonderful, heart-warming'

Barrett lauded the cooperation that has made the pre-competitive collaboration possible, calling it "wonderful, heart-warming, and just phenomenal." He said consortium members will ultimately use the new technology to go on to "beat each other over the head in the marketplace -- which is as it should be."

Representatives of semiconductor equipment manufacturers attended. They will use the tool assembled at Sandia to craft their commercial products for industry. "We look forward to getting one of these machines on the production floor in a couple of years," Barrett said.

The initial prototype, called the Engineering Test Stand, is not just a gleaming and complicated research tool occupying a 10x10-foot floor space, Chou said. It also represents "a history-making achievement."

Representing the three Department of Energy labs, which joined efforts in the partnership in a Virtual National Laboratory, John Gordon, Director of the Nuclear National Security Administration, said the tool's ability to print features that may one day measure as small as 20 to 40 atoms across "probably wasn't even a dream for today's pioneers in the industry."

At $250 million from 1997-2002, this largest industry-funded CRADA ever undertaken by the DOE, he said, "really is a partnership that works in every direction." The challenge has kept researchers on the cutting edge of their fields as they apply their expertise -- gained in national security projects -- to this problem. He said their efforts advance a strategic industry considered critical to the United States and demonstrate that a public-private partnership "can really work."

'We've done it'

Hosting the speakers, 8000 VP Mim John acknowledged the staff who are pushing the envelope of technology to its practical, theoretical limit for microchip patterning. Like the speakers who followed, she remarked on the foresight of the partners who supported the effort despite what Chou called "really intimidating risks."

"People four years ago said you can't do this," Mim said, "and by God, we've done it."

Chou pointed out that members of his company have worked on smaller collaborations with the DOE labs for "many, many years," and were always impressed. "It sometimes seemed literally magical -- things that it seemed couldn't be done were done."

In her remarks as the only member of Congress with two national labs in her district, Ellen Tauscher (D-Calif.), savored her role "representing the smartest people in the world."

"We like people who are smart," she said, "and we believe in the state of the art." She praised the relatively new National Nuclear Security Administration for helping remove Defense Program laboratories "from the bureaucratic kudzu," saying she was proud to show the business community that government can be "smaller, smarter, and leaner -- but not meaner."

Tauscher closed by predicting the partnership will create quality jobs, urging her listeners, "Let's get back to work." -- Nancy Garcia

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Sandia releases latest version of ALEGRA this month

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By Chris Burroughs

The latest version of ALEGRA, a computer code used by departments Labs-wide to model Z-machine implosions and hostile nuclear weapons environments, was released earlier this month.

"This release is significant because the new version turns ALEGRA into a true code framework," says Dan Carroll (9231), ALEGRA team leader. "It now can be much more easily used for a wider array of applications."

Besides departments at Sandia, some Department of Defense customers also employ ALEGRA to model non-nuclear weapons effects.

ALEGRA (the name stands for Arbitrary Lagrangian Eulerian General Research Application) is one of two code frameworks being developed by DOE's Accelerated Strategic Computing Initiative (ASCI) program. The idea behind these frameworks is to develop certain common capabilities needed by many application codes only once and let the other codes use these capabilities.

Dan says that ALEGRA has been "morphing" into a framework over the last year.

"Since ALEGRA was already a successful finite element code supporting many key application areas, the decision was made to move ALEGRA in the direction of becoming a framework to better support the codes in these application areas."

The culmination of this effort is the recent release of Version 4.0.

Sandia researchers initially developed ALEGRA in 1991 as a shock wave physics code used to model high-speed impact and penetration

phenomena involving a variety of materials. As computer hardware evolved, the code was rewritten to accommodate the newly developing massively parallel computational engines, like Sandia's Teraflop computer, ASCI Red.

In 1995 ALEGRA was expanded to model electromechanical properties -- piezoelectric materials -- giving researchers a new tool to simulate the shock-activated power supply in the neutron generator, for example.

Three years later ALEGRA integrated another advanced physics model with the capability to model magnetohydrodynamic (MHD) phenomena -- the interaction between magnetic fields and electrically conducting materials.

For researchers working with the Z accelerator, this aspect opens new horizons. ALEGRA provides the ability to understand the complexity of the formation and compression of hot plasmas to generate the extreme X-ray environment needed to simulate a nuclear explosion.

"ALEGRA is critical to the future success of the high-energy-density physics research performed in the Pulsed Power Center," says Tom Mehlhorn, Manager of Target and Z-Pinch Theory Dept. 1674. "It is already being used to understand and design experiments on the Z accelerator. As the capability matures, it will provide simulations that will lay the foundation for an upgrade to Z machine and to design and build future z-pinch machines."

He says the ALEGRA framework includes physics modules that allow his engineers and researchers to simulate most of the major activities in the high-energy-density physics program -- z-pinches, shock physics, radiation-hydro-dynamics, and electron-photon transport.

Dan says the Z machine work is only half the story of how ALEGRA is used. The other half falls in the area of modeling hostile environments -- the effects of exploding nuclear weapons on another nuclear weapon. One user is Mark Kiefer, Manager of Electromagnetics and Plasma Physics Analysis Dept. 1642.

"Basically, our efforts to use the ALEGRA framework are going very well," Mark says. "We are making progress much faster than we expected would be possible. Our efforts to migrate our simulation methods to the ALEGRA framework were dictated by our realization that we are at the limit of the complexity for our current simulation codes. We really cannot take these older codes any farther without a prohibitive amount of work.

"All of our observations can be summed up with the conclusion that we cannot succeed in our nuclear weapon or pulsed power applications without taking advantage of the ALEGRA framework. One of the big advantages of the framework that we are looking forward to exploiting is the ability to test new models and algorithms on a short time scale. This will allow my staff of engineers and scientists more time to do science and engineering."

His area uses ALEGRA to implement full-wave electromagnetic techniques for certifying the W76-1 to normal environments, for design and performance of the W76-1 radar fuze, to couple those techniques with charged particle-in-cell techniques for certifying to hostile environments, and for modeling power flow in pulsed power accelerators. -- Chris Burroughs

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Last modified: April 18, 2001

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