Uncovering the Hidden Nature of Metals

Tuesday, December 4, 2007

As good cooks know, the best baked goods result as much from the cooling process as from the baking process. The internal structure of a cookie changes as it cools to perfection. Disturb it too soon, and the texture never recovers. Remove it too late, and it’s a rock-hard disc, stuck to the pan.

As a youngster in Osnabrueck, Germany, Christoph Beckermann was more inclined to fix cars than bake cookies, but he did grow up to become an expert on cooling processes. His specific areas of expertise focus on thermal and fluid sciences—heat transfer, thermodynamics, and fluid dynamics—as they relate to metal casting and solidification.

“Metal casting has been around since at least 3000 BC,” says the director of the Solidification Laboratory in the Department of Mechanical and Industrial Engineering. “Yet there is a seemingly endless array of challenges and problems that relate to metal casting processes.”

Beckermann adds that metal casting is a worldwide industry worth hundreds of billions of dollars. In the airplane and automobile manufacturing industries, for instance, improved metal casting has led to vehicles that are significantly quieter, faster, and more fuel efficient. The University of Iowa is known as a world leader in casting simulation research, and external funding for Beckermann’s efforts has hovered around the half-million-dollar mark each year for the last 5 years.

After earning an undergraduate degree from the University of Hanover in 1981, Beckermann earned MS (1984) and PhD (1987) degrees from Purdue University. Since he joined The University of Iowa faculty 20 years ago, Beckermann’s research has ranged from the microscopic to the massive.

Beckermann conducts fundamental research on the physics of solidification and also collaborates with companies to help improve their casting processes of steel, aluminum, magnesium, and other metals. His industry partners in Iowa have included corporate giants IPSCO Steel (Muscatine) and Alcoa (Davenport), which produce rolled sheets and plates from massive slabs of steel and aluminum. He also works with smaller companies such as steel foundries Sivyer Steel Corporation (Bettendorf) and Keokuk Steel Castings (Keokuk), which produce shaped castings for the railroad, vehicle, and petroleum industries. The University of Northern Iowa’s Metal Casting Center also has drawn on Beckermann’s expertise to enhance its shaped casting techniques.

On the other end of the scale, Beckermann explores essential questions about what happens at the microscopic level when a liquid metal solidifies. When metals transform from liquid to solid, they form beautiful microscopic structures called “dendrites,” crystalline forms less than a millimeter wide with a branching, treelike appearance. To really understand how metals solidify, researchers must discover how these microstructures form and how they result in the engineering properties of metals, including strength, durability, and ductility.

“We simulate the physical conditions of casting by solving basic equations about heat transfer and fluid mechanics,” says the University of Iowa Foundation Distinguished Professor of Mechanical and Industrial Engineering. “We can then figure out at the microscopic and macroscopic level what happens to metals during three aspects of the casting process: the flow of the metal as it goes into the mold, the cooling process, and the creation of defects such as pores or cracks that can occur during solidification.

To unlock the secrets of metals processing, Beckermann and his staff— including research engineers and adjunct faculty members Richard Hardin and Kent Carlson (BS 1991, MS 1993 in mechanical engineering), six graduate students, and three undergraduate students— formulate numerical simulations and conduct experiments to determine how dendrites grow under different conditions as well as how the formation of dendrites affects the flow and solidification of metals.

Among other things, the researchers have determined that dendrites grow more quickly at the “front” of the flow.

“This makes sense,” Beckermann says, “because the tip of a dendrite is the most exposed. It experiences the most heat transfer and therefore grows most quickly.”

Theorizing that weightlessness should have a profound effect on dendrite formation, Beckermann convinced NASA to fund experiments to be carried out on the International Space Station.

“In space we could create a very quiescent melt that would really enhance our ability to test our theories and equations,” Beckermann says. “And we know the dendrites that form up there are simply beautiful.”

One of the most intriguing properties of dendrites is that their formation is remarkably similar regardless of the type of metal. In addition, some other fluids also form dendritic structures similar to those in metals. This similarity has allowed Beckermann to generalize from experiments with nonmetallic, organic substances whose transparency enables him to actually observe how the microscopic structures form during solidification. What he has discovered is quite remarkable.

“If you measure the radius of curvature of the very tip of the dendrite,” he says, “and then scale the rest of the structure— that is, divide every other feature by that radius—you can derive universal relations that provide the surface area, volume, and side-branch spacing for any dendrite.

“In other words, all dendrites seem to obey the same universal geometrical laws regardless of how they grow or the material they’re made of. This is basic physics; we’re learning something fascinating about nature that we did not know before.”

In another experiment, Beckermann observed solidification in situ by moving a thin slide containing a transparent substance through hot and cold environments. The data gathered from this research have helped him tackle the question of how bubbles form during the solidification process, much like the bubbles in an ice cube. One of the challenges of successfully casting metals is to prevent the growth of cracks and bubbles, which can lessen the product’s reliability.

Metal casting facilities around the world benefit from process simulation, and Beckermann’s lab is one of the leading contributors of custom-made software for process control and casting simulation. Despite the high price of a single CD that can contain millions of lines of code, it can be more cost effective for a company to invest in simulation technology than to repeatedly experiment with actual castings.

In addition to providing rich research collaborations, Beckermann’s industry ties also have enabled his students to land positions in the field, where they can apply their knowledge and skills beyond academe. One former student, Marc Schneider (BS 1989, MS 1991, PhD 1995 in mechanical engineering), now heads the development group at MAGMA Foundry Technology in Aachen, Germany. He leads a team of 28, including 16 PhD-level engineers and scientists who continually improve casting simulation software.

“The mix of fundamental and applied research I experienced in Professor Beckermann’s lab prepared me for the work I do today,” Schneider says. “He has an excellent reputation in both academic and foundry circles. I’ve even heard some people in the metal casting business refer to him as the ‘Tiger Woods of casting simulation research.’ Fortunately, I’ve been able to continue working with him on modeling of segregation, porosity, and other defects in castings.”

Beckermann’s contributions to the University and the community reach well beyond his lab. In addition to serving on the editorial board of three professional journals, he teaches a weeklong summer course to industry researchers. As chair of the Engineering Faculty Council through May 2007, he was intimately involved in designing the engineering curriculum, shaping tenure and promotion policies, and establishing college teaching policies. Beckermann’s collegiate and institutional service earned him the 2002 College of Engineering Service Award. Between attending meetings and leading a highpowered research lab, Beckermann also manages to find time to practice clarinet in preparation for the next performance of the Iowa City Community Band.

Beckermann’s passion for his work is palpable. He understands that metal casting is a very rich phenomenon in physics that poses countless fascinating challenges with an equally limitless potential for the development of ideas, theories, models, and solutions. And shifting to a larger frame of reference, he notes that since the advent of the Iron Age, people have recognized the significance of metal casting.

“The entire progress of society hinges on improving the production of steel, aluminum, and other metals,” Beckermann says. ”Five hundred years from now and beyond, people will still be making and using steel.”