Space Shuttle Takes Off With High Temperature Metal Alloy Crystal Growth Experiment

More than 20 years since its conception, a materials science experiment designed by a Northwestern University professor will be on board the space shuttle Endeavour when it launches today (Aug. 8), destined for the International Space Station.

Knowledge gleaned from the experiment could help improve the design of a variety of materials from steels to aluminum alloys.

Peter Voorhees, professor and chair of materials science and engineering at the Robert R. McCormick School of Engineering and Applied Science, began working on the project with NASA in 1986 when he was a postdoctoral researcher. The success of his first two experiments convinced NASA to fly the current experiment on the International Space Station.

Voorhees says his goal is to better understand the fundamental science of coarsening, a process that happens in nearly every material composed of two crystals, such as the high-temperature metal alloys used in jet engine turbine blades.

During coarsening, small particles shrink by losing atoms to larger particles, causing the larger particles to grow. In Voorhees' experiment, solid particles of tin will grow (coarsen) within a liquid lead-tin mixture. Understanding the process, says Voorhees, will help scientists and engineers learn how to control coarsening and use it to their advantage when designing materials.

Researchers conducting coarsening experiments on Earth have run into a major limitation: gravity. Gravity causes the particles to float to the top of the sample, which is not desirable. With his experiment conducted in the low-gravity conditions on the International Space Station, Voorhees will be able to study - once the samples return to Earth and to his lab - how the coarsening process works when the particles are evenly distributed.

In anticipation of Endeavour's launch, Voorhees and Amber Genau, one of his graduate students, prepared 20 samples of a lead-tin mixture to send to the space station. There astronauts will place them in a furnace specifically designed for this experiment. After the lead-tin mixture melts, the remaining spherical tin particles will be allowed to coarsen for a set amount of time before the samples are cooled with water to stop the coarsening process. The astronauts will run five cycles of the experiment so that the Voorhees and Genau can study the process over different lengths of time.

“Coarsening is used to tailor the mechanical properties of materials, but no one can predict how fast the process occurs,” said Voorhees. “Thus it is difficult to determine the evolution of a material's properties, such as strength, during coarsening. In some materials, such as turbine blades, the mechanical properties of these alloys are slowly decaying over time. From a materials standpoint, we want to know how fast this process occurs so that we can predict what's going to happen to a product, which is especially important for products like a turbine blade.”

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