Magazine article Science News

Metal Dendrites in Microgravity

Magazine article Science News

Metal Dendrites in Microgravity

Article excerpt

It looks like "a forest of tiny metal pine trees," says Martin E. Glicksman, a materials scientist at Rensselaer Polytechnic Institute in Troy, N.Y.

Each time a molten alloy cools, changing from a liquid to a solid, a roughedged carpet of treelike spindles sprouts along the interface where the two states meet. Scientists call these tiny branching structures dendrites, derived from the Greek word for tree.

When observing this metal forest under a microscope, one sees metal trees growing so closely together "that their trunks and branches intermingle," Glicksman said this week at a meeting of the Materials Research Society in Boston.

Indeed, every engine block or soda can hardening from molten alloy forms such dendritic sheets along the edge where the liquid turns solid. Once the alloy has completely hardened, the interlocking dendrites imprint in the material a complex three-dimensional pattern called the microstructure.

That pattern, says Glicksman, strongly affects the material's strength, ductility, and electrical properties, as well as its tendency to crack and corrode. Thus, in order to improve alloy quality, scientists want to understand more thoroughly how metal dendrites grow during solidification.

A key factor influencing dendritic growth is the convective currents of heat flowing in molten metal. On Earth, with its strong gravitational fields, those currents are difficult to control or avoid. So Glicksman and his colleagues proposed to measure dendritic growth in space. …

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