A hard new material with a soft touch

From Boston, at the fall meeting of the Materials Research Society.

Researchers are always searching for tougher polymers. Yet creating new materials can cost a bundle. A cheaper method is to mix a hard substance, or filler, into a known polymer, says Valerie V. Sheares of Iowa State University in Ames.

Now, Sheares has found that polymers spiced with unusual substances called quasicrystals are just as hard and wear just as well as those mixed with some of the best ceramic fillers. She also discovered that the materials made with quasicrystals are much less abrasive than polymers with other fillers.

Gears, bearings, or other machine parts coated with this material would produce little wear on other parts they touch, says Sheares. Her group is developing small parts and coatings for devices that need hard, scratch-resistant surfaces.

Quasicrystals are metal alloys with predictable patterns that aren’t as regular as those in true crystalline solids. Although quasicrystals possess desirable properties, such as extreme hardness and good wear resistance, they’re difficult to process by themselves into parts or coatings, says Sheares.

To circumvent this problem, Sheares’ team mixed dry powders of quasicrystals and a polymer, such as polyphenylene sulfide; placed the mixture in a mold; and applied heat and pressure. The polymer softened quickly, and the quasicrystal powder dispersed throughout it, she says.

The group made quarter-size disks of quasicrystal-filled polymers, then tested their properties. For example, the scientists dragged a steel ball across each disk like a needle across a record player. Not only did the disks wear well, but the balls remained round, showing little hint of abrasion, says Sheares.

When the researchers performed the same test with a polymer containing a common filler, such as alumina or silicon carbide, the disks themselves sometimes withstood the test as well as those containing quasicrystals, but the steel balls became so worn that they could stand flat on a table.

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