Technique yields hard but stretchy materials. (Metal Manipulation).
Metalworking is an ancient craft, with time-tested practices that go back thousands of years. But now, working within the modern context of nanotechnology, researchers have found a way to make strong yet stretchy stretch·y
adj. stretch·i·er, stretch·i·est
1. Capable of being stretched: a stretchy fabric.
2. Tending to stretch excessively.
Adj. 1. metals. Metallurgists might eventually incorporate such improved materials into countless applications, from micromechanical machines to biomedical bi·o·med·i·cal
1. Of or relating to biomedicine.
2. Of, relating to, or involving biological, medical, and physical sciences. implants.
In the Oct. 31 Nature, En (Evan) Ma and his colleagues at Johns Hopkins University Johns Hopkins University, mainly at Baltimore, Md. Johns Hopkins in 1867 had a group of his associates incorporated as the trustees of a university and a hospital, endowing each with $3.5 million. Daniel C. in Baltimore report that they've combined a standard metalworking technology--rolling--with a programmed sequence of cooling and heating steps to process copper into a form that contains both nanoscale and microscale crystal grains. The resulting material has six times the strength of unprocessed copper yet retains most of the metal's characteristic ductility ductility, ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together (see adhesion and cohesion). Ductility is important in wire drawing and sheet stamping. , or stretchiness Noun 1. stretchiness - the capacity for being stretched
elasticity, snap - the tendency of a body to return to its original shape after it has been stretched or compressed; "the waistband had lost its snap" .
In the 1980s, materials scientists discovered that solid metals are stronger when their crystalline grains are on the order of 100 nanometers or so in diameter. Unfortunately, nanocrystalline materials' superlative strength is usually accompanied by very low ductility.
Instead of accepting this apparent tradeoff, Ma and his colleagues sought a compromise. About 75 percent of their material's grains are just a couple of hundred nanometers wide, enhancing the metal's strength. The rest of the copper's crystals grow into larger, microscale grains. This combination gives the copper good ductility, says Ma.
The results are "really great," comments Julia Weertman of Northwestern University Northwestern University, mainly at Evanston, Ill.; coeducational; chartered 1851, opened 1855 by Methodists. In 1873 it absorbed Evanston College for Ladies. in Evanston, Ill. "You have a good increase in strength without having to sacrifice the ductility."
To give their material its unusual internal structure, the researchers first cooled a 1-inch cube of copper to nearly-200[degrees]C and then passed the frigid cube between heavy rollers, flattening it to about 1 millimeter in thickness. Then they heated the resulting sheet to 200[degrees]C for 3 minutes before returning it to room temperature.
This procedure is much easier than many methods for making nanocrystalline materials, which rely on compacting powders of nanoscale particles, says Ma. He and his coworkers now plan to repeat their experiments with other pure metals and with alloys.
The new process ought to be applicable to these materials, comments Ruslan Valiev of the Institute of Physics of Advanced Materials Advanced Materials is a leading peer-reviewed materials science journal published every two weeks. Advanced Materials includes Communications, Reviews, and Feature Articles from the cutting edge of materials science, including topics in chemistry, physics, at Ufa State Aviation Technical University in Russia. "It is important to check this experimentally, and I hope it will be done soon," he says.
A strong, pure metal processed with the new technique might even replace alloys for some applications, suggests Ma. In biomedical implants, for instance, a pure metal might reduce the likelihood of corrosion or adverse reactions adverse reactions,
n.pl unfavorable reactions resulting from administration of a local anesthetic; responsible factors include the drug used, concentration, and route of administration. to a metal mixture, he says.