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High-performance Materials History Part 1 - Metals


In the decades to come, however, there would be many more claimants to wonder-working glory—among them other metals, polymers, ceramics, blends called composites, and the electrically talented group known as semiconductors. Over the course of the 20th century, virtually every aspect of the familiar world, from clothing to construction, would be profoundly changed by new materials. High performance materials would also make possible some of the century's most dazzling technological achievements: airplanes and spacecraft, microchips and magnetic disks, lasers and the fiber-optic highways of the Internet. And behind all that lies another, less obvious, wonder—the ability of scientists and engineers to customize matter for particular applications by manipulating its composition and microstructure: they start with a design requirement and create a material that answers it.

Of the various families of metals represented among high performance materials, steel still stands supreme in both versatility and volume of production. Hundreds of alloys are made by adding chromium, nickel, manganese, molybdenum, vanadium, or other metals to the basic steel recipe of iron plus a small but critical amount of carbon. Some of these alloys are superstrong or ultrahard; some are almost impervious to corrosion; some can withstand constant flexing; some possess certain desired electrical or magnetic properties. Highly varied microstructures can be produced by processing the metal in various ways.

Until well into the 20th century, new steel alloys were concocted mainly by trial-and-error cookery, but steelmakers at least had the advantage of long experience—3 millennia of it, in fact. That wasn't the case with aluminum, the third most common element in Earth's crust, yet never seen in pure form until 1825. It was heralded as a marvel—light, silvery, resistant to corrosion—but the metal was so difficult to separate from its ore that it remained a rarity until the late 19th century, when a young American, Charles Martin Hall, found that electricity could pull aluminum atoms apart from tight-clinging oxygen partners. Extensive use was still blocked by the metal's softness, limiting it to such applications as jewelry and tableware. But in 1906 a German metallurgist named Alfred Wilm, by happy chance, discovered a strengthening method. He made an alloy of aluminum with a small amount of copper and heated it to a high temperature, then quickly cooled it. At first the aluminum was even softer than before, but within a few days it became remarkably strong, a change caused by the formation of minute copper-rich particles in the alloy, called precipitation hardening. This lightweight material became invaluable in aviation and other transportation applications.

In recent decades other high performance metals have found important roles in aircraft. Titanium, first isolated in 1910 but not produced in significant quantities until the 1950s, is one of them. It is not only light and resistant to corrosion but also can endure intense heat, a requirement for the skin of planes traveling at several times the speed of sound. But even titanium can't withstand conditions inside the turbine of a jet engine, where temperatures may be well above 2,000° F. Turbine blades are instead made of nickel- and cobalt-based materials known as superalloys, which remain strong in fierce heat while spinning at tremendous speed. To ensure they have the maximum possible resistance to high-temperature deformation, the most advanced of these blades are grown from molten metal as single crystals in ceramic molds.


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     Essay - Mary L. Good

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