Self-Healing Steel

So strong are some of today's steel alloys that four one-inch-square bars will easily support the weight of a 125-ton jet airliner. Yet even the best of these metals will crack and shatter if they are subjected to much greater stress. Earlier this month, a research team at the University of California's Lawrence Radiation Laboratory announced development of a super steel alloy that will bear as much as 4 times more pressure than common structural steels without breaking.

The brainchild of Engineers Victor F. Zackay and Earl R. Parker, the new alloy is called TRIP (for transformation-induced plasticity) steel. In effect, it can be stretched like Silly Putty or molten glass 2 1/2 to 4 1/2 times as far as present-day high-strength steel without fracturing its molecular structure. More important, when TRIP steel eventually reaches the point of crack-inducing stress, a solid-state chemical reaction is triggered that blunts small cracks just as they begin, then fills them in to prevent major wounds. The chemical change precipitating this "self-healing" process takes place on a near-atomic scale, and can be observed only with the aid of an electron microscope. The actual halting and filling in of a crack, however, can sometimes be seen with the naked eye.

Indefatigable? Oddly enough, producing Zackay and Parker's super steel involves no other ingredients than those already used in steel alloys. "It is a new combination of alloys normally used in various kinds of stainless steel," says Zackay. Once the two professors hit upon the basic composition, "the only variation from the production of ordinary stainless was a deformation of the steel at temperatures from 500DEG to 1,100DEG Fahrenheit," said Parker.

The TRIP process may well have wide applications in other areas of metallurgy. "We expect there will be an analogous series of alloys for titanium," says Zackay. "We just haven't had time to look for them." Titanium is used in jet aircraft, and although both engineers termed the idea of using TRIP-processed materials to prevent metal fatigue "pure speculation" at this point, it is not beyond the realm of possibility. Other conceivable uses of TRIP steel: storage tanks to withstand the super-coolness (as much as --450DEG F.) of liquid helium, hydrogen, nitrogen and oxygen; chemical-processing equipment; roller and ball bearings. TRIP, in the estimate of its discoverers, is capable of being produced commercially at prices competitive with other high-strength steels. It may some day be used in the manufacture of deep-diving descendants of such undersea vessels as the bathyscaphe and the three-man submarine Alvin, which is now exploring a canyon at the foot of the Atlantic shelf at depths of 1,000 fathoms.

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