Evolutionary Metallurgy

A host of new materials may soon emerge from a novel research approach that combines improved quantum mechanical techniques and a search algorithm inspired by biological evolution. Although the method is helpful in the development of products ranging from battery components to catalysts, the Danish group pioneering the technique is beginning with a search for new super-alloys. In general, theoretical methods for predicting the properties of various blends of metals have been unwieldy, and the characteristics of new alloys are usually determined experimentally. Considering the hundreds of thousands of possible combinations that can be formed with even a small number of metals, searches for better alloys typically require both patience and luck.

Now Jens Norskov (norskov@fysik.dtu.dk, 45-4525-3175) and colleagues at the Technical University of Denmark have managed to identify twenty of the most promising alloys out of nearly two hundred thousand combinations, without the need for time-consuming lab work. The researchers' method is based in part on maturing modeling techniques that rely on density functional theory (DFT), which can help predict material properties through the interactions of electron populations.

Rather than apply DFT to countless possible alloys, the researchers studied four-metal alloys that they selected with an algorithm that mimics Darwinian evolution. To begin, they designated a "living population"of alloys, each represented by genetic codes that consisted of various combinations of four metals selected from thirty-two candidate metals. New alloys were then formed through both mutations and random combinations that were the numerical equivalent of breeding between parent alloys. The most fit - or in this case, the most stable - alloys were allowed to survive as the population evolved.

The researchers duplicated the study with several different initial alloy populations, and each time the same final group of alloys survived. Several known super-alloys were among the survivors. Other survivors included a number of alloys that have not yet been thoroughly studied, but may hold particular promise, considering that they endured along with the super-alloys. The researchers point out that practical studies must consider more than stability in the search for novel materials. Nevertheless, the new method is an important step toward accelerating the search for beneficial alloys and other compounds, and reducing dependence on expensive and slow laboratory experiments. (G.H. Johannesson et al., Physical Review Letters, 24 June 2002.)