An unsolved mystery: The composition of bcc Cu alloy precipitates in bcc Fe and steels

Copper precipitation strengthened steels are of considerable technical importance. An application to a new bridge in Illinois is described. The Cu precipitates are body centered cubic (bcc) and a few nanometer in diameter at maximum strength. While recently published ab initio calculations of the mixing energy at 0 K predict that bcc Cu precipitates in bcc Fe should be pure Cu, literature data show that they contain almost 50% Fe according to atom probe tomography whereas combined small angle neutron and magnetic scattering predicts the composition is almost pure Cu. Possible sources of these differences are discussed. (c) 2006 Elsevier B.V. All rights reserved.