NANOSCALE STRUCTURE IN CRYSTALLINE SOLID-SOLUTION ALLOYS

The importance of local structure to the physical properties of alloys is receiving increasing attention. Recent measurements of the short-r ange nanoscale structure in metallic solid solution alloys reveal both the local chemical order and the chemically sensitive near neighbor d istances. These measurements are made possible by intense and tunable synchrotron X radiation; X-ray energy is adjusted to vary the x-ray sc attering contrast between atoms in the solid solution. We discuss the local structures in Ni/Fe binary alloys and compare the observed struc tures to trends calculated from first principles cluster models that i dentify the role of the focal bonding. The small cluster models are fo und to exhibit trends in agreement with measured Ni-Fe, Ni-Ni and Fe-F e near neighbor distances. From the cluster models we infer the mechan isms responsible for the observed average lattice and pair correlation lengths in NiFe alloys.