30th Annual SSRL Users' Meeting — October 9-10, 2003

The Structure of Ni-based Refractory Metal Glasses

M. L. Tokarz and J. C. Bilello

Center for Nanomaterials Sciences, Department of Materials Science, University of Michigan, Ann Arbor, MI 48109-2136

A series of Ni-based alloys of varying Nb/Sn concentrations was studied using the high resolution synchrotron powder diffraction beamline 2-1 and these results were correlated with a number of collary experiments using beamline 2-2, DSC, SEM and laboratory source x-rays. These alloys exhibited a glass transition temperature of ~ 600ºC for the entire composition range, where Ni concentration was nominally 60% and the Sn concentration ranged over 3, 5, 6.2 to 6.9%, with Nb the remainder. Specimens from all four concentrations appeared to be bulk glasses when studied with a standard lab x-ray source, but data taken on 2-1 indicated that there was a small, but persistent, nanocrystalline phase present for all samples with the exception of Ni60Nb35Sn5. This nanocrystalline residue was subsequently confirmed by Laue transmission diffraction experiments on beamline 2-2, which provided global information, and by the more limited field of view provided high resolution SEM. Analysis of the Radial Distribution Functions, particularly at 16KeV, which allowed access to a wider range of k-space, indicated that these materials show definite structural order out to 4 (possibly 5) nearest neighbors, and these nearest neighbor distances do not agree with those predicted from a random packing model. This result is very different from what one would normally associate with a traditional glass forming material.

Appreciation is expressed to Professor W. L. Johnson and Dr. C-Y. Haein for preparing the alloy samples and to DoE and DARPA for support.