DUCTILE INTERMETALLIC COMPOUNDSAlan M. Russell, Iowa State University, DMR 0413616

• At high temperature many intermetallic compounds are stronger, stiffer, and more oxidation resistant than ordinary metals.

• But their brittleness at room temperature severely limits their usefulness.

• A large family of rare earth intermetallics has recently been discovered to be ductile and tough at room temperature.1

YAg intermetallic is slightly flattened and dented after many hammer blows. The Gd5Si2Ge2 intermetallic in the foreground shattered into small pieces with just one hammer strike.

It was initially thought that the high ductility was caused by twinning or stress-induced phase transformations, but this NSF project has shown that is not the case.2

Calculations show that their bonding is less directional than that of most intermetallics, such as NiAl (see electron density plot below).3

Slip by dislocations with <111> Burgers vectors has also been observed in these ductile intermetallics - a surprising finding in a compound where the two elements differ greatly in both atomic size (18%) and electronegativity (0.5 eN).

Further study may suggest strategies to improve ductility in other intermetallics.

DUCTILE INTERMETALLIC COMPOUNDSAlan M. Russell, Iowa State University, DMR 0413616

References

1. Gschneidner, Jr. K.A., Russell A.M., Pecharsky A.O., Morris J.R., Zhang Z., Lograsso T.A., Hsu D.K., Lo C.H.C., Ye Y., Slager A.J., and Kesse D.C., "A family of ductile intermetallics", Nature Materials, Vol. 2, pp. 587–591, 2003.

2. Williams S., Brown D., Clausen B., Russell A., and Gschneidner K., “In-situ Neutron Diffraction Studies of Ductile Rare Earth B2 Intermetallics", Session on Plasticity from the Atomic Scale to Constitutive Laws, TMS Annual Meeting and Exposition, Orlando, FL, February, 2007.

3. Morris J.R., ,Ye Y.Y., Lee Y.B., Harmon B.N., Gschneidner K.A., and Russell A.M., "Ab initio calculation of bulk and defect properties of ductile rare-earth intermetallic compounds", Acta Materialia, Vol. 52, pp. 4849-4857, 2004.

DUCTILE INTERMETALLIC COMPOUNDSAlan M. Russell, Iowa State University, DMR 0413616