Processing of Nanostructured Alloys

Nanostructured metals exhibit interesting and useful properties owing to their extremely fine structural length scale.  Unfortunately, controlling grain size in the nanocrystalline regime has proven difficult as these materials represent a classical far-from-equilibrium state, containing a large volume fraction of high-energy interfaces.  Alloying presents an opportunity to reduce the energy penalty associated with nanostructure formation.  In our group, we employ experiments and atomistic computer simulations to study the role of alloying elements in nanostructure formation and stabilization.  In the experimental approach, we synthesize nanostructured Ni-W and Al-Mn using electrodeposition in aqueous and non-aqueous medium respectively.  The figure below shows that for both systems, as the solute content increases, the grain size decreases monotonically.  For the Ni-W system, atom probe tomography experiments and computer simulations show that the solute atoms (W) preferentially segregate to the grain boundaries, resulting in a thermodynamic reduction in grain boundary energy.   On the other hand, scanning transmission electron microscopy experiments indicate that for the Al-Mn system, Mn does not preferentially partition to the grain boundaries.  Instead, grain refinement can be attributed to electrode kinetics, where increasing Mn content in the electrolytic solution causes the grain nucleation rate to increase during electrodeposition, thus resulting in smaller grains.

Experimental grain size-composition relationship for electrodeposited Ni-W and Al-Mn alloys.  Transmission electron microscopy images show structural refinement over the range of alloying addition examined.  For the Ni-W system, nanocrystalline grain size scales with W content as a consequence of grain boundary segregation.  For the Al-Mn system, nanocrystalline grain formation can be attributed to electrode kinetics.

Published Articles:

Grain boundary segregation and thermodynamically stable binary nanocrystalline alloys
Trelewicz JR, Schuh CA; PHYSICAL REVIEW B   79 (9): Art. No. 094112 MAR 2009 (PDF)

Mesoscale structure and segregation in electrodeposited nanocrystalline alloys
Ruan S, Schuh CA; SCRIPTA MATERIALIA 59 (11): 1218-1221 DEC 2008 (PDF)

Microstructural evolution during the heat treatment of nanocrystalline alloys 
Detor AJ, Schuh CA; JOURNAL OF MATERIALS RESEARCH 22 (11): 3233-3248 NOV 2007 (PDF)

Measuring grain-boundary segregation in nanocrystalline alloys: direct validation of statistical techniques using atom probe tomography 
Detor AJ, Miller MK, Schuh CA; PHILOSOPHICAL MAGAZINE LETTERS 87 (8): 581-587 AUG 2007 (PDF)

Grain boundary segregation, chemical ordering and stability of nanocrystalline alloys: Atomistic computer simulations in the Ni-W system
Detor AJ, Schuh CA; ACTA MATERIALIA 55 (12): 4221-4232 JUL 2007 (PDF)

Strategy to improve the high-temperature mechanical properties of Cr-alloy Coatings
Gines MJL, Williams FJ Schuh CA; METALLURGICAL AND MATERIALS TRANSACTIONS A 38A (6): 1367-1370 JUN 2007 (PDF)

Tailoring and patterning the grain size of nanocrystalline alloys
Detor AJ, Schuh CA; ACTA MATERIALIA 55 (1): 371-379 JAN 2007 (PDF)

Solute distribution in nanocrystalline Ni-W alloys examined through atom probe tomography
Detor AJ, Miller MK, Schuh CA; PHILOSOPHICAL MAGAZINE 86 (28): 4459-4475 OCT 2006 (PDF)

Characterization of the microstructure and texture of nanostructured electrodeposited NiCo using electron backscatter diffraction (EBSD)
Bastos A, Zaefferer S,Raabe D, Schuh CA; ACTA MATERIALIA 54 (9) 2451-2462 May 2006 (PDF)

Nanostructured Ni-Co alloys with tailorable grain size and twin density
Wu BYC, Ferreira PJ, Schuh CA; METALLURGICAL AND MATERIALS TRANSACTIONS A 36A (7): 1927-1936 JUL 2005 (PDF)