Letter | Published:

Extreme creep resistance in a microstructurally stable nanocrystalline alloy

Nature volume 537, pages 378381 (15 September 2016) | Download Citation

Abstract

Nanocrystalline metals, with a mean grain size of less than 100 nanometres, have greater room-temperature strength than their coarse-grained equivalents, in part owing to a large reduction in grain size1. However, this high strength generally comes with substantial losses in other mechanical properties, such as creep resistance, which limits their practical utility; for example, creep rates in nanocrystalline copper are about four orders of magnitude higher than those in typical coarse-grained copper2,3. The degradation of creep resistance in nanocrystalline materials is in part due to an increase in the volume fraction of grain boundaries, which lack long-range crystalline order and lead to processes such as diffusional creep, sliding and rotation3. Here we show that nanocrystalline copper–tantalum alloys possess an unprecedented combination of properties: high strength combined with extremely high-temperature creep resistance, while maintaining mechanical and thermal stability. Precursory work on this family of immiscible alloys has previously highlighted their thermo-mechanical stability and strength4,5, which has motivated their study under more extreme conditions, such as creep. We find a steady-state creep rate of less than 10−6 per second—six to eight orders of magnitude lower than most nanocrystalline metals—at various temperatures between 0.5 and 0.64 times the melting temperature of the matrix (1,356 kelvin) under an applied stress ranging from 0.85 per cent to 1.2 per cent of the shear modulus. The unusual combination of properties in our nanocrystalline alloy is achieved via a processing route that creates distinct nanoclusters of atoms that pin grain boundaries within the alloy. This pinning improves the kinetic stability of the grains by increasing the energy barrier for grain-boundary sliding and rotation and by inhibiting grain coarsening, under extremely long-term creep conditions. Our processing approach should enable the development of microstructurally stable structural alloys with high strength and creep resistance for various high-temperature applications, including in the aerospace, naval, civilian infrastructure and energy sectors.

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References

  1. 1.

    Nanostructured materials: basic concepts and microstructure. Acta Mater . 48, 1–29 (2000)

  2. 2.

    & Creep and superplasticity in nanocrystalline materials: current understanding and future prospects. Mater. Sci. Eng. A 298, 1–15 (2001)

  3. 3.

    Unusual stress and grain size dependence for creep in nanocrystalline materials. Scr. Mater. 61, 96–99 (2009)

  4. 4.

    et al. Microstructure and mechanical properties of bulk nanostructured Cu–Ta alloys consolidated by equal channel angular extrusion. Acta Mater . 76, 168–185 (2014)

  5. 5.

    , , , & Mechanical properties of a high strength Cu–Ta composite at elevated temperature. Mater. Sci. Eng. A 638, 322–328 (2015)

  6. 6.

    Development of single crystal superalloys: a brief history. Adv. Mater. Process . 171, 26–30 (2013)

  7. 7.

    The Superalloys: Fundamentals and Applications (Cambridge Univ. Press, 2008)

  8. 8.

    , & Mechanical properties of nanocrystalline materials. Prog. Mater. Sci. 51, 427–556 (2006)

  9. 9.

    et al. Nanoscale room temperature creep of nanocrystalline nickel pillars at low stresses. Int. J. Plast. 41, 53–64 (2013)

  10. 10.

    et al. Effect of Ta solute concentration on the microstructural evolution in immiscible Cu-Ta Alloys. JOM 67, 2802–2809 (2015)

  11. 11.

    , , , & The role of Ta on twinnability in nanocrystalline Cu-Ta alloys. Mater. Res. Lett. (2016)

  12. 12.

    , & Calorimetric analysis of the grain growth in nanocrystalline copper samples. Nanostruct. Mater. 2, 587–595 (1993)

  13. 13.

    & Nickel-based superalloys for advanced turbine engines: chemistry, microstructure and properties. J. Propuls. Power 22, 361–374 (2006)

  14. 14.

    A model for boundary diffusion controlled creep in polycrystalline materials. J. Appl. Phys. 34, 1679–1682 (1963)

  15. 15.

    A first report on deformation-mechanism maps. Acta Metall . 20, 887–897 (1972)

  16. 16.

    et al. Atomic structure of nanoclusters in oxide-dispersion-strengthened steels. Nat. Mater. 10, 922–926 (2011)

  17. 17.

    et al. Nanostructured high-strength molybdenum alloys with unprecedented tensile ductility. Nat. Mater. 12, 344–350 (2013)

  18. 18.

    , & Five decades of the Zener equation. ISIJ Int. 38, 913–924 (1998)

  19. 19.

    Fast parallel algorithms for short-range molecular dynamics. J. Comput. Phys. 117, 1–19 (1995)

  20. 20.

    , , & Angular-dependent interatomic potential for the Cu–Ta system and its application to structural stability of nano-crystalline alloys. Acta Mater . 100, 377–391 (2015)

  21. 21.

    Materials processing by simple shear. Mater. Sci. Eng. A 197, 157–164 (1995)

  22. 22.

    , , & Review: processing of metals by equal-channel angular pressing. J. Mater. Sci. 36, 2835–2843 (2001)

  23. 23.

    & Observations and issues on mechanisms of grain refinement during ECAP process. Mater. Sci. Eng. A 291, 46–53 (2000)

  24. 24.

    & Double conical beam-rocking system for measurement of integrated electron diffraction intensities. Ultramicroscopy 53, 271–282 (1994)

  25. 25.

    The determination of the elastic field of an ellipsoidal inclusion, and related problems. Proc. R. Soc. Lond. A 241, 376–396 (1957)

  26. 26.

    Dislocations in a simple cubic lattice. Proc. Phys. Soc. 59, 256–272 (1947)

  27. 27.

    Diffusional viscosity of a polycrystalline solid. J. Appl. Phys. 21, 437–445 (1950)

  28. 28.

    & The stress/creep rate behaviour of precipitation-hardened alloys. Met. Sci . 10, 20–28 (1976)

  29. 29.

    , & Centroidal Voronoi tessellations: applications and algorithms. SIAM Rev. 41, 637–676 (1999)

  30. 30.

    , & Atomic-scale investigation of creep behavior in nanocrystalline Mg and Mg–Y alloys. Acta Mater . 99, 382–391 (2015)

  31. 31.

    , , & Grain-boundary diffusion creep in nanocrystalline palladium by molecular-dynamics simulation. Acta Mater . 50, 61–73 (2002)

  32. 32.

    , , & On the validity of the Hall-Petch relationship in nanocrystalline materials. Scr. Metall. 23, 1679–1683 (1989)

  33. 33.

    , & Softening of nanocrystalline metals at very small grain sizes. Nature 391, 561–563 (1998)

  34. 34.

    Structural nanocrystalline materials: an overview. J. Mater. Sci. 42, 1403–1414 (2007)

  35. 35.

    , & Design of stable nanocrystalline alloys. Science 337, 951–954 (2012)

  36. 36.

    & Estimation of grain boundary segregation enthalpy and its role in stable nanocrystalline alloy design. J. Mater. Res. 28, 2154–2163 (2013)

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Acknowledgements

M.R., and K.N.S. acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. This work was supported by US Army Research Laboratory under contract W911NF-15-2-0038. K.A.D. acknowledges A. J. Roberts and T. Luckenbaugh for synthesis of the Cu–Ta powder.

Author information

Affiliations

  1. Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005, USA

    • K. A. Darling
    •  & B. C. Hornbuckle
  2. School of Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85281, USA

    • M. Rajagopalan
    • , M. A. Bhatia
    •  & K. N. Solanki
  3. Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, USA

    • M. Komarasamy
    •  & R. S. Mishra

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Contributions

K.A.D., K.N.S. and R.S.M. equally contributed to the idea. K.A.D. and B.C.H. processed the nanocrystalline materials. M.K. performed the creep experiments. M.R. characterized the microstructure data and analysed deformation-mechanisms maps. M.A.B. performed the modelling work. K.N.S., K.A.D., M.R. and R.S.M. analysed the data. K.N.S., K.A.D., M.R. and R.S.M. wrote the paper. K.A.D. and M.R. edited the figures. K.A.D. supervised B.C.H., R.S.M. supervised M.K., and K.N.S. supervised M.R. and M.A.B.

Corresponding author

Correspondence to K. N. Solanki.

Reviewer Information Nature thanks J. Cormier, S. Forest and T. Perez Prado for their contribution to the peer review of this work.

Extended data

Supplementary information

Videos

  1. 1.

    Creep simulation of NC-Cu and NC-Cu-10at.%Ta

    (a-b) provides 2-D movies of 3-D atomistic creep simulations of NC- Cu and NC-Cu-10at.%Ta from t=0 to t=5ns. White atoms correspond to the GB configuration in NC Cu, while green atoms correspond to that of NC-Cu-10at.%Ta where the Ta atoms are color coded in blue. There is evidence of microstructural instability in (a) whereas in (b) the degree of coarsening is limited.

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https://doi.org/10.1038/nature19313

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