Impurity stabilization of nanocrystalline grains in pulsed laser deposited tantalum


Thermal stability of pulsed laser deposited (PLD) nanocrystalline tantalum was explored through in situ transmission electron microscopy (TEM) annealing over the temperature range of 800–1200 °C. The evolution of the nanostructure was characterized using grain size distributions collectively with electron diffraction analysis and electron energy loss spectroscopy (EELS). Grain growth dynamics were further explored through molecular dynamics (MD) simulations of columnar tantalum nanostructures. The as-deposited grain size of 32 nm increased by only 18% at 1200 °C, i.e., 40% the melting point of tantalum, conflicting with the MD simulations that demonstrated extensive grain coalescence above 1000 °C. Furthermore, the grain size remained stable through the reversible α-to-β phase transition near 800 °C, which is often accompanied by grain growth in nanostructured tantalum. The EELS analysis confirmed the presence of oxygen impurities in the as-deposited films, indicating that impurity stabilization of grain boundaries was responsible for the exceptional thermal stability of PLD nanocrystalline tantalum.

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Support for this work was provided for OKD, WW, and JRT by the National Science Foundation through Grant DMR-1410941. The authors gratefully acknowledge Michael Marshall of the Radiation–Solid Interaction Group at Sandia National Laboratories for his assistance in the preparation of the PLD samples and Dr. Eric Stach of the Center for Functional Nanomaterials at Brookhaven National Laboratory for his help with the EELS measurements. The authors would also like to thank Dr. Stephen Foiles of Sandia National Laboratories for valuable feedback on the MD simulations. Analytical TEM and atomistic simulations were conducted at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

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Correspondence to Jason R. Trelewicz.

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Donaldson, O.K., Wang, W., Hattar, K. et al. Impurity stabilization of nanocrystalline grains in pulsed laser deposited tantalum. Journal of Materials Research 32, 1351–1360 (2017).

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