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Characteristics of nanophase TiAl produced by inert gas condensation

Published online by Cambridge University Press:  31 January 2011

H. Chang
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801
C.J. Altstetter
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801
R.S. Averback
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801
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Abstract

Nanophase TiAl, with grain sizes in the range of 10–20 nm, was synthesized by magnetron sputtering in an inert gas atmosphere and consolidated, in situ, under vacuum. The properties of the powders and sintered compacts were studied by transmission electron microscopy, scanning electron microscopy, calorimetry, Rutherford backscattering, and x-ray diffraction. Samples compacted at 1.0 GPa at room temperature had a large fraction of amorphous phase, while samples compacted at the same pressure and 250 °C were predominantly the equilibrium γ phase. An enthalpy change of 22 kJ/g-atom was measured during a DSC scan over the temperature range 125–450 °C, which is approximately the range over which crystallization occurs. Nearly full density could be achieved by sintering at 450 °C without significant, concomitant grain growth. The Vickers microhardness of these samples at room temperature and at −30 °C revealed an inverse Hall–Petch relationship at small grain sizes, 10–30 nm, and the usual Hall–Petch behavior at larger grain sizes. A small component of indentation creep was also observed. The maximum hardness is 4 times larger than that of a cast TiAl specimen of the same composition. The Vickers hardness was also observed to decrease rapidly with temperature above 200 °C.

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Articles
Copyright
Copyright © Materials Research Society 1992

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