Elastic,micro- and macroplastic properties of polycrystalline beryllium |
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Authors: | B K Kardashev I B Kupriyanov |
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Institution: | 1.Ioffe Physical-Technical Institute,Russian Academy of Sciences,St. Petersburg,Russia;2.Joint Stock Company Bochvar High-Technology Research Institute of Inorganic Materials,Moscow,Russia |
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Abstract: | The Young’s modulus and the internal friction of beryllium polycrystals (size grain from 6 to 60 μm) prepared by the powder
metallurgy method have been studied as functions of the amplitude and temperature in the range from 100 to 873 K. The measurements
have been performed using the composite piezoelectric vibrator method for longitudinal vibrations at frequencies about 100
kHz. Based on the acoustic measurements, the data have been obtained on the elastic and inelastic (microplastic) properties
as functions of vibration stress amplitudes within the limits from 0.2 to 30–60 MPa. The microplastic deformation diagram
is shown to become nonlinear at the amplitudes higher than 5 MPa. The beryllium mechanical characteristics (the yield strength
σ
0.2, the ultimate strength σ
u
, and the conventional microscopic yield strength σ
y
) obtained with various grain sizes are compared. At room temperature, all the parameters satisfactorily obey the Hall-Petch
relationship, although there is no complete similarity. The temperature dependences are quite different, namely: σ
0.2(T) and σ
u
(T) decrease monotonically during heating from room temperature to higher temperatures; however, σ
y
(T) behaves unusually, and it has a minimum near 400 K. The different levels of stresses and the absence of similarity indicate
that the scattering of the ultrasound energy and the formation of a level of the macroscopic flow stresses in beryllium occur
on dislocation motion obstacles of different origins. |
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Keywords: | |
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