ultrasound action on strength properties of polycrystalline metals

76
THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS “ OF GALAŢI
FASCICLE VIII, 2006 (XII), ISSN 1221-4590
TRIBOLOGY
When 20.338 kHz high-intensity <strong>ultrasound</strong> was
applied to the molten system, a mixing of the melted
metal close to the solid-liquid interface and the
crucible wall due to cavitation was produced. Near
the solid surface, cumulative jets can be generated
and the diffusion layer is thinned due to enhanced
mass transport resulting from microstreaming. In our
experiment, these optimum conditions in cavitation
were studied in deionized water at ambient
temperature. The ultrasonic treatment of liquid metals
differed essentially from that of aqueous solutions
and organic liquids. This is due to the different nature
of cavitation nuclei and, hence different conditions
required for the initiation and development of
acoustic cavitation. Only fine solid particles (mainly
oxides, e.g. Al 2 O 3 in aluminum melt) can act as
cavitation nuclei in metallic melts. At the same time,
because the molten metals feature light opacity, the
cavitation cannot be studied directly.
4. CONCLUSION
In the cast of polycrystalline metals the deformation
process has been studied related with the grain
size in order to highlight the strength properties of
polycrystalline metals and to study the applicability
of the Hall-Petch (HP) equation.
A linear relationship between σ and d
−1 2
can
be established and it shows that HP equation is valid.
This study was making for samples solidified
under similar conditions both with and without high
power ultrasonic field presence. Our investigations on
aluminum revealed superior mechanical properties for
samples solidified in ultrasonic field.
Studies into the Hall-Petch relationship show
that the factor K is different in tension and
compression. No systematic studies have been done
on the effects of solutes on the K values and the
difference in tension and compression. In future this
represents another aims to investigate.
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