I [Image43.gif]
Internet Journal of the High Pressure School
http://www.unipress.waw.pl/ihps
Proceedings of the III International Warsaw, 13-16 Sept. 1999. Edited
by w. Lojkowski
PRESSURE EFFECT ON GRAIN BOUNDARY DIFFUSION IN Al BICRYSTALS
A.N.Aleshin1, R.G.Faulkner2, W.Lojkowski3 and L.S.Shvindlerman1
1
Institut of Solid State Physics, Russian Academy of Sciences, Moscow
district, 142432 Chernogolovka, Russia
2
Institute of Polymer Technology and Materials Eng., Loughborough
Univ.; Loughborough, Leicestershire, LE11, 3TU, UK
3
UNIPRESS, High Pressure Research Centre, Polish Academy of Sciences,
01-142 Warsaw, Sokolowska 29, Poland
The effect of pressure on the diffusion of zinc along a set of
high-angle grain boundaries (GBs) in Al bicrystals has been studied.
The GBs studied were of symmetrical tilt type with <100> and <110>
space axes and misorientation angles ranged from 33 to 46 . Two GBs
under investigation, namely the 37 <100> GB and the 39 <110> GB had
the crystallographic parameters close to special misorientations with
S 5 and S 9 respectively. The diffusion experiment was done at
temperature 553K (0.59 T[m]) and under argon gas pressure up to 1.2
GPa. Electron scanning microscopy (SEM) and Electron probe X-ray
microanalysis (EPMA) were used to reveal the behavior pattern of the
GB diffusion of Zn in Al bicrystals under high pressure. The SEM was
used to perform a comparative analysis of GB diffusion penetration
depths. The comparative analysis of GB diffusion penetration depths
under atmospheric pressure showed that 37 <100> and 39 <110> GBs
possessed special properties. Their penetration depths were small as
compared ones with the diffusional penetration depths of the 33 <100>
or 39 <100> GBs and 34 <110> or 46 <110> GBs, respectively. Two
GBs, namely the 39 <100> tilt GB and 39 <110> tilt GB whose
diffusion penetration depths were most different from each other have
been studied by the EPMA.
Two problems were in a focus of the investigation, namely influence of
GB structure on the value of activation volume [Image37.gif] (the
difference of volumes for diffusing complex in activated and basic
states) for GB diffusion, and the problem of compensation effect (CEF)
for GB diffusion under high pressure. The value of [Image38.gif] were
determined on the basis of the formula
[Image39.gif]
where the designations have a general sense.
Values of the double product [Image40.gif] were obtained in according
with Fisher's model for the GB diffusion
[Image41.gif] ,
where [Image42.gif] is GB concentration (the maximum local X-ray
intensity of GB diffusion field crossing section). It was found that
the activation volumes for 39 <110> and for 39 <100> GBs are equal
to 0.4W and 0.6W (W is the atomic volume). For 37 <100>, 34 <110>
and 46 <110> tilt GBs the GB diffusion is characterized by activation
volume ranged from 0.4 W to 0.6 W . In such a manner a conclusion that
activation volume is a structure-sensitive parameter may be drawn. The
closeness of the GB diffusion penetration depths of different GBs
under pressure equal to 1.2 GPa allows one to conclude that the CEF
takes place nad the compensation pressure is 1.2 GPa.
The research has been supported by a grant of Mianowski Foundation
(Kasa im.Jozefa Mianowskiego), Poland. Also support from the Royal
Society (UK), Exchange contract 638072.P652 is gratefully
acknowledged.
No part of this text can be reproduced without the written permission
of the authors.
Published with the permission of the authors of the article page.
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