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Submitted on 1 Jan 1987
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DISCUSSION : TRANSFORMATIONS AND INTERFACES II
J. San Juan
To cite this version:
J. San Juan. DISCUSSION : TRANSFORMATIONS AND INTERFACES II. Journal de Physique
Colloques, 1987, 48 (C8), pp.C8-539-C8-540. �10.1051/jphyscol:1987884�. �jpa-00227188�
JOURNAL DE PHYSIQUE
Colloque C8, suppl6ment au 11-12, T o m e 4 8 , dhcembre 1 9 8 7
DISCUSSION :
TRANSFORMATIONS AND INTERFACES I1
J. S A N JUAN
Dpto de Fisica del Estado Solido, Facultad de Ciencias, Aptdo 644, SP-48009 Bilbao, Spain
Along this brief comment I am not going to great all the papers presented at the session on Transformations and Interfaces I1 and that I exposed during the oral session, but only those that led to discussion afterwards, together with some personal remarks that I, as a rapporteur, consider that may be interesting.
A subject that caused a wide discussion was the internal friction (I.F.) due to surface layers deposited on samples. In the light of the papers shown, it is clear that the I.F. may allow to study not only the phase transition solid-liquid, as it has been observed by now, but also the phase transitions inherent in the liquid itself, as for instance the transitions smectic-nematic and nematic-isotropic observed by Dr. SAMATOWICZ [I] in liquid crystals. Nevertheless, in order that this type of studies may yield accurate quantitative information, there are two aspects that will have to be clarified because at this moment they are still a matter of discussion.
a) The influence of the substrate nature, because though Dr. SAMATOWICZ asserted that it didn't have any influence on the general aspects of the spectrum (Fig. 5 from Ell) it is obvious there is a strong distortion of the relative height of the peaks, depending on the substrate (Fig. 5 from [I] and Fig. 1 from C21).
b) The influence of the substrate superficial state, because this will have a strong influence on the internal friction spectrum as it was suggested by Prof. GONDI. In particular, Prof. FANTOZZI pointed out that in previous papers, a strong influence of the substrate deformation degree (aluminium) on the aspect of the internal friction spectrum had been observed C31.
Both aspects will have to be studied more systematically. In particular, a good characterization of the sample superficial state, is to be recommended.
Another point of interest are the papers presented on ordering and decomposition phenomena linked to long range diffusion processes C4.51. It has to been pointed out that the transformations controlled by this type of processes have been slightly studied up to now through internal friction, compared to the short range diffusion processes or to the transformations without diffusion. Because of that, it would be interesting to make more systematic internal friction studies on this type of processes, determining, among other parameters, the concentration influence as it was commented during the discussion.
On the other hand, in spite of having been more studied, the transformations without diffusion still are under discussion as it was clear after Dr. BIDAUX presented his paper C61, where the non-existence of pretransitional effects in the HCP-FCC transformation in cobalt was shown. These effects were discussed, together with the difference observed in the internal friction spectrum during the heating or the cooling. As I already pointed out during the discussion, I think this difference of the behaviour in the internal friction spectrum may be due to the effect of impurities that are able at high temperatures to migrate to the interphases, blocking them. Because of that, though it is true that many materials are not commercially available in high purity quality, as Dr. SCHALLER observed, for the case of cobalt, I think we all should make an effort to study these processes in high purity metals and alloys. This suggestion may be justified if we take into
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987884
C8-540 JOURNAL DE PHYSIQUE
accuunr: that the interphase-impurity interaction is an aspect of great interest not only in allotropic transformations, but also in any type of structural transformation of first order as the martensitic transformation may be.
Interesting remarks arose concerning internal friction in composite materials, particularly on WC-Co C71. Prof. FANTOZZI asked why neither the two Co phases usually observed by X-rays at R.T., nor the HCP-FCC transition were observed in the cobalt obtained in the WC-Co composite presented. Dr. SCHALLER pointed out that after the WC-Co elaboration process, cobalt is not at equilibrium due to the strong strains produced by the WC skeleton. The biggest part is found in the cubic phase at RT and though there is also a small part of the cobalt hexagonal phase, the usual HCP-FCC transformation does not take place, probably due to the high strength of the WC skeleton. The stabilization of the cubic phase, Dr. SCHALLER said, may be attributed to two types of phenomena: on one hand, the effect of the solute elements dissolved in the Co array during the elaboration process and on the other hand the size effect, because the Co powder is also cubic at R.T. In these conditions, the internal friction peak observed at about 900 K in WC-Co is perhaps due to dislocation movements in the Co cubic phase, so this process can only take place when the hexagonal phase is removed. Finally, Dr. Schaller added that it has to be kept in mind that the mechanical properties of the Co contained in the WC-Co composite are not the same as those for pure Co.
Finally, I want to point out the interest of the papers concerning high T superconductors presented by Dr. ALMOND C8,91 during his invited lecture. I thing that with these new materials a new field of study on internal friction is opened, because though the fundamental property is superconductivity, their technological development requires a good knowledge of their mechanical and microstructural properties. It is in this sense that I consider that internal friction techniques have a lot to say.
C11 Internal friction of solid samples covered with surface layer of liquid crystal D. Samatowicz
This conference
[21 Internal friction of metals covered with thin organic substance layer E. Denga
This conference
C31 Influence of plastic deformation on internal friction of aluminium with oil layer
B. Augustyniak, G. Fantozzi, W. Chomka J. de Phys.
44
(1983) C9-499[41 Kinetics of ordering in equatomic Co-Pt alloy E. Klugman, B. Augustyniak, H.J. Blythe This confence
C51 Critical stress-induced relaxational effects in relation to long-range ordering in AugCu and self-induced ordering in AuNi solid solution
G. Renaud, M. Belaklovsky, J. Hillairet This conference
C61 Study of the HCP-FCC phase transition in cobalt by internal friction and elastic modulus measurements in the KHz frequency range
J.E. Bidaux, R. Schaller, W. Benoit This con£ er enc e
C71 Internal friction of WC-Co hard metal J.J. Ammann, R. Schaller
This conference
C81 Ultrasonic attenuation in the high T superconductor YBa2Cu307 D.P. Almond, E. Lambson, G.A. Saunde$s, Wang Hong
This conference
C91 An ultrasonic study of the elastic properties of the normal and superconducting states of YBa Cu 0,
D.P. Almond,
