Nanocomposites and nanomaterials

Phase transformation induced by superplastic creep in the eutectic Sn-38wt%Pb alloy.
Shapovalov Yu.O.1, Korshak V.F.2
1 B. Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, 47 Nauky Ave., Kharkiv, 61103, Ukraine.
E-mail: shapovalov@ilt.kharkov.ua
2 V.N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv, 61022, Ukraine.

Fig. 1

The experiments were carried out on the cast alloy with subsequent compression by ~ 75% alloy. The alloy was aged during 5 years at room temperature prior mechanical tests. Mechanical tests were provided under conditions of creep at constant load and at room temperature. The structure of the samples was studied by use of electron microscope VEGA3 TESCAN. It was shown previously in [1] that the initial phase state of the alloy after preliminary compression is non-equilibrium. An investigation of the alloy after ageing in the course of 5 years has shown that equilibrium hadn’t been reached. Phase state of the alloy Sn-38wt%Pb under conditions when it is capable to reveal the superplasticity effect appears to be metastable during a significant period of time. During mechanical tests the samples were deformed to the relative elongations of more than 100 % that is the alloy was still capable to superplastic forming. Examination of the surface of the deformed samples revealed numerous stretched grains and most of the Pb-phase grains contained precipitation of the Sn-Phase with the size of inclusions from 1 μm to less than 500 nm (fig. 1).
Formation of the amorphous-like component, which has already been observed by authors in the investigated alloy, due to appearance of nanoscale precipitations of a new phase in the material allow to observe the superplastic behaviour at room temperature and after long ageing under certain conditions.

1.	Korshak V.F., Shapovalov Yu.A., Pal’-Val’ P.P., Mateichenko P.V. Changes in the structural phase state and elastic and inelastic properties of superplastic eutectic Sn–38% wt Pb alloy during the aging process.// Bull Russ Acad Sci Phys.–2011.–75.–P. 1345–1351