Physico-Chemical nanomaterials science

Effect of external mechanical stresses on the heat of phase transformation in two-component metastable alloys
Korshak V. F., Tkachenko N. V., Boyko Yu. I.
V. N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv, 61022, Ukraine
E-mail: Vera.F.Korshak@univer.kharkov.ua

We studied the changes in the heat of eutectic transformation in Sn-38wt.%Pb and Bi-43wt.%Sn alloys caused by the action of an external compressive stress σ during heating. The experiments were carried out using the differential thermal analysis method. The intervals of σ include stresses at which the alloys exhibit superplastic (SP) properties. 
It was found for the first time that the dependence of the specific heat of the eutectic transformation on σ has a nonmonotonic character (Fig. 1). The dashed line (2) in Fig. 1 corresponds to the specific melting heat of tin used as a standard [1].
The specific melting heat of the Sn-38wt.%Pb alloy decreases by ~46% with an increase in σ from 0 to ~2.5 MPa and then increases more than two times when σ increases to 5.7 MPa [2].  

Fig. 1. Dependence of the specific melting heat of the Bi-43wt.%Sn alloy on the value of the external compressive stress σ (curve 1).	
The dependence of the specific melting heat on σ correlates well with the dependence of elongation before destruction on the value of σ at room temperature. This may indicate that the stresses at which the most significant decrease in the specific melting heat is observed are optimal for the manifestation of the SP properties by alloys. 
We associate the specific melting heat changes with the initial stage of decay of supersaturated solid solutions, changes in the relative share of phases (solid solutions based on alloy components and the concentration of these solutions). 

1.	Korshak V. F. and Tkachenko M. V. Effect of Preliminary Deformation on Heat of Melting of Superplastic Eutectic Alloy Bi–43 wt. % Sn // The Physics of Metals and Metallography.-2013.-114, N 11.-PP. 962–967.
2.	Korshak V. F., Postavnichii I. V. and Tkachenko N. V. Changes in the Heat of Melting of a Superplastic Eutectic Sn–38 wt. % Pb Alloy due to Preliminary Plastic Deformation // The Physics of Metals and Metallography.-2015.-116, N 10.-PP. 1029–1034.