Theoretical modeling and experimental researches for testing of hypothesis of press down on formation of brittle s- phase in Fe-Cr alloys by using of formation coating on these alloys were carry out. The idea about press down on formation of brittle s- phase in Fe-Cr - alloys consist in the following: because the beginning of formation of s-particles from surface of sample, therefore the first author - leader of this Project has proposed about closing of sample's surface by coating. If the material of coating will as physical for as chemical compatibility with substrate then this heterogeneous material (since substrate and coating have different chemical compositions) will found in stable state.
The alloy with composition 53wt.%Fe-47wt% Cr (or 50at.%Cr) have been using as substrate. The goals of investigations including:
a) Research of possibility preparation coating, which provide for as physical for as chemical compatibility, on for
example the Fe-47Cr as substrate by using as electrochemical for as ion-plasma’s methods for press down on
formation of sigma-phase,
b) Investigation influence more long time of treatment on stability of two-player material Fe-47% Cr-substrate and
protect coating at 700 C without formation s- phase;
c) Research possibility for prevention of formation sigma-phase into alloys with austenite - ferrite structure.
For realization of physical compatibility coating and substrate necessary assess composition of coating with minimum of difference between parameters of crystal lattices of coating and substrate (with minimum of misfit lattices). For chemical compatibility coating and substrate need minimum of gradient chemical potentials of components. For formation of coating the alloys of such system were selected as result of modeling.
Using computer modeling of the phase diagram and thermodynamic properties of the Fe-Cr and for system, which include the alloys for coating, make is possible us selection composition of coating, which has the enthalpy mixing is equal the enthalpy formation for the Fe-50at. % Cr alloy. For obtain good adhesion of coating on substrate we have used as electrochemical method for as ion-plasma’s method with magnetron spraying.
We have used treatment at 700 C in during 100 hours of alloys with coatings, obtained by electrochemical method and too ion-plasma's method. The results obtained by X-ray structural and electron microscopy methods have proved that formation of s - phase have been press down for Fe-47%Cr alloy by using electrochemical method for applying special coating.
Thus hypothesis about press down on formation of sigma-phase in (Fe-Cr)-alloys by using preparation special coating with good as physical for as chemical compatibility with substrate is true.
The work is part of a research projects under the terms RFBR N 02-03-32621and grant B0056 of the Russian Federation Target Program “Integration”.