Influence of deformation and heat treatment of polycrystalline Ni_2.19Fe_0.04Mn_0.77Ga alloy on the microstructure evolution and development of the martensitic transformation

 

I. I. Musabirov¹, I. M. Safarov¹, I. Z. Sharipov¹, R. R. Mulyukov¹,  A. V. Mashirov², V. V. Koledov²

¹Institute for Metals Superplasticity Problems of Russian Academy of Sciences, Ufa, Russia

² Kotelnikov Institute of Radio-engineering and Electronics of RAS, Moscow, Russia
 

The paper is received on January 11, 2015

 

Abstract: The results of a study of the physical properties of polycrystalline Ni_2.19Fe_0.04Mn_0.77Ga alloy in initial cast state, after severe plastic deformation by torsion under pressure and after annealing of deformed material at temperatures of 400°C, 500°C, 600°C and 700°C are present. Record the temperature dependence of the magnetization and electrical resistivity in the initial cast alloy shows that the temperature intervals of the martensitic and magnetic transitions overlap. According to the study of the microstructure of the alloy in different structural states, the dependence of the average grain size of the recrystallized structure in the sample from the degree of annealing is established. It is shown that the martensitic structure of the material is observed only after annealing of the deformed alloy at 500°C. As a result of severe plastic deformation of the investigated alloy the ferromagnetic ordering is destroyed and the martensitic transformation is suppressed. Subsequent heat treatment of deformed alloy leads to a gradual recovery of ferromagnetic order.

Key words: shape memory effect, ferromagnetic shape memory effect, martensitic transformation, severe plastic deformation, NiMnGa alloys.