Effect of severe plastic deformation by torsion on the properties and structure of the Ni54Mn21Ga25 and Ni54Mn20Fe1Ga25 alloys

Effect of alloying additions and atomic disordering on the physical properties of magnetic Ni2MnGa-based shape memory alloys

“…In agreement with the results in [8,9,11,12], the experimental results shown in Fig. 4 also demonstrate that the temperature dependences of the thermoelec tric power of plastically deformed Ni 2 MnGa based alloys are linear functions over a wide temperature range, which is usually observed in amorphous sys tems.…”

“…It should be noted that annealing of plastically deformed samples can result in both an increase and a decrease in their linear sizes: compare the magnitudes and directions of the change in the relative elongation upon annealing of plastically deformed Ni 54 Mn 21 Ga 25 and Ni 48 Co 2 Mn 28.5 Ga 21.5 given in [12] and Fig. 3, respectively.…”

“…In [4][5][6][7][8][9][10][11][12], we showed that all magnetic Ni 2 MnGa based alloys undergo almost the same structural changes upon a change in the temperature or as a result of atomic disordering during MQ or HPT. At high temperatures, the structure of homogenized cast coarse grained (with a grain size of 0.3-0.8 mm) alloys is ordered according to the L2 1 type.…”

“…As follows from the experimental data shown in Fig. 3, the ΔL(T)/L 0 and α(T) depen dences in the plastically deformed alloys change irre versibly when the temperature is cycled from room temperature, as in the case of other alloys [6,8,12,13]. The irreversibility effect is maximal for all plasti cally deformed Ni 2 MnGa based in the same tempera ture range (500-550 K), where the transition from an amorphous-crystalline into nano and submicrocrys talline structures takes place.…”

“…In this work, we achieved disordering of an Ni 50 Mn 28.5 Ga 21.5 alloy with 2 at % Cu or Co by the following two methods: melt quenching (MQ) of thin 30 μm thick ribbons (at a rate of ~10 5 K/s) on a rotating copper wheel and severe plastic deformation via high pressure torsion (HPT) of disks 10 mm in diameter and 0.5 mm in thickness in Bridgman anvils through 5 revolutions. Earlier, we performed similar investigations of a nonstoichiometric Ni 54 Mn 21 Ga 25 [4][5][6][7][8][9][10][11] and a quaternary Ni 54 Mn 20 Fe 1 Ga 25 alloy with 1 at % Fe and the 3d 6 4s 2 valence shell [12].…”