Magnetic pulse controlled microstructure development in Co₄₉Ni₂₁Ga₃₀ single crystals

Abstract

A pulsed magnetic field (MF) up to 0.6 T leads to the generation of fine microstructure through the change in the dynamics of the interaction process between the MF and the magnetic- and microstructure in Co49Ni21Ga30 magnetic shape memory alloy single crystals. This paper addresses the impact of pulsed and permanent MF on the transformation behaviour in Co49Ni21Ga30. A pulsed MF can result in different microstructural accommodation processes in stress-induced martensite, as compared to an application of a mechanical stress or permanent MF. In a pulsed MF, the development of new nano-twin systems in the martensitic structure of the CoNiGa alloy and the formation of fine magnetic domains at the microscale are observed.

Structural changes driven by pulsed magnetic fields: comparison of off-stoichiometric CoNiGa and (CoNiCu)(AlGaIn) intermetallic compounds

“…4a-c) when, in addition to the larger twins observed after 5000 magnetic pulses of 0.3 T, nano twins are formed after another 50000 magnetic pulses of 0. The development of different nano-twin systems under pulsed MF shows that, in contrast to previously described multi-variant changes of the martensitic structure in CoNiGa alloys [9], another variant of material fatigue in the structure is possible. This is the development of a nano-twin structure under the influence of a magnetic field and preliminary application of an external load.…”

“…CoNiGa single crystals exhibit the formation of twinned martensite crystals (see [9] for example). In the case of the (CoNiCu)(AlGaIn) polycrystal, martensitic crystals are formed simultaneously with a massive movement of dislocations (Fig.…”

“…The setup for applying a pulsed magnetic field (MF) has been described in [9]. For the compression tests on a universal testing machine, non-magnetic fixtures (Ti alloy) were manufactured.…”

“…1 were combined and the coils were switched alternately. polycrystals were conducted using a special impulse magnetic driver, which has been described in detail earlier [9]. The test crystals had the dimensions 7.0×1.7×1.7 mm.…”

“…Coexistence of several twinned martensite variants was the main reason for the formation of the crack network leading to fracture in NiMnGa [8]. An attempt to control the magnetic shape memory by a pulsed magnetic field in CoNiGa resulted in some response, but fatigue effects duly appeared [9]. On the other hand, the multi-component (CoNiCu)(AlGaIn) single-phase high-entropy intermetallic showed a triclinically distorted B2 structure similar to TiZrHfCoNiCu and underwent a B2↔L10 martensitic transformation [10].…”