Abstract
This work focuses on the temperature evolution of the martensitic phase ε (hexagonal close packed) induced by the severe plastic deformation via High Speed High Pressure Torsion method in Fe57Mn27Si11Cr5 (at %) alloy. The iron rich alloy crystalline structure, magnetic and transport properties were investigated on samples subjected to room temperature High Speed High Pressure Torsion incorporating 1.86 degree of deformation and also hot-compression. Thermo-resistivity as well as thermomagnetic measurements indicate an antiferromagnetic behavior with the Néel temperature (TN) around 244 K, directly related to the austenitic γ-phase. The sudden increase of the resistivity on cooling below the Néel temperature can be explained by an increased phonon-electron interaction. In-situ magnetic and electric transport measurements up to 900 K are equivalent to thermal treatments and lead to the appearance of the bcc-ferrite-like type phase, to the detriment of the ε(hcp) martensite and the γ (fcc) austenite phases.
Highlights
The ability of some alloys to remember their shape at two different temperatures is called shape memory effect (SME), and the respective materials are referred to as shape memory alloys (SMAs)
As it is already known, the fcc-to-hcp transformation process is promoted by gliding of multiple Shockley partials of 1/6 fcc type on alternate {111} fcc planes that depends on crystal orientation [34]
It was reported that the grain size obtained in the severe plastic deformation (SPD) process of fcc materials is closely related to SFE value
Summary
The ability of some alloys to remember their shape at two different temperatures is called shape memory effect (SME), and the respective materials are referred to as shape memory alloys (SMAs). SME is governed by a non-diffusive first-order phase transformation called martensitic transformation (MT). During the MT the atoms move at distances smaller than the inter-atomic distances, and they go from an austenitic phase of high temperature and high symmetry (cubic type) to a martensitic phase of low temperature, with lower symmetry (tetragonal, orthorhombic, hexagonal).
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