Micostructure and Magnetic Properties in Nanostructured Fe and Fe-Based Intermetallics Produced by High-Pressure Torsion

Abstract

The microstructure and magnetic properties of nanostructured pure iron, FeCo and FeNi 3 produced by high-pressure torsion (HPT) were investigated. Electron backscattered diffraction (EBSD) technique was used to study the evolutions in microstructure and crystallographic texture during HPT, revealing that a weak deformation texture with an orientation of h110i bcc being parallel to the disc normal for pure iron and FeCo while h110i fcc was found to be parallel to the hoop direction of the HPT disc in FeNi 3 . The grain size of the HPTed materials was characterized by means of EBSD and transmission electron microscopy (TEM), and its influence on the coercivity was investigated. The other highlight of this paper is the use of a focused ion beam (FIB)-SEM dual beam instrument. This enabled us to obtain quite high image quality (IQ) values for the EBSD measurements even for the highly deformed microstructure in the current ferromagnetic intermetallics. Keywords: bulk nanostructured metals, severe plastic deformation, electron backscattered diffraction (EBSD), magnetic materials, coercivity, focused ion beam-scanning electron microscope (FIB-SEM)

Anomalous magnetic anisotropy and magnetic nanostructure in pure Fe induced by high-pressure torsion straining

“…The HPT process has also attracted attention in the field of magnetic materials [1,4,[6][7][8][9][10][11][12][13]. The characteristic nanostructures produced using the HPT process considerably modifies the crystal growth kinetics [8,9].…”

Synthesis of Nanostructured TiFe Hydrogen Storage Material by Mechanical Alloying via High‐Pressure Torsion

“…The hardness, which follows a behavior similar to the ones reported for most of the HPT-processed materials, [59][60][61] increases with increasing the shear strains at early stages of straining and saturates to a steady-state level of 800 HV at high shear strains. This steady-state hardness is 2-3 times higher than the hardness of HPT-processed Ti [62][63][64] and Fe [65][66][67] and about 20% smaller than the hardness of HPT-processed TiFe. [23] These results indicate that there are still microstructural heterogeneities from the disc center to disc edge even after ten turns of HPT.…”

“…The average grain size was estimated by averaging the two orthogonal axes of each colored area in the crystal orientation maps for about 100 grains. This average grain size is almost three times smaller than the grain size of HPT-processed Ti [62][63][64] and Fe [65][66][67] due to the formation of TiFe phase as well as due to the effect of Ti-Fe composite on hindering the recrystallization and grain boundary migration. [28][29][30][31] Automatic phase mapping using the ASTAR device in Figure 4e shows the presence of some amount of HCP phase even at 3-5 mm away from the disc center, suggesting that the mechanical alloying is not completed.…”

Emerging Opportunities in Manufacturing Bulk Soft-Magnetic Alloys for Energy Applications: A Review

“…Hosokawa et al explored HPT processing of pure Fe and Fe-Co and Fe-Ni 3 alloys. 79 HPT conducted at ambient temperatures resulted in drastically increased material hardness compared with the initial ingot because of grain refinement. Notably, the FCC-based FeNi 3 alloy exhausted the extent of cold working after initial deformation steps, while the BCC-based materials continued to harden at much larger deformation strains.…”