Nanocrystallization and magnetic properties of amorphous Nd9Fe85B6 subjected to high-pressure torsion deformation upon annealing

Abstract

A high number density ͑ϳ10 23 m −3 ͒ of ␣-Fe nanocrystals with a size below 10 nm has been induced in amorphous Nd 9 Fe 85 B 6 by high-pressure torsion deformation ͑HPTD͒ at room temperature. The amorphous Nd 9 Fe 85 B 6 subjected to HPTD presents a quite different crystallization behavior as compared with the nondeformed alloy. The growth activation energies E g = 0.9 eV for ␣-Fe nanocrystals and 0.5 eV for Nd 2 Fe 14 B nanocrystals are determined from the annealing time dependence of their size. The ␣-Fe/ Nd 2 Fe 14 B nanocomposite magnets prepared by the combination of HPTD and subsequent thermal annealing show enhanced magnetic properties due to a small grain size as compared with the magnets prepared by directly annealing amorphous Nd 9 Fe 85 B 6 .

High-Pressure Torsion of Machining Chips and Bulk Discs of Amorphous Zr<SUB>50</SUB>Cu<SUB>30</SUB>Al<SUB>10</SUB>Ni<SUB>10</SUB>

“…[3][4][5][6][7][8][9][10][11][12][13][14][15] The application includes the consolidation of metallic powders, [3][4][5] composites, [6][7][8][9][10][11][12] ball-milled powders, 13,14) amorphous powders, 15) amorphous ribbons, 16) and very recently machining chips. 17,18) Strain-induced amorphization was reported for some compounds, 19,20) whereas crystallization is detected in amorphous materials such as Cu 50 [21][22][23][24][25][26][27][28][29][30][31] It is well established that bulk amorphous materials have high strengths and high hardness [32][33][34][35] and it is known that processing through HPT leads to an increase in the strength of metallic materials. 1,<...>…”

“…17,18) Strain-induced amorphization was reported for some compounds, 19,20) whereas crystallization is detected in amorphous materials such as Cu 50 [21][22][23][24][25][26][27][28][29][30][31] It is well established that bulk amorphous materials have high strengths and high hardness [32][33][34][35] and it is known that processing through HPT leads to an increase in the strength of metallic materials. 1,2) In spite of many publications regarding the HPT processing of amorphous materials, [21][22][23][24][25][26][27][28][29][30][31] little attention has been paid to the strength of amorphous materials after processing by HPT.…”

Evolution of the amorphous structure in melt-spun Ti50Ni25Cu25 alloy subjected to high pressure torsion deformation

“…Without any doubt, an important role in the structural transformations under HPT processing is played by free volume evolution during HPT and local structural variations near shear bands [27]. In particular, an increase in free volume during HPT and diffusion activation due to free volume leads, during the HPT processing of amorphous MS Nd-Fe-B alloys, to the immiscibility of the amorphous phase with precipitation in the amorphous phase of the a-Fe phase nanocrystals [21,29]. In the MS TiNiCu amorphous alloy, the immiscibility of the amorphous phase with precipitation of nanocrystals of pure metals does not take place during HPT processing, but there occurs HPT-induced nanocrystallization with formation of very small nanocrystals of the B2 phase, with a size of about 3 nm [21].…”

Stability of an Amorphous TiCuNi Alloy Subjected to High‐Pressure Torsion at Different Temperatures

“…Plastic deformation in amorphous alloys at relatively low temperatures (<0.5 Tg) proceeds preferably in homogeneously by the formation of shear bands, and this leads to certain structure transformations, associated with the enhanced free volume and crystallization . As already noted above, it has been shown recently that SPD processing by HPT can lead to a modification of the amorphous phases . For example, in the case of Nd–Fe–B MS amorphous alloys, HPT processing leads to a separation of elements and nanocrystallization of α‐Fe‐nanocrystals (with a size of ≈20 nm) in the amorphous phase .…”