“…Meanwhile, Cu atoms tend to form clusters at the corner of two {110} facets, as the {110} planes in the body centered cubic structure have the lowest surface energy (Zhang et al, 2006). The Cu clustered region observed here is analogous to the scenario in soft magnetic FeSiNbBCu alloys, in that Cu clusters provide nucleation sites for Fe–Si crystals (Pradeep et al, 2015). Thus, the Cu clustered region observed in this work may further serve as preferential nucleation sites for α 1 particles. Figure 7 α 1 / α 2 Pseudo-binary free energy diagram of the alnico 8 alloy.…”
Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe-Co-rich and Νi-Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2-4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.
“…Meanwhile, Cu atoms tend to form clusters at the corner of two {110} facets, as the {110} planes in the body centered cubic structure have the lowest surface energy (Zhang et al, 2006). The Cu clustered region observed here is analogous to the scenario in soft magnetic FeSiNbBCu alloys, in that Cu clusters provide nucleation sites for Fe–Si crystals (Pradeep et al, 2015). Thus, the Cu clustered region observed in this work may further serve as preferential nucleation sites for α 1 particles. Figure 7 α 1 / α 2 Pseudo-binary free energy diagram of the alnico 8 alloy.…”
Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe-Co-rich and Νi-Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2-4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.
“…Although a small amount of boride was observed in A2, α-FeCo remained the major phase that was formed with the increasing amount of Au as shown by the XRD graphs in Figure 1. Its formation resulted in an increase in the amount of B and Nb in the amorphous matrix [20,21] as compared to the amount in the bulk composition thereby increasing both T g and T m [22,23]. Increase in the Nb content of the amorphous phase as a consequence of increase in the amount of α-FeCo with increasing Au content of the alloy resulted in the formation of FeNbSi Laves phase [24] for Au content of 1 at.-% and higher.…”
The effect of addition of gold (Au) on the structure and mechanical properties of (Fe0.5Co0.5)71Nb4Si5B20 BMG alloy was studied. Addition of Au formed crystals in the BMG alloy. Gradual increase in the amount of Au added to the BMG alloy resulted in an increase in the amount of crystallinity and hardness of the alloy. Hardness values in excess of 1100 HV were found in all the alloys with a maximum value of 1245 HV. The thermal transition temperatures were also found to increase with an increasing amount of Au. Corner cracks were produced in the alloy with 1.5 at.-% Au content showing a low indentation fracture toughness value of 2.98 MPa-m0.5.
“…previous reports on the chemical composition of such Fe 3 Si nanocrystals. 5,15 However, a careful inspection of the proximity histogram shows a slight deficiency of Si (by 1-2 at. %) compared to the stoichiometric Fe:Si ratio, being in a good agreement with the M€ ossbauer spectroscopy results.…”
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