Texture formation of hot-deformed nanocomposite Nd2Fe14B/α-Fe magnets by Nb andZn additionsY. L. Ma, Q. Shen, X. B. Liu, Y. Qiu, C. H. Li, A. R. Zhou, J. C. Sun, and D. M. Chen Citation: Journal of Applied Physics 115, 17A704 (2014); doi: 10.1063/1.4860942 View online: http://dx.doi.org/10.1063/1.4860942 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/115/17?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Anisotropic hot deformed magnets prepared from Zn-coated MRE-Fe-B ribbon powder (MRE=Nd+Y+Dy) J. Appl. Phys. 115, 17A725 (2014); 10.1063/1.4866086 Electrical and magnetic properties of hot-deformed Nd-Fe-B magnets with different DyF3 additions J. Appl. Phys. 114, 133902 (2013); 10.1063/1.4822026 Enhanced texture in die-upset nanocomposite magnets by Nd-Cu grain boundary diffusion Appl. Phys. Lett. 102, 072409 (2013); 10.1063/1.4793429 Textured Nd2Fe14B flakes with enhanced coercivity J. Appl. Phys. 111, 07A735 (2012); 10.1063/1.3679425 Enhanced coercivity in thermally processed ( Nd , Dy ) ( Fe , Co , Nb , B ) 5.5 ∕ α - Fe nanoscale multilayermagnets J. Appl. Phys. 97, 104308 (2005); 10.1063/1.1905788

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Texture formation of hot-deformed nanocomposite Nd2Fe14B/a-Fe magnetsby Nb and Zn additions

Y. L. Ma,1,2,a) Q. Shen,3 X. B. Liu,2 Y. Qiu,1 C. H. Li,1 A. R. Zhou,1 J. C. Sun,1

and D. M. Chen1

1College of Metallurgical and Materials Engineering, Chongqing University of Science and Technology,Chongqing 401331, China2Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA3College of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054,China

(Presented 5 November 2013; received 23 September 2013; accepted 14 October 2013; published

online 9 January 2014)

The effect of Zn addition on the magnetic properties and microstructure of bulk hot-deformed

(NdDy)11.5Fe82.5�xNbxB6 (x¼ 0–2) alloys has been investigated. The remanence (Br) and coercivity

(Hci) can be enhanced substantially by the addition of Nb and can be further improved by the

combined addition of Nb and Zn. The addition of Nb increases the volume fraction of intergranular

phase and promotes more Zn to diffuse into the grain boundary. This grain boundary with changed

properties may benefit the c-axis texture formation during hot-deformation. Additionally, the

coercivity of alloys with both Nb and Zn increased up to 22% with increasing deformation ratio,

which may be due to the further diffusion of Zn into the grain boundary and the enhancement of

magnetic decoupling effect between Nd2Fe14B grains. VC 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4860942]

Bulk anisotropic nanocomposite RE2Fe14B/a-Fe (RE is

rare earth) alloys have attracted considerable interests due to

their lower rare earth content and higher theoretical energy

product than conventional RE-Fe-B.1,2 However, it is still a

great challenge to obtain bulk anisotropic nanocomposite alloys

with good magnetic properties by hot-deformation since little

RE-rich phase is contained, which is important to the develop-

ment of aligned platelet-shaped grains with c-axis parallel to

the press direction.3–5

In order to enhance the formation of c-axis texture in the

RE-lean precursor, many efforts have been made by applying

various methods, such as blending RE-rich melt-spun pow-

ders with RE-lean or a-Fe powders and a severe hot

deformation.6–9 Among the various methods, the additions

of low melting-point elements have been proved to be effec-

tive in greatly improving the texture development in RE-lean

precursor. Lee et al. and Gabay et al. obtained the bulk ani-

sotropic nanocomposite RE-Fe-B magnets by applying the

hot deformation combined with Cu and Al additions.10,11

The maximum energy product [(BH)m] of 37.3 MGOe was

obtained by hot-deformation and blending melt-spun powder

of MQP-15-7 with Nd-Cu powder.12 Moreover, our previous

studies have shown that Zn addition can improve the micro-

structure and magnetic properties of hot-deformed (HD)

nanocomposite RE-Fe-Nb-B magnets.13,14 However, Li

et al. found that the texture and magnetic properties of bulk

anisotropic RE-lean alloys can be also enhanced by Nb dop-

ing, which has a very high melting-point.15 To clarify the

effects of element additions on the evolution of microstruc-

ture and magnetic properties, the Nb doping, and Zn addition

in hot-deformed nanocomposite magnets have been investi-

gated in this work.

Alloy ingots of (NdDy)11.5Fe81.5�xNbxB6 (x¼ 0, 0.5, 1,

1.5, 2) prepared by induction melting were melt-quenched

onto a copper wheel rotating at a surface speed of 26 m/s

under Ar atmosphere. The ribbons were then crushed into

powder with a size of 150–200 lm. The starting ribbons

were well blended with pure Zn powder (0–2 wt. %) in the

glove box. Then, the mixture was put into the tungsten car-

bide mold, and then hot-pressed in the vacuum hot-press fur-

nace at a temperature of 700 �C for 2 min. The compressive

stress was 450 MPa. Hot-deformed magnets were prepared

by hot deforming the hot-pressed samples at about

800–850 �C with a pressure of 40–60 MPa. The hot deforma-

tion rate was 0.03 mm/s. The specimens were treated by nu-

merical control wire cutting and the magnetic properties of

magnets were measured by vibrating sample magnetometer.

The structure and microstructure of hot-deformed magnets

were examined by X-ray diffraction (XRD) with a Cu-Karadiation and transmission electron microscopy (TEM),

respectively.

Fig. 1 shows the magnetic properties of HD

(NdDy)11.5Fe81.5�xNbxB6 (x¼ 0–2) with different Zn addi-

tion. For HD magnets with Zn-free, the magnetic properties

increase largely with increasing Nb content. The enhanced

performance results from the formation of the c-axis texture

of Nd2Fe14B. As shown in Figs. 2(a) and 2(e), the c-axis tex-

ture is developed after 2% Nb addition, since the intensity of

(00 l) peaks and peaks with direction close to (00 l), such as

(006) and (105) peaks, increase largely. For the mechanism

of performance enhancement by Nb addition, Li et al. have

pointed out that Nb can be enriched at the amorphous graina)Electronic mail: ylma023@gmail.com

0021-8979/2014/115(17)/17A704/3/$30.00 VC 2014 AIP Publishing LLC115, 17A704-1

JOURNAL OF APPLIED PHYSICS 115, 17A704 (2014)

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boundary, which can improve the grain refinement and pro-

mote the c-axis texture formation during hot-deformation,

thus leading to the better magnetic properties.15

For HD magnets with 1% Nb, the magnetic properties

increase largely with Zn content increasing from 0 to 2 wt.

%, and Hci and (BH)m increase from 146 kA/m and 51 kJ/m3

to 670 kA/m and 175 kJ/m3, respectively, according to Fig.

1. From Figs. 2(c) and 2(d), it can be seen that the c-axis tex-

ture is improved greatly after 2 wt. % Zn addition. The

enhancement of magnetic properties can be ascribed to the

developed c-axis texture and improved microstructure by Zn

addition, which has been discussed in detail at our previous

papers.13,14

However, the magnetic properties of HD magnets with

different Nb content display very different variation trends

with increasing Zn addition as shown in Fig. 1. For HD mag-

nets with Nb-free, the magnetic properties increase little

with increasing Zn from 0 to 2 wt. %, and Hci increases from

97 kA/m to 130 kA/m and (BH)m increases from 24 kJ/m3 to

38 kJ/m3. On the other hand, (BH)m reaches its maximal

value at Zn content of 1 wt. % and is 165 kJ/m3 for HD mag-

nets with 2% Nb. When Zn content increases to 2 wt. %, Br

and (BH)m decrease to 0.99 T and 127 kJ/m3.

The magnetic properties are intimately related to the

microstructure evolution. Fig. 3 shows the TEM micrographs

of HD magnets with different additions. As shown in Fig. 3,

the microstructure of hot-pressed (NdDy)11.5Fe82.5B6 alloys

with 2 wt. % Zn addition consists of uniform and equiaxial

grains with size of about 60 nm. However, the HD magnets,

with a poor c-axis texture according to Fig. 2(b), have a very

inhomogeneous microstructure and grain size is more than

150 nm, which leads to poor magnetic properties since Br

and Hci of nanocomposite magnets are sensitive to the grain

size. For HD (NdDy)11.5Fe80.5Nb2B6 with 1 wt. % Zn, the

grains are elongated and aligned on the whole normal to the

press direction and platelet-shaped with thickness of about

100 nm and length of more than 300 nm. At the same time,

the c-axis texture is well developed according to the XRD

pattern in Fig. 2(f), since peaks of (105) and (006) become

the strongest peaks. The uniform microstructure and strong

c-axis texture can lead to improved magnetic properties.

Thus, the good Br and Hci values can be obtained.

Our previous studies have shown that the addition of Zn

can improve markedly the texture formation and magnetic

properties of HD nanocomposite Nd-Fe-Nb-B magnets.13,14

The improvement mechanism was considered to be that Zn

can diffuse easily during hot-pressing and hot-deformation

and be enriched at amorphous grain-boundaries, which is

helpful to the growth of oriented Nd2Fe14B grains and

increase the decoupling effect between Nd2Fe14B grains.

However, that does not answer why the Zn addition cannot

improve the microstructure and magnetic properties of HD

Nd-Fe-B magnets without Nb. For HD Nd-Fe-B alloys, the

Nd-rich intergranular phase is believed to be critical to the

c-axis texture formation, which has a low melting-point and

can provide a mass transport pass for growth of favorably

oriented Nd2Fe14B grains during hot-deformation.4,5

FIG. 1. Magnetic properties of HD (NdDy)11.5Fe82.5�xNbxB6 (x¼ 0� 2)

with different Zn addition.

FIG. 2. XRD patterns of HD (NdDy)11.5Fe82.5�xNbxB6 (x¼ 0� 2) with dif-

ferent Zn addition (y¼ 0� 2 wt. %): (a) x¼ 0, y¼ 0; (b) x¼ 0, y¼ 2; (c)

x¼ 1, y¼ 0; (d) x¼ 1, y¼ 2; (e) x¼ 2, y¼ 0; (f) x¼ 2, y¼ 1; and (g) x¼ 2,

y¼ 2.

17A704-2 Ma et al. J. Appl. Phys. 115, 17A704 (2014)

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128.235.251.160 On: Thu, 18 Dec 2014 07:58:39

According to Fig. 2(a), the (NdDy)11.5Fe82.5B6 alloy consists

of two phases, Nd2Fe14B and a spot of a-Fe. Since nanocom-

posite Nd2Fe14B/a-Fe alloys contain little Nd-rich intergra-

nular phase, the fine equiaxed-grains in the hot-pressed

alloy grow randomly during hot-deformation, leading to the

poor c-axis texture and magnetic properties of HD

(NdDy)11.5Fe82.5B6 alloy. Additionally, it is also difficult for

Zn to diffuse into the matrix particle during hot-pressing and

hot-deformation as the little amount of intergranular phase

which provides the fast-diffusion pass. Thus, Zn addition has

little effect on the microstructure and magnetic properties of

HD (NdDy)11.5Fe82.5B6 alloy.

With increasing Nb content, as shown in Fig. 1, the rem-

anence and coercivity of HD alloys increase largely and are

further improved by Zn addition. However, the effect of Zn

addition is very different with increasing Nb. With increas-

ing Zn addition, HD (NdDy)11.5Fe81.5Nb1B6 alloy has good

magnetic properties at the Zn content of 2 wt. %, but HD

(NdDy)11.5Fe80.5Nb2B6 alloy reaches its maximal (BH)m

when the content of Zn addition is only 1 wt. %. For nano-

composite Nd2Fe14B/a-Fe alloys, Nb addition can enhance

the formation of amorphous grain boundary.15 On the one

hand, it can also improve the grain refinement and texture

formation during hot-deformation, thus the magnetic proper-

ties of HD alloys increase with increasing Nb content.

On the other hand, the amorphous intergranular phase can

provide the fast-diffusion pass for Zn atoms during

hot-working, and Zn is enriched at the grain boundary after

hot-deformation, which can further improve the texture for-

mation and coercivity. Thus, with increasing Nb content, the

volume fraction of intergranular phase increases and more

Zn can be enriched at grain boundaries. However, Zn can

react with Nd2Fe14B and resulting in the formation of other

phases such as a-Fe, Nd-Zn, and Fe-Zn during hot-working,

which decrease the content of hard magnetic phase.13 When

Nb content is up to 2%, more Zn can diffuse into the inter-

granular phase, leading to the introduction of more

non-magnetic phases. From the XRD pattern shown in Fig.

2(g), it can be seen the content of a-Fe in the HD

(NdDy)11.5Fe80.5Nb2B6 with 2 wt. % Zn is higher than

that without Zn. Thus, the magnetic properties of HD

(NdDy)11.5Fe80.5Nb2B6 magnets decrease after the addition

of 2 wt. % Zn due to the introducing of too much

non-magnetic phases.

Additionally, we found the coercivity of HD

(NdDy)11.5Fe81.5Nb1B6 with 2 wt. % Zn has a special varia-

tion tendency. It increases up to 22% first, and then decreases

gradually with increasing deformation. This may result from

that the grain boundary diffusion of Zn can lead to the

enhancement of magnetic decoupling effect between

Nd2Fe14B grains, which may be dominant in the early stage

of hot-deformation.

In summary, a way for improving the HD nanocom-

posite Nd2Fe14B/a-Fe magnets has been provided by com-

bining Nb and Zn additions. The magnetic properties and

microstructure can be only improved in that alloys with

Nb by Zn diffusion along the grain boundary. With

increasing Nb content to 2%, the maximal value of (BH)m

of 165 kJ/m3 was obtained by less Zn addition, resulting

from the good microstructure and strong c-axis texture.

Additionally, the coercivity of HD (NdDy)11.5Fe81.5Nb1B6

with Zn addition increased first with increasing deforma-

tion due to the further diffusion of Zn into the grain

boundary.

This work was supported by the National Natural

Science Foundation of China (No. 51201191), the Research

Foundation of Chongqing Education Committee (No.

KJ121415), and the Chongqing Natural Science Foundation

(No. CSTC2012JJA50004).

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(2007).8D. Lee et al., J. Appl. Phys. 99, 08B516 (2006).9Y. G. Liu et al., Appl. Phys. Lett. 94, 172502 (2009).

10A. M. Gabay et al., J. Magn. Magn. Mater. 302, 244 (2006).11D. Lee et al., IEEE Trans. Magn. 40, 2904 (2004).12X. Tang et al., Appl. Phys. Lett. 102, 072409 (2013).13Y. L. Ma et al., J. Magn. Magn. Mater. 322, 2419 (2010).14Y. L. Ma et al., IEEE Trans. Magn. 45, 2605 (2009).15J. Li, Y. Liu, and Y. L. Ma, J. Magn. Magn. Mater. 324, 2292 (2012).

FIG. 3. TEM of hot-pressed (a) and hot-

deformed (b) (NdDy)11.5Fe82.5B6 with

2 wt. % Zn addition and hot-deformed

(c) (NdDy)11.5Fe80.5Nb2B6 magnets

with 1 wt. % Zn addition.

17A704-3 Ma et al. J. Appl. Phys. 115, 17A704 (2014)

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