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Mechanical alloying o Fe100-x-yNbxBy (x=5, 10; y=10, 15): F om pu e
powde mix u e o amo phous phase
J.J. Ipus, J.S. Blázquez, V. F anco, A. Conde*
Dp o. Física de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P.O.
Box 1065, 41080, Se illa, Spain.
Abs ac
The mechanical alloying p ocess o Fe75Nb10B15 and Fe85Nb5B10 sys ems has been
s udied om an ini ial mix u e o elemen al powde s. The amo phiza ion p ocess is
moni o ed by X- ay di ac ion, Mössbaue spec oscopy and magne iza ion
measu emen s. An amo phous phase (wi h a Cu ie empe a u e o ~250 K) is o med
a e 400 h milling only o Fe75Nb10B15 alloy, whe eas a bcc supe sa u ed solid solu ion
is he inal p oduc a e milling Fe85Nb5B10 alloy. Fo bo h cases, a dispe sion o ~10 %
in he Fe con en o he powde pa icles pe sis s a e 400 h milling. Powde pa icle
size, C con en and la ice pa ame e o bcc phase a e la ge o he alloy wi h he
highes Nb con en .
Keywo ds: A. Nanos uc u ed in e me allics; A. Magne ic in e me allics; C. Mechanical
alloying and milling.
*Co esponding au ho : P o . A. Conde
Depa amen o de Física de la Ma e ia Condensada. Uni e sidad de Se illa.
Apa ado 1065, 41080 Se illa (Spain).
Phone : (34) 95 455 28 85/ Fax : (34) 95 461 20 97
E-mail: [email p o ec ed]
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1 In oduc ion
Nanoc ys alline ma e ials a e de ined by a c ys al size below 100 nm. As a limi ,
amo phous ma e ials a e solid sys ems whe e he s uc u al long ange o de is los .
These ma e ials ha e ecei ed much a en ion due o hei physical p ope ies
(mechanical and magne ic), which a e clea ly di e en om hose exhibi ed by
con en ional mic os uc u es and, in some cases, imp o e hei echnological
applicabili y [1,2,3]. One way o ob ain nanoc ys alline ma e ials is by pa ial
de i i ica ion o a p ecu so amo phous alloy du ing con olled he mal annealing. This
echnique con ols he mic os uc u e o ma e ials and hus op imizes he p ope ies o
he inal p oduc . Ano he possibili y is mechanical alloying, which has become a e y
e sa ile echnique o di ec ly p oduce me as able mic os uc u es (amo phous,
nanoc ys allines, supe sa u a e solid solu ion, e c) [1] om elemen al powde s o alloys.
Du ing his milling p ocess he ma e ial is submi ed o ac u e and cold welding
phenomena, as well as in ensi e plas ic de o ma ion, which de ine he powde
mo phology, mic os u u e and p ope ies. The con inuous s o ing o de ec s in he
c ys alline phase du ing milling p ocess uns abilizes i , leading o nanoc ys alline and/o
amo phous s uc u es [1].
Nanoc ys alline Fe-M-B ype alloys (M= Z , Nb, e c), so-called Nanope m [4],
a e a ac i e due o hei so magne ic p ope ies a e op imum he mal ea men and
a e used in comme cial applica ions such as elecommunica ions, mic o de ices and
powe elec onics [5,6]. Al hough hese sys ems a e gene ally ob ained by apid
quenching and subsequen annealing, nanoc ys alline alloys o hese composi ions can
be di ec ly ob ained by mechanical alloying o elemen al powde s. As so magne ic
p ope ies depend on he s uc u e o he ma e ial [7,8,9], i s s uc u al cha ac e iza ion
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is a e y impo an ask o unde s and he sys em beha io and o p edic i s possible
echnological capabili ies.
In his s udy, wo Fe100-x-yNbxBy (x=5, y=10 and x=10, y=15) alloys we e
p oduced by mechanical alloying om a mix u e o pu e elemen s and hei
mo phological, composi ional and mic os uc u al e olu ion, as well as hei he mal
s abili y, we e s udied as a unc ion o milling ime. The amo phiza ion o he e na y
FeNbB sys em by apid quenching me hods has been s udied p e iously [10]. Whe eas
composi ions simila o Nb10 can be ob ained in amo phous s uc u e, hose simila o
Nb5 can no be ob ained as amo phous.
2 Expe imen al
Fe100-x-yNbxBy (x=5, y=10 and x=10, y=15) composi ions we e p epa ed by ball
milling in a plane a y mill F i sch Pul e ise e 4 Va io om elemen al powde s ( 99 %
pu i y), wi h pa icle size d <200 m o Fe and Nb and d <1 mm o B. Fo simplici y,
he s udied alloys will be named in he ollowing by hei Nb con en : Nb10 o
Fe75Nb10B15 and Nb5 o Fe85Nb5B10. The ini ial powde mass was 30 g and he ball o
powde a io was 10:1. The o a ional speed o he disk which suppo s he ials was
150 pm and ha o he ials was 300 pm in opposi e di ec ion. A e selec ed imes,
some powde was aken ou om he ials o cha ac e ize he mo phology, composi ion,
mic os uc u e and he mal e olu ion. The opening and closing o he ials was done
unde a gon a mosphe e in a Sa on Omega glo e box o a oid oxygen and humidi y
con amina ion.
Pa icle size dis ibu ion and mo phology we e s udied by scanning elec on
mic oscopy (SEM) using seconda y elec ons (SE) and backsca e ed elec ons (BSE)
modes in a Jeol JSM-6460 LV ope a ed a 30 kV. Composi ional e olu ion was s udied
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by ene gy dispe si e X- ay (EDX) analysis using an Incax-sigh o Ox o d Ins umen s.
Phase composi ion and s uc u e we e s udied om X- ay di ac ion (XRD), using Cu
K adia ion, and Mössbaue spec ome y (MS). Mössbaue spec a we e eco ded a
oom empe a u e in a ansmission geome y using a 57Co(Rh) sou ce. Values o he
hype ine pa ame e s we e ob ained by i ing wi h NORMOS p og am [11]. The
isome shi , I, was quo ed ela i e o ha o -Fe a oom empe a u e.
Magne iza ion was measu ed using a maximum applied ield o 1.5 T, in he
empe a u e ange om 77 o 440 K, e e y 15 K, in a ib a ing sample magne ome e
(VSM). The alues o magne iza ion we e ob ained by ex apola ion o ze o ield o he
linea i ing o he high ield magne iza ion. The mal cha ac e iza ion o he samples
was s udied by di e en ial scanning calo ime y (DSC) using a Pe kin-Elme DSC7 in
A a mosphe e.
3 Resul s
3.1 Mo phology and composi ion
Figu e 1 shows SEM images o bo h alloys ob ained a e di e en milling
imes. Fo bo h alloys a sho milling imes, <20 h, he pa icles a e o med by join
laye s and inclusions, which p esen di e en composi ion. In o de o app ecia e his
he e ogenei y in mo e de ail, igu e 2 shows SE ( igu e 2a) and BSE ( igu e 2b) images
aken on a ypical pa icle a e 2 h milling o Nb10 alloy. Figu e 2c shows EDX
spec a aken on he di e en poin s ma ked in igu e 2a. The A spec um, on a da k
inclusion, only shows he emission line o bo on besides he ypical backg ound a low
ene gy, so his zone is ich in his ligh elemen . The B and C spec a show zones ich in
Fe and Nb, espec i ely. The e o e, he he e ogenei y o he indi idual powde pa icles
is e idenced o sho milling imes in he condi ions used in his s udy.
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A e 20 h milling, he powde s show po es and c acks on hei su ace o Nb10
and Nb5 alloys bu no clea laye s and, o longe milling imes, 100 h,
agglome a ion o powde is obse ed. This p ocess seems o depend on milling
condi ions, as o he au ho ha e de ec ed agglome a ion o pa icles much ea lie o
simila composi ions (e.g. a e 5 and 15 h o Fe84Nb7B9 alloy wi h mo e ene ge ic
milling condi ions [12]). The pa icles ha o m hese agglome a es a e la ge o Nb10
han o Nb5 alloy. A e 400 h milling, he agglome a es a e no obse ed o Nb10
alloy bu , o Nb5 alloy, he pa icles a e s ill agglome a ed.
F om SEM images, a s a is ical analysis o he a e age pa icle size e olu ion,
<d>, has been pe o med o e ~100 pa icles pe sample (Figu e 3) o bo h alloys.
A e 20 h milling, <d> inc eases o e <d> > 200 m o bo h alloys. As milling ime
inc eases, a dec ease in <d> is obse ed and, abou 100 h milling, his alue is
s abilized, being smalle o Nb5 alloy (~ 25 m) han o Nb10 alloy (~ 50 m). This
indica es ha a s a iona y si ua ion be ween cold welding and ac u e has been
achie ed.
The composi ional e olu ion was s udied by EDX om a s a is ical se o ~20
pa icles o each sample. As B con en canno be quan i a i ely measu ed by EDX,
composi ional analysis o he sys ems is e e ed o he ela i e amoun s o Fe and Nb.
In igu e 4, his og ams o Fe con en o he powde pa icles a e p esen ed o Nb10 and
Nb5 alloys a e di e en milling imes. Fo sho milling imes, ≤5 h, i is possible o
ind Nb ich pa icles and a high ac ion o Fe ich pa icles in bo h alloys. A e 10 h
milling, in Nb5 alloy a s ong educ ion in he b oadening o he composi ional
dis ibu ion, ΔCFe, is obse ed (calcula ed as he di e ence in Fe/Fe+Nb a io be ween
he Fe iches and he Fe poo es powde pa icles ound). Howe e , his educ ion
occu s o 20 h in he Nb10 alloy, being a wide composi ional dis ibu ion o he alloy

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wi h a highe Nb con en . Fo longe milling imes, > 20 h, he b oadening o he
dis ibu ion o Fe con en is almos cons an and, a he end o he s udied ange, he e is
no a unique composi ion bu a ce ain b oadening is ound (ΔCFe =16 a . % o Fe o
Nb10 and 8 a . % o Fe o Nb5).
Small Fe con amina ion is ha d o measu e in such Fe ich composi ions.
Howe e , C is easily quan i ied as he ini ial powde mix u e o his s udy is C ee.
The e o e, igu e 5 shows he C concen a ion as a unc ion o he milling ime. Fo
bo h alloys, a linea inc ease wi h he milling ime is obse ed in he explo ed ange,
being he amoun o C highe o Nb10 (~2 a . %) alloy han o Nb5 (~1 a . %) alloy
a e 400 h milling, in ag eemen wi h he expec ed inc ease o ha dness as Nb inc eases
in Fe based alloys [13]. Simila C con amina ion has been ound in o he ball milled
sys ems [14].
3.2 S uc u al e olu ion
3.2.1 X- ay di ac ion
Figu e 6 shows he XRD pa e ns o bo h alloys as a unc ion o milling ime.
Fo sho milling imes,  20 h, a sligh b oadening o (110) di ac ion peak o he α-
Fe phase can be obse ed o bo h alloys. The ull wid h a hal maximum (FWHM) is
app oxima ely he same o bo h alloys a his s age; FWHM inc eases om 0.26 o 0.52
± 0.10º om 1 o 20 h, espec i ely. This e ec can be ela ed wi h he dec ease o he
c ys alline size and an inc ease o mic os ains.
A e 50 h milling, a s ong b oadening o (110) peak is obse ed, as well as a
shi o lowe alues o 2 posi ion o his peak. Mo eo e , he di e en maxima o bcc-
Nb a e no longe de ec ed. These e ec s a e ela ed o he Nb inco po a ion in o he bcc-
Fe la ice and o he o ma ion o he supe sa u a ed solid solu ion. Fo longe milling
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imes, >200 h, he XRD pa e n o Nb10 alloy shows a halo cen e ed a 2 ~ 44º and
he -Fe (200) peak is educed, being unapp eciable o =400h. This is ela ed o he
o ma ion o he amo phous phase in he powde pa icles.
3.2.2 Mössbaue spec ome y
Mössbaue spec a along wi h he hype ine magne ic ield dis ibu ions o he
di e en samples a e shown in igu es 7 and 8 o Nb10 and Nb5, espec i ely.
Mössbaue spec a we e i ed using a e omagne ic si e con ibu ion wi h HF =33 T o
pu e α-Fe phase (si e-F) and wo hype ine magne ic ield dis ibu ions; one o low
ield con ibu ions, D1 ( om 0 o 10 T) and o he o high ield con ibu ions, D2 (>8
T). Fu he mo e, o he si e con ibu ion bu pa amagne ic wi h quad upola spli ing
~0.5 mm/s (si e-P) is necessa y o i he spec a o Nb10 o long milling imes. I is
wo h men ioning ha , o such complex sys ems as he s udied he e, he e is ambigui y
be ween low ield e omagne ic si es (< 5 T) and pa amagne ic ones. Fo 10 h
milling, he spec a only show a sex e wi h na ow abso p ion peak (wid h ~0.30 mm/s)
and hype ine magne ic ield 33 T o bo h alloys, indica ing ha he α-Fe la ice has no
been signi ican ly a ec ed by milling, in ag eemen wi h EDX (he e ogeneous powde
pa icles, no eally alloyed) and XRD (la ice pa ame e close o pu e α-Fe) esul s.
Fo Nb10 alloy spec a a  20 h, wo new con ibu ions appea , D1 and D2.
This shows he exis ence o Fe a oms in h ee di e en main en i onmen s: i s (si e-
F), pu e bcc-Fe phase en i onmen ; second (D1), Nb ich en i onmen s; and hi d (D2),
Fe ich en i onmen s. This la e con ibu ion can be ela ed wi h Fe a oms in he α-Fe
phase bu in he p esence o impu i ies o Nb, B and/o C (due o con amina ion by he
g inding media) o o Fe a oms a he in e ace egion o nanoc ys als [15]. Howe e , in
he Nb5 alloy, along wi h he c ys alline con ibu ion, si e-F, only he D2 dis ibu ion is
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obse ed (D1 is negligible). This means ha , in Nb5 alloy, Nb ich en i onmen s a e
no as signi ican as in Nb10 alloy, as i would be expec ed.
4 Discussion
4.1 Simula ion o powde size e olu ion
As i was p e iously men ioned, o 20 h milling, c acks a e obse ed in he
pa icles su ace, which may cause he ac u e o he pa icles when he milling
con inues. The change in he e olu ion end o <d> could be asc ibed o changes in he
mechanical p ope ies o he sys em due o apid accumula ion o de ec s in o he
pa icles [16]. This changes he balance be ween he wo p ocesses esponsible o he
e olu ion o <d>: ac u e and cold welding. In ac , a quali a i e change in he
mechanical beha io o he powde is clea ly obse ed o milling imes longe han 50
h. Un il 50 h milling, he powde s icks on he ial wall and ball su ace. Howe e , o
longe milling imes he powde de aches om milling media su aces, no iceably
inc easing he amoun o loose powde .
Based on hese wo p ocesses, a basic simula ion algo i hm was pe o med o
ob ain a i s app oxima ion o he endency ollowed by <d> du ing milling. The ini ial
sys em consis o 500 equally sized pa icles. Once a andom pa icle is chosen, i s
p obabili y o be cold welded wi h ano he pa icle is de ined by Pcw =exp(-di/dc). This
exp ession depends on he size o he i pa icle, di, and a c i ical size, dc. Pa icles wi h
di>dc will end o ac u e, while i di <dc, he pa icle will end o join wi h ano he . As
can be in e ed om he expe imen al e olu ion o <d>, dc is no cons an du ing he
milling p ocess. In ou simple simula ion, only wo di e en alues o dc we e used
(suppo ed by he ab up change in he mechanical p ope ies de ec ed be ween 20 and
50 h. A dc alue 100 imes he ini ial size was used o ep oduce he apid inc ease in
<d> a sho milling imes. Fo long milling imes, he cons an expe imen al alue o
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<d> was used as dc. Simula ion esul s ep oduce he expe imen al ones a e p ope ly
escaling he i e a ion s eps wi h he milling ime (see igu e 3).
4.2 Simula ion o composi ional e olu ion
EDX esul s indica e ha he composi ion o pa icles is no unique, e en a long
milling ime bu composi ional dis ibu ions achie e a s a iona y si ua ion. The
pa ame e ΔCFe was simula ed conside ed a sys em o pa icles de ined by a 100
componen s bina y a ay, being 0 o Nb and 1 o Fe (1 % in composi ional esolu ion).
Two andom pa icles will in e ac changing a po ion o hei a ays wi h he same
alea o y size. The e o e, powde pa icles size and numbe emain unchanged and only
composi ional e olu ion is simula ed in his e y simple simula ion. Resul s a e shown
in igu e 9a along wi h expe imen al ones o compa ison. Expe imen al and simula ion
esul s ag ee e en quan i a i ely (once i e a ion s eps a e con enien ly escaled),
showing a s a iona y si ua ion o he sys em wi h a composi ional dis ibu ion and,
he e o e, he exis ence o a ce ain deg ee o he e ogenei y (ΔCFe =18 a . % o Fe o
Nb10 and 14 a . % o Fe o Nb5).
O he pa ame e which enables o ollow he composi ional e olu ion is he mos
p obable Fe con en in he pa icles, CFe, (shown in igu e 9b). This pa ame e apidly
dec eases wi h he milling ime close o he nominal composi ion o bo h alloys. A e
20 h milling, CFe= 89 and 95 ± 2 a . % o Nb10 and Nb5, espec i ely. An inc ease
wi h espec o he nominal composi ions (88 and 94 a . % o Nb10 and Nb5,
espec i ely), al hough in o he expe imen al e o , would no be su p ising and could
be expec ed due o Fe con amina ion om milling media. The e olu ion o CFe was also
ob ained om he simple simula ion desc ibed abo e (also shown in igu e 9b, using he
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16
 Fo milling imes ≥50 h, he only phase p esen in he samples is a bcc
Fe(Nb,B) supe sa u a ed solid solu ion o bo h alloys. A e 400 h, only o he
alloy wi h he highes Nb con en , he p esence o amo phous phase is e idenced
by an amo phous halo obse ed by XRD, as well as he de ec ion o an
exo he mic p ocess in DSC asc ibed o c ys alliza ion. This amo phous phase is
s able up o 850 K.
 Fo he alloy wi h he lowes Nb con en , a e 50 h milling no new Fe a omic
si es appea , being he mo e impo an con ibu ion a 33 T. Howe e , o he
alloy wi h he highes Nb con en , he Fe a omic en i onmen con inuously
e ol es inc easing he ac ion o pa amagne ic en i onmen s.
 The Cu ie ansi ion o amo phous phase in he alloy wi h he highes Nb con en
is below oom empe a u e (~250 K). This phase, de ec ed by magne iza ion
measu emen o milling imes ≥200 h, was also de ec ed by X- ay di ac ion
and Mössbaue spec oscopy echniques.
Acknowledgmen s
This wo k was suppo ed by he Spanish Go e nmen and EU FEDER (P ojec
MAT 2004-04618) and by he PAI o he Regional Go e nmen o Andalucía (P ojec
P06-FQM-01823). J.J.I. acknowledges a ellowship om he Spanish Minis y o
Educa ion and Science. J.S.B. acknowledges a esea ch con ac om he Regional
Go e nmen .
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[25] D. Hende son, J. Non-c ys . Solids 30 (1979) 301-315.
[26] A. Makino, K. Suzuki, A. Inoue, T. Masumo o, Ma e . Sci. Eng. A 179-180
(1994) 127-131.
In e me allics. Vol. 16. Núm. 9. 2008. Pag. 1073-1082
h p://dx.doi.o g/10.1016/j.in e me .2008.06.006
19
Figu e cap ions
Figu e 1. SEM images o bo h alloys a e selec ed milling imes.
Figu e 2. a) SE image, b) BSE image o a ypical pa icle o Nb10 alloy a e 2 h milling
and c) EDX spec a o selec ed poin s indica ed in a).
Figu e 3. Expe imen al and simula ed da a o he a e age powde pa icles size as a
unc ion o he milling ime o bo h alloys.
Figu e 4. His og ams o he pe cen age o Fe con en in o al Fe+Nb con en o bo h
alloys a selec ed milling imes.
Figu e 5. C con en as a unc ion o milling ime o bo h alloys. The slopes o he
di e en i ed lines a e also indica ed.
Figu e 6. XRD pa e ns o bo h alloys a e selec ed milling imes.
Figu e 7. Mössbaue spec a and hype ine magne ic ield dis ibu ions o Nb10 alloy
a e selec ed milling imes.
Figu e 8. Mössbaue spec a and hype ine magne ic ield dis ibu ions o Nb5 alloy
a e selec ed milling imes.
Figu e 9. Expe imen al and simula ed alues o a) ΔCFe and b) CFe as a unc ion o he
milling ime (expe imen al) and i e a ion s eps (simula ion). Ho izon al lines a 88 and
94 a .% Fe co espond o he nominal alues o Nb10 and Nb5, espec i ely. I e a ion
s eps axes ha e been con enien ly escaled o show he ag eemen wi h he
expe imen al da a.
Figu e 10. a) La ice pa ame e , b) minimum c ys al size and c) maximum mic os ain
as a unc ion o milling ime o bo h alloys.
Figu e 11. A ea ac ion o he di e en Mössbaue con ibu ions o he o al i ing as a
unc ion o milling ime o bo h alloys.
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20
Figu e 12. Magne iza ion cu es as a unc ion o empe a u e o Nb10 alloy a e 100,
200, 300 and 400 h milling.
Figu e 13. DSC scans a 40 K/min o bo h alloys a e selec ed milling imes. Symbols
a e supe imposed o e he cu es o dis inguish hem.
Figu e 14. XRD pa e ns o Nb5 alloy a e di e en hea ed empe a u es.
Figu e 15. XRD pa e ns o Nb10 alloy a e di e en hea ed empe a u es.
Figu e 16. Mössbaue spec a and hype ine magne ic ield dis ibu ion o Nb5 alloy
a e annealed ea men .
Figu e 17. Mössbaue spec a and hype ine magne ic ield dis ibu ion o Nb10 alloy
a e annealed ea men .
In e me allics. Vol. 16. Núm. 9. 2008. Pag. 1073-1082
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21
Figu e 1
2 h
500

m
20 h
500

m
200

m
100 h
100

m
400 h
Nb10
500

m
2 h
20 h
500

m
100

m
100 h
50

m
400 h
Nb5

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22
Figu e 2
50 m
A
B
C
B
Fe.
Nb
0
2 keV
c
)
a
)
b)
Fe.
Nb
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23
Figu e 3
0 100 200 300 400
0
100
200
300
Nb10
Nb5
i e a ion s ep (x103)
<d> [m]
milling ime [h]
0 5 10 15 20 25 30 35
simula ed
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24
Figu e 4
4
8
12
2
4
6
2
4
2
4
6
Nb10
0.2 0.4 0.6 0.8
1.0
2
4
% Fe
4
8
12 Nb5
2 h
4
8
10 h
2
4
6
20 h
4
8
12
50 h
0.2 0.4 0.6 0.8 1.0
4
8
400 h
% Fe
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25
Figu e 5
0 100 200 300 400
0.0
0.6
1.2
1.8
C [%]
milling ime [h]
N5B
N10B
(7 ±2)*10-4 a . % C /h
(3.6±0.3)*10-3 a . % C /h
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32
Figu e 12
100 200 300 400
0
30
60
90
120
400 h
300 h
200 h
100 h
M
0
[emu/g]
T [K]

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33
Figu e 13
400 500 600 700 800 900 1000
empe a u e [K]
400 h
400 h 50 h
50 h
20 h
20 h
5 h
5 h
Nb10
Nb5
0.2 W/g (exo)
dH/d
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34
Figu e 14
40 50 60
600 K
800 K
as-milled
2

[deg ee]
1000 K
500 1000
0,286
0,288
T [K]
a [nm]
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35
Figu e 15
40 50 60
600 K
800 K
as-milled
2

[deg ee]
1000 K
500 1000
0
50
100
T [K]
X
C
[%]
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36
Figu e 16
0,1
0,2
0,08
0,16
0,24
0,2
0,4
-8 -6 -4 -2 0 2 4 6 8
0 5 10 15 20 25 30 35
0,2
0,4
0,6
as-milled
600 K
ela i e ansmi ion
p obabili y
800 K
eloc y [mm/s]
B
hyp
[T]
1000 K
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37
Figu e 17
0,1
0,2
-8 -6 -4 -2 0 2 4 6 8
0,1
0,2
0,03
0,06
0 5 10 15 20 25 30 35
0,1
as-milled
p obabili y
eloci y [mm/s]
ela i e ansmi ion
600 K
800 K
B
hyp
[T]
1000 K