Influence of Hot Compaction on Microstructure and Magnetic Properties of Mechanically Alloyed Fe(Co)-based Amorphous Compositions

Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 In luence o ho compac ion on mic os uc u e and magne ic p ope ies o mechanically alloyed Fe(Co)-based amo phous composi ions J.J. Ipus1, J.M. Bo ego1, J.S. Blázquez1, M. S oica2,3, V. F anco1, A. Conde1 1 Depa amen o de Física de la Ma e ia Condensada, ICMSE-CSIC, Uni e sidad de Se illa, P.O. Box 1065, 41080, Se illa, Spain 2 IFW D esden, Ins i u e o Complex Ma e ials, D-01069, D esde, Ge many 3 Poli ehnica Uni e si y Timisoa a, 300006, Timisoa a, Romania Abs ac Amo phous Fe75Nb10B15 and (Fe70Co30)75Nb10B15 alloys we e p epa ed by mechanical alloying om he elemen al cons i uen s and ho compac ed a di e en empe a u es wi hin he supe cooled liquid egion. A e compac ion, he mic os uc u e s udied by X- ay di ac ion shows an inc ease in he c ys alline ac ion o bo h composi ions. Magne ic p ope ies and magne ic en opy change o compac ed samples o he Co- ee alloy we e enhanced wi h espec o he powde sample, meanwhile, a de e io a ion in hese p ope ies was obse ed o he Co con aining alloy a e compac ion. Bo h changes could be asc ibed o an en ichmen in bo on in he amo phous phase. Keywo ds: Amo phous and nanoc ys alline alloys, Mechanical alloying, Ho compac ion, Magne ocalo ic e ec Co esponding au ho : Ja ie S. Blázquez e-mail: [email p o ec ed] Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 In oduc ion Nanoc ys alline and/o amo phous alloys ha e ecei ed la ge a en ion om he scien i ic communi y in he las yea s due o hei a ac i e physical p ope ies (mechanical, magne ic, e c), Pa icula ly, Hi pe m ype alloys [ 1 ] we e de eloped in 1998 o ex end he good so magne ic p ope ies p esen ed by Nanope m ype alloys [ 2 ] de eloped in he 80’s o highe empe a u es, as he Co addi ion inc eases he magne ic momen and he Cu ie empe a u e o bo h he amo phous and he c ys alline phases [ 3 ]. These sys ems ha e been commonly p epa ed by apid quenching echniques. Howe e , mechanical alloying has become an impo an ool in ma e ials science as an al e na i e ou e o di ec ly p epa e hese amo phous and nanoc ys alline mic os uc u es in a wide composi ional ange [ 4 ]. Th ough his echnique, s a ing om a mix u e o pu e elemen s o p ealloyed ma e ials, i is possible o p ocess easily and economically a la ge amoun o powde , which is an ad an age om he comme cial applica ions poin o iew. Fo example, al hough Co-based bulk amo phous samples ha e been p oduced by apid solidi ica ion echniques such as coppe mold cas ing [ 5 , 6 , 7 ], bulk samples wi h shapes and dimensions ha canno be ob ained by di ec cas ing ha e been success ully p oduced by powde compac ion [ 8 , 9 ]. In ac , o ob ain bulk amo phous and/o nanoc ys alline samples in o de o co e p ac ical needs, powde should be compac ed a e milling. Compac ion o amo phous powde s in o a bulk sample p ese ing he ini ial mic os uc u e is a p ima y equi emen bu di icul o pe o m. P essing a oom empe a u e usually leads o mechanical deg ada ion o he compac s and high empe a u e compac ion is needed o ob ain good in e pa icle binding. The use o a binding ma e ial enhances he mechanical s abili y o he compac bu gene ally de e io a es i s magne ic p ope ies, as he amoun o magne ic ma e ial is educed. I is wo h no ing ha applying high empe a u es du ing compac ion could lead o an undesi able coa sening o he c ys als and e en c ys alliza ion o he amo phous phase. In his wo k, wo amo phous Fe(Co)NbB alloys a e p epa ed by mechanical alloying. Bulk samples we e ob ained by ho p essing wi hin he supe cooled liquid egion wi hou he use o any binding ma e ial. Mic os uc u e and magne ic p ope ies as a unc ion o he compac ion empe a u e a e s udied and compa ed o hose o he as- milled powde s. Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 Expe imen al Amo phous (Fe1-XCoX)75Nb10B15 (X=0, 0.30) alloys we e p epa ed ia mechanical alloying s a ing om pu e c ys alline Fe, Nb and Co and in e me allic FeB powde s in o de o enhance he inco po a ion o ha d bo on in o he ma ix [ 10 ]. Milling was pe o med in a plane a y mill F i sch Pul e ise e 4 Va io, wi h s eel balls (10 mm diame e ) and ha dened s eel ials (250 cm3), ini ial powde mass o 30 g and a ball o powde a io o 10:1. The o a ional speed o he disc which suppo s he ials was 350 pm and ha o he ials was 700 pm in opposi e di ec ion. Powde samples we e aken ou o s udy hei mic os uc u e, he mal s abili y and magne ic p ope ies a e 20 and 40 h milling. Disk-shaped samples 10 mm diame e and 4 mm hick we e p epa ed by compac ion o powde s using an uniaxial ho p ess unde a acuum o 10-3 Pa. The powde was hea ed a 0.67 K s-1 up o he consolida ion empe a u e, compac ed unde a p essu e o 700 MPa o 1.5 min and hen cooled down o oom empe a u e using A low. Densi y o he compac ed samples, ob ained om A chimedes me hod, shows, o (Fe0.7Co0.3)75Nb10B15 alloy, an inc ease om 5.30.4 g/cm3 o he sample compac ed a 753 K o 6.90.5 g/cm3 o sample compac ed a highe empe a u es. In he case o he Co- ee alloy, densi y inc eases om 6.10.4 g/cm3 o he sample compac ed a 773 K o 6.90.5 g/cm3 o sample compac ed a highe empe a u es. This indica es abou 90 % o he expec ed densi y o a bulk amo phous sample o hese composi ions. Mic os uc u al cha ac e iza ion was s udied by X- ay di ac ion using Cu-Kα adia ion in a B uke D8I di ac ome e and scanning elec on mic oscopy using a Zeiss Au iga C ossbeam Focused Ion Beam (FIB)-Scanning Elec on Mic oscopy (SEM). SEM images we e aken on in si u polished su aces using Ga ion beam in FIB mode. 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 a a hea ing a e o 20 K/min in a con inuous A low. Magne ic p ope ies we e s udied using a Lakesho e 7407 ib a ing sample magne ome e wi h a maximum applied magne ic ield o 1.5 T. Iso he mal magne iza ion cu es we e measu ed on pa allelepipeds o abou 1x1x3 mm in size in a empe a u e ange om 100 o 753 K wi h inc emen s o 10 K. Spon aneous speci ic magne iza ion, σ0, was ob ained om he ex apola ion o high ield magne iza ion cu es o ze o ield. Cu ie empe a u e, Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 TC, was calcula ed as he in lexion poin o σ0(T) cu es. Hys e esis loops as a unc ion o empe a u e we e eco ded in a empe a u e ange o 100-753 K wi h s eps o 50 K. Iso he mal magne ic en opy change, ΔSM, due o he applica ion o a magne ic ield, was calcula ed by p ocessing he empe a u e and ield dependen magne iza ion cu es using a nume ical app oach o he exp ession: 2 1 0 H M H H M S dH T         , (1) whe e M is he magne iza ion and T he empe a u e and H1 and H2 a e he minimum and maximum applied ields. The pa ial de i a i es a e eplaced by ini es di e ences and he in eg a ion is pe o med nume ically. This p ocedu e was pe o med wi h he help o he Magne ocalo ic E ec Analysis P og am [ 11 ]. The bulk samples we e cu in o small pa allelepipeds and i s longes axis was aligned wi h he applied ield o minimize he demagne izing ield. In he case o powde samples he una oidable demagne izing ac o , ND, is conside ed as 1/3 [ 12 ] o loosely packed sphe ical samples, in o de o co ec he iso he mal magne iza ion cu es as: app D H H N M , (2) whe e Happ is he applied magne ic ield and H is he in e nal ield. The e ige an capaci y ep esen s a measu e o he ene gy ans e ed be ween he ho and cold ese oi s. In his s udy he e ige an capaci y, RCFWHM, was calcula ed as he p oduc o he peak magne ic en opy change imes he ull wid h a hal maximum o he peak. Resul s and Discussion The mic os uc u al e olu ion o powde samples was ollowed by XRD. Figu e 1 shows he XRD pa e ns o samples a e 20 and 40 h milling o bo h s udied composi ions, along wi h he decon olu ion (a Gausssian p o ile o desc ibe he amo phous halo and a Lo en zian p o ile o he nanoc ys alline α-Fe ype phase) used o ex ac he ac ion o phases om he pa e ns when possible. I is shown ha , a e he o ma ion o he bcc Fe-Co(NbB) supe sa u a ed solid solu ion, he de elopmen o an amo phous phase akes place and i s ac ion inc eases as he c ys alline one dec eases. Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 An almos comple ely amo phous ma e ial is ob ained o Fe75Nb10B15 alloy a e 20 h milling and o he (Fe0.7Co0.3)75Nb10B15 alloy a e 40 h. DSC eco ds p esen ed in igu e 2a show he he mal s abili y o he powde samples a e 40 h o bo h composi ions. Di e en p ocesses can be obse ed in he scans. A low empe a u es, a gas deso p ion p ocess s a ing a ~390 K ollowed by a b oad s uc u al elaxa ion p ocess a ~500 K. Bo h ea u es a e ypically obse ed in powde samples [ 13 ]. Al hough i is no ully accep ed he exis ence o glass ansi ion o amo phous sys ems no ob ained by apid quenching, an exo he mic ea u e is obse ed ha could be named as Tg (inse o Fig. 2a) and es ima ed a Tg ~760 and 785 K o (Fe0.7Co0.3)75Nb10B15 and Fe75Nb10B15 alloys, espec i ely, and he onse empe a u e o he main c ys alliza ion p ocess was measu ed a Ton ~815 and 850 K o (Fe0.7Co0.3)75Nb10B15 and Fe75Nb10B15samples, espec i ely. In o de o pe o m he ho compac ion o he powde samples, one o he a ge s was o e ain he p e iously obse ed mic os uc u e o he ini ial powde . The e o e, empe a u es close bu below he c ys alliza ion empe a u es we e selec ed o compac ion: 753, 773 and 793 K o (Fe0.7Co0.3)75Nb10B15 alloy and 773, 793, 803 and 813 K o Fe75Nb10B15 alloy. A comp omise has been aken be ween he hea ing a e o he ho -p ess (limi ed o 0.67 K/min) and he DSC hea ing a e needed o ge a signi ican signal o noise a io. A ange o empe a u es has been explo ed o minimize he in luence o he di e en a es on he conclusions de i ed. A e compac ion, he mic os uc u e o bulk samples was examined by XRD and he same decon olu ion p ocedu e used o he case o as-milled powde was applied o he compac ed samples, as shown in igu e 1. La ice pa ame e does no p esen signi ican changes wi h compac ion (a=2.8780.005 Å o bo h composi ions). All alues a e highe han ha o pu e bcc-Fe. This ac could be explained by he in luence o Nb a oms in o he la ice. [ 14 , 15 ]. A e ho compac ion, whe eas o he Fe75Nb10B15 sample XC inc eases up o ~0.10 ega dless compac ion empe a u e, o he (Fe0.7Co0.3)75Nb10B15 sample XC con inuously inc eases wi h empe a u e, eaching ~0.16 o he sample compac ed a 793 K. This inc emen in XC is in ag eemen wi h he close p oximi y o he compac ion empe a u e o he c ys alliza ion empe a u e in (Fe0.7Co0.3)75Nb10B15 (T =22 K) han in Fe75Nb10B15 alloy (T =37 K). Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 DSC scans showing he he mal s abili y o compac ed samples a e p esen ed in igu es 2b-c. F om hese scans we can see ha he low empe a u e p ocesses, T <750 K, obse ed in powde samples and asc ibed o mic os uc u al elaxa ion, ha e disappea ed o all compac ed samples. Mo eo e , no impo an changes in he peak empe a u e a e obse ed a e compac ion o Fe75Nb10B15 alloy. Fo he (Fe0.7Co0.3)75Nb10B15 alloy, whe eas o samples compac ed a 753 and 773 K no signi ican changes a e obse ed in he peak empe a u es, an inc ease o ~10 K is de ec ed o he sample compac ed a 793 K. This change in he c ys alliza ion empe a u e o he (Fe0.7Co0.3)75Nb10B15 alloy could be asc ibed o a pa ial consump ion o he ans o ma ion due o c ys alliza ion o he bcc-(FeCo) ype phase. Mo eo e , small composi ional changes in he amo phous phase (e.g. an en ichmen in bo on con en ) du ing compac ion a he highes empe a u e could also lead o an inc ease in he c ys alliza ion empe a u e o he FeCo-based amo phous alloys [ 16 ]. Coe ci i y, HC, a oom empe a u e shows a educ ion a e compac ion om ~2 and ~4 kA/m o Fe75Nb10B15 and (Fe0.7Co0.3)75Nb10B15 powde s, espec i ely, down o ~1 kA/m o bo h composi ions. This d op in HC could be asc ibed o elaxa ion phenomena in he samples due o annealing du ing compac ion. Spon aneous speci ic magne iza ion alues o compac ed samples p esen di e en beha io s o each alloy. Fo he Fe75Nb10B15 alloy a oom empe a u e a con inuous inc ease om ~46 emu/g (powde ) up o ~54 emu/g (compac ed a 813 K) wi h compac ion empe a u e is obse ed. Howe e , o he (Fe0.7Co0.3)75Nb10B15 alloy no impo an changes in σ0 a e obse ed a oom empe a u e. The empe a u e dependence o σ0 is p esen ed in igu e 3 o he di e en samples. I is obse ed ha TC o he (Fe0.7Co0.3)75Nb10B15 alloy does no change a e compac ion a 753 and 773 K wi h espec o he alue obse ed o he powde sample, wi h TC =563 K. Howe e , a educ ion down o TC =533 K o he sample compac ed a 793 K is obse ed. Fo he Fe75Nb10B15 samples, TC inc eases om 320 K, o he powde sample, up o 340 K o each compac ed sample om 773 K o 803 K, bu a smalle inc ease (TC =330 K) is obse ed o he sample compac ed a 813 K. These ea u es could be ela ed o composi ional changes (a be e dissolu ion o bo on) in he amo phous ma ix du ing he compac ion. In ac , an inc ease in bo on con en in amo phous Fe-B leads o an inc ease in TC o ~20 K/a .% B [ 17 ], as well as an inc ease in σ0 [ 18 ]. In he case o Co-B amo phous alloys, a dec ease o ~30 K/a .% B in TC is epo ed [ 19 ]. Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 Figu e 4 shows he empe a u e dependence o coe ci i y o Fe75Nb10B15 sample compac ed a 813 K. All samples exhibi a simila beha io . An ini ial inc ease o he coe ci i y can be seen as he measu emen empe a u e eaches TC and hen a dec ease is obse ed o highe empe a u es. The ini ial end can be explained by a supp ession o he exchange coupling in be ween he emaining nanoc ys als as he amo phous ma ix become pa amagne ic. Abo e he Cu ie empe a u e o he amo phous phase, he g adual disappea ance o he dipola coupling be ween nanoc ys als causes a educ ion in coe ci i y as hey app oach he supe pa amagne ic egime as empe a u e inc eases [ 20 ]. The empe a u e dependence o he magne ic en opy change, ΔSM, o a magne ic ield change o 1 T is shown in igu e 5 o all s udied samples. I can be seen ha , a e compac ion, a ~15 K inc ease o he peak empe a u e akes place o he Fe75Nb10B15 alloy. Fo he (Fe0.7Co0.3)75Nb10B15 alloy he peak empe a u e shows a educ ion o ~20 K only o he sample compac ed a he highes empe a u e. The peak empe a u e, Tpk, as a unc ion o he compac ed one, Tcomp, o bo h alloys is p esen ed in igu e 6a. The shi o he peak empe a u e o bo h alloys ag ees wi h he shi obse ed in TC and could be asc ibed o he inc ease in B con en in he amo phous phase du ing ho empe a u e compac ion. In ac , an inco po a ion as small as ~0.7 a .% B in he amo phous ma ix could explain he obse ed shi s o he peak empe a u e o bo h composi ions as epo ed in [17,18]. The e olu ion o he peak alue o ΔSM and e ige an capaci y as a unc ion o compac ion empe a u e a e p esen ed in igu e 6 (b and c). A con inuous educ ion in he peak alue o |ΔSM| o compac ed (Fe0.7Co0.3)75Nb10B15 samples wi h espec o he as- milled one can be obse ed. Howe e , o he case o Fe75Nb10B15 alloy an inc ease o ~13% in he peak alue o ΔSM o compac ed samples is obse ed. The con inuous educ ion o he (Fe0.7Co0.3)75Nb10B15 alloy a e compac ion could be asc ibed o he p og essi e c ys alliza ion du ing ho compac ion. In he o he case, he inc ease obse ed o he Fe75Nb10B15 samples a e compac ion can be explained by he e ec o bo on inco po a ion in he amo phous ma ix which enhances he magne ic momen in Fe-based amo phous alloys [10, 21 ], in ag eemen wi h he inc ease o TC. The e ige an capaci y shows wo di e en beha io s o he wo di e en composi ions. In he case o Fe75Nb10B15 alloy his alue dec eases wi h espec o ha o powde sample, which is ela ed o he sha pening o he ΔSM cu e due o a educ ion o Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 he TC dis ibu ion wi h inc easing compac ion empe a u e, as no mally obse ed o powde samples [ 22 , 23 , 24 ]. Fo he (Fe0.7Co0.3)75Nb10B15 alloy signi ican changes in RC a e no ini ially obse ed bu a la ge educ ion is measu ed a e compac ion a 793 K, which can be explained by he educ ion in he peak alue o SM due o he pa ial c ys alliza ion o his sample. The e a e wo p ocesses which cause B en ichmen o he amo phous phase: c ys alliza ion o he α-Fe ype phase and dissolu ion o he emnan bo on inclusions. In he o me case, a e a 10 % c ys alliza ion he composi ion o he esidual amo phous phase, neglec ing he p esence o B inclusions, should be (FeCo)72Nb11B17, which could easonably accoun o he bo on en ichmen . Howe e , p e ious s udies on Fe-Z -B [ 25 ] epo on he dissolu ion o bo on inclusions a e high empe a u e ea men . In o de o conside his mechanism, SEM mic og aphs we e ob ained on c oss sec ions o compac ed samples a e being polished using a beam o Ga ions. Figu e 7 shows hese SEM images a he lowes and highes compac ion empe a u es o Fe75Nb10B15 (Fig. 7a and 7b) and (Fe0.7Co0.3)75Nb10B15 alloy (7c-7d), espec i ely. B inclusions a e s ill clea ly obse ed as da k spo s ( egions o low in e ac ion wi h elec ons due o he low a omic numbe o B a oms) in he compac ed samples, e en a he highes compac ion empe a u e, and no signi ican changes a e e iden wi h espec o he samples compac ed a lowe empe a u es. Howe e , sligh bo on inco po a ion om he inclusions, below ou esolu ion, canno be disca ded. Conclusions Mechanically alloyed Fe75Nb10B15 and (Fe0.70Co0.30)75Nb10B15 powde composi ions we e ho compac ed a di e en empe a u es and he e olu ion o he mic os uc u al and magne ic p ope ies we e s udied. A ound 10 % c ys alline ac ion was de eloped a e compac ion wi hin he supe cooled liquid egion o Fe75Nb10B15 samples. Fo he (Fe0.70Co0.30)75Nb10B15 samples a con inuous inc ease up o XC ~16% was obse ed. The magne ic p ope ies show changes wi h he compac ion empe a u e o bo h composi ions. Small inc eases in he oom empe a u e spon aneous speci ic magne iza ion, he Cu ie empe a u e and he peak alue o he magne ic en opy change Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 o he Fe75Nb10B15 alloy we e obse ed. Fo he case o (Fe0.7Co0.3)75Nb10B15 alloy a educ ion in TC and he peak alue o he magne ic en opy change was e idenced, while σ0 is almos cons an . In bo h cases, changes in TC could be explained a e a small bo on en ichmen o he amo phous phase du ing compac ion. C ys alliza ion o he α-Fe ype phase can explain he enhancemen o σ0 in Fe75Nb10B15 alloy as well as i s cons an alue in (Fe0.7Co0.3)75Nb10B15 alloy while he peak alue o |SM| dec eases. Acknowledgemen s This wo k was suppo ed by he Spanish Minis y o Science and Inno a ion (MICINN) and EU FEDER (p ojec MAT2013-45165-P) and he PAI o he Regional Go e nmen o Andalucía. Re e ences [ 1 ] M.A. Willa d, D.E. Laughlin, M.E. McHen y, D. Thoma, K. Sicka us, J.O. 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Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 Figu e 5. 100 200 300 400 -0.6 -0.4 -0.2 0.0 Fe75Nb10B15 powde 773 K 793 K 803 K 813 K SM (J kg-1K-1) T (K) 400 500 600 700 -0.8 -0.6 -0.4 -0.2 0.0 (Fe70Co30)75Nb10B15 powde 753 K 773 K 793 K SM (J kg-1K-1) T (K) Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 Figu e 6. 0.4 0.6 0.8 |SM pk| (J kg-1K-1) (b) 293 740 760 780 800 820 40 50 60 70 (c) TComp (K) |RCFWHM| (J kg-1) 320 340 540 570 (a) Tpk (K) Jou nal o Alloys and Compounds, 653 (2015) 546-551 h p://dx.doi.o g/10.1016/j.jallcom.2015.09.074 Figu e 7.