SOFT NANOCRYSTALLINE MAGNETIC POWDERS OBTAINED BY MECHANICAL ALLOYING AND ANNEALING

Transcription

1 SOFT NANOCRYSTALLINE MAGNETIC POWDERS OBTAINED BY MECHANICAL ALLOYING AND ANNEALING Viorel Pop Babeş-Bolyai University, Faculty of Physics, Cluj-Napoca, Romania Ionel Chicinaş Materials Science and Technology Dept., Technical University of Cluj-Napoca, Romania Olivier Isnard Laboratoire de Cristallographie, CNRS, associé à l Université Joseph Fourier et à l INPG, Grenoble, France Jean Marie Le Breton Groupe de Physique des Matériaux, UMR CNRS 6634, Université de Rouen, France I. Chicinaş, V. Pop, O. Isnard, J.M. Le Breton, Proc. Materiaux 2002 Congress, ISBN (on CD), Tours, France I. Chicinaş, V. Pop, O. Isnard, J. Magn. Magn. Mater (2002) 885 I. Chicinaş, V. Pop, O. Isnard, J.M. Le Breton, J. Juraszek, J. Alloys and Compounds 352 (2003) 34 V. Pop, O. Isnard, I. Chicinaş, J. Alloys and Compounds 361 (2003) 144 I. Chicinaş, V. Pop, O. Isnard, J. Mater. Science 39 (2004) 5305

2 E. Gaffet, G. Le Caër, Encyclopaedia of Nanoscience and Nanotechnology, American Scientific Publishers, Editor H.S. Nalwa, vol. 5 (2004) In Lilliput, Gulliver noted that there are some laws and customs in this Empire very peculiar [1], an observation which might apply to nanophased materials too. Nanophased materials behave indeed differently from their macroscopic counterparts because their characteristic sizes are smaller than the characteristic length scales of physical phenomena occurring in bulk materials. [1] J.Swift, Gulliver s Travels, Ch ). on-line. literature.com/swift/gulliver/.

3 INTRODUCTION

4 Nanocrystalline materials (d < 100 nm) obtained by: vapour - inert gas condensation, sputtering, plasma processing, vapour deposition liquid - electrodeposition, rapid solidification solid - mechanical alloying, severe plastic deformation, spark erosion

5 Nanocrystalline materials (d < 100 nm) obtained by: vapour - inert gas condensation, sputtering, plasma processing, vapour deposition liquid - electrodeposition, rapid solidification solid - mechanical alloying, severe plastic deformation, spark erosion mechanical alloying nanostructured ANNEALING modifies the structure and microstructure r B hard and soft = µ 0 r magnetic materials r ( H + M) M M r B D A H B C -H c H hard permanent magnets µ >> 0 magnetic cores magnetic circuits soft E O F -M r c H Curie temperature, T c

6 mechanical alloying Metastable phases F Metastable Energy barrier Instable Thermodynamic equilibrium conditions Stable

7 D 1 D 2 C 1 D 1 B 1 C 2 B 1 B 2 D - ductile component B - brittle component MA Mechanical alloying involves the synthesis of materials by high-energy milling C 3 C - composite (compound) MM Mechanical milling refers to the process of milling pure metals or compounds without solid state reaction

8 Materials obtained by mechanical alloying: superalloys with high performance at high temperatures; instable structures/microstructures (inclusive amorphous alloys), starting from crystalline intermetallic compounds; intermetallic compounds with nanocrystalline/amorphous structure and high melting point, not easy to obtain by conventional methods; solid solution by increasing the solubility range; non miscible solid solution; Compus Crystalline intermetalic intermetallic cristalin compound Metastable crystalline phases; quasicrystals; composite materials. Free energy Energia libeă A and B mixed components Amestec al componenţilor A şi B Aliaj amorf Amorphous alloys A AB n m B

9 Soft magnetic nanocrystalline materials

10 Soft magnetic nanocrystalline materials Nanocrystalline soft magnetic materials partial crystallisation a nanocrystalline two-phase materials + } an amorphous matrix

11 Soft magnetic nanocrystalline materials Nanocrystalline soft magnetic materials partial crystallisation a nanocrystalline two-phase materials + } an amorphous matrix negative magnetostriction compensates positive magnetostriction

12 Soft magnetic nanocrystalline materials Nanocrystalline soft magnetic materials partial crystallisation a nanocrystalline two-phase materials + } an amorphous matrix negative magnetostriction compensates positive magnetostriction for Fe V cr %

13 Soft magnetic nanocrystalline materials Nanocrystalline soft magnetic materials partial crystallisation a nanocrystalline two-phase materials + } an amorphous matrix negative magnetostriction compensates positive magnetostriction for Fe V cr % D < L ex ; L ex = A / K1 D = nanocrystallite diameter L ex = magnetic exchange length A and K 1 = exchange and anisotropy constants

14 Soft magnetic nanocrystalline materials Nanocrystalline soft magnetic materials partial crystallisation a nanocrystalline two-phase materials + } an amorphous matrix for Fe negative magnetostriction V cr % D < L ex ; L ex = A / K1 D = nanocrystallite diameter L ex = magnetic exchange length A and K 1 = exchange and anisotropy constants compensates positive magnetostriction G. Herzer, IEEE Trans. Magn. MAG-25 (1989) D<15 nm 3327; IEEE Trans. Magn. MAG-26 (1990) 1397 for α-fe(si) and α-fe nanocrystals present in Finemet (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) and respectively Nanoperm (Fe 84 Zr 3.5 Nb 3.5 B8Cu 1 )

15 Soft magnetic nanocrystalline materials vanish of the coercivity in superparamagnetic regime low permeability

16 Soft magnetic nanocrystalline materials vanish of the coercivity in superparamagnetic regime low permeability soft magnetic nanostructures small ferromagnetic crystallites coupled by exchange interactions low coercivity and high permeability

17 Soft magnetic nanocrystalline materials vanish of the coercivity in superparamagnetic regime low permeability soft magnetic nanostructures small ferromagnetic crystallites coupled by exchange interactions low coercivity and high permeability The local anisotropies are randomly averaged out by exchange interactions so that there is no anisotropy net effect on the magnetisation process.

18 L ex D / ; = = = = ex ex ex L D K N K K K A L D L N D A K K D K A J K J A J D K J K H s s i s s c = = µ µ µ ; * G. Herzer, IEEE Trans. Magn. MAG-26 (1990) 1397 R. Alben, J.J. Becker, M.C. Chi, J. Appl. Phys, 49 (1978) 1653 Random Anisotropy Model: D < L ex *

19 L ex D / ; = = = = ex ex ex L D K N K K K A L D L N D A K K D K A J K J A J D K J K H s s i s s c = = µ µ µ ; K A D J K J D J K A J K H s s i s s c µ µ µ ; D > L ex = (A/K 1 ) 1/2 * G. Herzer, IEEE Trans. Magn. MAG-26 (1990) 1397 R. Alben, J.J. Becker, M.C. Chi, J. Appl. Phys, 49 (1978) 1653 Random Anisotropy Model: D < L ex * The magnetisation process is determined by domain wall pinning. The theory predicts:

20 Soft magnetic nanocrystalline materials

21 Soft magnetic nanocrystalline materials Grain size, D(nm)

22 Fe-Ni alloys around the Permalloy composition and Fe- Ni-Mo alloys, namely Supermalloy, are well known for their high performances as soft magnetic materials.

23 EXPERIMENTAL

24 Material preparation Material characterisation milling of the powders in a high energy planetary mill heat treatments (temperatures and duration) X-rays diffraction (XRD) electron microscopy morphology phase composition checked by EDX magnetic measurements: K; µ 0 H 8 T Mössbauer spectrometry

25 It was obtained: Ni 3 Fe nanocrystalline powders Supermalloy (Ni 79 Fe 16 Mo 5 ) nanocrystalline powders Starting materials: Ni carbonyl powder 123, (5-7 µm) Fe NC powder (Höganas), (< 40 µm) Mo powder (Sinterom, Cluj-Napoca) (<10 µm) Mechanical alloying experiments: NiFe (3:1, %at) milled in Ar atmosphere for 1-52 hours NiFeMo (79:16:5 - %gr) milled in Ar atmosphere for 4 16 hours Annealing: Ni 3 Fe in vacuum/330 C for 0,5, 1, 2, 3 and 8 hours Supermalloy in vacuum/350 C 0,5, 1, 2, 3 and 4 hours

26 RESULTS AND DISCUSSIONS

27 The presence of the first order internal stresses acts at a macroscopic level and modifies the lattice parameters and consequently produces an angular shift of the X-ray diffraction peaks. The second-order internal stresses act at a microscopic level of the crystallites and produce a broadening of the X-ray diffraction peaks. L. Castex, J.L. Lebrun, G. Maeder, J.M. Sprauel, Determination de contraintes résiduelles par diffraction des rayons X, Publications scientifiques et techniques de l ENSAM, Paris vol.22 (1981), See also

28 Ni 3 Fe

29 Ni 3 Fe Intensité Intensity (unit. (a.u.) arb.) theta (degrés) 2 θ ( ) the second order internal stresses Fe broadening of the diffraction peaks Fe Ni 3 Fe decreasing of the crystallites dimension Ni ss 1h 1h+330 C/1h 2h 2h+ 330 C/1h 3h 3h+330 C/1h 4h 4h+330 C/1h 6h 6h+330 C/1h 8h 8h+330 C/1h 10h 10h+330 C/1h 12h 12h+330 C/1h Ni 3 Fe phase formation the first order internal stresses Intensity (a.u.) Intensité (u.a.) peaks shift to lower 2θ angles peaks shift to HIGHER 2θ angles relaxation of the first order internal stresses Ni 3 Fe 2 theta Ni θ ( ) 1h 1h+ 330 C/1h 2h 2h+ 330 C/1h 3h 3h+ 330 C/1h 4h 4h+ 330 C/1h 6h 6h+ 330 C/1h 8h 8h+ 330 C/1h 10h 10h+ 330 C/1h 12h 12h+ 330 C/1h ss

30 Ni 3 Fe (311) Ni 3 Fe Ni 1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h as milled Intensity (a.u.) Intensity (a.u.) 1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h 14 h 16 h 20 h 24 h +300 C/30min +330 C/1h One annealing time Different milling time 1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h +330 C/3h 1 h 2 h 3 h 4 h 6 h 8 h 10 h 12 h +330 C/12h +330 C/8h ss theta 92 (degrees) θ ( )

31 Ni 3 Fe (311) Ni 3 Fe Ni 0 h 0.5 h 1 h 2 h 3 h 12 h milled 1 h 0 h 0.5 h 1 h 2 h 3 h 12 h milled 2 h 0 h 0.5 h 1 h 2 h 3 h 12 h milled 3 h Intensity (a.u.) Intensity (a.u.) 0 h 0.5 h 1 h 2 h 3 h 12 h 0 h 0.5 h 1 h 2 h 3 h 8 h 0 h 0.5 h 1 h 2 h 3 h 8 h milled 4 h milled 6 h milled 8 h One milling time Different annealing time 0 h 0.5 h 1 h 2 h 3 h 8 h milled 10 h 0 h 0.5 h 1 h 2 h 3 h 8 h milled 12 h 0 h 1 h milled 14 h 0 h 1 h milled 16 h 0 h 1 h milled 20 h theta (degrees) 2 θ ( ) 0 h 1 h milled 24 h ss

32 Ni 3 Fe (311) 0 h Intensity (a.u.) Intensity (a.u.) theta ( d e g rees) θ ( ) 0.5 h 1 h 2 h 3 h 12 h 0 h 0.5 h 1 h 2 h 3 h 12 h 0 h 0.5 h 1 h 2 h 3 h 8 h ss milled 1 h milled 4 h milled 6 h

33 Ni 3 Fe according to Scherrer s formula: D K λ = ; β β K β cosθ β 1/2 FWHM 1 / 2 =. 0 9 mean size of the nanocrystallites, D I I max I max /2 I max /2 β 1/2 I i Background D = 12 nm - 52 h milling 22 nm - 24 h milling 2 θ

34 Ni 3 Fe ss 12 h M 2 (a.u.) T C (Ni) T C (Ni 3 Fe) T C (Fe) T( o C)

35 Ni 3 Fe *H. Hasegawa, J. Kanamori, J. Phys. Soc. Jap. 33 (1972) M s (µ B /f.u.) annealed recuit Fe 1-x Ni x in the reach nickel region* x M Fe and M Ni =ct K 295 K Temps milling de time broyage (hours) (h) 4.8 M Ni-Fe when Ni 3 Fe % T = 4 K M s M (µ B /f.u.) Ni Fe: MA 24h/330 o C 8h 3 T= 4 K M s (µ B f.u.) T = 300 K not annealed 300 C/30min 330 C/1h 330 C/3h 330 C/8-12h µ H(T) milling time (hours)

36 Ni 3 Fe o 12 h x 10 h 8 h 6 h M (µ B /f.u.) h 3 h 2 h 4.2 T = 4 K h ss annealing time(hours) o 12 h x 10 h 8 h 6 h h M (µ B /f.u.) T = 300 K 3 h 2 h h ss annealing time (hours)

37 Ni 3 Fe 2.00 T = 330 C (M t -M 0 )/M 0 (%) milled 4 h milled 6 h milled 8 h annealing time (hours)

38 Speed (mm/s) Speed (mm/s) Velocity ( mm / s ) Velocity ( mm / s ) h 16h 24h h 48h 52h h annealed α-fe 3h Ni 3 Fe Temps milling de time broyage (hours) (h) Mössbauer Intensité Mossbauer intensity (%) (%) Ni 3 Fe Absorption (%) Absorption ( % ) 4h 8h Absorption (%) Absorption ( % ) 10h h Mössbauer spectrometry Ni 3 Fe powders

39 Ni 3 Fe 4.5 M s (µ B /f.u.) Mean hyperfine field (T) recuit 4 K 295 K Temps de broyage (h) Milling time, t (hours) m

40 Ni3Fe Ni particles Fe particles The particles morphology of the Ni75-Fe25 powders mixture (start sample - ss)

41 Ni3Fe The particles morphology of the Ni-Fe powders mixture after 4h mechanical milling.

42 Ni3Fe The particles morphology of the Ni3Fe powders after 12h mechanical alloying.

43 Ni 3 Fe Ni Fe 60µm initial mixed powders (ss) 200µm milled 12 hours Energy dispersive X-ray analysis (EDX)

44 Ni 3 Fe 12.0 milling time (hours) Ni Fe 3 M = const. s Ni+Fe+Ni Fe (Ni-Fe) o C o T 1 >330 C T >T annealing time (hours) Milling Annealing - Transformation (MAT) diagram V. Pop, O. Isnard, I. Chicinaş, J. Alloys and Compounds 361 (2003) 144

45 SUPERMALLOY; Ni79Fe16Mo5

46 SUPERMALLOY the second order internal stresses broadening of the diffraction peaks peaks shift to lower 2θ angles Intensity (a.u.) Intensity (a.u.) Theta ( ) (110) Mo The X-ray diffraction patterns of the as supermalloy milled samples (4, 6, 7, 8, 10, 12, 16 h), of the Ni3Fe (obtained after 12 h milled and annealing 3 hours at 330 C) and of the starting sample (ss 0 h milled). For clarity, the spectra have been shifted vertically. decreasing of the crystallites dimension Intensity (a.u.) Ni Fe Mo Ni 3 Fe 16h 12h 10h 8h 7h 6h 4h Ni 3 Fe ss Supermalloy formation the first order internal stresses peaks shift to HIGHER 2θ angles relaxation of the first order internal stresses (111) (200) Ni Ni 3 Fe Theta ( ) 16h 12h 10h 8h 7h 6h 4h Ni 3 Fe ss

47 SUPERMALLOY hours milling hours milling 700 Intensity (a.u.) C/4h 350 C/2h 350 C/1h 350 C/ 30 min as milled Intensity (a.u.) as milled 350 C/4h 350 C/2h 350 C/1h 350 C/ 30 min Theta ( ) Ni3Fe ss Ni 3 Fe ss Theta ( ) d = k λ β cosθ β -FWHM d = 11 nm - 16 h milling and annealing at 350 C for 2 hours in order to remove second order internal stresses The influence of the annealing conditions on the solid-state reaction of Supermalloy formation on 6 and 8 hours milled sample. The indicated annealing conditions are temperature/time. Ni 3 Fe and ss refer to the compound obtained after 12 h milled and annealing 3 hours at 330 C and the starting powder mixture respectively.

48 SUPERMALLOY Ni particles Fe particles Mo particles The Ni, Fe and Mo maps on starting sample (0 hours milling) and on the 12 hours milled sample. It can observe the chemical homogeneity of the Supermalloy powders obtained by mechanical alloying and the particles morphology, too.

49 CONCLUSIONS

50 Ni 3 Fe The Ni 3 Fe intermetallic compound is obtained after 8-10 hours of milling. A mean crystallite size of 22 ± 2 nanometers was obtained after 12 hours of milling and 3 hours of annealing at 330 C in order to remove the internal stresses. The influence of the annealing on the solid-state reaction of the Ni 3 Fe phase formation is very efficient for the 4 h-milled sample. In this case, an annealing for 30 minutes at 300 C is enough to produce the Ni 3 Fe as a majority phase in the sample. It was shown from magnetic measurements that the annealing influence on the Ni 3 Fe phase formation is more effective for lower annealing times. Generally, after the formation of the Ni 3 Fe phase, M s decreases at longer milling times, this results probably from the presence of the antisite disorder in the Ni 3 Fe structure induced by milling. As a result of the reduction of the anti-site crystallographic positions, the annealing of the samples milled for 20 h or more induces a small increase of the spontaneous magnetisation in comparison with the as milled samples. In order to discuss the correlation between milling time and annealing time to obtain the Ni 3 Fe phase in the sample volume, a Milling Annealing - Transformation (MAT) diagram is proposed.

51 SUPERMALLOY; Ni 79 Fe 16 Mo 5 The Supermalloy powders were obtained after 12 hours of milling. A mean crystallite size of 11 ± 2 nanometers was obtained after 16 hours of milling and 2 hours of annealing at 350 C in order to remove the internal stresses. On the other hand, the Supermalloy formation has been found to be improved by annealing. Thus, the Supermalloy powders were obtained after 8 h milling and 4 hours annealing at 350 C too. The SEM and X-ray microanalysis show that the chemical homogeneity and composition and morphology of the powder particles are in good agreement with the results of the X-ray diffraction studies The magnetic properties of these nanocrystalline Supermalloy powders are expected to be very good for applications as soft magnetic materials.

52 Danke! Thank You!

53 Hard Magnetic Nanocrystalline Materials high anisotropy + large magnetisation Hard phase exchange Soft phase exchange-spring magnets δ = π A / K D cr 2δ h h h D cr = soft phase critical dimension δ h = width of domain wall in the hard phase A h and K h are the exchange and anisotropy constants h

54 MECHANICAL ALLOYING Hard magnetic materials 100 T = 300 K 50 M(emu/g) Hard phase Hard phase/fe_rec_1 min/560 o C Hard phase/fe_rec_3 min/560 o C Hard phase/fe_rec_10 min/560 o C H(T)