Magnetic properties of HVOF thermally sprayed coatings obtained from nanostructured powders

Surface & Coatings Technology 201 (2006) 1805 – 1813 www.elsevier.com/locate/surfcoat

Magnetic properties of HVOF thermally sprayed coatings obtained from nanostructured powders M. Cherigui a,⁎, N.E. Fenineche a , A. Gupta b , G. Zhang a , C. Coddet a a

LERMPS-UTBM, site de Sévenans, 90010 Belfort cedex, France b University Campus, Khandwa Road, Indore 452017, India

Received 2 February 2006; accepted in revised form 7 March 2006 Available online 19 April 2006

Abstract The development of amorphous and nanocrystalline materials has attracted significant interest in the field of new materials design. Indeed, the different properties, especially the magnetic properties of materials, are largely enhanced when the size of crystallites becomes nanometric. Besides, the presence of nanocrystalline structure implicates a macroscopic behaviour fairly different from the conventional microstructured materials. In this context, the microstructure and magnetic properties deposits obtained by High Velocity Oxy-Fuel (HVOF) from nanostructured FeSibased feedstock powders were investigated. Ultra fine grain FeSi-based coatings were synthesised. X-ray analysis shows the formation of amorphous and nanostructured phases in some coatings. Mössbauer measurements confirmed also the presence of the amorphous phase. Magnetic measurements revealed a ferromagnetic character for all the coatings. Though the presence of nanostructure has a significant effect to modify magnetic properties, the results also indicated that the boron, niobium and copper incorporated in the feedstock-milled powders have little effect on these properties. © 2006 Elsevier B.V. All rights reserved. Keywords: Microstructure; HVOF; Nanostructured coating; Magnetic properties; Mössbauer

1. Introduction Nanomaterials are in the early stage of development in spite of their interesting properties compared at same conventional materials [1]. These nanomaterials have been receiving increasing attention because of their impressive combination of strength and toughness, as well as magnetic and mechanical properties [2,3]. Recently, an important issue concerns to produce massive nanocrystalline parts with several processes are being developed [3,4]. In particular, nanocrystalline coatings deposited by thermal spraying have been the subject of intense research activities during the last decade [5–7]. Thermal spraying has also recently been proven to be a successful technique for producing thick, near net shaped, nanostructured or ultra-fine grained deposits [8], which could be of interest for some magnetic applications. ⁎ Corresponding author. Tel.: +33 3 84 58 32 43; fax: +33 3 84 58 32 86. E-mail address: [email protected] (M. Cherigui). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.03.008

Due to the large diversity of their physical properties, FeSi alloys are of significant commercial and academic interests. Iron silicides can be used as starting materials for many multicomponent technical alloys. For example, β-FeSi2 and Fe2Si5 alloys with small amounts of Cu are considered as attractive new materials for high temperature thermoelectric applications [9,10]. The choice of FeSiB is justified by the thermal stability of the residual amorphous phase enriched in boron and the good magnetic properties related to the presence of silicon where the boron increases the possibility of having an amorphisation of alloys [11]. Moreover, FeSiB amorphous have been widely used as a magnetic core material used in electric generator construction [12–14]. For industrial products the most commonly used material is the amorphous Fe73,5Si13,5B9Cu1Nb3 alloy. High-level of magnetic properties can also be obtained by the presence of a nanocrystalline structure that may be formed under thermal processing of this material. The formation of such

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nanocrystalline structure, consisting of DO3 solid solution is supposed to be stimulated by the presence of Cu and Nb atoms [11,15–19]. The objective of this study is to produce FeSi-based coatings from nanostructured powders using the HVOF thermal spraying process and analyse their microstructure and magnetic properties. 2. Experimental procedure 2.1. Coatings preparation and characterisation Thermal spraying was carried out with a Sulzer Metco CDS system on copper substrates. Methane was used as a fuel gas and nitrogen as the carrier gas to transport the powder from the feeder to the gun. Rectangular sheets of 70 × 25 mm2 and a thickness of 0.8 mm were mounted on a cylindrical holder rotated at 200 rpm. The HVOF gun was placed in front of the substrates at a stand-off distance of 250 mm. HVOF authorises the powder to be heated in the gas stream and deposited onto the substrate at very high speeds. The thermal spraying parameters (Table 1) were optimised to produce dense coatings. X-ray diffraction (XRD) diagram was obtained from the powder and the coated surfaces using a SIEMENS D5000 X-ray diffractometer (λ = 0.1789 nm). The diffraction traces were recorded at a speed of 0.05 s− 1. The magnetic measurements for the powders and the deposits were done with a hysteresismeter Bull M 2000 SIIS apparatus at ambient temperature. For taking Mössbauer measurement of the samples 57Fe Mössbauer spectrometry was used in conventional constant acceleration drive (model Wissel of Mössbauer Driving Unit, MR260A for transmission and MDU-1000 for CEMS) with 57Co source in a Rh Matrix saving strength of ∼30 mCi. The following are the specification of the powder samples and coatings in Mössbauer measurements: Powder Samples (i) Transmission Geometry (ii) Sealed Proportional counter detector

ques, only mechanical alloying has been used to produce large quantities of nanostructured powders for possible commercial use [20]. Mechanical milling is reportedly employed to synthesize nanostructured powders of varying compositions [21]. Powders used in the present work are Fe93.5Si6.5, Fe86.5Si13.5, Fe75Si6.5B18.5, Fe75Si15B10 and Fe73.5Si13.5B9Nb3Cu1 (atomic percentage). These powders were obtained by ball milling of the Fe-based powder with additions of Si, B, Nb and Cu elements. Ball milling was carried out during 50 h using a planetary highenergy ball mill (Retsch PM 400). 30 mm diameter steel balls and 250 ml volume vials were used. Four vials were mounted on a planar disc. The vials move in a circular and opposite direction compared to the disc rotation. The rotation speeds of the disc and vials were respectively 300 rpm and 600 rpm. 3. Results and discussion 3.1. Powder structural state Fig. 1 presents the X-ray diffraction of the ball milled powders. The results of this characterization suggest that an ordered state of the structure was formed by mechanical alloying. Indeed, only the fundamental peaks of the intermetallic structures are visible in the X-ray diagram. No other phase than Fe3Si and Fe2B were detected. Zhou et al. also noted the formation of the Fe3Si phase when they developed nanostructured FeSi alloys by mechanical alloying for different silicon concentrations [22]. In addition to the Fe3Si phase, the Fe2B phase was also formed in the case of FeSiB nanostructured alloys elaborated from amorphous ribbons [23,24]. Concerning the FINEMET (FeSiBNbCu), Chattoraj et al. [25] and Grognet et al. [26] noted the formation of the Fe3Si phase elaborated by rapid quenching technique. Table 2 gives the position and the width of the fundamental peak (110) for the five powders. The interatomic distance (xm) determined using Eq. (1) [27,28] is also given in the same table as well as the size of the coherently diffracting domains calculated by the Scherrer and Wagner methods. xm ¼

Coatings (i) Back scattering geometry or CEMS (Conversion electron Mössbauer Spectroscopy) (ii) Gas filled proportional counter with (95% Helium + 5% Methane) gas mixture

1:23⁎k 2sinh

ð1Þ

Where θ is the diffraction angle and λ is the wavelength (0.1789 nm). From Table 2, it appears that the alloying addition leads to an increase in the interatomic distance. This increase is particularly

2.2. Feedstock powder

Table 1 Spraying parameters

Elaboration of nanostructured feedstock powders is the first step for the synthesis of nanostructured coatings. These nanostructured powders can be produced by several techniques; they include mechanical alloying, gas condensation, thermochemical method, crystallisation of amorphous alloys, vapor deposition, spray conversion processing, sputtering, electrodeposition, and sol–gel processing [20]. Among these techni-

Fuel flow rate “Methane” (SLPM) Oxygen gas flow rate (SLPM) Oxygen rate in the mixture CH4/O2 (%) Nitrogen carrier gas flow rate (SLPM) Powder feed rate (g min− 1) Spray distance (mm) Scanning step (mm) Scanning velocity (mm s− 1)

145 350 0.4 20 35 250 12 50

M. Cherigui et al. / Surface & Coatings Technology 201 (2006) 1805–1813

(a)

Fe3Si

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(a)

Fe3Si

Fe3Si

Fe3Si

Fe3Si

Fe3Si

(b)

(d)

Intensity

Intensity

(b)

(c)

Fe2B

Fe2B

(d) (e)

Fe2B

(e) 20

30

40

50

60

70

80

90

100

110

2 θ (deg.) 20

30

40

50

visible in the case of the last alloy because the atomic radius of niobium is much higher compared to the other elements. Moreover, the addition of niobium and copper produced a signification reduction of the peak width. Table 2 gives also the size of coherently diffracting domains estimated by the Scherrer and Wagner methods for the five Table 2 Results of the fitting of the first diffraction maximum in the XRD patterns of various powders and coatings Location Peak xm of the width (Å) peak (2θ (nm) on deg.)

Size of coherently diffracting domains (nm)

52.70 52.62 52.50 52.63 52.47

1.508 0.766 0.963 0.604 0.449

2.479 2.486 2.488 2.483 2.491

7 14 11 17 23

9 17 13 39 45

Coatings Fe6.5at.%Si Fe13.5at.%Si Fe6.5at.%Si18.5at.%B Fe15at.%Si10at.%B F13.5at.%Si9at.%B3at.%Nb1at.%Cu

52.77 52.63 52.50 52.63 52.42

0.426 0.441 0.568 0.674 0.466

2.476 2.482 2.488 2.482 2.491

24 23 18 15 22

34 32 20 20 30

80

90

100

110

powders. In both cases, the sizes are in the nanometric range. The two methods give however a significant divergence in the values of size. The Wagner method is most appropriate because it takes into account the microdistortion stresses of the structure. These results are in agreement with those obtained by Gupta et al. [28] who studied the effect of the addition of copper and niobium on the structural state and the magnetic properties of the FeSiB amorphous alloy elaborated by rapid quenching.

35

Scherrer Wagner

Powders Fe6.5at.%Si Fe13.5at.%Si Fe6.5at.%Si18.5at.%B Fe15at.%Si10at.%B Fe13.5at.%Si9at.%B3at.%Nb1at.%Cu

70

Fig. 2. X-ray diffraction patterns: (a) Fe93.5Si6.5, (b) Fe86.5Si13.5, (c) Fe75Si6.5B18.5, (d) Fe75Si15B10 and (e) Fe73.5Si13.5B9Nb3Cu1.

30

Coercivity (Oe)

Alloys

60

2θ

Fig. 1. X-ray diffraction patterns of powders: (a) Fe93.5Si6.5, (b) Fe86.5Si13.5, (c) Fe75Si6.5B18.5, (d) Fe75Si15B10 and (e) Fe73.5Si13.5B9Nb3Cu1.

25

1: Fe93.5Si6.5 (Hc = 0.3 Oe), 2: Fe86.5Si13.5 (Hc = 22 Oe), 3: Fe75Si6.5B18.5 (Hc = 17 Oe), 4: Fe75Si15B10 (Hc = 25 Oe), 5: Fe73.5Si13.5B9Nb3Cu1 (Hc = 29 Oe)

20 15 10 5 0

1

2

3

4

5

Powders type Fig. 3. Evolution of coercivity as function as powders type.

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(a)

1800

(b)

4πM (A.m/kg)

4πM (A.m/kg)

2000 1350 1500 900 1000 450

500

H (Oe)

H (Oe)

0 -2500

-1500

-500

500

1500

0

2500 -5000

-450 -900 -1350 -1800

(c) 2000

60 40 20 0 - 20 0 -60 -40 -20 - 40 - 60

-3000

-1000 -500

1000

3000

-1000

20

40

-1500

60

-60

-40

-2000

150 100 50 0 -20-50 0 -100 -150 -200

5000

20

40

60

(d)

4πM (A.m/kg)

600

4πM (A.m/k)

1500 400 1000 200

500

H (Oe)

H (Oe)

0 -200

-150

-100

0

0

0

-500 -500

0 0

500

1000

1500

2 000

-5000

-3000

-1000

1000

3000

5 000

-200 200

-1000

60 100

30

-1500 -2000

-400 0

0 -50

-25 -30 0

25

-60

50

-600

-60

-

40 -20 0 -100 -200

(e) 800

4πM (A.m/kg)

600 400 200

H (Oe) 0 -5000

-3000

-1000 -200

1000

3000

5000

150

-400

100 50

-600

0

-800

-60

-40

-20-50 0

20

40

60

-100 -150

Fig. 4. Hysteresis loops: (a) Fe93.5Si6.5, (b) Fe86.5Si13.5, (c) Fe75Si6.5B18.5, (d) Fe75Si15B10 and (e) Fe73.5Si13.5B9Nb3Cu1.

20

40

60

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Fig. 2 shows the XRD diagram of the different coatings. For the FeSi coating (Fig. 2a), the diffractogramme reveals that the majority phase has the cubic structure α1-Fe3Si(DO3). This is characteristic for the low silicon content in FeSi alloys. This result appears consistent with the ones obtained for rapidly quenched Fe100−xSix alloys [29] and mechanically alloyed FeSi powders [30], despite the high cooling rate associated with the rapid solidification of the individual splats (107 K/s) [31] in the thermal spraying process. This is, to a certain extent, apparently conflicting with some literature results obtained on these alloys after melt spinning; a technique providing with very similar solidification rates. The likely reason for this is associated to the fact that crystallization of the deposited amorphous occurred in the as-deposited material at subsequent passages of the thermal spray torch. Indeed, crystallization of similar types of alloys was shown to take place for temperatures in the range 450–600 °C [32]. Comparatively, the effect of B and B–Nb–Cu dopings on the microstructure is visible. The XRD diagrams corresponding to the alloys doped with these elements all show a more or less pronounced amorphous hillock at the base of the Fe3Si peak. This is more clearly visible in Fig. 2c for the FeSiB alloy. The reason for the formation of higher amount of amorphous in these alloys compared to the FeSi ones is twofold. Firstly, the alloying elements increase the ability to retrain the amorphous phase during the rapid quenching associated with the splat deposition. Secondly, they also improve the thermal stability of the deposited mixture so that a lower amount of amorphous phase has crystallized subsequently. While referring in Table 2, it can be observed that the sizes of the coherently diffracting domains are lower for the FeSiB alloys indicating that a finer structure was maintained for these alloys. 3.3. Magnetic characterization 3.3.1. Powders The values of the powder coercivity are plotted in Fig. 3 as a function of chemical composition of alloys. In general, the powder coercivity increases with the addition of non-magnetic element (Fig. 3). This slight increase is due to the presence of boron, niobium and copper which can be regarded as nonmagnetic inclusions. These inclusions act on the magnetic behavior of the FeSi alloy by forming shutting domains which contribute to stop the Bloch's wall move and, consequently, increase the coercivity. 3.3.2. Coatings The coating coercivities were clearly reduced compared to that of powders except for Fe93.5Si6.5 and Fe75Si6.5B18.5. Fig. 4 shows the hysteresis loops of the various coatings. The decrease in the coercivity level is probably due to the presence of the mixture amorphous and nanostructured phases. In addition, in the case of powders, the time of mechanical alloying was clearly not sufficient to obtain a complete solid solution. Fig. 6 presents the coercivity values according to the deposit type. Except

Fe75Si6.5B18.5, it was noted the same trend in evolution of this field as the one recorded for the case of powders (Fig. 5). It is clear that the higher additions of boron contribute to increase coercivity. This phenomenon can be explained by the nonmagnetic character of copper, niobium and boron. However, for the coatings, it was noted that for FeSiB, the coercivity did not follow the same evolution noted in the case of the powder. This result is probably due to the volatilization of boron during projection. A same remark can be noted in the case of Fe93.5Si6.5 coating where a significant increase in coercivity was noted compared to the initial powder. This increase is probably due to an increase of the coherently diffracting domains of the deposit (34 nm) which is greater compared with that of powder (9 nm) (Table 2). Such behavior (decrease in coercivity with the decrease in grain size) was observed by other studies for the Fe– Co, Co–Ni and Fe–Ni alloys obtained by mechanical alloying [33,34]. The evolution of coercivity can also be related to the effects of thermal spray technique. Indeed, the tendency of the coercivity variation in the case of coatings is highly different to that of powders. This difference is probably due to the structural changes which can be occurring during and after the thermal spray process. 3.4. Mössbauer spectrum 3.4.1. Powders The Mössbauer spectroscopy allowed by the intermediary of the atoms probed to obtain information about the formation process of iron-based alloys, and on the other hand, get information concerning the local change of magnetic properties. Results of Fe93.5Si6.5 microstructured powder and coating studied in our preceding work [35] were presented for comparing them with this study results. Fig. 6a presents the Mössbauer spectrum of this last. It can be fitted with four substrates with hyperfine field values of 33 T, 31 T, 28 T and 23.5 T. These hyperfine fields correspond to solid solution of Si in bcc Fe. The relative areas of the four sextets can be used to obtain the approximate Si composition. The latter is about 19% which can correspond to Fe3Si phase. 1: Fe93.5Si6.5 (Hc = 15 Oe), 2: Fe86.5Si13.5 (Hc = 14.75 Oe), 3: Fe75Si6.5B18.5 (Hc = 26 Oe), 4: Fe75Si15B10 (Hc = 12.5 Oe), 5: Fe73.5Si13.5B9Nb3Cu1 (Hc = 17 Oe)

30

Coercivity (Oe)

3.2. Coating structural state

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25 20 15 10 5 0 1

2

3

4

5

Coatings type Fig. 5. Evolution of coercivity as function as coatings type.

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(a)

(b)

Fe93.5Si6.5 (nanostructured powder)

Intensity (arb. units)

Intensity (arb.units)

Fe93.5Si6.5 (microstructured powder)

-8

-6

-4

-2

0

2

4

6

8

-8

-6

-4

Velocity (mm/s)

(c)

-2

0

2

4

6

8

Velocity (mm/s)

(d)

Fe75Si6.5B18.5

Intensity (arb.units)

Intensity (arb. units)

Fe86.5Si13.5

-8

-6

-4

-2

0

2

4

6

8

-8

-6

-4

Velocity (mm/s)

(e)

-2

0

2

4

6

8

Velocity (mm/s)

(f)

Fe73.5Si13.5B9Nb3Cu1

Intensity (arb. units)

Intensity (arb.units)

Fe75Si15B10

-8

-6

-4

-2

0

2

4

6

8

Velocity (mm/s)

-8

-6

-4

-2

0

2

4

6

8

Velocity (mm/s)

Fig. 6. Mössbauer spectrum of powders: (a) Fe93.5Si6.5 (micro), (b) Fe93.5Si6.5 (nano), (c) Fe86.5Si13.5, (d) Fe75Si6.5B18.5, (e) Fe75Si15B10 and (f) Fe73.5Si13.5B9Nb3Cu1.

Mössbauer spectrum of Fe93.5Si6.5 nanostructured powder fitted with four sextets (Fig. 6b) is very similar to that of the microstructural powder. It has the same hyperfine field value as that for Fe93.5Si6.5 microstructural powder. The relative area of the four sextets in this case is slightly differently and that gives a composition of about 16 at.% Si. For Mössbauer spectrum of Fe86.5Si13.5 powder fitted with four sextets (Fig. 6c), a sharp sextet corresponding to bcc Fe (BHF = 32.9 T) dominates. However, it was found necessary to include one doublet also. From the relative areas of the four sextets the composition of this sample gives a Si concentration of about 3 at.%. The doublet that occupies about 7% of the total

area may be due to some oxidation of the sample during preparation. The spectrum of Fe75Si6.5B18.5 (Fig. 6d) could also be fitted with four sextets and one doublet. The analysis of this sample in terms of binominal distribution is not expected to be very reliable because, while Si goes substitutionally, B is expected to go at the interstitial sites. However, in this case also the sextet corresponding to 33 T dominates and the approximate metalloid concentration comes out to be less than 3%. Concerning the spectrum of Fe75Si15B10 (Fig. 6e), it has also been fitted with four sextets but their fields are very different from those corresponding to solution of Si in Fe. Only the hyperfine field of 26.6T corresponds to Fe2B phase was noted.

M. Cherigui et al. / Surface & Coatings Technology 201 (2006) 1805–1813

Finally, Fe73.5Si13.5B9Nb3Cu1 powder could be fitted with three sextets and one singlet. Singlet is quite sharp and may correspond to some non-magnetic phase of Fe and Nb. Among the three magnetic components, the sextet with field 32.9 T dominates (79% area). This again suggests that in the magnetic fields the amount of metalloid is very small (a few % only).

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3.4.2. Coatings Concerning the result of CEMS of the coatings (Fig. 7a1, b1, c1) gives respectively the CEMS of the Fe93.5Si6.5 (obtained from microstructured powder), Fe93.5Si6.5 (obtained from nanostructured) and Fe86.5Si13.5. The spectra have been fitted assuming a single distribution of hyperfine fields. The corresponding field distributions are also shown in (Fig. 7a2,

(a2)

Probability

Intensity (arb.units)

(a1)

-8

-6

-4

-2

0

2

4

6

8

10

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5

10

15

20

25

Velocity (mm/s)

Bhf (T)

(b1)

(b2)

30

35

40

45

50

Probability

Intensity (arb.units)

-10

-8

-6

-4

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0

2

4

6

8

10

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5

10 15 20 25 30 35 40 45 50 55 60

Velocity (mm/s)

Bhf (T)

(c1)

(c2)

Probability

Intensity (arb.units)

-10

-10

-8-

6

-4-

2

0

2

Velocity (mm/s)

4

6

8

10

-5

0

5

10 15 20 25

30 35 40 45 50 55

Bhf (T)

Fig. 7. Mössbauer spectrum of coatings: (a) Fe93.5Si6.5 (micro), (b) Fe93.5Si6.5 (nano), (c) Fe86.5Si13.5, (d) Fe75Si6.5B18.5, (e) Fe75Si15B10 and (f) Fe73.5Si13.5B9Nb3Cu1.

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(d2)

-10

Probability

Intensity (arb.units)

(d1)

-8

-6

-4

-2

0

2

4

6

8

10

-5

0

5

10

Velocity (mm/s)

20

25

30

35

25

30

35

40

Bhf (T)

(e2)

Probability

Intensity (arb.units)

(e1)

-10

15

-8

-6

-4

-2

0

2

4

6

8

10

-5

0

Velocity (mm/s)

5

10

15

20

40

Bht (T) Fig. 7 (continued).

b2, c2). In the three cases the dominant peak of the field distribution covers the range of 35–25 T. In addition, another peak appears around 9 T. The height of this peak is maximum in Fe93.5Si6.5 obtained from microstructured powder and almost disappears in Fe86.5Si13.5. Thus the area under this peak seems to be related with Si concentration. Smaller peaks are not significant and may be due to the limited statistics of the data. The broad peak in the range 25–30 T essentially encompasses the three fields of 33 T, 31 T and 28 T corresponding to the solid solution of Si in bcc-Fe. Thus, this broad peak in the field distribution indicates the bcc FeSi solid solution. We obtained a broad distribution instead of three separate components of 33 T, 31 T and 28 T because of a higher degree of disorder in the system. The second peak near 9T may correspond to some regions in the system having higher Si concentration (representing some compositional inhomogenity in the system). Fig. 7d1 gives the CEMS of Fe75Si15B10. The spectrum has been fitted with a combination of a sharp sextet corresponding to bcc Fe and a hyperfine field distribution. It was necessary to incorporate one crystalline component to get a good fitting of the data. Fig. 7d2 gives the hyperfine distribution. One may note that in contrast to FeSi systems, in this case the field distribution is very broad which is typical of amorphous phase.

Thus, it appears in this case that about 19% of Fe is in the bcc-Fe form and the remaining part is amorphous. Further in the present case field distribution is very broad and extends up to 0 field. This is in contrast to the typical field distribution of FeSiB amorphous alloy. This again suggests higher composition inhomogeniety in the amorphous phase. In the case of Fe73.5Si13.5B9Nb3Cu1, two phases are clearly seen: (i) a sharp sextet corresponding to bcc Fe containing about 35% of total iron, (ii) a broad sextet typical of amorphous phase with metalloid content. In this case also field distribution is very broad extending to 0 T, indicating a higher composition inhomogeniety. The hyperfine field component close to 0 T may be due to some non-magnetic FeNb alloy. 4. Conclusion FeSi based alloys have been studied in order to produce ferromagnetic thermal spraying coatings and elucidate the structural and magnetic properties changes as a function of the B, Nb and Co presence. It has been shown that coatings produced present a soft ferromagnetic character. Additions of non-magnetic elements like boron, niobium and copper incorporated in the feedstock

M. Cherigui et al. / Surface & Coatings Technology 201 (2006) 1805–1813

milled powders have little effect on these properties. It has also shown the presence of amorphous and nanostructure phases in the coatings. The nanostructure phase has a significant effect to modify magnetic properties of deposits. The zone, rich of niobium presented in the case of FINEMET coating which is regarded as defects anchoring Bloch walls and consequently involves an increase of coercivity, can present a benefit factor to form a deposit with multi-layer which is an advantage for some magnetic application like magnetic shielding. Indeed, these results permit to conclude that FeSiBNbCu can be regarded as the best powder to produce coatings intended to this type of magnetic applications. Acknowledgements The authors express their thanks for the assistance provided by the UMR 5060 CNRS-UTBM group (University of BelfortFrance) and the NIPSON Company (Belfort-France). References [1] L.L. Shaw, D. Goberman, R. Ren, M. Gell, S. Jiang, Y. Wang, T.D. Xiao, P. R. Strutt, Surf. Coat. Technol. 130 (2000) 1. [2] R.W. Siegel, Nanostruct. Mater. 4 (1994) 121. [3] H. Gleiter, Acta Mater. 48 (2000) 1. [4] D.G. Morris, Materials Science Foundations, vol. 2, Trans. Tech. Publications, Zurich, 1998. [5] H.G. Jiang, M.L. Lau, E.J. Lavernia, Nanostruct. Mater. 10 (1998) 169. [6] J. He, M. Ice, E.J. Lavernia, Metall. Mater. Trans. 2 (1999) 237. [7] T. Grosdidier, A. Tidu, H.L. Liao, Scr. Mater. 44 (2001) 387. [8] G. Ji, T. Grosdidier, H.L. Liao, J.P. Morniroli, C. Coddet, Intermetallics 13 (2005) 596. [9] I. Nishida, Phys. Rev., B 7 (1973) 2710. [10] I. Yamauchi, T. Okamoto, H. Ohata, I. Ohnaka, J. Alloys Compd. 260 (1997) 162.

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