Milling amorphous FeSiB ribbons with vibratory ball and disc mills

Powder Technology 441 (2024) 119816 Available online 29 April 2024 0032-5910/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/). Milling amorphous FeSiB ribbons with vibratory ball and disc mills Rosa María Aranda a , * , Raquel Astacio b , Petr Urban b , Beatriz Aranda a , Francisco G. Cuevas a a Department of Chemical Engineering, Physical Chemistry and Materials Science, Escuela T´ ecnica Superior de Ingeniería, Universidad de Huelva, Campus El Carmen, Avda. Tres de marzo s/n, 21071 Huelva, Spain b Department of Materials and Transportation Engineering and Science, Escuela T´ ecnica Superior de Ingeniería, Universidad de Sevilla, Camino de los Descubrimientos s/ n, 41092 Seville, Spain HIGHLIGHTS GRAPHICAL ABSTRACT •Production of amorphous powder by mechanical milling of ribbon. •Use of vibratory disc and ball mill for Fe 78 Si 9 B 13 ribbon milling. •Amorphous powder with a d (0.5) =47 μ m in 150 min with a vibratory disc mill. •Amorphous powder with a d (0.5) =48 μ m in 90 min with a vibratory ball mill. ARTICLE INFO Keywords: Melt spinning Metglas alloy Amorphization Mechanical milling ABSTRACT Fe, Si and B powders, mixed with atomic composition Fe 78 Si 9 B 13 , are subjected after arc melting to a melt spinning process, which is optimized to obtain the greatest amount of amorphous ribbon. The amorphous ribbons are milled to powder form in a vibratory ball mill and a vibratory disc mill, taking care of maintaining the amorphous character. Ribbons and powders have been characterized by X-ray diffraction (XRD), laser diffraction, SEM and TEM microscopy, and differential scanning calorimetry (DSC). The amorphous character and particle size of the powders are characterized as a function of the mill charge and the milling time. It is shown that the use of the ball mill is appropriate for obtaining small quantities of amorphous or nanocrystalline powder, while the disc mill can process larger quantities of powder in a shorter time. The particle sizes obtained for milling times between 10 and 150 min range between 26 and 412 μ m, ready for use in powder metallurgy processes. * Corresponding author. E-mail address: [email protected] (R.M. Aranda). Contents lists available at ScienceDirect Powder Technology journal homepage: www.journals.elsevier.com/powder-technology https://doi.org/10.1016/j.powtec.2024.119816 Received 19 February 2024; Received in revised form 11 April 2024; Accepted 28 April 2024 Powder Technology 441 (2024) 119816 2 Table 1 Review of milling of Fe-base amorphous ribbons. (BRR =Ball – Ribbons ratio; AM =Amorphous matrix; RT =Room temperature). Alloy Year Mill Vial / Balls BRR RPM Atmosphere / T (◦C) Milling time Powder size ( μ m) Result – Time Ref. Fe 78 Si 9 B 13 1989 LS 10 K Glen Mills – – – – – 250 μ m Fe 3 B + α -Fe +AM –? [39] Fe 66 Co 18 Si 1 B 15 1990 HEBM 8000 SPEX Steel – – – / RT 24 h – α -Fe(Co) +AM – 3 h α -Fe(Co) +[Fe(Co) 2 ]B + AM – 12 h Crystalline – 24 h [24] Fe 78 Si 9 B 13 1990 HEBM 8000 SPEX Steel – – – / RT 24 h – α -Fe(Si) +AM – 3 h Nanocrystalline α -Fe(Si) – 24 h [24] Fe 72 Co 8 Si 8 B 12 1992 HEBM 8000 SPEX Steel – – – / RT 24 h – α -Fe(Co) +[Fe(Co) 2 ]B –? Crystalline – 24 h [25] Fe 65 Ni 17 Si 7 B 11 1992 HEBM 8000 SPEX Steel – – – / RT 24 h – AM – 24 h [25] Fe 78 Si 9 B 13 1993 HEBM 8000 SPEX Steel 4.5:1 – Ar / RT Air / RT O 2 / RT 26 h – α -Fe(Si) +Fe 2 B +AM – < 20 h Crystalline – 26 h α -Fe(Si) +Fe 2 B +AM – < 4 h Crystalline – 5 h α -Fe(Si) +Fe 2 B +AM – < 1.5 h Crystalline – 2 h [26] Fe 78 Si 9 B 13 1994 HEBM 8000 SPEX Hardened Steel WC 5:1 20:1 – Ar / RT 24 h – Traces of α -Fe(Si) +AM – 1.5 h α -Fe(Si) +Fe 2 B +AM – 15 min [35] Fe 78 Si 9 B 13 1995 HEBM Attritor 01-IID Union Process 750 Stainless steel 100:1 – N 2 / cryo. 100 h – Traces of α -Fe(Si) +Fe 2 B +AM – 5 h Nanocrystalline α -Fe(Si) +Fe 2 B – >100 h [36] Fe 77.2 Mo 0.8 Si 9 B 13 1997 HEPBM WL1 Stainless steel / Hardened steel 40:1 – Ar / RT 307 h – AM – <9 h Nanocrystalline α -Fe(Si) – 135 h [40] Fe 40 Ni 40 P 14 B 6 1999 HEPBM – – – Ar / RT 90 h – AM – <5 h Nanocrystalline γ-(Fe, Ni) +(Fe, Ni) 3 (P,B) – > 11 h [41] Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 2000 HEPBM WL1 Stainless steel 25:1 240 N 2 / 4 ◦C 100 h 15 μ m – 16 h 2–3 μ m – 100 h AM – <16 h Nanocrystalline α -Fe(Si) – 100 h [42] Fe 77 Al 2.14 Ga 0.86 P 8.4 C 5 B 4 Si 2.6 2004 HEPBM PM4000 Retsch Hardened steel 15:1 250, 200 and 150 Ar / RT 1 h – AM – 1 h [43] Fe 77 Al 2.14 Ga 0.86 P 8.4 C 5 B 4 Si 2.6 2004 HEPBM PM4000 Retsch Agate – – Ar / RT 10 h 300 μ m – [44] Fe 40 Ni 40 P x Si 20-x x =10 or 14 2004 HEPBM P7 Frisch – 50:1 30:1 350 (x =10) 450 (x =14) Vacuum / RT 16 h (x =10) 6 h (x = 14) ≥50 μ m Ni-rich silicides+Fe-rich phosphides +Fe(Si) +Fe (Ni) +AM (x =10) – 16 h AM (x =14) – 6 h [45] Fe 78 Si 9 B 13 2005 HEBM 8000 SPEX – 5:1 – Ar / RT – 50 μ m 140 μ m 350 μ m – [46] Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 2005 HEBM Agate 10:1 – Ar / RT 3.5 h – AM – <2 h α -Fe +AM – >2 h to <3.5 h [47] Fe 41 Ni 20 Co 20 Zr 7 B 12 2007 HEPBM P5 Frisch Steel – 250 Ar / RT 27 h – AM – <27 h [48] Fe 73 Si 16 B 7 Nb 3 Cu 1 2007 Ball mill Stainless steel – 167 - / RT 36 h 60% wt < 45 μ m – [49] Fe 83 Zr 6 B 10 Cu 1 2007 HEPBM P4 Frisch Hardened steel 12:1 300 Ar / RT 24 h 250 μ m – 2 h 50 μ m – 6 h α -Fe +AM – 2 h [50] (continued on next page) R.M. Aranda et al. Powder Technology 441 (2024) 119816 3 1. Introduction Amorphous metals are very attractive materials with outstanding properties. Mechanical [1], magnetic [2] or corrosion [3] behaviour, among others, can improve with the microstructural disorder of these materials. Several methods can be considered to reach the intrinsically instable amorphous structure in metallic materials. These techniques are based on the extremely rapid cooling of a liquid to impinge ordering [4,5], atoms in vapour state deposited individually on a cold substrate [6], the disorder caused by ion irradiation [7], solid state reaction [8], or solidstate mechanical processes in which the internal structure of the materials is highly disordered [9]. Despite the final goal of any of these techniques is to obtain an amorphous structure, some other objectives should also be considered for specific uses. For instance, a high productivity, or obtaining a final Table 1 (continued) Alloy Year Mill Vial / Balls BRR RPM Atmosphere / T (◦C) Milling time Powder size ( μ m) Result – Time Ref. 100–150 μ m – 8 h Fe 73.5 Si 16.5 B 6 Nb 3 Cu 1 2007 HEPBM PM4000 Retsch Hardened steel 7:1 200 Ar / RT 200 h – α -Fe (Si) +AM – <30 h (AM >90 wt% – 12 h) (AM >70 wt% – 30 h) Nanocrystalline α -Fe(Si) – 140 h [51] Fe 90 Zr 10 2007 HEPBM AGO–2 Stainless steel 40:1 300, 400 600, 1000 Ar / RT 120 min Nanocrystalline + residual AM – 30 min Crystalline – 30 min [52] Fe 78 Si 9 B 13 2008 HEPBM P6 Frisch Stainless steel / Hardened steel 20:1 400 Ar / RT Air / RT 60 h – AM – <8 h α -Fe(Si) +AM – >8 h Nanocrystalline α -Fe(Si) – 24 h Nanocrystalline α -Fe(Si) +Fe 2 B – >24 h AM – <3 h α - Fe(Si) +AM – >8 h Nanocrystalline α -Fe(Si) – 30 h [53] Fe 77 Nb 7 B 15 Cu 1 2009 HEPBM PM4000 Retsch Hardened steel 15:1 200 – / RT 5 h >45 μ m α - Fe(Si) +AM – 5 h [31] Fe 81 Cu 2 Nb 3 Si 14 2012 HEPBM QM – 3SP2 – 20:1 200 Ar / RT 2 h 150 μ m AM – 2 h [54] Fe 32 Ni 52 Zr 3 B 13 2014 HEBM 8000 SPEX Hardened steel 4:1 – N 2 / RT 16 h – Fe(Ni) +AM – 30 min Fe(Ni) +Zr 3 Ni 20 B 6 +AM – 4 h Crystalline – 8 h [55] Fe 79.7-x Nb 0.3 Cr x B 20 (x =11.5–13% at) 2014 HEPBM PM200 Retsch Hardened steel 50:1 550 – / RT 90 h 1–3 μ m – 10 h α -Fe +AM – 6 h [56] Fe 80 Si 7 B 13 2014 HEBM Shaker-type milling Stainless steel 4:1 – Ar / RT 70 h 1 μ m – 70 h α -Fe +AM – 70 h [57] Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 2015 HEBM Stainless steel 24:1 750 Ar / RT 65 min – α -Fe(Si) +AM – 24 min α -Fe(Si) +Fe 3 B +Fe 2 B + AM – 36 min [33] [(Fe 0.5 Co 0.5 ) 0.75 B 0.2 Si 0.05 ] 96 Nb 4 2015 HEPBM P5 Frisch WC 10:1 200 Ar/ RT – <300 μ m – [58] Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 2015 HEBM Stainless steel 24:1 750 Ar / RT 45 min – α -Fe(Si) +Fe 3 B +Fe 2 B + Fe 23 B 6 +AM – 45 min [59] Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 2016 HEBM Stainless steel 24:1 750 Ar / RT 45 min 7 μ m – 45 min α -Fe(Si) +Fe 3 B +Fe 2 B + Fe 23 B 6 +AM – 45 min [20] Fe 80 Nb 10 B 10 2017 HEPBM PM400 Retsch Hardened steel 10:1 200 Ar / RT 60 h – α -Fe(Si) +AM – 60 h [60] FeCoNiSi 0.4 Al 0.4 2020 HEPBM QM – QX4 30:1 300 Ar / RT 60 h – – [61] Sm 10.5 Fe 89.5 2020 HEBM 8000 SPEX – 20:1 1725 Ar / RT 10 h – Sm 2 Fe 9 + α -Fe +AM – 0.5 h Sm 2 Fe 17 +Sm 2 Fe 9 + α -Fe +AM – 1 h α -Fe +AM – 2 to 5 h α -Fe – 5 h SmFe 9 + α -Fe +AM – ≥ 7 h [62] Fe 80 Si 1 P 10 C 9 2022 HEBM 8000D SPEX Hardened steel 1725 25:1 N 2 / - 90 ◦C - 50 ◦C 4 h <60 μ m AM – 4 h [63] R.M. Aranda et al. Powder Technology 441 (2024) 119816 4 alloy without contamination, is always desirable. Thus, vapour deposition or ion irradiation are not much productive; mechanical alloying usually requires a process control agent to balance the welding and fracturing processes of the powder particles, remaining as impurity in the final composition of the powder; and the cooling rate of atomisation does not always get completely amorphous powders. The melt spinning process is therefore the most extended technique to produce amorphous materials, in form of ribbons, showing a high productivity and compositional control. On the other hand, the amorphization process should on times finish in producing a bulk metallic glass (BMG) with the desired composition and geometry. However, obtaining BMGs is not always possible, being limited by the cooling rate that can be allowed for a particular composition at the time that the amorphous structure is maintained. For instance, soft magnetic materials with outstanding properties, obtained in amorphous state from Fe-Si-B-Nb-Cu alloys, can be obtained in bulk form with approximately a maximum diameter of 22 mm, but thicker sections irremediably produce crystalline structures [10,11]. In the search for Fe-based glasses with bigger dimensions, studies are being conducted using 3D printing technology such as the direct metal laser sintering process, with Fe-Cr-Mo-C-B alloys reaching a critical size of 45 mm [12]. Studying the glass forming ability and stability of new developed compositions is a tedious work, although artificial intelligence is now being used to make predictions [13]. (a)(b) Fig. 1. Image and detail of the vessels of (a) the vibratory ball mill, VBM and (b) the vibratory disc mill, VDM. (a)(b) Fig. 2. Image of (a) the melt spun Fe 78 Si 9 B 13 ribbon showing an initial inhomogeneous and a final well-formed zone, and (b) folded final part of the ribbon. R.M. Aranda et al. Powder Technology 441 (2024) 119816 5 There are however other options to obtain BMGs, for instance, melt spun ribbons can be stacked to form the final shape, although this shape is generally as simple as a toroid. To form more complex shapes, it is possible to work with amorphous powders that must be mixed with an agglomerant [14]. If the presence of the agglomerant wants to be avoided, powders must be processed through powder metallurgy (PM) techniques. Unfortunately, the use of high or relatively high temperatures in traditional PM compromise the stability of the amorphous microstructure. Recently, field assisted sintering techniques (FAST), with the common characteristic of being very fast as compared to diffusive processes [15], have been considered. These techniques are based on the Joule heat generated by the passage of an electric current through the powder mass. Spark plasma sintering is the most extended technique, and it has been recently applied to consolidate amorphous Albase [16–18] or Fe-base [19,20] powders. Nevertheless, much quicker techniques, with dwelling times in the order of seconds instead of minutes, as electrical resistance sintering [21] or capacitor electrical discharge [22], are also being considered. For any of these FAST techniques to be applied, the appropriate powder particles in amorphous state and with the adequate granulometry is needed. Probably, the most extended way to obtain such impurity-free powders is by milling melt spun ribbons. The study of the mechanical milling process of amorphous ribbons has been very intense in recent decades. The objective is not only to obtain amorphous powders, but also to understand the mechanical crystallization process produced by room temperature deformation [23], which leads to materials with specific microstructures. In general, crystallization achieved by heat treatments or mechanically initially results in a microstructure composed of nanocrystals embedded in an amorphous matrix, but there could be differences in the crystalline phases formed (which may or may not be beneficial for specific applications). Another difference is the difficulty to control the amount and size of the nanocrystals produced mechanically. In 1989, Pak and Chu published the first study on the milling of Febase amorphous ribbons, but it was not until 1990 that Trudeau et al. carried out a systematic study on the crystallization of ribbons by milling [24]. Fe 66 Co 18 Si 1 B 15 and Fe 78 Si 9 B 13 ribbons were milled in a high energy ball mill. The Fe 66 Co 18 Si 1 B 15 ribbons required 24 h to reach the full crystallization (after the appearance of α -Fe(Co) at 3 h, and Fe(Co) 2 B after 12 h). In contrast, in the Fe 78 Si 9 B 13 alloy, after 24 h of milling, only the α -Fe(Si) phase was observed. Two years later, the same researchers studied the effect of the addition of Ni and Co, concluding that the addition of Co accelerated the crystallization process, and the presence of Ni slowed it down [25]. In addition, they studied the influence of the atmosphere used during the milling process, being the O 2 the one that quicker produced a mechanical crystallization, while the use of protective atmospheres, such as Ar, slowed down the crystallization process. In contrast, the presence of O 2 could inhibit the crystallization of some phases [26]. Since then, many researchers have followed this route to obtain amorphous as well as nanocrystalline or crystalline powders. A review of the research carried out in the last decades on mechanical milling of Febase amorphous ribbons is shown in Table 1. According to the literature, the process is mostly carried out in high energy mills with hardened steel or tungsten carbide vessels, under protective atmosphere (Ar or N 2 ), and with stop times to avoid high temperature during milling. On times cryogenic temperatures are used to help preserving the amorphous state [18,27]. Two types of high energy mills are the mostly used [28–30], ball mills (HEBM) and planetary ball mills (HEPBM). The average size of the powder particles obtained from these mills is in the range of 7–300 μ m, most of them below 100 μ m. The use of HEPBM requires low ball-to-ribbon load ratios and low rotation speeds if the amorphous microstructure must be preserved. For instance, ratios between 15:1 and 5:1 and speeds between 150 and 200 rpm allow prolonging the milling of Fe 77 Nb 7 B 15 Cu 1 ribbons up to 40 h while maintaining the initial microstructure [31,32]. Likewise, other compositions as Ni 59 Zr 20 Ti 16 Si 5 retain the initial state after 9 h at a speed of 250 rpm and charge ratios of 10:1 and 5:1 [33]. With Fe 78 Si 9 B 13 ribbons, a charge ratio of 20:1 and rotational speed of 400 rpm allowed Fig. 3. XRD patterns of the initial, transition, and final zones of the melt spun Fe 78 Si 9 B 13 ribbons. Fig. 4. TEM image and diffraction pattern of the melt spun Fe 78 Si 9 B 13 showing the amorphous structure of the final zone of the ribbon. Fig. 5. XRD of the initial ribbon, and after cutting it in a knives mill for 3 min and sieved at sizes smaller and bigger than 0.5 mm. R.M. Aranda et al. Powder Technology 441 (2024) 119816 6 to obtain amorphous powders with milling times of up to 8 h in protective atmosphere, and <3 h in air. However, the higher energy achieved with a 24:1 ratio and 750 rpm can only be applied to Finemet (Fe 73,5 Si 13,5 B 9 Nb 3 Cu 1 ) ribbons for up to 24–36 min if the amorphous state must be preserved [20,34]. On the other hand, when using HEBM with amorphous Fe 78 Si 9 B 13 ribbons, with ratios of 20:1 and protective atmosphere, the milling time should be <1.5 h to preserve the initial microstructure [35], and with ratios of 100:1 and cryogenic temperatures the material is still amorphous after 5 h of milling [36]. Regarding the effect of milling on Fe-base alloys for magnetic applications, the presence of nanocrystals improves the thermal stability and enhances soft magnetic properties over its amorphous counterpart. In addition, a decrease in the size of the nanocrystals leads to a reduction in the coercivity of the material [37]. This behaviour was first observed for the partially nanocrystalline Finemet alloys, and later for the Nanoperm and Hitperm alloys. For instance, the Finemet alloy is obtained by annealing the amorphous alloy at a temperature between 480 and 550 ◦C for 1 h, resulting in the presence of α -Fe(Si) and a small amount of Fe 3 Si crystals with sizes smaller than 10 nm in a weakly ferromagnetic Fe-Nb-B amorphous matrix. The material turns out to have excellent soft magnetic properties, largely dependent on the average size of the nanocrystals, and thus on the synthesis and annealing parameters [38]. However, other types of HEBM, as well as lower energy mills are also available, although are almost unexplored for these purposes. In this work, melt spun amorphous ribbons of Fe-Si-B were prepared and transformed to powder form by using two types of vibratory mills. The first one is a two-vessels ball mixer mill (vibratory ball mill, VBM) with a low ball-to-ribbon ratio (used range 2:1–1:1). On the other hand, a vibratory disc mill (VDM), whose operating principle can be likened in terms of energy to that of high-energy mills, has also been tested. The influence of the processing parameters on the powders obtained and their microstructure is analysed in this study, considering that maintaining the amorphous microstructure can result advantageous, because the nanocrystallisation process on times required to improve magnetic properties is better carried out, in general, by heat treating the amorphous powders. 2. Materials and methods Elemental iron (ATOMET 1001HP, purity >99.4%, Rio Tinto, Montreal, Canada), silicon (Amperit 170, purity >99.6%, Flame Spray Technologies, Duiven, The Netherlands) and boron (Boron crystalline, purity >98%, Alfa Aesar, Schwerte, Germany) powders were mixed to give the desired composition of Fe 78 Si 9 B 13 (a simple composition of amorphous alloys known as Metglass [64]). The mix of 7 g of powder was pressed at 450 MPa to obtain a green compact 8 mm in diameter, valid to be arc melted. The arc melting process (Edmund Bühler MAM-1, Bodelshausen, Germany) was carried out in Ar atmosphere after Tigettering, and repeated for 3 times to obtain a homogeneous alloy. Ribbons were obtained by melt spinning (Edmund Bühler SC, Bodelshausen, Germany) using a rectangular nozzle of 0.4 ×10 mm 2 under different conditions: 1050–1250 ◦C with a wheel surface speed of 21–35 m/s, a nozzle-wheel distance of 0.3–0.7 mm and an ejection overpressure of 100–400 mbar in a chamber at 800 mbar. The microstructure of melt-spun ribbons was examined with X-rays diffraction (XRD, Bruker D8 Advance, Allentown, United States) with Cu-K α radiation and 2θ from 20 to 80◦(only the range 35–55◦is shown for more detail), and transmission electron microscopy (TEM, Philips CM200 at 200 KV, Amsterdam, The Netherlands). For TEM studies, specimens were prepared by precision ion polishing system (PIPS, Gatan 691, Pleasanton, CA, United States). The thermal stability study of the ribbons was carried out in a differential scanning calorimeter (DSC, TA Instruments 2010, New Castle, DE, United States) with a heating rate of 20 ◦C/min under Ar atmosphere. Selected zones of the ribbons, identified as amorphous, were then initially crushed in a knives mill (Moulinex MC3001, Lyon, France) for 3 min, and sieved fractions lower and higher than 5 mm were finally milled under different conditions: 3–6 g loads processed in a two-vessels VBM (Retsch MM301, Haan, Germany) with tungsten carbide ball (ball diameter 10 mm and ball weight 6 g, ball to powder ratio in the range (a) ( b ) Fig. 6. SEM micrographs of the ribbons cut for 3 min in a knives mill: fraction with (a) particle size <0.5 mm; and (b) particle size >0.5 mm. R.M. Aranda et al. Powder Technology 441 (2024) 119816 7 2:1–1:1) and vial, for 30–150 min and vibrating frequency of 10 to 30 Hz; and 10–30 g loads processed in a VDM (Retsch RS100, Haan, Germany) with hardened steel disc and vial, for 10–150 min and vibrating frequency of 50 and 60 Hz (this makes the disc inside the milling reaching 700 and 1400 rpm respectively). Each milling time was studied independently, without extracting material of the mill at intermediate times. Fig. 1 shows the two types of mills used in this work. Obtained powders were microstructurally and thermally characterized by XRD, scanning electron microscopy (SEM, Thermo Fisher Scientific FEI Teneo, Waltham, MA, United States), TEM, and DSC, and the granulometry by SEM and laser diffraction (Malvern Panalytical Mastersizer 2000, Malvern, UK). (The mean size values obtained from laser diffraction should be considered with care because of the flake shape of the powders and the measurement mechanism of this process). The measurement of the absolute density of the powders is performed with a pycnometer (Accupyc II 1340, Micromeritics, USA). The tap density of the powders is determined according to the procedure followed in the ISO 3953:2011 standard [65]. The fluidity of the powders is determined from the Hall fluidimeter, following the procedure described in the ISO 4490:2011 standard [66]. The procedure followed to determine the compressibility of powders is that set out in the ISO 3927:2017 standard [67]. 3. Results 3.1. Melt spinning process Ribbons obtained in the melt spinner show two different zones for the studied composition (Fig. 2). The firstly formed part is inhomogeneous and brittle, with a typical thickness higher than 40 μ m, whereas the final part is well-shaped and ductile, being possible to bend it up to 180◦without breaking. The typical thickness of this zone varies between 17 and 35 μ m depending on the processing conditions, always with a width of about 10 mm. XRD shows that the initial zone of the ribbon is not amorphous, whereas the end is an amorphous material (Fig. 3). The transition zone between them shows an intermediate result in XRD. Results obtained with XRD have been confirmed by TEM (Fig. 4). The amorphous microstructure is confirmed for the final zone of the ribbon. Nevertheless, despite the aforementioned is the general behaviour for the melt spinning process, the processing parameter affect the results regarding the amorphous character, and the length of the final zone of the ribbon. Thus, high ejection pressures increase the flow on the wheel surface, resulting in thicker and more homogeneous ribbons, but thicker ribbons may result in nanocristalizaci´ on of the material or complete loss of the amorphous character. Similarly, low wheel speeds result in better finished ribbons, although the amorphous character of the ribbon can be Fig. 7. Granulometry of the powders obtained after milling in a mixer mill at 30 Hz for different loads and starting particles sizes, with milling times of: (a) 90 min; and (b) 150 min. (c) Detailed results for milling times of 90, 120 and 150. R.M. Aranda et al. Powder Technology 441 (2024) 119816 8 compromised. For the maximum speed of 35 m/s the ribbons contain many voids and start to break up into narrower ribbons. Furthermore, high crucible-wheel distances and low ejection temperatures affect negatively to the quality of the ribbons. From the above evidences, it is revealed that the optimum melt spinning conditions for the Fe 78 Si 9 B 13 alloy, with good amorphization according to XRD and TEM, is produced with a tank overpressure of 200 mbar, ejection temperature of 1250 ◦C, crucible - wheel distance of 0.4 mm and wheel speed of 28 m/s. With these conditions, used in the rest of this study, the process efficiency, measured as the amorphous fraction of the ribbon, reaches the 90%. (a) ( b ) Fig. 8. SEM micrographs of cut ribbons smaller than 0.5 mm milled for (a) 90 min with a load in each vessel of 3 and 6 g and (b) 150 min with a load in each vessel of 3 and 6 g. ( a ) ( b ) Fig. 9. XRD of milled ribbons <0.5 mm with: (a) a load of 4 g and milling times of 0 to 150 min; and (b) milling time of 150 min and loads of 3 to 6 g. ( a ) ( b ) Fig. 10. TEM image and diffraction pattern of milled powders processed with a load of 4 g and a milling time of (a) 30 min and (b) 150 min (diffraction spots correspond to α -Fe). R.M. Aranda et al. Powder Technology 441 (2024) 119816 9 3.2. Amorphous ribbon milling processes 3.2.1. Manual fragmentation and cutting in a knives mill The ribbons are manually fractured to pieces of about 10 mm and processed in a knives mill for 3 min. The cut ribbons are then sieved to separate the fractions smaller and bigger than 0.5 mm. This is carried out to ensure a greater homogeneity in the granulometry of the powders to be finally obtained. XRD results verify that, due to the low energy of the process, there are no significant microstructural changes with respect to the original ribbons, and the cut ribbons remain completely amorphous in both cases (Fig. 5). The morphological study by SEM (Fig. 6) shows that the cut ribbons adopt a flakes-shaped morphology, with mean sizes according to laser diffraction of 387 and 625 μ m respectively, and the actual sizes that can be seen in Fig. 6. 3.2.2. Vibratory ball mill, VBM It was first checked that frequencies of 10 and 20 Hz were insufficient to significantly reduce the particle size even for very long milling periods (tested times of up to 90 min), so, all experiences were carried out with a frequency of 30 Hz. The ball-to-ribbon load ratios were: for 3 g 2:1, for 4 g 3:2, for 5 g 6:5 and for 6 g 1:1. It was also found that, at this frequency, it was necessary to stop for 10 min every 30 min of milling, to avoid an excessive increase of the temperature in the vessels that could alter the amorphous microstructure of the starting material. Fig. 7 shows the particle size obtained for some milling times as a function of the vessel load and the starting cut ribbons size (results for other milling times follow the same trend). As expected, higher milling times and lower loads in the vessels, make the particle size to decrease. The size distribution has a similar shape for the different experiences, but for low loads and starting particle size of <5 mm, a wider size (a) ( b ) Fig. 11. (a) Granulometry and (b) SEM micrographs of a 10 g sample of cut ribbons <0.5 mm milled at 1400 rpm for 10 min. ( a ) ( b ) Fig. 12. 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