Intermetallics 141 (2022) 107432 Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet Structure, mechanical properties and nanocrystallization of (FeCoCrNi)-(B, Si) high-entropy metallic glasses S. Leila Panahi a, Jordina Fornell b, Catalin Popescu c, Eloi Pineda a, d, e, Jordi Sort b, f, Pere Bruna a, d, e, * a Departament de Física, Universitat Politècnica de Catalunya - BarcelonaTech, 08019, Barcelona, Spain b Departament de Física, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain c CELLS-ALBA Synchrotron Light Facility, Cerdanyola, Barcelona, 08290, Spain d Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya – BarcelonaTech, 08028, Barcelona, Spain e Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya - BarcelonaTech, 08019, Barcelona, Spain f Institució Catalana de Recerca i Estudis Avançats, 08010, Barcelona, Spain A R T I C L E I N F O A B S T R A C T Keywords: New high-entropy metallic glasses were produced by adding B and Si to the Fe25Co25Cr25Ni25 high entropy alloy. High-entropy alloys Extremely hard materials were obtained by inducing structural relaxation and nanocrystallization in the original Synchrotron radiation amorphous metals. In this work we study the effects of the composition and annealing treatments on the Nanoindentation structure and the mechanical properties. The changes in structure during heating treatments were determined by Metallic glass in situ synchrotron X-ray diffraction and the mechanical behavior was studied by nanoindentation. The me­ chanical properties of the as-quenched glasses were tuned through the annealing treatments, obtaining amor­ phous/nanocrystalline composites appropriate for highly demanding, wear resistance applications. The relative amount of B and Si is shown to determine the main nanocrystalline phase, FCC or BCC, which has a key influence on the mechanical properties. 1. Introduction crystalline/amorphous dual phase with improved hardness. Medina et al. [11] explained the improvement of the mechanical properties of The necessity of new metals with unique properties has become more the FeCoCrNiMn HEA after the addition of C by the shift from a crys­ important than ever for the development of demanding, new applica­ talline to an amorphous structure. Thus, the production of HEA with a tions, ranging from medical implants to ship surface coatings and sport total or partial amorphous structure is revealed as a practical way to equipment [1]. Among the new type of alloys recently designed, high widen the range of materials and compositions with tailored properties. entropy alloys (HEA) stand out due to the combination of high hardness, High entropy alloys are multicomponent alloys, with a concentration high strength, high corrosion resistance and high temperature softening between 5 and 35 at% of each element, and large entropy of mixing resistance [2–5]. HEAs can be used as coatings [6] and in new [12]. In comparison to multicomponent alloys forming intermetallic manufacturing technologies [7]. In turn, metallic glasses (MG) have compounds and complex microstructures, which make them brittle and been thoroughly studied in recent years due to their distinctive me­ difficult to process, HEAs tend to be solid solutions with body-centered chanical, chemical and magnetic properties [8]. The possibility of (BCC) or face-centered (FCC) cubic structures. Metallic glasses are also combining the excellent properties of these two types of alloys, multicomponent alloys, but they retain the amorphous structure when rendering the so-called high-entropy metallic glasses (HEMG), is an quenching from the liquid state. Large, negative values of mixing interesting strategy to obtain new materials with further optimized enthalpy and relatively large atomic size differences tend to stabilize the performance. Some steps in this direction have recently been done in the liquid structure and inhibit crystallization, thus promoting FeCoCrNi system. Li et al. [9] produced this HEA with a high under­ glass-forming ability [13]. HEAs and MGs share in common the presence cooling obtaining the enhancement of its compressive yield strength. of a single structural phase, crystalline or amorphous respectively, with Xiao et al. [10], through the addition of Mn, produced a the different components of the alloy being dissolved in the structure. * Corresponding author. Departament de Física, Universitat Politècnica de Catalunya - BarcelonaTech, 08019, Barcelona, Spain. E-mail address: pere.bruna@upc.edu (P. Bruna). https://doi.org/10.1016/j.intermet.2021.107432 Received 16 September 2021; Received in revised form 14 November 2021; Accepted 27 November 2021 Available online 3 December 2021 0966-9795/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). S.L. Panahi et al. Intermetallics 141 (2022) 107432 While in HEA the different components are usually of similar atomic improvement of the mechanical properties. size, in order to promote the crystallization of a solid solution, the MG-forming systems contain elements with dissimilar atomic sizes in 2. Materials and methods order to hinder crystallization [14]. With the aim of exploring new materials with exceptional properties, (FeCoCrNi)(B,Si) master alloys were produced by arc-melting of pure we produced rapidly quenched alloys combining the equiatomic, HEA elements: Iron sheet (99.9 wt%), Cobalt lumps (99.5 wt%), Chromium Fe25Co25Cr25Ni25 composition with B and Si, which are elements known lumps (99.95 wt%), Nickel wire (99.98 wt%), Boron lumps (99 wt%), to enhance glass-forming ability. By systematically changing the content and Silicon lumps (99.999 wt%). The compositions studied in this work of B and Si we determined the range of compositions with higher glass- are Fe20Co20Cr20Ni20B20, Fe20Co20Cr20Ni20B15Si5, Fe20Co20Cr20 forming ability as detailed in [15], producing new HEMGs. Fig. 1 sum­ Ni20B10Si10, Fe18.75Co18.75Cr18.75Ni18.75B10Si15 and Fe17.5Co17.5Cr17.5 marizes the results of this previous study [15] together with some new Ni17.5B10Si20, labeled as AB20, AB15Si5, AB10Si10, AB10Si15 and compositions produced since then. All the materials were produced by AB10Si20, respectively. For comparison purposes the B and Si free rapid solidification with exactly the same production parameters, thus Fe25Co25Cr25Ni25 HEA (in this article labeled as alloy A) was also pro­ expecting the same quenching rate. Fig. 1 shows a clear zone in the duced. The arc-melting process was performed on a water-cooled copper ternary HEA-B-Si diagram where glass forming ability is high enough to plate in a Ti-gettered argon atmosphere to avoid oxidation. The master obtain completely amorphous alloys. In this work, in order to study the alloys were re-melted three times to assure the compositional homoge­ effect of composition, glass relaxation and crystallization on the me­ neity. Afterwards, amorphous ribbons were prepared from the alloys by chanical properties we selected the compositions with best melt spinning at a linear speed of 40 m s− 1. The thickness and the width glass-forming ability, emphasized with circles in Fig. 1. of the resulting ribbons were of 20–30 μm and 4 mm, respectively. For One of the most used techniques to study the mechanical properties the study of the mechanical properties as a function of structural state, and the deformation process at the nanoscale is nanoindentation. This the as-cast ribbons of AB20 and AB10Si10 were annealed at different technique offers many advantages and it requires only small volumes of temperatures (673, 723, 773, 823, 873, 923, 973 K) with a heating rate test material [16]. Several mechanical properties related to the elastic of 6 K min− 1, under a flow of Nitrogen, keeping the samples at the and plastic deformation response can be assessed from the maximum temperature for 60 min and then cooling it down to room load-displacement (P-h) curves recorded during the nanoindentation temperature at a cooling rate of 6 K min− 1. Differential Scanning Calo­ process [17]. The method of Oliver and Pharr [18] allows extracting the rimetry (DSC) was performed in a NETZSCH DSC 404 with a heating rate hardness and the Young’s modulus from parameters measured directly of 20 K min− 1 under N2 atmosphere with flow rate of 50 mL min− 1. on the unloading part of the P-h curve: the load at the peak (Pmax), the The structural and compositional properties of the samples were maximum penetration depth (hmax), the residual depth after unloading investigated by Synchrotron Powder X-Ray Diffraction (XRD) at the (hr) and the slope of the upper portion of the unloading curve, known as MSPD beamline of ALBA Synchrotron [21] with an incident mono­ the contact stiffness (sw). The particular response of the material de­ chromatic wavelength of 0.4246 Å focused down to 20 × 20 pends on many factors like the crystal structure, the chemical compo­ μm2(FWHM). The crystallization of the samples was studied in-situ using sition and/or the microstructure [19]. Moreover, in some materials, a Linkam hot stage, refrigerated with a closed circuit of water and the phenomena like pile-up or sink-in, that depend only on plastic properties sample open to the air to maximize the angular range of the spectra and [20], can occur, yielding differences in the contact area. avoid artifacts from the scattering of the Linkam windows. The samples In this work the mechanical properties of the new HEMGs [15] are were heated at 20 K min− 1 from room temperature up to 793 K (the studied by nanoindentation and they are correlated with their crystal­ maximum temperature achieved by the hot stage), held at this temper­ lization behavior studied by in-situ X-ray diffraction in a synchrotron ature for 2 h and cooled down to room temperature at 100 K min− 1. source. Different microstructural states are obtained by applying ther­ Patterns were collected with a time acquisition of 1s every 5 s using a mal treatments on the as-quenched amorphous samples. The tailoring of Rayonix CCD detector. A diffraction without sample was taken at room the structural and microstructural state achieves an outstanding temperature to have the background signal. The diffraction pattern at each temperature and the one of the background has been subtracted after intensity normalization. The diffraction was performed on the as-quenched ribbons; this may introduce some artifacts in the detected intensities of the Bragg reflections due to possible texture of the growing crystalline phases. However, the production of powder for the XRD analysis was discarded in order to avoid structural changes originated due to the milling process. Scanning Electron Microscopy (SEM) was carried out in a Zeiss NEON 40 device and the images were analyzed using ImageJ software [22]. The mechanical properties of all the HEMGs, were investigated by nanoindentation from where hardness (H) and reduced Young’s modulus (Er) values were extracted using the method of Oliver and Pharr and averaging the results from 15 indentations. In particular, the hardness is defined as H=Pmax/A, where A is the projected contact area and the reduced elastic modulus Er is obtained by: √̅̅̅ π sw Er = √̅̅̅ 2β A where β is a constant dependent on the geometry of the indenter tip (β = 1.034 for a Berkovich indenter). The elastic energy was determined by integrating the unloading response over the range hmax to hr and the Fig. 1. Compositions of the produced materials, detailing their amorphous plastic energy was calculated from the area enclosed between the (blue circles), crystalline (red triangles) or partially crystalline (green squares) loading and unloading curves. The indentations were performed using as-quenched structure. The compositions analyzed in the present paper are an Anton-Paar, NHT2 model, nanoindenter armed with a Berkovich marked with circles. 2 ­ ­ S.L. Panahi et al. Intermetallics 141 (2022) 107432 pyramidal-shaped diamond tip. The maximum applied load was 10 mN 3.2. In-situ crystallization with a holding time of 5 s (30 s loading, 5 s holding and 30 s unloading), with loading/unloading rates of 20 mN min− 1. The thermal drift was The crystallization of the samples was analyzed in order to assess the kept below 0.005 nm s− 1. role of Si and B and characterize the emerging phases. According to the value of the ratio η = Si/B, and the DSC signal (Fig. 2) we can distinguish 3. Results and discussion two different regions. For η ≤ 1, there are two crystallization events below 873 K, except for η = 0, where the second crystallization occurs 3.1. Thermal characterization above 873 K. For values of η larger than 1, there is only one crystalli­ zation event and, for η = 2 the crystals are already present in the as- All the samples characterized in this study were completely amor­ quenched sample. The in-situ crystallization was monitored in a phous in their as-quenched state except AB10Si20, in which XRD shows Linkam hot-stage. The thermal protocol followed to crystallize the some crystalline peaks perceptible over the amorphous halo (as can be samples was the following: 1) heating ramp of 20 K min− 1 from room observed in [15] and also in Fig. 7 in section 3.2). This particular sample temperature up to 793 K; 2) isothermal annealing at 793 K for 120 min; is then composed of a small fraction of crystalline particles embedded in 3) cooling to room temperature at 100 K min− 1. the amorphous matrix. The analysis of the DSC curves (Fig. 2) shows a Fig. 3 shows the crystallization for the case η = 0. The left panel different crystallization behavior depending on the B and Si contents. shows the evolution of the intensity of the diffraction peaks with the AB20 shows a fast crystallization process and a second exothermic re­ temperature. The amorphous character of the as-quenched state is action at much higher temperatures. AB15Si5 and AB10Si10 show a clearly seen by the low intensity of the broad peak between 10 and 15◦ . crystallization reaction split in two peaks, while AB10Si15 shows a This broad peak is replaced by sharp lines at temperatures close to 790 K single crystallization event at higher temperatures. The broader and signaling the nucleation and growth of the crystalline phases. The con­ smaller exothermic event for the AB10Si20 composition is a conse­ tinuity of the lines indicates the existence of only one crystallization quence of the existence of already formed nanocrystalline particles in event while the increase in brightness of the lines shows the increase in the as-quenched ribbons as detected by XRD (see Fig. 7). Besides the volume fraction of the crystalline phases. There is not any signature of number of crystallization events, the presence of Si in the samples also new phases in addition to the ones appearing at 790 K. Therefore, with a changes the temperatures of the first and second crystallizations. The holding time of 120 min at 793 K the second crystallization event difference between the two processes is maximum in AB20 composition detected by DSC is not reached in the X-ray diffractograms. while they are almost overlapped in AB15Si5 and AB10Si10. The right panel of Fig. 3 shows the intensity versus the diffraction We can quantify the glass forming ability (GFA) and the thermal angle for selected temperatures. The crystallization pattern is complex stability against crystallization by the reduced glass transition temper­ with multiple low intensity peaks. The main phases that can be identi­ ature Trg = Tg/Tm (where Tg and Tm are the glass transition and melting fied are a solid solution with an FCC structure, the observed peaks temperatures, respectively) and the supercooled liquid region ΔTx = correspond to (111), (200), (220) and (311) reflections, and two borides: Tx1-Tg, respectively. The computed values obtained from the DSC curves Fe3B and CoB. However, the intrinsic chemical disorder characteristic of are shown in Table 1. As an example of such determination, Fig. S1 of the high-entropy alloys tends to produce crystalline phases with a mixture of supplementary materials shows a magnified view of the region around the main elements, thus it can be expected that the Fe3B and CoB phase Tg in sample AB10Si15 and the tangent lines used to find the Tg value. contain other metal elements. This complexity of the crystalline phases The values of Trg are in the range between 0.5 and 0.6. These relatively was previously analyzed in detail by Mössbauer spectroscopy [15], low values indicate that these compositions are not likely to be produced showing that the Mössbauer spectra of the boride phases presented as bulk metallic glasses. One exception is the AB10Si15 sample that hyperfine parameters that differed from the ones corresponding to a presents a slightly higher value. This sample is also the one that shows a pure Fe-boride phase, thus confirming the presence of other elements higher resistance to crystallization with the maximum value of ΔTx. (Cr, Co or Ni) in the structure. The overall structure of the phases can be These results suggest that the compositional range maximizing GFA is identified but, similarly to other works in this type of materials [23,24], found for a total metalloid content between 20 and 25 at% and a ratio of the exact distribution of metal atoms inside the borides (or silicides in Si/B contents between 3/2 and 2/3. the case of Si containing samples below) cannot be determined by the techniques used in this study. Besides the two identified borides, the three more intense peaks between 18 and 20◦ can be attributed to a more complex boride close to the Fe3Ni3B structure and to the intermetallic phase Cr3Ni2, although the identification of this latter phase is ambig­ uous. Thus, the first crystallization can be summarized in the following way: η = 0: amorphous → FCC + MB + M3B + M6B where M stands for metallic atoms. As explained before, in this experi­ ment the second crystallization event observed by DSC cannot be reached. However, in ref. [15] it was shown that increasing the tem­ perature induces the formation of an M2B phase and the disappearance of the M3B phase. The crystallization for the case η = 1/3 can be seen in Fig. 4. The 2D map clearly shows that two crystallization processes take place in this composition. Firstly, the amorphous phase crystallizes in a BCC struc­ ture, likely a solid solution, with the peaks at 12, 17 and 21◦ corre­ sponding to the reflections (110), (200) and (211), respectively. After reaching the maximum temperature in the furnace, the second crystal­ lization takes place with the nucleation and growth of an FCC structure Fig. 2. DSC of the as quenched samples applying a heating rate of 20 K min− 1. together with two borides, CrFeB and FeB. There is no clear set of peaks The label of the samples indicates their B content (10,15,20 at%) and Si content that can be ascribed to a silicide phase, thus it is reasonable to assume (0,5,10,15,20 at%), being A = FeCoCrNi. 3 S.L. Panahi et al. Intermetallics 141 (2022) 107432 Table 1 The glass transition temperature (Tg), onset of the first crystallization event (Tx1), melting temperature (Tm), supercooled liquid region (ΔTx) and reduced glass transition temperature (Trg) for the completely amorphous samples, indicating label and the Si/B ratio η. Alloy Label η Tg (K) Tx1 (K) Tm (K) ΔTx (K) Trg FeCoCrNi A – – – – – – (FeCoCrNi)80B20 AB20 0 744 788 1353 44 0.55 (FeCoCrNi)80B15Si5 AB15Si5 1/3 720 769 1337 41 0.54 (FeCoCrNi)80B10Si10 AB10Si10 1 753 810 1349 57 0.56 (FeCoCrNi)75B10Si15 AB10Si15 3/2 763 871 1203 108 0.63 (FeCoCrNi70B10Si20 AB10Si20 2 812 852 1278 – – Fig. 3. Crystallization of the AB20 sample (η = 0). Left panel: 2D map of the crystalline peaks showing their intensity (in a color scale) versus the diffraction angle 2θ (x axis) and the temperature T (y axis). Right panel: diffractograms of selected temperatures, from the initial amorphous phase to the highest temperature with phase identification. Fig. 4. Crystallization of the AB15Si5 sample (η = 1/3). Left panel: 2D map of the crystalline peaks showing their intensity (in a color scale) versus the diffraction angle 2θ (x axis) and the temperature T (y axis). Right panel: diffractograms of selected temperatures from the initial amorphous phase to the highest temperature with phase identification. η = 1/3: amorphous → BCC → BCC + FCC + MB(Si) + M2B(Si) that the small amount of Si atoms is present in the other crystalline phases or in a residual amorphous fraction. The crystallization path for where (Si) means the possible presence of this element in the structure, this case is, thus: although not confirmed. The composition with η = 1 also presents a double crystallization 4 S.L. Panahi et al. Intermetallics 141 (2022) 107432 reaction (see Fig. 5). The first one takes places below 793 K and, like the the as-quenched state can be identified as a solid solution with a BCC previous composition, it can be ascribed to a solid solution with a BCC structure that continuously grows when increasing temperature. After structure. However, contrary to η = 1/3, in the case of η = 1 there is a the full treatment of the sample (120 min at 793 K) besides the BCC simultaneous crystallization of boride and silicide phases. In particular, phase, several peaks appear that are compatible with a Ni2Si phase. peaks corresponding to Fe2B, Ni2Si and Cr1.64Fe0.35B0.96 can be identi­ There are no clear peaks corresponding to borides, although the peaks at fied and can be globally identified as phases with an M2(B,Si) structure, 11.4◦ and 12.2◦ are consistent with a Ni2B phase. Thus, the crystalli­ although some of the peaks can also be ascribed to a Co2B phase. The zation path is: second crystallization event maintains the previous phases and it in­ duces the nucleation and growth of a solid solution with an FCC struc­ η = 2: amorphous + BCC → BCC + M2(Si, B) ture, resulting in the following global crystallization path: Summarizing, the analyzed crystallization paths show a clear trend η = 1: amorphous → BCC + M2(B,Si) → BCC + FCC + M2(B,Si) with the Si content. When there is no Si present in the HEMG (η = 0) the system crystalizes in an FCC structure together with a complex combi­ The last of the studied compositions with a completely amorphous nation of borides, including a metastable M3B phase, and some inter­ structure in the as-quenched state corresponds to the case η = 3/2 and, metallic phases. Adding Si (η > 0) changes the structure of the principal contrary to the previous cases, it only presents one crystallization event crystalline phase, that now is BCC instead of FCC. Moreover, the first in Fig. 2. From the 2D map of Fig. 6 it could seem that there are two boride to crystallize is no longer the metastable M3B but the stable M2B. different crystallization stages, however, looking at the selected dif­ In the compositions with two crystallization events (η ≤ 1), the second fractograms in the right side panel it can be seen that all the peaks are crystallization induces the growth of the FCC structure that coexists with already present at the beginning of the crystallization, although some of the BCC phase. In the compositions with low Si content (η = 1/3), there them are masked by the halo corresponding to the amorphous matrix in is also the formation of MB phase. Increasing the Si content (η = 1) which the crystalline phases grow. In a similar way than in the case η = implies the crystallization of only M2B and M2Si phases. Finally, for the 1, the main existing crystalline phase is a solid solution with a BCC compositions with the highest Si content (η = 3/2 and η = 2) the second structure that grows simultaneously with borides and silicides. In crystallization disappears obtaining a microstructure composed only of a particular, the peaks can be identified with Ni2Si and Cr2B phases. The BCC solid solution and M2(B,Si) crystals. peaks at around 11◦ and 17◦ are not identified but can be compatible with Fe5Si3 or Ni3Si phases if some texture is assumed. Unlike the other 3.3. Nanoindentation compositions with less Si, in this case there is no growth of an FCC structure. What it can be observed, however, is that after a relatively Fig. 8 (left) shows the load-displacement curves of all the samples in short time at 793 K (approximately 30 min) the peaks corresponding to the as-quenched state, including composition A for reference. In addi­ the BCC solid solution begin to decrease in intensity at the expenses of tion to the different penetration depths, the slope of the unloading part borides and silicides. Therefore, in this composition the crystallization of the indentation curves, related to the contact stiffness, indicates a path is more simple and can be summarized as follows: different value of the reduced Young’s modulus (Er). From these curves the hardness (H) and Er can be calculated and the values are shown in η = 3/2: amorphous → BCC + M2(Si,B) Table 2. The last of the studied compositions corresponds to the case η = 2, Fig. 8 (right) shows the change of these magnitudes as a function of which is partially crystalline in the as-quenched state, although the the composition for the as-quenched samples. The large increase in majority of the as-quenched structure remains amorphous (see Fig. 7). hardness from the base composition (⁓ 4 GPa) to the B and Si con­ Despite this double character of the structure, the study of the crystalline taining alloys (⁓14–18 GPa) can be explained by the strong nature of phases is interesting in order to have a better picture of the effect of Si in the (B,Si)-M interatomic bonds and the change from an FCC to an the crystallization path of this family of HEMGs. The crystals present in amorphous structure, where the absence of long-range order and crys­ talline defects increases the resistance to plastic deformation. There is no Fig. 5. Crystallization of the AB10Si10 sample (η = 1). Left panel: 2D map of the crystalline peaks showing their intensity (in a color scale) versus the diffraction angle 2θ (x axis) and the temperature T (y axis). Right panel: diffractograms of selected temperatures from the initial amorphous phase to the highest temperature with phase identification. 5 S.L. Panahi et al. Intermetallics 141 (2022) 107432 Fig. 6. Crystallization of the AB10Si15 sample (η = 3/2). Left panel: 2D map of the crystalline peaks showing their intensity (in a color scale) versus the diffraction angle θ (x axis) and the temperature T (y axis). Right panel: diffractograms of selected times after reaching the maximum temperature in the hot stage. Fig. 7. Crystallization of the AB10Si20 sample (η = 2). Left panel: 2D map of the crystalline peaks showing their intensity (in a color scale) versus the diffraction angle θ (x axis) and the temperature T (y axis). Right panel: diffractograms of selected temperatures from the initial partially crystalline phase to the highest temperature with phase identification. clear trend in the values of H or Er as a function of composition, all B in the remaining amorphous phase, thus increasing the hardness of the amorphous samples showing outstanding high hardness values, three glass matrix. times as hard as stainless steels [25]. It is interesting to compare the hardness and elastic modulus values However, the highest values of these magnitudes are found for of the as-quenched alloys studied here with other high-entropy alloys of AB10Si20, i.e. the alloy that has the major content of B and Si and, in similar compositions probed also by nanoindentation [31,32]. In these addition, contains some nanocrystals embedded in its amorphous references the maximum loads were between 10 and 30 mN, similar to structure (as seen in Fig. 13 of reference [15] and in Fig. S2 of the the ones in the present work, although some differences could be ex­ supplementary materials). It is expected that the elastic properties of a pected due to the measures were done at a strain rates of 5 × 10− 2 s− 1 in material are related to its atomic bonding in a way that compositions the case of ref. [31]. Fig. 9 displays the values of the Young’s modulus with stronger bonds exhibit higher values of Er [26]. There are two versus hardness for several alloys that also contain Fe, Co and Cr in the possible contributions to the maximum values of H and Er in the base composition and additions of other elements like, Cu, Si or Al to AB10Si20 alloy. On the one hand, the large amount of Si creates stronger tailor their properties. From this figure, it is clear that the microalloying covalent bonds between this element and the metallic elements [27,28]. with Al and the incorporation of Mn in the base composition are bene­ On the other hand, the mechanical properties can be enhanced in ficial for the elastic modulus but it produces only a moderate increase in glass/nanocrystalline composites due to the role of nanocrystals in the hardness. All these compositions present a diversity of microstruc­ hindering shear band propagation [29,30]. In addition, in the case of tures depending on the particular composition and alloying element and AB10Si20, the precipitation of the BCC phase rises the content of Si and comprise FCC, BCC, mixture of BCC and FCC and also a mixture of FCC 6 S.L. Panahi et al. Intermetallics 141 (2022) 107432 Table 2 crystallization of the hard M3B phase also contributes to the increase in Hardness (H), reduced Young’s modulus (Er), plastic energy (Up), elastic energy the strength of the sample [28]. At annealing temperatures higher than (Uel), wear resistance (H/Er) and elastic recovery (Uel/Utot) measured by 773 K, Er remains almost constant while the hardness decreases. The nanoindentation. final state of the sample is composed by FCC crystals together with the H Er Up (nJ) Uel Utot H/Er Uel/ stable boride M2B. The decrease in hardness can be explained by the Samples (GPa) (GPa) (nJ) (nJ) Utot growth of the FCC phase which has low hardness compared to the A 4.1 122 1.04 0.247 1.28 0.034 0.19 amorphous state. With increasing the annealing temperature, the (2) (5) (3) (8) (4) (2) (2) hardness decreases gradually as the grain growth of the FCC phase oc­ AB20 14.4 167 0.353 0.343 0.69 0.086 0.49 curs [36]. The average size of the crystalline grains changes from 70 nm (6) (5) (2) (2) (1) (5) (1) AB15Si5 12.5 150 0.405 0.351 0.75 0.084 0.46 at 773 K up to 185 nm at 973 K [15]. Thus, the decrease of the hardness (5) (7) (6) (2) (1) (6) (1) can be explained by the conventional Hall-Petch equation [37] that AB10Si10 15.5 162 0.367 0.356 0.72 0.095 0.49 predicts an increase of the strength with decreasing grain size due to (6) (2) (7) (3) (1) (3) (1) dislocation pile-up at grain boundaries. AB10Si15 12.6 155 0.401 0.345 0.74 0.081 0.46 For the AB10Si10 alloy, Fig. 10 (right), the data shows a more (4) (2) (2) (2) (3) (3) (1) AB10Si20 17.7 176 0.28 0.361 0.64 0.100 0.56 complex behavior. The hardness and reduced elastic modulus increase (7) (4) (2) (2) (2) (5) (3) up to a clear maximum that occurs when annealing at 723 K, before the crystallization onset. At higher annealing temperatures, both H and Er decrease during the first crystallization step where a BCC solid solution and HCP phases. The composition with the highest elastic modulus is together with an M2(B,Si) phase appear [15]. In the second crystalliza­ Al3(FeCoCrNiCu) that consists of a BCC phase in a dendritic configura­ tion step, in which the BCC phase is replaced by FCC, Er increases again. tion. The addition of B and/or Si extraordinarily improves the hardness, The decrease of both hardness and modulus at the final stages of the while the change in the elastic modulus is less significant. This increase crystallization can be attributed to the grain growth of the FCC phase. of hardness opens a new route to design new high-entropy alloys with Therefore, in the AB10Si10 material, the maximum value of the hard­ improved properties seeking for a combination of constituent elements ness occurs for a fully amorphous, although structurally relaxed, capable to induce amorphous structures. structure. In order to study the effect of nanocrystallization on the mechanical More information can be extracted from the ratio between hardness properties, two of the compositions, AB20 and AB10Si10, were selected. and reduced elastic modulus (H/Er), and from the elastic recovery, i.e. These two alloys have the same total atomic content of metalloids but different Si/B ratio, thus we consider them as representative of the whole set of samples. As discussed above, they show different crystal­ lization reactions, forming FCC or BCC crystals respectively at the initial stages. The samples were annealed up to different temperatures, from below the glass transition up to full crystallization. It is well known that below Tg a heat treatment causes changes in the physical and mechan­ ical properties of glasses due to structural relaxation. The decrease of excess free volume during this process causes a reduction of atomic mobility and an increase of Young’s modulus and hardness [26,33–35]. The results of H and Er for the two compositions are shown in Fig. 10 and are detailed in Table 3. Fig. 10 (left), corresponding to AB20, shows a progressive increase of both H and Er up to the annealing at 773 K. According to our previous characterization [15], after annealing at 773 K the sample is composed of nanocrystals (FCC and M3B) embedded in an amorphous matrix. At this point, the maximum values of the hardness and reduced Young’s modulus are reached, being 24 GPa and 215 GPa, respectively. The increase of such mechanical properties between the as-quenched and the annealed amorphous samples can be attributed to the annihilation of excess free volume associated to the structural Fig. 9. Comparison of Young modulus and hardness for several compositions relaxation of the glass [35]. At higher annealing temperatures, the [31,32]. The circle indicates the compositions investigated in this study. Fig. 8. Load-displacement of nanoindentation curves (left) and variation of hardness (H) and reduced Young’s modulus (Er) (right) for as quenched ribbons at room temperature. 7 S.L. Panahi et al. Intermetallics 141 (2022) 107432 Fig. 10. Variation of hardness (H) and reduced elastic modulus (Er) as a function of annealing temperature for AB20 (left) and AB10Si10 (right). Table 3 Hardness (H), reduced Young’s modulus (Er), plastic energy (Up), elastic energy (Uel), wear resistance (H/Er) and elastic recovery (Uel/Utot) measured by nano­ indentation for AB20 and AB10Si10 samples for different annealing temperatures. T H (GPa) Er (GPa) Up (nJ) Uel (nJ) Utot (nJ) H/Er Uel/Uto (K) AB20 AB10Si10 AB20 AB10Si10 AB20 AB10Si10 AB20 AB10Si10 AB20 AB10Si10 AB20 AB10Si10 AB20 AB10Si10 aq 14.5 15.6 (6) 167 162 (2) 0.353 0.3 (2) 0.343 0.43 (9) 0.696 0.7 (2) 0.086 0.095 (4) 0.492 1 (2) (6) (5) (2) (2) (4) (6) (5) 673 16.1 18.3 (5) 184 170 (8) 0.341 0.329 (7) 0.326 0.372 (3) 0.67 0.70 (1) 0.087 0.107 (7) 0.49 0.53 (2) (2) (3) (8) (3) (2) (1) (2) 723 20 (2) 29.9 (5) 211 212 (8) 0.276 0.296 (6) 0.329 0.382 (4) 0.605 0.68 (1) 0.094 0.141 (7) 0.54 0.56 (2) (6) (5) (2) (7) (7) (1) 773 25 (2) 21.3 (2) 216 168 (4) 0.198 0.198 (6) 0.382 0.382 (3) 0.58 0.58 (1) 0.11 0.126 (3) 0.66 0.66 (2) (7) (6) (3) (1) (1) (2) 823 22 (3) 16.7 (9) 213 192 (5) 0.247 0.318 (4) 0.345 0.330 (2) 0.59 0.648 (6) 0.10 0.087 (6) 0.58 0.509 (7) (5) (2) (3) (2) (2) (2) 873 18 (3) 13.7 (6) 210 194 (6) 0.307 0.384 (5) 0.316 0.302 (3) 0.623 0.686 (8) 0.09 0.069 (5) 0.507 0.44 (1) (20) (5) (2) (7) (1) (8) 923 17.5 13.5 (7) 200 188 (5) 0.301 0.394 (8) 0.352 0.302 (6) 0.653 0.70 (2) 0.085 0.071 (5) 0.54 0.43 (2) (2) (20) (5) (3) (8) (7) (1) 973 16.7 10.4 (3) 210 168 (3) 0.327 0.472 (2) 0.307 0.307 (5) 0.634 0.779 (7) 0.079 0.062 (2) 0.48 0.39 (1) (2) (7) (7) (2) (9) (2) (1) the ratio between the elastic energy (Uel) and the total energy (elastic the contact area. In Fig. 11 the SEM image of a typical indentation of plus plastic, Up) [33,38]. The H/Er ratio is related to the elastic strain to AB20 annealed at 873 K is shown in the inset, together with the pro­ failure and it is a suitable parameter to describe the wear resistance of jected and the pile-up area calculated using ImageJ software. Additional the sample [17,39]. These values for all the analyzed compositions are SEM images of both samples (AB20 and AB10Si10) at selected temper­ shown in Table 2, while for all the annealing temperatures of samples atures are shown in Fig. S3 of the supplementary materials. AB20 and AB10Si10 are shown in Table 3. Among all the studied com­ Fig. 11 shows the fluctuation of the pile-up area as a function of the positions, AB10Si20 shows the highest wear resistance and elastic re­ covery, showing that the presence of nanocrystals and larger amount of metalloid percentage helps to improve these mechanical properties. For the completely amorphous samples, AB10Si10 is the one with the better wear resistance, while all have similar values of the elastic recovery. Focusing on compositions AB20 and AB10Si10 annealed at different temperatures, the wear resistance shows a similar behavior as the hardness, being maximum after annealing at 773 K for AB20 and at 723 K for AB10Si10. However, the elastic recovery is similar, around the 50%, in all cases, being maximum in the two compositions after annealing at 773 K. Thus, the combination of nanocrystals and a relaxed amorphous matrix yields the best performance in terms of energy recovery. The analysis of the SEM images of the indents yields information of the sink-in and pile-up phenomena [40]. Pile-up effect happens when the surface is indented heavily and the localized plastic deformation zone pushes upward the surrounding material. On the other hand, sink-in happens when the plastic zone tends to shift away from the indented area. In crystalline materials, the formation of pile-up along a specific directional line around the indent can be related to the crys­ tallographic orientation and to the crystal symmetry [41]. The method of Oliver and Pharr to compute the hardness does not consider the effect Fig. 11. Measured pile-up area for different annealing temperatures for the of pile-up and it can induce an overestimation of the calculated hardness AB20 and AB10Si10 samples. In the inset, typical SEM image of an indentation [42] and also influences the elastic modulus determination by changing in the AB20 sample (left), definition of the area to compute the projected area in yellow (middle) and the pile-up area in yellow (right). 8 S.L. Panahi et al. Intermetallics 141 (2022) 107432 annealing temperature for samples AB20 and AB10Si10. It can be seen metallic glass alloys with tailored mechanical properties within the that in both samples there is no formation of pile-up until annealing at (FeCoCrNi)100-x-yBxSiy system. The high content of Cr is expected to give 723 K. At this temperature, the structure is mainly amorphous although these materials a good corrosion resistance, an aspect that will be the AB20 sample contains some fraction of nanocrystals. The plastic characterized in future works. The combination of wear and corrosion deformation of amorphous metals involves an increase of the internal resistance, high hardness and the thermal stability up to relatively high free volume. This effect is less pronounced in the as-quenched samples temperatures point out this family of alloys as adequate materials for which already contain a large amount of free volume. At higher highly demanding applications. annealing temperatures the behavior of the two compositions is different. For the AB20 sample, the pile-up reaches its maximum at the Data availability end of the first crystallization at 823 K. At this temperature, the structure consists of an FCC solid solution together with the M3B phase. As the The raw/processed data required to reproduce these findings can be crystallization progress and this boride is replaced by M2B and the FCC shared upon request to the corresponding author. grains grow, the pile-up area steadily decreases. On the contrary, for the AB10Si10 sample, after an increase of the pile-up as the amorphous Authorship statement structure relaxes before crystallization, the pile-up area is reduced to zero during the first crystallization event in which the structure consists All persons who meet authorship criteria are listed as authors, and all mainly of BCC and M2(B,Si) phases. As the BCC is replaced by the FCC authors certify that they have participated sufficiently in the work to one, the pile-up area continuously grows until reaching its maximum take public responsibility for the content, including participation in the value in the fully crystallized sample. The effect of the pile-up is higher concept, design, analysis, writing, or revision of the manuscript. on the hardness than on the elastic modulus because the first is inversely Furthermore, each author certifies that this material or similar material dependent on the area while the second on the square root of the area. has not been and will not be submitted to or published in any other The pile-up effect increases when the strain hardening exponent de­ publication before its appearance in Intermetallics. creases [43]. Therefore, the fully crystallized samples of AB10Si10 behave more plastically than the AB20 composition. However, for the Declaration of competing interest samples annealed only up to the first crystallization, where AB20 sample contain the M3B phase, the behavior is reversed, being more plastic this The authors declare that they have no known competing financial composition than the AB10Si10 alloy. interests or personal relationships that could have appeared to influence Some overestimation of H could happen due to the formation of the the work reported in this paper. pile-up. In a latter article [44], Oliver and Pharr reviewed the limitations of their original model and noticed that a convenient parameter that Acknowledgements illustrates the possible influence of pile-up formation on the mechanical properties is the ratio hf/hmax, which is independent of the indentation Research Project PID2020-112975 GB-I00 funded by MCIN/AEI/ depth in self-similar geometries, such as the Berkovich indenter. For 10.13039/501100011033. L. Panahi acknowledges the financial sup­ conical or Berkovich indenters, when this ratio is smaller than 0.7, like port from Generalitat de Catalunya through a FI grant 2018FI_B_00502. in the present case, the little pile-up observed does not have a strong P. Bruna and E. Pineda acknowledge the financial support from Gen­ influence on the obtained results. Conversely, their original method eralitat de Catalunya grant 2017-SGR-42. J. S. acknowledges the Span­ becomes more inaccurate for hf/hmax > 0.7. ish Government (grant MAT2017-86357-C3-1-R and associated FEDER) and the Generalitat de Catalunya (grant 2017-SGR-292) for financial 4. Conclusions support. X-ray diffraction experiments were performed at MSPD beam­ line at ALBA Synchrotron with the collaboration of ALBA staff (Alba In this paper we have studied a new family of high entropy metallic experiment 2018022691). The authors acknowledge the priceless help glasses characterizing the structure by X-ray diffraction and the me­ of Dr. Trifon Trifonov at the facilities of the Barcelona Research Center chanical properties by nanoindentation. The main results obtained can in Multiscale Science and Engineering. be summarized as follows: Appendix A. Supplementary data • An addition of 10 at% of B and 15 at% of Si to the base equiatomic FeCoCrNi composition maximizes the glass forming ability and Supplementary data to this article can be found online at https://doi. thermal stability of the amorphous phase. org/10.1016/j.intermet.2021.107432. • For Si/B ratios lower or equal than one the alloys present two crys­ tallization events while for higher values of this ratio there is only References one crystallization peak. Moreover, as the amount of Si increases the main crystalline phase changes from FCC to BCC. [1] L. Maillé, C. Sant, P. Aubert, P. Garnier, Morphological and mechanical properties • The amorphous samples show an outstanding hardness due to the study of [WO3/W]n nanoscale multilayers, Thin Solid Films 479 (2005) 201–206. strong nature of the (B,Si)-M bonds and the absence of crystalline https://doi:10.1016/j.tsf.2004.11.203. [2] Y.Y. Chen, T. Duval, U.D. Hung, J.W. Yeh, H.C. Shih, Microstructure and structure. However, the amorphous samples with relaxed structure electrochemical properties of high entropy alloys-a comparison with type-304 and nanocrystalline inclusions show further enhancement of these stainless steel, Corrosion Sci. 47 (2005) 2257–2279. https://doi:10.1016/j.corsci mechanical properties. .2004.11.008. [3] P. Koželj, S. Vrtnik, A. Jelen, S. Jazbec, Z. Jagličić, S. Maiti, M. Feuerbacher, • The evaluation of the mechanical properties as a function of the W. Steurer, J. Dolinšek, Discovery of a superconducting high-entropy alloy, Phys. annealing temperature reveals that the higher values of hardness are Rev. Lett. 113 (2014) 107001. https://doi:10.1103/PhysRevLett.113.107001. found in a structure composed of nanocrystals embedded in a relaxed [4] B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie, A fracture-resistant high-entropy alloy for cryogenic applications, Science 345 amorphous matrix in the case of the Si-free alloys and in a relaxed (2014), 1153-1148, https://doi:10.1126/science.1254581. amorphous structure in the Si-containing alloys. [5] H.F. Li, X.H. Xie, K. Zhao, Y.B. Wang, Y.F. Zheng, W.H. Wang, L. Qin, In vitro and • The wear resistance and elastic recovery are higher in the partially in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass, crystalline samples. Acta Biomater. 9 (2013) 8561–8573. https://doi:10.1016/j.actbio.2013.01.029. [6] Y. Cai, Y. Chen, Z. Luo, F. Gao, L. Li, Manufacturing of FeCoCrNiCux medium- entropy alloy coating using laser cladding technology, Mater. Des. 133 (2017) These results give the basic guidelines to design new high-entropy 91–108. https://doi:10.1016/j.matdes.2017.07.045. 9 S.L. Panahi et al. Intermetallics 141 (2022) 107432 [7] P. Wang, P. Huang, F.L. Ng, W.J. Sin, S. Lu, M.L.S. Nai, Z.L. Dong, J. Wei, stainless steel, Adv. Mater. Res. (2007) 26–28. https://doi:10.4028/www.sc Additively manufactured CoCrFeNiMn high-entropy alloy via pre-alloyed powder, ientific.net/amr.26-28.1165. Mater. Des. 168 (2019) 107576. https://doi.org/10.1016/j.matdes.2018.107576. [26] W. Guo, P.P. Choi, J.B. Seol, Amorphous phase separation in an Fe-based bulk [8] T. Burgess, M. Ferry, Nanoindentation of metallic glasses, Mater. Today 12 (2009) metallic glass, Mater. Lett. 190 (2017) 161–164. https://doi:10.1016/j.matlet.20 24–32. https://doi:10.1016/S1369-7021(09)70039-2. 17.01.012. [9] J. Li, W. Jia, J. Wang, H. Kou, D. Zhang, E. Beaugnon, Enhanced mechanical [27] K.H. Kong, K.C. Kim, W.T. Kim, D.H. Kim, K. Dh, Microstructural features of properties of a CoCrFeNi high entropy alloy by supercooling method, Mater. Des. multicomponent FeCoCrNiSix alloys, Appl. Microsc. 45 (2015) 32–36. 95 (2016) 183–187. https://doi:10.1016/j.matdes.2016.01.112. [28] I. Szlufarska, R.K. Kalia, A. Nakano, P. Vashishta, Atomistic mechanisms of [10] L.L. Xiao, Z.Q. Zheng, S.W. Guo, P. Huang, F. Wang, Ultra-strong nanostructured amorphization during nanoindentation of SiC: a molecular dynamics study, Phys. CrMnFeCoNi high entropy alloys, Mater. Des. 194 (2020) 108895. https://doi:10 Rev. B Condens. Matter 71 (2005) 1–11. https://doi:10.1103/PhysRevB.71. .1016/j.matdes.2020.108895. 174113. [11] L. Zendejas Medina, M.V. Tavares da Costa, E.M. Paschalidou, G. Lindwall, [29] J. Eckert, A. Kübler, L. Schultz, Mechanically alloyed Zr55Al10Cu30Ni5 metallic L. Riekehr, M. Korvela, S. Fritze, S. Kolozsvári, E.K. Gamstedt, L. Nyholm, glass composites containing nanocrystalline W particles, J. Appl. Phys. 85 (1999) U. Jansson, Enhancing corrosion resistance, hardness, and crack resistance in 7112–7119, https://doi.org/10.1063/1.370519. magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon, Mater. [30] D.C. Hofmann, J.-Y. Suh, A. Wiest, G. Duan, M.-L. Lind, M.D. Demetriou, W. Des. 205 (2021) 109711. https://doi:10.1016/j.matdes.2021.109711. L. Johnson, Designing metallic glass matrix composites with high toughness and [12] D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related tensile ductility, Nature 451 (2008) 1085–1089. https://doi:10.1038/nat concepts, Acta Mater. 122 (2017) 448–511. https://doi:10.1016/j.actamat.2016.0 ure06598. 8.081. [31] S. Sinha, R.A. Mirshams, T. Wang, S.S. Nene, M. Frank, K. Liu, R.S. Mishra, [13] I. Szlufarska, A. Nakano, P. Vashishta, A crossover in the mechanical response of Nanoindentation behavior of high entropy alloys with transformation-induced nanocrystalline ceramics, Science 309 (2005) 911–914. https://doi:10.1126/sc plasticity, Sci. Rep. 9 (2019) 1–11. https://doi:10.1038/s41598-019-43174-x. ience.1114411. [32] Y. Sun, P. Chen, L. Liu, M. Yan, X. Wu, C. Yu, Z. Liu, Local mechanical properties of [14] Q. Hu, S. Guo, J.M. Wang, Y.H. Yan, S.S. Chen, D.P. Lu, K.M. Liu, J.Z. Zou, X. AlxCoCrCuFeNi high entropy alloy characterized using nanoindentation, R. Zeng, Parametric study of amorphous high-entropy alloys formation from two Intermetallics 93 (2018) 85–88. https://doi:10.1016/j.intermet.2017.11.010. new perspectives: atomic radius modification and crystalline structure of alloying [33] Y. Cheng, C. Cheng, Relationships between hardness,elastic modulus and the work, elements, Sci. Rep. 7 (2017) 1–12. https://doi:10.1038/srep39917. Appl. Phys. Lett. 73 (1998) 614–616, https://doi.org/10.1063/1.121873. [15] S.L. Panahi, M. Garcia-ramón, E. Pineda, P. Bruna, New (FeCoCrNi)-(B,Si) high- [34] E. Pellicer, S. Pané, K.M. Sivaraman, O. Ergeneman, S. Suriñach, M.D. Baró, B. entropy metallic glasses, study of the crystallization processes by X-ray di ff raction J. Nelson, J. Sort, Effects of the anion in glycine-containing electrolytes on the and Mössbauer spectroscopy, J. Non-Cryst. Solids 547 (2020) 120301. https://do mechanical properties of electrodeposited Co-Ni films, Mater. Chem. Phys. 130 i:10.1016/j.jnoncrysol.2020.120301. (2011) 1380–1386. https://doi:10.1016/j.matchemphys.2011.09.032. [16] D.H. Lee, J.A. Lee, Y. Zhao, Z. Lu, J.Y. Suh, J.Y. Kim, U. Ramamurty, M. Kawasaki, [35] F.H. Duan, J. Pan, Y. Lin, Y. Li, Significant structural relaxation in a Mo-O binary T.G. Langdon, J. il Jang, Annealing effect on plastic flow in nanocrystalline amorphous alloy, J. Non-Cryst. Solids 514 (2019) 10–14. https://doi:10.1016/j.jno CoCrFeMnNi high-entropy alloy: a nanomechanical analysis, Acta Mater. 140 ncrysol.2019.03.038. (2017) 443–451. https://doi:10.1016/j.actamat.2017.08.057. [36] B. Gludovatz, E.P. George, R.O. Ritchie, Processing, Microstructure and mechanical [17] L.C.R. Aliaga, J. Fornell, S. Suriñach, M.D. Baró, C.S. Kiminami, C. Bolfarini, W. properties of the CrMnFeCoNi high-entropy alloy, JOM (J. Occup. Med.) 67 (2015) J. Botta, J. Sort, Comparative study of nanoindentation on melt-spun ribbon and 2262–2270. https://doi:10.1007/s11837-015-1589-z. bulk metallic glass with Ni60Nb37B3 composition, J. Mater. Res. 28 (2013) [37] A. Leitner, V. Maier-Kiener, D. Kiener, Extraction of flow behavior and Hall–petch 2740–2746. https://doi:10.1557/jmr.2013.260. parameters using a nanoindentation multiple sharp tip approach, Adv. Eng. Mater. [18] W.C. Oliver, G.M. Pharr, An improved technique for determining hardness, 19 (2017) 1–9. https://doi:10.1002/adem.201600669. J. Mater. Res. 7 (1992) 1564–1583, https://doi.org/10.1557/JMR.1992.1564. [38] M.T. Attaf, Connection between the loading curve models in elastoplastic [19] L.S. Zhang, Preparation of CoCrFeNiCuMnSix high entropy alloys and their indentation, Mater. Lett. 58 (2004) 3491–3498. https://doi:10.1016/j.matlet.200 microstructure and properties, Adv. Mater. Res. 750–752 (2013) 615–618. https 4.06.049. ://doi:10.4028/www.scientific.net/AMR.750-752.615. [39] A. Leyland, A. Matthews, On the significance of the H/E ratio in wear control: a [20] Z. Zhang, Elastic Properties of Bulk-Metallic Glasses Studied by Resonant nanocomposite coating approach to optimised tribological behaviour, Wear 246 Ultrasound Spectroscopy, PhD Diss, University of Tennessee, 2008. (2000) 1–11. https://doi:10.1016/S0043-1648(00)00488-9. [21] F. Fauth, I. Peral, C. Popescu, M. Knapp, The New Material Science Powder [40] M. Sullivan, Measuring, Evaluating, and Describing Pile-Up and Sink-In during Diffraction Beamline at ALBA Synchrotron, Powder Diffr., 2013. https://doi:10.1 Nanoindentation of Thin Films on Substrates, PhD diss, Auburn University, 2015. 017/S0885715613000900. [41] R.A. Mirshams, A.K. Srivastava, Effect of pile-up on nanoindentation [22] C.A. Schneider, W.S. Rasband, K.W. Eliceiri, NIH Image to ImageJ: 25 years of measurements of polycrystalline bulk metals, Adv. Mater. Res. 853 (2014) image analysis, Nat. Methods 9 (2012) 671–675. https://doi:10.1038/nmeth.2089. 143–150. https://doi:10.4028/www.scientific.net/AMR.853.143. [23] T. Qi, Y. Li, A. Takeuchi, G. Xie, H. Miao, W. Zhang, Soft magnetic Fe25Co25Ni25(B, [42] D. Beegan, S. Chowdhury, M.T. Laugier, The nanoindentation behaviour of hard Si)25 high entropy bulk metallic glasses, Intermetallics 66 (2015) 8–12. https://doi and soft films on silicon substrates, Thin Solid Films 466 (2004) 167–174. https:// :10.1016/j.intermet.2015.06.015. doi:10.1016/j.tsf.2004.03.006. [24] H. Zhang, X.C. Zhong, Y.Z. He, W.H. Li, W.F. Wu, G. Chen, S. Guo, Effect of high [43] P. Burik, L. Pešek, L. Voleský, Effect of pile-up on the mechanical characteristics of configuration entropy and rare earth addition on boride precipitation and steel with different strain history by depth sensing indentation, Met. 2014 - 23rd mechanical properties of multi-principal-element alloys, J. Mater. Eng. Perform. 26 Int. Conf. Metall. Mater. Conf. Proc. 2 (2014) 629–633. (2017) 3750–3755. https://doi.org/10.1007/s11665-017-2831-3. [44] W.C. Oliver, G.M. Pharr, Measurement of hardness and elastic modulus by [25] X.F. Wang, X.P. Yang, Z.D. Guo, Y.C. Zhou, H.W. Song, Nanoindentation instrumented indentation: advances in understanding and refinements to characterization of mechanical properties of ferrite and austenite in duplex methodology, J. Mater. Res. 19 (2004) 3–20, https://doi.org/10.1557/ jmr.2004.19.1.3. 10