- Email: [email protected]
Corrosion properties of amorphous, partially, and fully crystallized Fe68Cr8Mo4Nb4B16 alloy
Journal of Alloys and Compounds 826 (2020) 154123
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Corrosion properties of amorphous, partially, and fully crystallized Fe68Cr8Mo4Nb4B16 alloy ~o a, G. Zepon b, *, G.Y. Koga b, D.A. Godoy Pe rez a, F.H. Paes de Almeida a, D.D. Coimbra V. Roche c, J.-C. Lepretre c, A.M. Jorge Jr. b, C.S. Kiminami b, C. Bolfarini b, A. Inoue d, e, f, W.J. Botta b a ~o em Ci^ ~o Carlos, Rod. Washington Luiz, km 235, Sa ~o Carlos, SP, s-Graduaça Programa de Po encia e Engenharia de Materiais, Universidade Federal de Sa 13565-905, Brazil b ~o Carlos, Rod. Washington Luiz, km 235, Sa ~o Carlos, SP, 13565-905, Brazil Departamento de Engenharia de Materiais, Universidade Federal de Sa c Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, 38 000, Grenoble, France d International Institute of Green Materials, Josai International University, Togane, 283-8555, Japan e Institute of Massive Amorphous Metal Science, China University of Mining Technology, Xuzhou, 221116, China f Department of Physics, King Abdulaziz University, Jeddah, 22254, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 October 2019 Received in revised form 25 January 2020 Accepted 30 January 2020 Available online 7 February 2020
In this work, the corrosion behavior of amorphous and partially crystallized Fe68Cr8Mo4Nb4B16 alloys has been studied. Fully amorphous ribbons were prepared by melt spinning and then partially and fully crystallized at different heat treatment temperatures. The corrosion behavior was evaluated in chloriderich media at different pHs, ranging from acidic to alkaline. An exceptionally high corrosion resistance was observed for the new Fe68Cr8Mo4Nb4B16 amorphous alloy in the proposed media and pHs. The amorphous phase containing corrosion-resistant alloying elements such as chromium and molybdenum led to the formation of a highly stable passivating film, which coated and protected the active exposed metal surface. Partially crystallized samples heated up to 700 C still grant the formation of a corrosionresistant passivating layer. The presence of such a layer was correlated to the non-percolation of crystals embedded into the corrosion-resistant amorphous matrix. The corrosion resistance of fully crystalline annealed ribbons and as-cast ingots did not present the similar superior corrosion performance. This behavior was assigned to element partitioning throughout the crystallization, particularly chromium, which led to a non-homogeneous structure that preferentially triggered and held pitting corrosion along with the percolated crystalline material. These results indicate that the Fe68Cr8Mo4Nb4B16 alloy is a candidate for corrosion resistant coating where the suppression of crystallization is unavoidable. © 2020 Elsevier B.V. All rights reserved.
Keywords: Fe-based amorphous alloy Crystallization nanostructure Corrosion resistance
1. Introduction Metallic glasses present remarkable and distinguished attributes compared to conventional alloys [1,2]. Among most of bulk metallic glass (BMG) systems, Fe-based ones are interesting to be used as protective materials because they present elevated crystallization temperature, high hardness, and excellent resistance to wear and corrosion at a relatively low cost [3e5]. Also, some Febased BMGs have even been produced using commercially grade precursors [6e10], aiming to extend their potential industrial
* Corresponding author. E-mail address: [email protected] (G. Zepon). https://doi.org/10.1016/j.jallcom.2020.154123 0925-8388/© 2020 Elsevier B.V. All rights reserved.
application. Fe-based alloys are also versatile to design a variety of microstructure with tailored properties, including excellent corrosion resistance. Besides fully amorphous Fe-based alloys [11,12], metallic glass matrix composites [13,14] and high-entropy amorphous alloys [15,16] are still under interest. Designing corrosion resistant amorphous Fe-based alloys must consider alloying elements that increase the glass-forming ability (GFA) and ensure passive film formation. Boron addition is used to improve the GFA of Fe-based alloys, while chromium is essential to grant the corrosion resistance [17e19]. In this sense, different corrosion-resistant amorphous FeeCreB-based alloys have been reported [20e23]. Given the relatively small number of elements, the FeeCreNbeB system is interesting to produce corrosion-resistant amorphous alloys and
2
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
Fig. 1. Comparative XRD patterns of the arc-melted ingot, as-melt spun ribbons, spun ribbons heat-treated at 620 C, 700 C and 850 C of the Fe68Cr8Mo4Nb4B16 alloy.
coatings. Koga et al. [24] showed that even having low Cr content, the Fe60Cr8Nb8B24 (at.%) amorphous alloy presents high corrosion resistance in acidic chloride-rich electrolytes, which is considerably superior to ferritic or austenitic stainless steels. A coating with a high fraction of amorphous phase was obtained by HVOF with good resistances to wear [25] and corrosion [26]. The resulted coating presented a high hardness (838 HV0.3) and excellent wear
resistance granted by the microstructure composed of nanocrystalline hard borides embedded in an amorphous matrix [25], which was confirmed by another study using the Fe57Cr9Nb13B21 amorphous/nanocrystalline coating [27]. Although presenting good corrosion resistance [26], Fe60Cr8Nb8B24 nanocrystalline/amorphous HVOF coatings did not display the similar outstanding corrosion resistance recognized in the fully amorphous alloy with the same composition [24]. Therefore, understanding the influence
Fig. 2. SEM images of the arc-melted Fe68Cr8Mo4Nb4B16 alloy. (a), (c) and (d) BSE images; (b) EDX mapping. The numbers 1 to 12 indicate the regions where EDX quantitative measurements have been performed.
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra Table 1 Local chemical composition (%at.) measured by EDXof the different phases shown in Fig. 2(c) and (d). Phase
Region
Fe
Cr
Nb
Mo
MB MB MB MB MB Fe-a Fe-a M3B2 M3B2 M3B2 M3B2 M2B
1 2 3 4 5 6 7 8 9 10 11 12
47.4 46.5 47.2 47.2 47.5 90.0 90.2 79.4 64.6 63.5 65.1 83.1
16.1 18.0 17.8 17.0 17.8 8.4 8.2 8.0 12.7 12.4 11.8 13.00
14.1 13.4 13.3 13.6 13.1 0.1 0.2 6.7 9.4 9.2 8.7 1.7
22.4 22.1 21.7 22.2 21.6 1.5 1.4 5.9 13.3 14.9 14.4 2.2
of partial crystallization in Fe-based amorphous alloys is paramount to leverage the application of this sort of material as protective coatings. Crystallization of amorphous Fe-based alloys is considered as one of the main reasons that significantly impair the corrosion resistance [28], and hence recent efforts have been devoted to find new compositions with high glass-forming ability and elevated crystallization temperatures. The stability of the passive films in stainless-type glass-forming steels depends on the interplay between structure and chemistry, especially related to iron, chromium, and molybdenum. Indeed, Duarte et al. [29] have evaluated the corrosion behavior of fully amorphous and crystallized Fe50Cr15Mo14C15B6 alloys and found that crystallization yields to the formation of Cr-depleted phases more prone to corrode selectively together with Mo-rich phases. However, depending on the crystallization degree and sequence, the corrosion resistance is little impaired for this Fe50Cr15Mo14C15B6 alloy composition.
3
In this work, a novel Fe-based amorphous alloy is proposed, namely Fe68Cr8Mo4Nb4B16 (composition in %at.). Fully amorphous ribbons were produced by melt spinning, and different heat treatments were applied, aiming to obtain partially and fully crystallized samples. These samples were carefully characterized by different techniques, and their corrosion behavior in chloride-rich media and different pHs (from acidic to alkaline) was evaluated. The results were also compared to the same alloy ingot produced by conventional arc-melting process. 2. Experimental The alloy with composition Fe68Cr8Mo4Nb4B16 at.% was prepared by arc-melting in a protective Ar atmosphere. The used elements Fe, Cr, Nb, and B have a purity of 99.98 mass%, >99%, 99.8%, and 99.5%, respectively. Chemical homogeneity of the alloy was ensured by flipping and remelting it several times. The as-cast ingot was then melt-spun under Ar using a copper wheel with a surface speed of 30 m/s. The ribbons were 20 to 25 mm-thick and 3 mmwide. The glass transition temperature and crystallization temperatures of the melt-spun ribbon were evaluated by DSC using a Netzsch 404 equipment. A heating rate of 40 C/min was employed. Based on the results of thermal analysis, the melt-spun ribbons were heat-treated at three different temperatures, namely 620 C,
Table 2 Chemical composition (%at.) measured by EDX of the region 1 shown in Fig. 3 (c).
EDX (%at.) Considering boron Theoretical
Fe
Cr
Nb
Mo
B
79.98 67.24 68
10.11 8.5 8
5.43 4.5 4
4.48 3.76 4
e 16 16
Fig. 3. TEM images of the Fe68Cr8Mo4Nb4B16 alloy in the as-melt spun ribbon condition. (a) Bright-field, (b) dark-field (c) selected-area electron diffraction pattern, (d) STEM brightfield, (e) STEM dark-field.
4
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
Fig. 4. DSC curve (40 C/min up heating) of theFe68Cr8Mo4Nb4B16 alloy in the as-melt spun ribbon condition.
700 C, and 850 C. The heat treatments were carried out using an electric furnace in which the sample is placed inside a quartz tube. The quartz tube was evacuated, and the heat treatments were carried out under Ar flow to avoid oxidation of the alloy. The heat treatment protocol consisted of heating the sample at a heating rate of 20 C/min up to the desired temperature. When the target temperature was reached, the resistance was turned off, except the sample annealed at 850 C that remained at this temperature for 2 h. All samples were cooled through the Ar flow. Microstructural characterization of the arc-melted ingot, asmelt spun ribbon, and annealed ribbons was carried out by X-ray diffraction (XRD) using a Siemens D5005 diffractometer with KaCu-radiation with curved graphite monochromator. The microstructure of the arc-melted ingot was analyzed by scanning electron microscopy (SEM) using a Phillips XL 30 FEG equipped with a Bruker Nano XFlash 6|60 EDX Detector. Foils for transmission electron microscopy (TEM) observations were prepared by ion
Fig. 5. TEM images of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heat-treated at 620 C (a) bright-field, (b) dark-field (c) selected-area electron diffraction pattern, (d) bright field and EDX microanalysis.
milling in a Gatan PIPS 691 equipment. TEM observation was conducted with a FEI Tecnai LaB6 and a FEI Tecnai FEG G2F20 with scanning transmission (STEM) and energy dispersive X-ray (EDX) detectors, both operating at 200 kV. A conventional three-cell set-up was used to evaluate the corrosion resistance of the Fe68Cr8Mo4Nb4B16 alloys in all process conditions, i.e., arc-melted ingot, as-melt spun ribbon, and annealed ribbons. A platinum grid and a saturated calomel electrode (SCE) were used as counter and reference electrodes, respectively. The working electrodes were the amorphous ribbons, the ribbons annealed at 620 C, 700 C and 850 C, and the arcmelted ingot, all with the same nominal Fe68Cr8Mo4Nb4B16 composition. Chloride-rich electrolytes containing 35 g/l of NaCl were considered to analyze the resistance against pitting corrosion in acidic (pH 3), alkaline (pH 10), and mildly acidic (pH 5.5) conditions. Demineralized water and high-purity NaCl, H2SO4, and NaOH were used to prepare the solutions. Electrochemical measurements were performed in naturally aerated condition at room temperature, 25 ± 2 C. Potentiodynamic polarization curves were recorded after 1 h at open-circuit conditions to ensure the steadystate to be reached, using a 1 mV/s of scan rate to cover between e 200 mV vs. the open-circuit potential up to þ1250 mV vs. SCE. The corrosion potential (Ecorr) and the corrosion current density (icorr) were determined by Tafel’s extrapolation. Measurements for each sample tested in different electrolytes were repeated once to ensure repeatability. 3. Results and discussion 3.1. Microstructural characterization The arc-melted ingot of the Fe68Cr8Mo4Nb4B16 alloy presented a very complex structure composed of a-Fe (bcc), MB, M2B, and M3B2-type borides as can be seen in the XRD pattern shown in Fig. 1. These borides are composed of different amounts of the metallic elements M of the alloy, as discussed later on. The M2B boride is presented in two allotropic forms, tetragonal and orthorhombic. Both variants are usually reported together since they appear due to stacking faults along with the crystal structure [30]. Fig. 2 displays SEM images showing the complex structure of the arc-melted ingot. MB-boride was identified as the bright block-like primary phase presented in Fig. 2 (a) and (c). EDX analyses (see the EDX map in Fig. 2 (b) and quantitative EDX in Table 1) show that
Fig. 6. A dark-field TEM image of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heattreated at 700 C. The inset presents a selected-area electron diffraction pattern, showing a residual amorphous phase and that crystals are in the nanosize range.
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
this phase is enriched in Nb and Mo. Such primary phase is embedded in an a-Fe matrix with chemical composition of approximately Fe-8%at. Cr. The relatively low chromium content of the a-Fe may considerably impair the corrosion resistance of this alloy. Another (Mo,Nb)-rich phase was identified as the M3B2 phase, which presents a eutectic-like morphology. Finally, a darker plate-like phase enriched in Cr and depleted in Nb and Mo can also be seen in Fig. 2(a) and (b), which was identified as the M2B-boride. Some of the M2B-type borides seem to be formed in a eutectic-like reaction such as that highlighted in Fig. 2 (d). It is worth mentioning that the EDX measurements must be taken as a qualitative analysis since boron could not be measured in the used detector. The XRD pattern (Fig. 1) suggests that the as-melted spun ribbon has a fully amorphous structure. TEM images (Fig. 3) confirm the fully amorphous structure. No nanocrystalline grains can be observed in the bright- and dark-field images, Fig. 3(a) and (b), respectively, and only amorphous halos can be seen in the electron diffraction pattern (Fig. 3 (c)). Fig. 3(d) and (e) present STEM images of the same sample and EDX analyses were carried out within the region marked as #1. The local chemical composition measured by EDX is presented in Table 2. The final chemical composition is very close to the theoretical one if 16 %at. of boron content is considered (boron cannot be detected by the employed EDX). Fig. 4 displays the DSC curve of the melt-spun ribbon during heating. The glass transition temperature (Tg) of the Fe68Cr8Mo4Nb4B16 alloy was identified as 527 C. The onset temperature of crystallization (Tx) is 561 C. Three crystallization exothermic peaks were found at 579 C, 663 C and 779 C. Therefore, the melt-spun ribbon was subjected to heat treatments at 620 C, 700 C and 850 C, which are above to each crystallization temperature. The ribbon annealed at 620 C presented an XRD pattern (Fig. 1) that indicates the formation of the c-phase (with I-43 m space group and lattice parameter of a ¼ 8.8278 Å). Small reflections suggest the formation of the M23B6 borides. TEM images (Fig. 5) show that smaller than 50 nm crystallites were formed within an amorphous matrix. The selected area electron diffraction pattern shown in Fig. 5 (c) presents ring reflections confirming the formation of the c-phase and M23B6. Local EDX analyses were carried out in the regions identified as #1 (crystalline phase) and #2 (amorphous phase) in Fig. 5 (d). One can see that the chemical composition of both regions is quite similar (not considering the boron content, which cannot be detected and, therefore, no information about its distribution can be inferred), suggesting that the crystallization of the first phases from the amorphous phase takes place without considerable diffusion. Therefore, phases with
5
chemical composition close to the theoretical composition of the alloy are formed. When the melt-spun ribbon is annealed at 700 C (Fig. 6), the aFe starts to form. The resulting structure is composed of c-phase, M23B6 borides, a-Fe, and an amorphous matrix remains as indexed in the XRD pattern of Fig. 1. TEM images (Fig. 6(a) and (b)) show a large volume of crystallites smaller than 50 nm present in an amorphous matrix. The XRD pattern of the melt-spun ribbon annealed at 850 C shows that the c-phase, M23B6 boride, and amorphous phase no longer exist and that the structure is composed of a-Fe and different borides, namely, M2B, M3B2, MB and MB2. This result indicates that during crystallization, poor-boron phases are firstly formed, such as M23B6, because less diffusion is necessary to achieve their chemical composition. Increasing temperature and consequently diffusion, boron is capable of diffusing and concentrating, forming richer-boron phases such as M3B2, M2B, MB and MB2. The electron diffraction pattern of the annealed (at 850 C) ribbon presented in Fig. 7 (c) shows that the alloy is fully crystallized. The crystallites formed after such heat treatment are larger than 100 nm as can be seen by TEM images in Fig. 7(a) and (b). 3.2. Corrosion resistance Polarization curves in chloride-rich acidic (pH 3 and 5.5) and alkaline (pH 10) media of the Fe68Cr8Mo4Nb4B16 alloy processed in the different ascribe conditions are shown in Fig. 8. Table 3 summarizes the values of the corrosion potential (Ecorr) and of the corrosion current density (icorr). Fully amorphous ribbons (as melt-spun) exhibit outstanding corrosion resistance in all tested conditions, as demonstrated by the noblest Ecorr values, negligible values of icorr, between 107and 106 A/cm2, and a well-defined passivation plateau at low current density levels, between 106 and 105 A/cm2. Indeed, amorphous Fe-based alloys with relatively low Cr contents (<10 wt%) have been reported to be extremely corrosion-resistant in chloride-rich electrolytes [24,31,32], with properties comparable and even better to than high-performance austenitic stainless steel grades, such as the 316L. The quick formation and growth of a very stable passivating film in Fe-based amorphous alloys containing corrosion-resistant alloying elements such as Cr are attributed to the elevated reactivity of the alloy’s surface. Being more metastable and homogeneous than their crystalline equivalent, the surface of amorphous alloys undergoesa rapid selective dissolution of elements such as iron with the concomitant enrichment of chromium and
Fig. 7. TEM images of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heat-treated at 850 C (a) bright-field, (b) dark-field, and (c) selected-area electron diffraction pattern.
6
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra Table 3 Ensemble of the electrochemical parameters from the potentiodynamic polarization curves in Fig. 8. Electrolyte
Sample
0.6 M NaCl pH 3.0
As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot
0.6 M NaCl pH 5.5
0.6 M NaCl pH 10.0
Fig. 8. Potentiodynamic polarization curves of the Fe68Cr8Mo4Nb4B16 samples exposed to chloride-rich (a) and (b) acidic and (c) alkaline media.
molybdenum, enabling the formation of a dense, adherent, and protective oxygen-rich Cr- and Mo-compounds [33]. Interesting to note the presence of spikes of current density upon anodic polarization of the amorphous ribbons, which can be
C C C
C C C
C C C
Ecorr (mVSCE)
icorr (A/cm2)
241 284 240 475 604 145 117 260 291 378 178 198 222 255 390
1.2 2.2 2.2 4.2 3.8 7.5 2.4 2.8 4.9 7.5 1.7 1.4 2.3 3.1 1.1
106 106 106 104 104 107 107 106 105 105 107 106 106 105 104
ascribed to metastable pits. The frequency and the intensity of the metastable pitting occurrence seem to be more pronounced with increasing alkalinity. Molybdenum addition in stainless steels is recognized to increase the resistance against pitting corrosion in a chloride-rich acidic environment. This element is even considered to calculate the so-called pitting resistance equivalent number in stainless steels (PREn ¼ %Cr þ 3.3%Mo þ 16%N) [34]. However, studies of Mo-containing stainless steels in chloride-rich alkaline electrolytes have shown unexpected results [35,36], in which the addition of molybdenum did not improve the localized corrosion resistance of some stainless steels in alkaline medium. Despite the occurrence of metastable pits upon anodic polarization, it is worth to highlight that no stable pitting corrosion was observed even for polarization as high as þ1000 mV relative to the Ecorr. The spun ribbon heat-treated at 620 C displayed similar Ecorr and slightly superior icorr values compared to those of the fully amorphous samples. However, the appearance of a dissolution peak followed by a passivation plateau with associated higher current density is seen after annealing the samples at 620 C, especially for corrosion in alkaline conditions. Cr-depleted zones are formed upon crystallization of the amorphous alloys, representing preferential regions for corrosion. With small crystalline fraction, in this case c-phase and M23B6phases, the preferential dissolution of the samples annealed at 620 C induces a roughened surface from which a passive film forms upon anodic polarization. This passive film is highly protective against pitting corrosion, as highlighted by its stability greater than þ1000 mV. However, due to the prior preferential dissolution and consequent surface roughening, this film is less efficient than that formed on the fully amorphous ribbons. As the heat treatment temperature increases, the amorphous fraction decreases, and other crystalline phases appear. As discussed before, the samples annealed at 700 C exhibits a remaining amorphous phase and, besides the c-phase and M23B6 crystals, it also contains a-Fe. As a result, compared to the annealed sample at 620 C, the Ecorr decreases, and the icorr increases, but with comparable current density values at the passivation plateau. Although less resistant than the passivating film formed on the amorphous sample, annealing at 620 C and 700 C still enabled passivation with relatively low associated current density. The satisfactory passivation ability even with the presence of crystals has been ascribed to the blockage of the preferential dissolution by the remaining corrosion-resistant amorphous phase because of the small size of the crystals and, primarily, due to the lack of the percolation among them [28]. This suggests that, after the initial dissolution of the crystals, the surface is likely to be formed only by
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
7
Fig. 9. SEM micrographs, backscattered electron, of the surface after potentiodynamic polarization measurements of: a) as-spun ribbon, b) ribbon heat-treated at 620 C, c) ribbon heat-treated at 700 C, and d) ribbon heat-treated at 850 C, and e) ingot produced by arc-melting; (e) SEM micrograph, secondary electron, of the arc-melted Fe68Cr8Mo4Nb4B16 crystalline alloy to highlight the extended corrosion damage after corrosion testing.
the remaining amorphous phase that enables the passive film formation. Nonetheless, ribbons annealed at 850 C did not display the excellent corrosion resistance observed for amorphous ribbons in acidic and alkaline chloride-rich media. Compared to the fully amorphous ribbons, the annealed ones present icorr values up to 2 order of magnitudes superior (105 against 107, respectively). As the crystallization progresses, a more heterogeneous structure is formed with an advanced chemical partitioning phenomenon. This can be verified by the coexistence of different phases after annealing at 850 C. Also, corrosion susceptible crystals forming a percolated morphology induce the dissolution through the material, causing the absence of an effective passive film formation, i.e. plateau with high current density values. The detrimental aspect of advanced crystallization is highlighted by the polarization curves of as-cast ingots that exhibit icorr values between 104 and 105A/cm2, which are up to 3 orders of magnitude higher than the 107 and 106A/cm2 values of icorr displayed for the amorphous alloys of the same composition and the absence of passivation plateau. Fig. 9 shows the surface of the samples after the potentiodynamic polarization measurements. Almost no corrosion products
are seen at the surface of the as-spun ribbon and the ribbons heattreated at 620 C, Fig. 9a and b, respectively. As both samples presented negligible corrosion current density, low current density along the passivation plateau, and no transpassivation event, the corrosion damage was insignificant. Corrosion products, even if small, are nevertheless detected after testing the ribbons heattreated at 700 C, Fig. 9c, indication of the transition of corrosionresistant/corrosion susceptible microstructure due to the formation of phases more prone to corrode. The corrosion loss upon crystallization is confirmed by the significant presence of corrosion products at the surface of the ribbons heat-treated at 850 C, Fig. 9d, and confirmed by the severely corroded surface of the arcmelted ingot, Fig. 9e and f. Indeed, the ultimate fate of the highly corrosion-resistant fully-amorphous ribbons at the completion of the crystallization seems to be the complete loss of the corrosion resistance given the presence of multiple and enlarged phases that are likely to induce preferential dissolution and the absence of any protective layer. The general trends clearly point out to the outstanding corrosion resistance of the new Fe68Cr8Mo4Nb4B16 glassy alloy in chloriderich acidic and alkaline media. The fully amorphous nature and
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
8
the presence of corrosion-resistant alloying elements such as chromium and molybdenum drive the formation of a highly stable passivating film covering the active bare metal surface. Partially crystallized samples heat-treated at 620 C and 700 C still allow the formation of a resistant passive film due to the non-percolated morphology of the crystals embedded within the corrosionresistant amorphous matrix. In practice, this means that this alloy can be applied by coating processes, such as HVOF, since the alloy temperature, after amorphization, does not increase above 700 C. Crystalline Fe68Cr8Mo4Nb4B16 annealed ribbons, and as-cast ingots did not display the same excellent corrosion resistance due to the partitioning of elements during crystallization, especially chromium, resulting in the structural inhomogeneity that preferentially triggers and sustains pitting corrosion along the percolated crystalline network.
4. Conclusions Fully amorphous Fe68Cr8Mo4Nb4B16 alloy exhibited excellent corrosion resistance in chloride rich electrolyte and was attributed to the formation of a highly protective passivating film. Metastable pitting was seen, especially in alkaline conditions; however, no transpassivation event occurred even for anodic polarization as large as þ1000 mV relative to the corrosion potential. Small corrosion resistance loss was found in the first crystallization events. This was attributed to the reduced chemical differences of the first crystals coming from the amorphous phase and their non-percolated nature. As the crystallization progressed, several different crystalline phases appeared, forming a more continuous crystalline network prone to corrode and, therefore, the corrosion resistance started to be severally compromised.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement ~o: Conceptualization, Methodology, Investigation, D.D. Coimbra Formal analysis, Visualization, Writing - original draft, Writing review & editing. G. Zepon: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing, Supervision. G.Y. Koga: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing. D.A. rez: Methodology, Investigation, Writing - review & Godoy Pe editing. F.H. Paes de Almeida: Methodology, Investigation, Writing - review & editing. V. Roche: Methodology, Validation, Formal analysis, Writing - review & editing. J.-C. Lepretre: Methodology, Validation, Formal analysis, Writing - review & editing. A.M. Jorge: Methodology, Validation, Formal analysis, Writing - review & editing. C.S. Kiminami: Conceptualization, Formal analysis, Writing - review & editing, Funding acquisition. C. Bolfarini: Conceptualization, Formal analysis, Writing - review & editing, Funding acquisition. A. Inoue: Conceptualization, Formal analysis, Writing review & editing. W.J. Botta: Conceptualization, Validation, Formal analysis, Writing - original draft, Writing - review & editing, Supervision, Funding acquisition.
Acknowledgments The authors are grateful for the financial support granted by ~o de AperfeiçoaFAPESP (process n 2013/05987-8), Coordenaça mento de Pessoal de Nível Superior - Brasil (CAPES) - Finance code 001 and CNPq. The authors are also grateful for electron microscopy facilities from the Laboratory of Structural Characterization of ~o Carlos (LCE/DEMa/UFSCar). Federal University of Sa
References [1] M. Ashby, A. Greer, Metallic glasses as structural materials, Scripta Mater. 54 (2006) 321e326, https://doi.org/10.1016/j.scriptamat.2005.09.051. [2] C. Suryanarayana, A. Inoue, Bulk Metallic Glasses, second ed., 2017, https:// doi.org/10.1201/9781315153483. [3] K. Asami, S.-J. Pang, T. Zhang, A. Inoue, Preparation and corrosion resistance of Fe-Cr-Mo-C-B-P bulk glassy alloys, J. Electrochem. Soc. 149 (2002), B366, https://doi.org/10.1149/1.1490537. [4] C.A.C. Souza, D.V. Ribeiro, C.S. Kiminami, Corrosion resistance of Fe-Cr-based amorphous alloys : an overview, J. Non-Cryst. Solids 442 (2016) 56e66, https://doi.org/10.1016/j.jnoncrysol.2016.04.009. [5] C. Suryanarayana, A. Inoue, Iron-based bulk metallic glasses, Int. Mater. Rev. 58 (2013) 131e166, https://doi.org/10.1179/1743280412Y.0000000007. [6] A. Inoue, X.M. Wang, Bulk amorphous FC20 (Fe-C-Si) alloys with small amounts of B and their crystallized structure and mechanical properties, Acta Mater. 48 (2000) 1383e1395, https://doi.org/10.1016/S1359-6454(99)003948. [7] H. Li, S. Yi, Fabrication of bulk metallic glasses in the alloy system FeeCeSieBePeCreMoeAl using hot metal and industrial ferro-alloys, Mater. Sci. Eng. A (2007) 449e451, https://doi.org/10.1016/j.msea.2006.02.262, 189e192. rdos, L.K. Varga, J. Lendvai, Thermal stability and glass [8] M. Shapaan, A. Ba forming ability of cast ironephosphorus amorphous alloys, Mater. Sci. Eng. A 366 (2004) 6e9, https://doi.org/10.1016/j.msea.2003.08.053. [9] J. Cheney, K. Vecchio, Development of quaternary Fe-based bulk metallic glasses, Mater. Sci. Eng. A 492 (2008) 230e235, https://doi.org/10.1016/ j.msea.2008.03.019. [10] G. Koga, L. Otani, A. Silva, V. Roche, R. Nogueira, A. Jorge, C. Bolfarini, C. Kiminami, W. Botta, Characterization and corrosion resistance of boroncontaining-austenitic stainless steels produced by rapid solidification techniques, Materials (Basel) 11 (2018) 2189, https://doi.org/10.3390/ ma11112189. [11] J. Li, L. Yang, H. Ma, K. Jiang, C. Chang, J.Q. Wang, Z. Song, X. Wang, R.W. Li, Improved corrosion resistance of novel Fe-based amorphous alloys, Mater. Des. 95 (2016) 225e230, https://doi.org/10.1016/j.matdes.2016.01.100. [12] H. Xia, Q. Chen, C. Wang, Evaluating corrosion resistances of Fe-based amorphous alloys by YCr/Mo values, J. Rare Earths (2017), https://doi.org/ 10.1016/S1002-0721(17)60926-8. [13] A. Zarebidaki, A. Seifoddini, T. Rabizadeh, Corrosion resistance of Fe 77 Mo 5 P 9 C 7.5 B 1.5 in-situ metallic glass matrix composites, J. Alloys Compd. 736 (2018) 17e21, https://doi.org/10.1016/j.jallcom.2017.11.138. [14] Y. Zhang, B. Song, J. Ming, Q. Yan, M. Wang, C. Cai, C. Zhang, Y. Shi, Corrosion mechanism of amorphous alloy strengthened stainless steel composite fabricated by selective laser melting, Corrosion Sci. (2019), https://doi.org/ 10.1016/j.corsci.2019.108241. [15] J. Ding, A. Inoue, Y. Han, F.L. Kong, S.L. Zhu, Z. Wang, E. Shalaan, F. Al-Marzouki, High entropy effect on structure and properties of (Fe,Co,Ni,Cr)-B amorphous alloys, J. Alloys Compd. 696 (2017) 345e352, https://doi.org/ 10.1016/j.jallcom.2016.11.223. [16] F. Wang, A. Inoue, F.L. Kong, S.L. Zhu, E. Shalaan, F. Al-Marzouki, W.J. Botta, C.S. Kiminami, Y.P. Ivanov, A.L. Greer, Formation, stability and ultrahigh strength of novel nanostructured alloys by partial crystallization of highentropy (Fe 0.25 Co 0.25 Ni 0.25 Cr 0.125 Mo 0.125 ) 86‒89 B 11‒14 amorphous phase, Acta Mater. (2019), https://doi.org/10.1016/ j.actamat.2019.03.019. [17] W.H. Wang, Roles of minor additions in formation and properties of bulk metallic glasses, Prog. Mater. Sci. 52 (2007) 540e596, https://doi.org/10.1016/ j.pmatsci.2006.07.003. [18] Z.P. Lu, C.T. Liu, Role of minor alloying additions in formation of bulk metallic glasses: a review, J. Mater. Sci. 39 (2004) 3965e3974, https://doi.org/10.1023/ B:JMSC.0000031478.73621.64. [19] C.T. Liu, Z.P. Lu, Effect of minor alloying additions on glass formation in bulk metallic glasses, Intermetallics 13 (2005) 415e418, https://doi.org/10.1016/ j.intermet.2004.07.034. [20] W.J. Botta, J.E. Berger, C.S. Kiminami, V. Roche, R.P. Nogueira, C. Bolfarini, Corrosion resistance of Fe-based amorphous alloys, J. Alloys Compd. 586 (2014) S105eS110, https://doi.org/10.1016/j.jallcom.2012.12.130. [21] S.J. Pang, T. Zhang, K. Asami, A. Inoue, Bulk glassy Fe-Cr-Mo-C-B alloys with high corrosion resistance, Corrosion Sci. 44 (2002) 1847e1856, https:// doi.org/10.1016/S0010-938X(02)00002-1. [22] C.A.C. Souza, M.F. de Oliveira, J.E. May, W.J. Botta, N.A. Mariano, S.E. Kuri,
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
[23]
[24]
[25]
[26]
[27]
[28]
C.S. Kiminami, Corrosion resistance of amorphous and nanocrystalline FeeMeB (M¼Zr, Nb) alloys, J. Non-Cryst. Solids 273 (2000) 282e288, https:// doi.org/10.1016/S0022-3093(00)00174-5. P.H. Tsai, A.C. Xiao, J.B. Li, J.S.C. Jang, J.P. Chu, J.C. Huang, Prominent Fe-based bulk amorphous steel alloy with large supercooled liquid region and superior corrosion resistance, J. Alloys Compd. 586 (2014) 94e98, https://doi.org/ 10.1016/j.jallcom.2013.09.186. G.Y. Koga, R.P. Nogueira, V. Roche, A.R. Yavari, A.K. Melle, J. Gallego, C. Bolfarini, C.S. Kiminami, W.J. Botta, Corrosion properties of FeeCreNbeB amorphous alloys and coatings, Surf. Coating. Technol. 254 (2014) 238e243, https://doi.org/10.1016/j.surfcoat.2014.06.022. G.Y. Koga, R. Schulz, S. Savoie, A.R.C. Nascimento, Y. Drolet, C. Bolfarini, C.S. Kiminami, W.J. Botta, Microstructure and wear behavior of Fe-based amorphous HVOF coatings produced from commercial precursors, Surf. Coating. Technol. 309 (2017) 938e944, https://doi.org/10.1016/ j.surfcoat.2016.10.057. G.Y. Koga, A.M. Jorge Junior, V. Roche, R.P. Nogueira, R. Schulz, S. Savoie, A.K. Melle, C. Loable, C. Bolfarini, C.S. Kiminami, W.J. Botta, Production and corrosion resistance of thermally sprayed Fe-based amorphous coatings from mechanically milled feedstock powders, Metall. Mater. Trans. A 49 (2018) 4860e4870, https://doi.org/10.1007/s11661-018-4785-y. Y. Guo, G.Y. Koga, A.M. Jorge, S. Savoie, R. Schulz, C.S. Kiminami, C. Bolfarini, W.J. Botta, Microstructural investigation of Fe-Cr-Nb-B amorphous/nanocrystalline coating produced by HVOF, Mater. Des. 111 (2016) 608e615, https://doi.org/10.1016/j.matdes.2016.09.027. M.J. Duarte, A. Kostka, J.A. Jimenez, P. Choi, J. Klemm, D. Crespo, D. Raabe, F.U. Renner, Crystallization, phase evolution and corrosion of Fe-based metallic glasses: an atomic-scale structural and chemical characterization study, Acta Mater. 71 (2014) 20e30, https://doi.org/10.1016/
9
j.actamat.2014.02.027. [29] M.J. Duarte, J. Klemm, S.O. Klemm, K.J.J. Mayrhofer, M. Stratmann, S. Borodin, a H. Romero, M. Madinehei, D. Crespo, J. Serrano, S.S.A. Gerstl, P.P. Choi, D. Raabe, F.U. Renner, Element-resolved corrosion analysis of stainless-type glass-forming steels, Science 341 (2013) 372e376, https://doi.org/10.1126/ science.1230081. [30] L. Yijian, H. Jian, Borides in microcrystalline Fe-Cr-Mo-B-Si alloys, J. Mater. Sci. 26 (1991) 2833e2840, https://doi.org/10.1007/BF02387759. [31] M. Madinehei, P. Bruna, M.J. Duarte, E. Pineda, J. Klemm, F.U. Renner, Glassformation and corrosion properties of FeeCreMoeCeB glassy ribbons with low Cr content, J. Alloys Compd. 615 (2014) S128eS131, https://doi.org/ 10.1016/j.jallcom.2013.12.245. [32] K. Hashimoto, What we have learned from studies on chemical properties of amorphous alloys? Appl. Surf. Sci. 257 (2011) 8141e8150, https://doi.org/ 10.1016/j.apsusc.2010.12.142. [33] H. Habazaki, Corrosion of amorphous and nanograined alloys, in: Shreir’s Corros, 2010, pp. 2192e2204, https://doi.org/10.1016/B978-0444527875.00107-4. [34] R.W. Revie, H.H. Uhlig, Corrosion and Corrosion Control, fourth ed., WileyInterscience, New Jersey, 2008. [35] T.J. Mesquita, E. Chauveau, M. Mantel, N. Kinsman, V. Roche, R.P. Nogueira, Lean duplex stainless steels-The role of molybdenum in pitting corrosion of concrete reinforcement studied with industrial and laboratory castings, Mater. Chem. Phys. 132 (2012) 967e972, https://doi.org/10.1016/ j.matchemphys.2011.12.042. [36] T.J. Mesquita, E. Chauveau, M. Mantel, N. Kinsman, R.P. Nogueira, Anomalous corrosion resistance behavior of Mo-containing SS in alkaline media: the role of microstructure, Mater. Chem. Phys. 126 (2011) 602e606, https://doi.org/ 10.1016/j.matchemphys.2011.01.013.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Corrosion properties of amorphous, partially, and fully crystallized Fe68Cr8Mo4Nb4B16 alloy ~o a, G. Zepon b, *, G.Y. Koga b, D.A. Godoy Pe rez a, F.H. Paes de Almeida a, D.D. Coimbra V. Roche c, J.-C. Lepretre c, A.M. Jorge Jr. b, C.S. Kiminami b, C. Bolfarini b, A. Inoue d, e, f, W.J. Botta b a ~o em Ci^ ~o Carlos, Rod. Washington Luiz, km 235, Sa ~o Carlos, SP, s-Graduaça Programa de Po encia e Engenharia de Materiais, Universidade Federal de Sa 13565-905, Brazil b ~o Carlos, Rod. Washington Luiz, km 235, Sa ~o Carlos, SP, 13565-905, Brazil Departamento de Engenharia de Materiais, Universidade Federal de Sa c Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, 38 000, Grenoble, France d International Institute of Green Materials, Josai International University, Togane, 283-8555, Japan e Institute of Massive Amorphous Metal Science, China University of Mining Technology, Xuzhou, 221116, China f Department of Physics, King Abdulaziz University, Jeddah, 22254, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 October 2019 Received in revised form 25 January 2020 Accepted 30 January 2020 Available online 7 February 2020
In this work, the corrosion behavior of amorphous and partially crystallized Fe68Cr8Mo4Nb4B16 alloys has been studied. Fully amorphous ribbons were prepared by melt spinning and then partially and fully crystallized at different heat treatment temperatures. The corrosion behavior was evaluated in chloriderich media at different pHs, ranging from acidic to alkaline. An exceptionally high corrosion resistance was observed for the new Fe68Cr8Mo4Nb4B16 amorphous alloy in the proposed media and pHs. The amorphous phase containing corrosion-resistant alloying elements such as chromium and molybdenum led to the formation of a highly stable passivating film, which coated and protected the active exposed metal surface. Partially crystallized samples heated up to 700 C still grant the formation of a corrosionresistant passivating layer. The presence of such a layer was correlated to the non-percolation of crystals embedded into the corrosion-resistant amorphous matrix. The corrosion resistance of fully crystalline annealed ribbons and as-cast ingots did not present the similar superior corrosion performance. This behavior was assigned to element partitioning throughout the crystallization, particularly chromium, which led to a non-homogeneous structure that preferentially triggered and held pitting corrosion along with the percolated crystalline material. These results indicate that the Fe68Cr8Mo4Nb4B16 alloy is a candidate for corrosion resistant coating where the suppression of crystallization is unavoidable. © 2020 Elsevier B.V. All rights reserved.
Keywords: Fe-based amorphous alloy Crystallization nanostructure Corrosion resistance
1. Introduction Metallic glasses present remarkable and distinguished attributes compared to conventional alloys [1,2]. Among most of bulk metallic glass (BMG) systems, Fe-based ones are interesting to be used as protective materials because they present elevated crystallization temperature, high hardness, and excellent resistance to wear and corrosion at a relatively low cost [3e5]. Also, some Febased BMGs have even been produced using commercially grade precursors [6e10], aiming to extend their potential industrial
* Corresponding author. E-mail address: [email protected] (G. Zepon). https://doi.org/10.1016/j.jallcom.2020.154123 0925-8388/© 2020 Elsevier B.V. All rights reserved.
application. Fe-based alloys are also versatile to design a variety of microstructure with tailored properties, including excellent corrosion resistance. Besides fully amorphous Fe-based alloys [11,12], metallic glass matrix composites [13,14] and high-entropy amorphous alloys [15,16] are still under interest. Designing corrosion resistant amorphous Fe-based alloys must consider alloying elements that increase the glass-forming ability (GFA) and ensure passive film formation. Boron addition is used to improve the GFA of Fe-based alloys, while chromium is essential to grant the corrosion resistance [17e19]. In this sense, different corrosion-resistant amorphous FeeCreB-based alloys have been reported [20e23]. Given the relatively small number of elements, the FeeCreNbeB system is interesting to produce corrosion-resistant amorphous alloys and
2
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
Fig. 1. Comparative XRD patterns of the arc-melted ingot, as-melt spun ribbons, spun ribbons heat-treated at 620 C, 700 C and 850 C of the Fe68Cr8Mo4Nb4B16 alloy.
coatings. Koga et al. [24] showed that even having low Cr content, the Fe60Cr8Nb8B24 (at.%) amorphous alloy presents high corrosion resistance in acidic chloride-rich electrolytes, which is considerably superior to ferritic or austenitic stainless steels. A coating with a high fraction of amorphous phase was obtained by HVOF with good resistances to wear [25] and corrosion [26]. The resulted coating presented a high hardness (838 HV0.3) and excellent wear
resistance granted by the microstructure composed of nanocrystalline hard borides embedded in an amorphous matrix [25], which was confirmed by another study using the Fe57Cr9Nb13B21 amorphous/nanocrystalline coating [27]. Although presenting good corrosion resistance [26], Fe60Cr8Nb8B24 nanocrystalline/amorphous HVOF coatings did not display the similar outstanding corrosion resistance recognized in the fully amorphous alloy with the same composition [24]. Therefore, understanding the influence
Fig. 2. SEM images of the arc-melted Fe68Cr8Mo4Nb4B16 alloy. (a), (c) and (d) BSE images; (b) EDX mapping. The numbers 1 to 12 indicate the regions where EDX quantitative measurements have been performed.
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra Table 1 Local chemical composition (%at.) measured by EDXof the different phases shown in Fig. 2(c) and (d). Phase
Region
Fe
Cr
Nb
Mo
MB MB MB MB MB Fe-a Fe-a M3B2 M3B2 M3B2 M3B2 M2B
1 2 3 4 5 6 7 8 9 10 11 12
47.4 46.5 47.2 47.2 47.5 90.0 90.2 79.4 64.6 63.5 65.1 83.1
16.1 18.0 17.8 17.0 17.8 8.4 8.2 8.0 12.7 12.4 11.8 13.00
14.1 13.4 13.3 13.6 13.1 0.1 0.2 6.7 9.4 9.2 8.7 1.7
22.4 22.1 21.7 22.2 21.6 1.5 1.4 5.9 13.3 14.9 14.4 2.2
of partial crystallization in Fe-based amorphous alloys is paramount to leverage the application of this sort of material as protective coatings. Crystallization of amorphous Fe-based alloys is considered as one of the main reasons that significantly impair the corrosion resistance [28], and hence recent efforts have been devoted to find new compositions with high glass-forming ability and elevated crystallization temperatures. The stability of the passive films in stainless-type glass-forming steels depends on the interplay between structure and chemistry, especially related to iron, chromium, and molybdenum. Indeed, Duarte et al. [29] have evaluated the corrosion behavior of fully amorphous and crystallized Fe50Cr15Mo14C15B6 alloys and found that crystallization yields to the formation of Cr-depleted phases more prone to corrode selectively together with Mo-rich phases. However, depending on the crystallization degree and sequence, the corrosion resistance is little impaired for this Fe50Cr15Mo14C15B6 alloy composition.
3
In this work, a novel Fe-based amorphous alloy is proposed, namely Fe68Cr8Mo4Nb4B16 (composition in %at.). Fully amorphous ribbons were produced by melt spinning, and different heat treatments were applied, aiming to obtain partially and fully crystallized samples. These samples were carefully characterized by different techniques, and their corrosion behavior in chloride-rich media and different pHs (from acidic to alkaline) was evaluated. The results were also compared to the same alloy ingot produced by conventional arc-melting process. 2. Experimental The alloy with composition Fe68Cr8Mo4Nb4B16 at.% was prepared by arc-melting in a protective Ar atmosphere. The used elements Fe, Cr, Nb, and B have a purity of 99.98 mass%, >99%, 99.8%, and 99.5%, respectively. Chemical homogeneity of the alloy was ensured by flipping and remelting it several times. The as-cast ingot was then melt-spun under Ar using a copper wheel with a surface speed of 30 m/s. The ribbons were 20 to 25 mm-thick and 3 mmwide. The glass transition temperature and crystallization temperatures of the melt-spun ribbon were evaluated by DSC using a Netzsch 404 equipment. A heating rate of 40 C/min was employed. Based on the results of thermal analysis, the melt-spun ribbons were heat-treated at three different temperatures, namely 620 C,
Table 2 Chemical composition (%at.) measured by EDX of the region 1 shown in Fig. 3 (c).
EDX (%at.) Considering boron Theoretical
Fe
Cr
Nb
Mo
B
79.98 67.24 68
10.11 8.5 8
5.43 4.5 4
4.48 3.76 4
e 16 16
Fig. 3. TEM images of the Fe68Cr8Mo4Nb4B16 alloy in the as-melt spun ribbon condition. (a) Bright-field, (b) dark-field (c) selected-area electron diffraction pattern, (d) STEM brightfield, (e) STEM dark-field.
4
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
Fig. 4. DSC curve (40 C/min up heating) of theFe68Cr8Mo4Nb4B16 alloy in the as-melt spun ribbon condition.
700 C, and 850 C. The heat treatments were carried out using an electric furnace in which the sample is placed inside a quartz tube. The quartz tube was evacuated, and the heat treatments were carried out under Ar flow to avoid oxidation of the alloy. The heat treatment protocol consisted of heating the sample at a heating rate of 20 C/min up to the desired temperature. When the target temperature was reached, the resistance was turned off, except the sample annealed at 850 C that remained at this temperature for 2 h. All samples were cooled through the Ar flow. Microstructural characterization of the arc-melted ingot, asmelt spun ribbon, and annealed ribbons was carried out by X-ray diffraction (XRD) using a Siemens D5005 diffractometer with KaCu-radiation with curved graphite monochromator. The microstructure of the arc-melted ingot was analyzed by scanning electron microscopy (SEM) using a Phillips XL 30 FEG equipped with a Bruker Nano XFlash 6|60 EDX Detector. Foils for transmission electron microscopy (TEM) observations were prepared by ion
Fig. 5. TEM images of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heat-treated at 620 C (a) bright-field, (b) dark-field (c) selected-area electron diffraction pattern, (d) bright field and EDX microanalysis.
milling in a Gatan PIPS 691 equipment. TEM observation was conducted with a FEI Tecnai LaB6 and a FEI Tecnai FEG G2F20 with scanning transmission (STEM) and energy dispersive X-ray (EDX) detectors, both operating at 200 kV. A conventional three-cell set-up was used to evaluate the corrosion resistance of the Fe68Cr8Mo4Nb4B16 alloys in all process conditions, i.e., arc-melted ingot, as-melt spun ribbon, and annealed ribbons. A platinum grid and a saturated calomel electrode (SCE) were used as counter and reference electrodes, respectively. The working electrodes were the amorphous ribbons, the ribbons annealed at 620 C, 700 C and 850 C, and the arcmelted ingot, all with the same nominal Fe68Cr8Mo4Nb4B16 composition. Chloride-rich electrolytes containing 35 g/l of NaCl were considered to analyze the resistance against pitting corrosion in acidic (pH 3), alkaline (pH 10), and mildly acidic (pH 5.5) conditions. Demineralized water and high-purity NaCl, H2SO4, and NaOH were used to prepare the solutions. Electrochemical measurements were performed in naturally aerated condition at room temperature, 25 ± 2 C. Potentiodynamic polarization curves were recorded after 1 h at open-circuit conditions to ensure the steadystate to be reached, using a 1 mV/s of scan rate to cover between e 200 mV vs. the open-circuit potential up to þ1250 mV vs. SCE. The corrosion potential (Ecorr) and the corrosion current density (icorr) were determined by Tafel’s extrapolation. Measurements for each sample tested in different electrolytes were repeated once to ensure repeatability. 3. Results and discussion 3.1. Microstructural characterization The arc-melted ingot of the Fe68Cr8Mo4Nb4B16 alloy presented a very complex structure composed of a-Fe (bcc), MB, M2B, and M3B2-type borides as can be seen in the XRD pattern shown in Fig. 1. These borides are composed of different amounts of the metallic elements M of the alloy, as discussed later on. The M2B boride is presented in two allotropic forms, tetragonal and orthorhombic. Both variants are usually reported together since they appear due to stacking faults along with the crystal structure [30]. Fig. 2 displays SEM images showing the complex structure of the arc-melted ingot. MB-boride was identified as the bright block-like primary phase presented in Fig. 2 (a) and (c). EDX analyses (see the EDX map in Fig. 2 (b) and quantitative EDX in Table 1) show that
Fig. 6. A dark-field TEM image of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heattreated at 700 C. The inset presents a selected-area electron diffraction pattern, showing a residual amorphous phase and that crystals are in the nanosize range.
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
this phase is enriched in Nb and Mo. Such primary phase is embedded in an a-Fe matrix with chemical composition of approximately Fe-8%at. Cr. The relatively low chromium content of the a-Fe may considerably impair the corrosion resistance of this alloy. Another (Mo,Nb)-rich phase was identified as the M3B2 phase, which presents a eutectic-like morphology. Finally, a darker plate-like phase enriched in Cr and depleted in Nb and Mo can also be seen in Fig. 2(a) and (b), which was identified as the M2B-boride. Some of the M2B-type borides seem to be formed in a eutectic-like reaction such as that highlighted in Fig. 2 (d). It is worth mentioning that the EDX measurements must be taken as a qualitative analysis since boron could not be measured in the used detector. The XRD pattern (Fig. 1) suggests that the as-melted spun ribbon has a fully amorphous structure. TEM images (Fig. 3) confirm the fully amorphous structure. No nanocrystalline grains can be observed in the bright- and dark-field images, Fig. 3(a) and (b), respectively, and only amorphous halos can be seen in the electron diffraction pattern (Fig. 3 (c)). Fig. 3(d) and (e) present STEM images of the same sample and EDX analyses were carried out within the region marked as #1. The local chemical composition measured by EDX is presented in Table 2. The final chemical composition is very close to the theoretical one if 16 %at. of boron content is considered (boron cannot be detected by the employed EDX). Fig. 4 displays the DSC curve of the melt-spun ribbon during heating. The glass transition temperature (Tg) of the Fe68Cr8Mo4Nb4B16 alloy was identified as 527 C. The onset temperature of crystallization (Tx) is 561 C. Three crystallization exothermic peaks were found at 579 C, 663 C and 779 C. Therefore, the melt-spun ribbon was subjected to heat treatments at 620 C, 700 C and 850 C, which are above to each crystallization temperature. The ribbon annealed at 620 C presented an XRD pattern (Fig. 1) that indicates the formation of the c-phase (with I-43 m space group and lattice parameter of a ¼ 8.8278 Å). Small reflections suggest the formation of the M23B6 borides. TEM images (Fig. 5) show that smaller than 50 nm crystallites were formed within an amorphous matrix. The selected area electron diffraction pattern shown in Fig. 5 (c) presents ring reflections confirming the formation of the c-phase and M23B6. Local EDX analyses were carried out in the regions identified as #1 (crystalline phase) and #2 (amorphous phase) in Fig. 5 (d). One can see that the chemical composition of both regions is quite similar (not considering the boron content, which cannot be detected and, therefore, no information about its distribution can be inferred), suggesting that the crystallization of the first phases from the amorphous phase takes place without considerable diffusion. Therefore, phases with
5
chemical composition close to the theoretical composition of the alloy are formed. When the melt-spun ribbon is annealed at 700 C (Fig. 6), the aFe starts to form. The resulting structure is composed of c-phase, M23B6 borides, a-Fe, and an amorphous matrix remains as indexed in the XRD pattern of Fig. 1. TEM images (Fig. 6(a) and (b)) show a large volume of crystallites smaller than 50 nm present in an amorphous matrix. The XRD pattern of the melt-spun ribbon annealed at 850 C shows that the c-phase, M23B6 boride, and amorphous phase no longer exist and that the structure is composed of a-Fe and different borides, namely, M2B, M3B2, MB and MB2. This result indicates that during crystallization, poor-boron phases are firstly formed, such as M23B6, because less diffusion is necessary to achieve their chemical composition. Increasing temperature and consequently diffusion, boron is capable of diffusing and concentrating, forming richer-boron phases such as M3B2, M2B, MB and MB2. The electron diffraction pattern of the annealed (at 850 C) ribbon presented in Fig. 7 (c) shows that the alloy is fully crystallized. The crystallites formed after such heat treatment are larger than 100 nm as can be seen by TEM images in Fig. 7(a) and (b). 3.2. Corrosion resistance Polarization curves in chloride-rich acidic (pH 3 and 5.5) and alkaline (pH 10) media of the Fe68Cr8Mo4Nb4B16 alloy processed in the different ascribe conditions are shown in Fig. 8. Table 3 summarizes the values of the corrosion potential (Ecorr) and of the corrosion current density (icorr). Fully amorphous ribbons (as melt-spun) exhibit outstanding corrosion resistance in all tested conditions, as demonstrated by the noblest Ecorr values, negligible values of icorr, between 107and 106 A/cm2, and a well-defined passivation plateau at low current density levels, between 106 and 105 A/cm2. Indeed, amorphous Fe-based alloys with relatively low Cr contents (<10 wt%) have been reported to be extremely corrosion-resistant in chloride-rich electrolytes [24,31,32], with properties comparable and even better to than high-performance austenitic stainless steel grades, such as the 316L. The quick formation and growth of a very stable passivating film in Fe-based amorphous alloys containing corrosion-resistant alloying elements such as Cr are attributed to the elevated reactivity of the alloy’s surface. Being more metastable and homogeneous than their crystalline equivalent, the surface of amorphous alloys undergoesa rapid selective dissolution of elements such as iron with the concomitant enrichment of chromium and
Fig. 7. TEM images of the Fe68Cr8Mo4Nb4B16 melt-spun ribbon heat-treated at 850 C (a) bright-field, (b) dark-field, and (c) selected-area electron diffraction pattern.
6
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra Table 3 Ensemble of the electrochemical parameters from the potentiodynamic polarization curves in Fig. 8. Electrolyte
Sample
0.6 M NaCl pH 3.0
As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot As-melt spun Annealed 620 Annealed 700 Annealed 850 As-cast ingot
0.6 M NaCl pH 5.5
0.6 M NaCl pH 10.0
Fig. 8. Potentiodynamic polarization curves of the Fe68Cr8Mo4Nb4B16 samples exposed to chloride-rich (a) and (b) acidic and (c) alkaline media.
molybdenum, enabling the formation of a dense, adherent, and protective oxygen-rich Cr- and Mo-compounds [33]. Interesting to note the presence of spikes of current density upon anodic polarization of the amorphous ribbons, which can be
C C C
C C C
C C C
Ecorr (mVSCE)
icorr (A/cm2)
241 284 240 475 604 145 117 260 291 378 178 198 222 255 390
1.2 2.2 2.2 4.2 3.8 7.5 2.4 2.8 4.9 7.5 1.7 1.4 2.3 3.1 1.1
106 106 106 104 104 107 107 106 105 105 107 106 106 105 104
ascribed to metastable pits. The frequency and the intensity of the metastable pitting occurrence seem to be more pronounced with increasing alkalinity. Molybdenum addition in stainless steels is recognized to increase the resistance against pitting corrosion in a chloride-rich acidic environment. This element is even considered to calculate the so-called pitting resistance equivalent number in stainless steels (PREn ¼ %Cr þ 3.3%Mo þ 16%N) [34]. However, studies of Mo-containing stainless steels in chloride-rich alkaline electrolytes have shown unexpected results [35,36], in which the addition of molybdenum did not improve the localized corrosion resistance of some stainless steels in alkaline medium. Despite the occurrence of metastable pits upon anodic polarization, it is worth to highlight that no stable pitting corrosion was observed even for polarization as high as þ1000 mV relative to the Ecorr. The spun ribbon heat-treated at 620 C displayed similar Ecorr and slightly superior icorr values compared to those of the fully amorphous samples. However, the appearance of a dissolution peak followed by a passivation plateau with associated higher current density is seen after annealing the samples at 620 C, especially for corrosion in alkaline conditions. Cr-depleted zones are formed upon crystallization of the amorphous alloys, representing preferential regions for corrosion. With small crystalline fraction, in this case c-phase and M23B6phases, the preferential dissolution of the samples annealed at 620 C induces a roughened surface from which a passive film forms upon anodic polarization. This passive film is highly protective against pitting corrosion, as highlighted by its stability greater than þ1000 mV. However, due to the prior preferential dissolution and consequent surface roughening, this film is less efficient than that formed on the fully amorphous ribbons. As the heat treatment temperature increases, the amorphous fraction decreases, and other crystalline phases appear. As discussed before, the samples annealed at 700 C exhibits a remaining amorphous phase and, besides the c-phase and M23B6 crystals, it also contains a-Fe. As a result, compared to the annealed sample at 620 C, the Ecorr decreases, and the icorr increases, but with comparable current density values at the passivation plateau. Although less resistant than the passivating film formed on the amorphous sample, annealing at 620 C and 700 C still enabled passivation with relatively low associated current density. The satisfactory passivation ability even with the presence of crystals has been ascribed to the blockage of the preferential dissolution by the remaining corrosion-resistant amorphous phase because of the small size of the crystals and, primarily, due to the lack of the percolation among them [28]. This suggests that, after the initial dissolution of the crystals, the surface is likely to be formed only by
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
7
Fig. 9. SEM micrographs, backscattered electron, of the surface after potentiodynamic polarization measurements of: a) as-spun ribbon, b) ribbon heat-treated at 620 C, c) ribbon heat-treated at 700 C, and d) ribbon heat-treated at 850 C, and e) ingot produced by arc-melting; (e) SEM micrograph, secondary electron, of the arc-melted Fe68Cr8Mo4Nb4B16 crystalline alloy to highlight the extended corrosion damage after corrosion testing.
the remaining amorphous phase that enables the passive film formation. Nonetheless, ribbons annealed at 850 C did not display the excellent corrosion resistance observed for amorphous ribbons in acidic and alkaline chloride-rich media. Compared to the fully amorphous ribbons, the annealed ones present icorr values up to 2 order of magnitudes superior (105 against 107, respectively). As the crystallization progresses, a more heterogeneous structure is formed with an advanced chemical partitioning phenomenon. This can be verified by the coexistence of different phases after annealing at 850 C. Also, corrosion susceptible crystals forming a percolated morphology induce the dissolution through the material, causing the absence of an effective passive film formation, i.e. plateau with high current density values. The detrimental aspect of advanced crystallization is highlighted by the polarization curves of as-cast ingots that exhibit icorr values between 104 and 105A/cm2, which are up to 3 orders of magnitude higher than the 107 and 106A/cm2 values of icorr displayed for the amorphous alloys of the same composition and the absence of passivation plateau. Fig. 9 shows the surface of the samples after the potentiodynamic polarization measurements. Almost no corrosion products
are seen at the surface of the as-spun ribbon and the ribbons heattreated at 620 C, Fig. 9a and b, respectively. As both samples presented negligible corrosion current density, low current density along the passivation plateau, and no transpassivation event, the corrosion damage was insignificant. Corrosion products, even if small, are nevertheless detected after testing the ribbons heattreated at 700 C, Fig. 9c, indication of the transition of corrosionresistant/corrosion susceptible microstructure due to the formation of phases more prone to corrode. The corrosion loss upon crystallization is confirmed by the significant presence of corrosion products at the surface of the ribbons heat-treated at 850 C, Fig. 9d, and confirmed by the severely corroded surface of the arcmelted ingot, Fig. 9e and f. Indeed, the ultimate fate of the highly corrosion-resistant fully-amorphous ribbons at the completion of the crystallization seems to be the complete loss of the corrosion resistance given the presence of multiple and enlarged phases that are likely to induce preferential dissolution and the absence of any protective layer. The general trends clearly point out to the outstanding corrosion resistance of the new Fe68Cr8Mo4Nb4B16 glassy alloy in chloriderich acidic and alkaline media. The fully amorphous nature and
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
8
the presence of corrosion-resistant alloying elements such as chromium and molybdenum drive the formation of a highly stable passivating film covering the active bare metal surface. Partially crystallized samples heat-treated at 620 C and 700 C still allow the formation of a resistant passive film due to the non-percolated morphology of the crystals embedded within the corrosionresistant amorphous matrix. In practice, this means that this alloy can be applied by coating processes, such as HVOF, since the alloy temperature, after amorphization, does not increase above 700 C. Crystalline Fe68Cr8Mo4Nb4B16 annealed ribbons, and as-cast ingots did not display the same excellent corrosion resistance due to the partitioning of elements during crystallization, especially chromium, resulting in the structural inhomogeneity that preferentially triggers and sustains pitting corrosion along the percolated crystalline network.
4. Conclusions Fully amorphous Fe68Cr8Mo4Nb4B16 alloy exhibited excellent corrosion resistance in chloride rich electrolyte and was attributed to the formation of a highly protective passivating film. Metastable pitting was seen, especially in alkaline conditions; however, no transpassivation event occurred even for anodic polarization as large as þ1000 mV relative to the corrosion potential. Small corrosion resistance loss was found in the first crystallization events. This was attributed to the reduced chemical differences of the first crystals coming from the amorphous phase and their non-percolated nature. As the crystallization progressed, several different crystalline phases appeared, forming a more continuous crystalline network prone to corrode and, therefore, the corrosion resistance started to be severally compromised.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement ~o: Conceptualization, Methodology, Investigation, D.D. Coimbra Formal analysis, Visualization, Writing - original draft, Writing review & editing. G. Zepon: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing, Supervision. G.Y. Koga: Conceptualization, Methodology, Investigation, Formal analysis, Visualization, Writing - original draft, Writing - review & editing. D.A. rez: Methodology, Investigation, Writing - review & Godoy Pe editing. F.H. Paes de Almeida: Methodology, Investigation, Writing - review & editing. V. Roche: Methodology, Validation, Formal analysis, Writing - review & editing. J.-C. Lepretre: Methodology, Validation, Formal analysis, Writing - review & editing. A.M. Jorge: Methodology, Validation, Formal analysis, Writing - review & editing. C.S. Kiminami: Conceptualization, Formal analysis, Writing - review & editing, Funding acquisition. C. Bolfarini: Conceptualization, Formal analysis, Writing - review & editing, Funding acquisition. A. Inoue: Conceptualization, Formal analysis, Writing review & editing. W.J. Botta: Conceptualization, Validation, Formal analysis, Writing - original draft, Writing - review & editing, Supervision, Funding acquisition.
Acknowledgments The authors are grateful for the financial support granted by ~o de AperfeiçoaFAPESP (process n 2013/05987-8), Coordenaça mento de Pessoal de Nível Superior - Brasil (CAPES) - Finance code 001 and CNPq. The authors are also grateful for electron microscopy facilities from the Laboratory of Structural Characterization of ~o Carlos (LCE/DEMa/UFSCar). Federal University of Sa
References [1] M. Ashby, A. Greer, Metallic glasses as structural materials, Scripta Mater. 54 (2006) 321e326, https://doi.org/10.1016/j.scriptamat.2005.09.051. [2] C. Suryanarayana, A. Inoue, Bulk Metallic Glasses, second ed., 2017, https:// doi.org/10.1201/9781315153483. [3] K. Asami, S.-J. Pang, T. Zhang, A. Inoue, Preparation and corrosion resistance of Fe-Cr-Mo-C-B-P bulk glassy alloys, J. Electrochem. Soc. 149 (2002), B366, https://doi.org/10.1149/1.1490537. [4] C.A.C. Souza, D.V. Ribeiro, C.S. Kiminami, Corrosion resistance of Fe-Cr-based amorphous alloys : an overview, J. Non-Cryst. Solids 442 (2016) 56e66, https://doi.org/10.1016/j.jnoncrysol.2016.04.009. [5] C. Suryanarayana, A. Inoue, Iron-based bulk metallic glasses, Int. Mater. Rev. 58 (2013) 131e166, https://doi.org/10.1179/1743280412Y.0000000007. [6] A. Inoue, X.M. Wang, Bulk amorphous FC20 (Fe-C-Si) alloys with small amounts of B and their crystallized structure and mechanical properties, Acta Mater. 48 (2000) 1383e1395, https://doi.org/10.1016/S1359-6454(99)003948. [7] H. Li, S. Yi, Fabrication of bulk metallic glasses in the alloy system FeeCeSieBePeCreMoeAl using hot metal and industrial ferro-alloys, Mater. Sci. Eng. A (2007) 449e451, https://doi.org/10.1016/j.msea.2006.02.262, 189e192. rdos, L.K. Varga, J. Lendvai, Thermal stability and glass [8] M. Shapaan, A. Ba forming ability of cast ironephosphorus amorphous alloys, Mater. Sci. Eng. A 366 (2004) 6e9, https://doi.org/10.1016/j.msea.2003.08.053. [9] J. Cheney, K. Vecchio, Development of quaternary Fe-based bulk metallic glasses, Mater. Sci. Eng. A 492 (2008) 230e235, https://doi.org/10.1016/ j.msea.2008.03.019. [10] G. Koga, L. Otani, A. Silva, V. Roche, R. Nogueira, A. Jorge, C. Bolfarini, C. Kiminami, W. Botta, Characterization and corrosion resistance of boroncontaining-austenitic stainless steels produced by rapid solidification techniques, Materials (Basel) 11 (2018) 2189, https://doi.org/10.3390/ ma11112189. [11] J. Li, L. Yang, H. Ma, K. Jiang, C. Chang, J.Q. Wang, Z. Song, X. Wang, R.W. Li, Improved corrosion resistance of novel Fe-based amorphous alloys, Mater. Des. 95 (2016) 225e230, https://doi.org/10.1016/j.matdes.2016.01.100. [12] H. Xia, Q. Chen, C. Wang, Evaluating corrosion resistances of Fe-based amorphous alloys by YCr/Mo values, J. Rare Earths (2017), https://doi.org/ 10.1016/S1002-0721(17)60926-8. [13] A. Zarebidaki, A. Seifoddini, T. Rabizadeh, Corrosion resistance of Fe 77 Mo 5 P 9 C 7.5 B 1.5 in-situ metallic glass matrix composites, J. Alloys Compd. 736 (2018) 17e21, https://doi.org/10.1016/j.jallcom.2017.11.138. [14] Y. Zhang, B. Song, J. Ming, Q. Yan, M. Wang, C. Cai, C. Zhang, Y. Shi, Corrosion mechanism of amorphous alloy strengthened stainless steel composite fabricated by selective laser melting, Corrosion Sci. (2019), https://doi.org/ 10.1016/j.corsci.2019.108241. [15] J. Ding, A. Inoue, Y. Han, F.L. Kong, S.L. Zhu, Z. Wang, E. Shalaan, F. Al-Marzouki, High entropy effect on structure and properties of (Fe,Co,Ni,Cr)-B amorphous alloys, J. Alloys Compd. 696 (2017) 345e352, https://doi.org/ 10.1016/j.jallcom.2016.11.223. [16] F. Wang, A. Inoue, F.L. Kong, S.L. Zhu, E. Shalaan, F. Al-Marzouki, W.J. Botta, C.S. Kiminami, Y.P. Ivanov, A.L. Greer, Formation, stability and ultrahigh strength of novel nanostructured alloys by partial crystallization of highentropy (Fe 0.25 Co 0.25 Ni 0.25 Cr 0.125 Mo 0.125 ) 86‒89 B 11‒14 amorphous phase, Acta Mater. (2019), https://doi.org/10.1016/ j.actamat.2019.03.019. [17] W.H. Wang, Roles of minor additions in formation and properties of bulk metallic glasses, Prog. Mater. Sci. 52 (2007) 540e596, https://doi.org/10.1016/ j.pmatsci.2006.07.003. [18] Z.P. Lu, C.T. Liu, Role of minor alloying additions in formation of bulk metallic glasses: a review, J. Mater. Sci. 39 (2004) 3965e3974, https://doi.org/10.1023/ B:JMSC.0000031478.73621.64. [19] C.T. Liu, Z.P. Lu, Effect of minor alloying additions on glass formation in bulk metallic glasses, Intermetallics 13 (2005) 415e418, https://doi.org/10.1016/ j.intermet.2004.07.034. [20] W.J. Botta, J.E. Berger, C.S. Kiminami, V. Roche, R.P. Nogueira, C. Bolfarini, Corrosion resistance of Fe-based amorphous alloys, J. Alloys Compd. 586 (2014) S105eS110, https://doi.org/10.1016/j.jallcom.2012.12.130. [21] S.J. Pang, T. Zhang, K. Asami, A. Inoue, Bulk glassy Fe-Cr-Mo-C-B alloys with high corrosion resistance, Corrosion Sci. 44 (2002) 1847e1856, https:// doi.org/10.1016/S0010-938X(02)00002-1. [22] C.A.C. Souza, M.F. de Oliveira, J.E. May, W.J. Botta, N.A. Mariano, S.E. Kuri,
~o et al. / Journal of Alloys and Compounds 826 (2020) 154123 D.D. Coimbra
[23]
[24]
[25]
[26]
[27]
[28]
C.S. Kiminami, Corrosion resistance of amorphous and nanocrystalline FeeMeB (M¼Zr, Nb) alloys, J. Non-Cryst. Solids 273 (2000) 282e288, https:// doi.org/10.1016/S0022-3093(00)00174-5. P.H. Tsai, A.C. Xiao, J.B. Li, J.S.C. Jang, J.P. Chu, J.C. Huang, Prominent Fe-based bulk amorphous steel alloy with large supercooled liquid region and superior corrosion resistance, J. Alloys Compd. 586 (2014) 94e98, https://doi.org/ 10.1016/j.jallcom.2013.09.186. G.Y. Koga, R.P. Nogueira, V. Roche, A.R. Yavari, A.K. Melle, J. Gallego, C. Bolfarini, C.S. Kiminami, W.J. Botta, Corrosion properties of FeeCreNbeB amorphous alloys and coatings, Surf. Coating. Technol. 254 (2014) 238e243, https://doi.org/10.1016/j.surfcoat.2014.06.022. G.Y. Koga, R. Schulz, S. Savoie, A.R.C. Nascimento, Y. Drolet, C. Bolfarini, C.S. Kiminami, W.J. Botta, Microstructure and wear behavior of Fe-based amorphous HVOF coatings produced from commercial precursors, Surf. Coating. Technol. 309 (2017) 938e944, https://doi.org/10.1016/ j.surfcoat.2016.10.057. G.Y. Koga, A.M. Jorge Junior, V. Roche, R.P. Nogueira, R. Schulz, S. Savoie, A.K. Melle, C. Loable, C. Bolfarini, C.S. Kiminami, W.J. Botta, Production and corrosion resistance of thermally sprayed Fe-based amorphous coatings from mechanically milled feedstock powders, Metall. Mater. Trans. A 49 (2018) 4860e4870, https://doi.org/10.1007/s11661-018-4785-y. Y. Guo, G.Y. Koga, A.M. Jorge, S. Savoie, R. Schulz, C.S. Kiminami, C. Bolfarini, W.J. Botta, Microstructural investigation of Fe-Cr-Nb-B amorphous/nanocrystalline coating produced by HVOF, Mater. Des. 111 (2016) 608e615, https://doi.org/10.1016/j.matdes.2016.09.027. M.J. Duarte, A. Kostka, J.A. Jimenez, P. Choi, J. Klemm, D. Crespo, D. Raabe, F.U. Renner, Crystallization, phase evolution and corrosion of Fe-based metallic glasses: an atomic-scale structural and chemical characterization study, Acta Mater. 71 (2014) 20e30, https://doi.org/10.1016/
9
j.actamat.2014.02.027. [29] M.J. Duarte, J. Klemm, S.O. Klemm, K.J.J. Mayrhofer, M. Stratmann, S. Borodin, a H. Romero, M. Madinehei, D. Crespo, J. Serrano, S.S.A. Gerstl, P.P. Choi, D. Raabe, F.U. Renner, Element-resolved corrosion analysis of stainless-type glass-forming steels, Science 341 (2013) 372e376, https://doi.org/10.1126/ science.1230081. [30] L. Yijian, H. Jian, Borides in microcrystalline Fe-Cr-Mo-B-Si alloys, J. Mater. Sci. 26 (1991) 2833e2840, https://doi.org/10.1007/BF02387759. [31] M. Madinehei, P. Bruna, M.J. Duarte, E. Pineda, J. Klemm, F.U. Renner, Glassformation and corrosion properties of FeeCreMoeCeB glassy ribbons with low Cr content, J. Alloys Compd. 615 (2014) S128eS131, https://doi.org/ 10.1016/j.jallcom.2013.12.245. [32] K. Hashimoto, What we have learned from studies on chemical properties of amorphous alloys? Appl. Surf. Sci. 257 (2011) 8141e8150, https://doi.org/ 10.1016/j.apsusc.2010.12.142. [33] H. Habazaki, Corrosion of amorphous and nanograined alloys, in: Shreir’s Corros, 2010, pp. 2192e2204, https://doi.org/10.1016/B978-0444527875.00107-4. [34] R.W. Revie, H.H. Uhlig, Corrosion and Corrosion Control, fourth ed., WileyInterscience, New Jersey, 2008. [35] T.J. Mesquita, E. Chauveau, M. Mantel, N. Kinsman, V. Roche, R.P. Nogueira, Lean duplex stainless steels-The role of molybdenum in pitting corrosion of concrete reinforcement studied with industrial and laboratory castings, Mater. Chem. Phys. 132 (2012) 967e972, https://doi.org/10.1016/ j.matchemphys.2011.12.042. [36] T.J. Mesquita, E. Chauveau, M. Mantel, N. Kinsman, R.P. Nogueira, Anomalous corrosion resistance behavior of Mo-containing SS in alkaline media: the role of microstructure, Mater. Chem. Phys. 126 (2011) 602e606, https://doi.org/ 10.1016/j.matchemphys.2011.01.013.