Advances in Materials Science and Engineering

Advances in Materials Science and Engineering / 2017 / Article

Research Article | Open Access

Volume 2017 |Article ID 2703986 |

Viera Homolová, Lucia Čiripová, "Experimental Investigation of Isothermal Section of the B-Cr-Fe Phase Diagram at 1353 K", Advances in Materials Science and Engineering, vol. 2017, Article ID 2703986, 7 pages, 2017.

Experimental Investigation of Isothermal Section of the B-Cr-Fe Phase Diagram at 1353 K

Academic Editor: Pavel Lejcek
Received28 Feb 2017
Accepted20 Apr 2017
Published11 May 2017


The isothermal section of the B-Cr-Fe ternary system was studied experimentally at 1353 K. X-ray diffraction and scanning electron microscopy equipped with EDX analyzer were used for determination of phase equilibria and composition of the coexisting phases in the B-Cr-Fe model alloys after long-term annealing (1500–2205 h). Two iron borides FeB and Fe2B, six chromium borides Cr2B, Cr5B3, CrB, Cr3B4, CrB2, and CrB4 and also iron and chromium solid solutions (α(Fe,Cr), α(Cr,Fe), γ(Fe,Cr)) and β-rhombohedral B were observed in the alloys. High solubilities of the third element in binary borides and no ternary phase were found. Based on the experimental results, isothermal section of the B-Cr-Fe system at 1353 K was determined.

1. Introduction

The knowledge about phase equilibria of the B-Cr-Fe system is important in several fields of materials research. The system is subsystem of various complex alloys, for example, modified ferritic steels for energy industry [13], steels for production abrasive, and corrosion-resistant components [4]. Information about the system is also important for study of boride coatings on various alloys and metals, including iron [5, 6].

Borides of transition metals, including chromium borides, have unique combination of thermal, mechanical, magnetic, and electrophysical properties and are being widely used in atomic power and chemical industry [7, 8].

The B-Cr-Fe system has been experimentally studied by only a few authors. Gorbunov and Bodurjan [9] investigated system at 1373 K after annealing for 320 h and Chepiga and Kuzma [10] at 973 and 1173 K after annealing for 400 and 750 h, respectively. In the works [9, 10], some questionable phases were found. CrB6 boride, found by Gorbunov and Bodurjan [9] and also by Chepiga and Kuzma [10], is not boride, but it is oxyboride as it was later clarified [11]. Besides the phase, Gorbunov and Bodurjan [9] found Cr4B and Cr2B5 phases. The phase that was predicted as Cr2B5 was not observed by any other investigators neither in ternary B-Cr-Fe [10] nor in binary B-Cr system [12]. Regarding the Cr4B phase, it was shown that the phase is orthorhombic Cr2B phase [13]. The phase constitution of the system at 1373 K was investigated also by Gianoglio et al. [14], but, however, only in region up to 50 at% boron.

The present work is focused on experimental study of phase equilibria of the B-Cr-Fe system at 1353 K in the entire composition range after long time annealing within 1500–2205 h that guarantee to achieve equilibrium state.

2. Experimental Procedure

High purity powders of Fe (99.98%), B (99.9%), and Cr (99.99%) were used as input material for the production of twenty B-Cr-Fe alloys. Powders were mixed, pressed into cylindrical pellets at a pressure of 700 MPa, and subsequently melted. The melting was carried out in an argon arc furnace on water cooled copper plate in argon atmosphere of 99.999% purity. The solidified alloys (15 g) were remelted several times in order to achieve good homogeneity. The final chemical compositions of the produced alloys were determined by atomic absorption spectroscopy; see Table 1. The alloys were then sealed into evacuated silica glass tubes with titanium turnings and annealed at 1353 K within 1500–2205 h. After the annealing, the samples were quenched into cold water.

Composition [at.%]AnnealingIdentified phases

17Fe-65B-18Cr1353 K/1848 hCrB2, CrB4, FeB
33Fe-62B-5Cr1353 K/1848 hB, FeB, CrB4
8Fe-56B-36Cr1353 K/1848 hCr3B4, CrB
50Fe-40B-10Cr1353 K/1848 hFe2B, FeB
32Fe-40B-28Cr1353 K/1848 hCrB, FeB, Cr2B
15Fe-40B-45Cr1353 K/1848 hCrB, Cr2B, Cr5B3
15Fe-25B-60Cr1353 K/1848 hCr2B, α(Cr,Fe)
8Fe-10B-82Cr1353 K/1848 hCr2B, α(Cr,Fe)
5Fe-52B-43Cr1353 K/1848 hCrB, Cr3B4
48Fe-10B-42Cr1353 K/1848 hCr2B, α(Fe,Cr)
70Fe-10B-20Cr1353 K/1848 hCr2B, α(Fe,Cr)
8Fe-62B-30Cr1353 K/1848 hCrB2, Cr3B4
10Fe-25B-65Cr1353 K/1848 hCr2B, α(Cr,Fe)
3Fe-35B-62Cr1353 K/1848 hCr2B, Cr5B3
10Fe-38B-52Cr1353 K/1848 hCrB, Cr2B, Cr5B3
37Fe-45B-18Cr1353 K/2205 hFe2B, FeB, Cr2B
23Fe-45B-32Cr1353 K/1500 hCr2B, CrB, FeB
29Fe-51B-20Cr1353 K/1688 hCr3B4, CrB, FeB
20Fe-52B-28Cr1353 K/1688 hCr3B4, CrB, FeB
45Fe-30B-25Cr1353 K/2205 hCr2B, Fe2B, γ(Fe,Cr)

The annealed material was studied by X-ray diffraction (Philips X’Pert Pro) and scanning electron microscopy (JEOL JSM-7000F) equipped with “Thermal FEG” and INCA EDX analyzer. The analyzer enables quantitative analysis for elements above and including atomic number 5 (boron). Backscattered electron image mode of scanning electron microscopy was used to study the alloy microstructure.

3. Results and Discussion

All phases identified by experimental method in alloys are given in Table 1. Two iron borides FeB and Fe2B, six chromium borides Cr2B, Cr5B3, CrB, Cr3B4, CrB2, and CrB4, and also iron and chromium solid solutions (α(Fe,Cr), α(Cr,Fe), γ(Fe,Cr)) and β-rhombohedral B were found in alloys. The borides in the system form at high temperatures. Most of them form from the liquid during production process of the alloys. Following long-term isothermal annealing leads to achievement of equilibrium chemical compositions of the phases. Crystallographic phase data of observed borides are given in Table 2. The CrB4 boride was found in 17Fe-65B-18Cr and 33Fe-62B-5Cr alloys. This phase, known from binary B-Cr system [12], has not been observed in ternary B-Cr-Fe system till now [9, 10]. The Cr2B5 boride that was found by Gorbunov and Bodurjan at 1373 K after annealing for 320 h was not found. No ternary phase was found in the B-Cr-Fe system. It is in accordance with the mentioned literature [9, 10, 14].

PhasePearson symbolSpace groupReference


Figure 1 shows SEM microstructure of the selected alloys. EDX-spectra of the borides in alloys are illustrated on Figure 2. X-ray diffraction patterns of the selected alloys are shown on Figure 3.

Four three-phase equilibria FeB+CrB4+B (Figure 1(d)), FeB+CrB4+CrB2, FeB+CrB2+Cr3B4, and FeB+Cr3B4+CrB (Figure 3(a)) were found in the part of phase diagram with boron content up 50 at.% (Figure 4). There are some differences between phase equilibria presented in this paper and equilibria at 1373 K from work [9], as shown in Table 3. The differences in this part of the phase diagram are connected with the CrB6 and Cr2B5 phases [9]. However, the CrB6 phase, as was mentioned in introduction, is not right determined. The existence of Cr2B5 boride was not confirmed by present experimental results.

[9] [14]

FeB B CrB6
FeB CrB6 Cr2B5
FeB Cr2B5 CrB2
FeB CrB2 Cr3B4
FeB CrB Cr3B4
FeB Fe2B Cr2BFeB Fe2B Cr2B
FeB Cr2B CrBFeB Cr2B CrB
Cr2B Cr5B3 CrBCr2B Cr5B3 CrB
Fe2B α(Fe,Cr) γ(Fe,Cr)Fe2B α(Fe,Cr) γ(Fe,Cr)
Fe2B α(Fe,Cr) Cr2BFe2B α(Fe,Cr) Cr2B
Cr2B Cr4B α(Cr,Fe)

A part of the isothermal section of the phase diagram with boron range 33–50 at.% contains three three-phase equilibria CrB+Cr5B3+Cr2B (Figure 3(c)), FeB+Cr2B+Fe2B, and FeB+CrB+Cr2B (Figure 4). The same three-phase equilibria were found also at 1373 K in the works [9, 14].

Two three-phase equilibria Fe2B+Cr2B+γ(Fe,Cr) (Figure 3(f)) and Cr2B+γ(Fe,Cr)+α(Fe,Cr) are in the iron rich corner of the phase diagram at the temperature 1353 K (Figure 4). About 9 at.% of chromium was found in the γ(Fe,Cr)-phase in 45Fe-30B-25Cr alloy with phase equilibria Fe2B+Cr2B+γ(Fe,Cr). Both Gorbunov and Bodurjan [9] and Gianoglio et al. [14] found Fe2B+Cr2B+α(Fe,Cr) and Fe2B+γ(Fe,Cr)+α(Fe,Cr) equilibria at 1373 K (Table 3), however, with different amount of chromium in the α(Fe,Cr)-phase in Fe2B+Cr2B+α(Fe,Cr) equilibrium, about 35 at% of Cr according to [9] and 18 at% according to [14]. The differences between observed phase fields of the part of isothermal section in the present work at 1353 K and in works [9, 14] at 1373 K indicate that the equilibrium phase fields are changed at temperature from temperature range 1353–1373 K.

All found borides dissolve third element. It is illustrated by EDX-spectra on Figure 2. Cr2B phase has the highest solubility of the third element among all borides in the system. The boride dissolves up to 39 at.% of Fe. The solubility is high also in CrB, FeB, and Fe2B phases. It was found that Fe2B contains up to 15 at.% of chromium and FeB dissolves up to 16 at.% of Cr. The CrB phase dissolves up to 15 at.% of Fe. Besides them, high solubility of iron is observed also in Cr3B4 boride, Figure 2(c), that contains up to 15 at.% of Fe. Various amounts of dissolved iron were measured also in other chromium borides. In particular, Cr5B3 contains up to 6 at.% of Fe, CrB2 dissolves up to 2 at.% of Fe, Figure 2(b), and CrB4 contains up to 7 at.% of Fe, Figure 2(a).

All the mentioned experimental results, that is, equilibrium phase compositions and composition of phases, were used to determine the isothermal section of B-Cr-Fe phase diagram at 1353 K that is shown in Figure 4.

4. Conclusions

In the work, phase equilibria of the B-Cr-Fe model alloys at 1353 K were studied experimentally. The achieved results can be summarized as follows:(i)Two iron borides FeB and Fe2B, six chromium borides Cr2B, Cr5B3, CrB, Cr3B4, CrB2, and CrB4, and also iron and chromium solid solutions (α(Fe,Cr), α(Cr,Fe), γ(Fe,Cr)) and β-rhombohedral B are equilibrium phases in the system at 1353 K.(ii)8 three-phase equilibria were found in the phase diagram at the temperature.(iii)Solubilities of the third element in all binary borides were determined. High solubilities were found in Cr2B, CrB, Cr3B4, FeB, and Fe2B phases.(iv)No ternary phase was found.

Based on the experimental results, isothermal section of the B-Cr-Fe system at 1353 K was established.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.


The present work was supported by Slovak Grant Agency (VEGA) under Grant no. 2/0153/15. Thanks are also due to Dr. P. Repovský for help at production of alloys.


  1. M. Klimenkov, E. Materna-Morris, and A. Möslang, “Boron effect on the microstructure of 9% Cr ferritic-martensitic steels,” Journal of Nuclear Materials, vol. 462, pp. 280–288, 2015. View at: Publisher Site | Google Scholar
  2. H. M. Heo, E. H. Jeong, S. H. Kim, and J. R. Kim, “Comparison between effect of b and n on the microstructure of modified 9Cr-2W steel during aging and creep,” Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, vol. 670, pp. 106–111, 2016. View at: Publisher Site | Google Scholar
  3. L. Falat, V. Homolová, L. Čiripová, P. Ševc, and M. Svoboda, “Ageing effects on microstructure, mechanical properties, and fracture behaviour of 9Cr-1.5Mo-1Co-VNbBN martensitic steel welded joint for high temperature application,” Advances in Materials Science and Engineering, vol. 2017, Article ID 6824385, 14 pages, 2017. View at: Publisher Site | Google Scholar
  4. S. Q. Ma, J. D. Xing, H. G. Fu et al., “Interfacial morphology and corrosion resistance of Fe–B cast steel containing chromium and nickel in liquid zinc,” Corrosion Science, vol. 53, p. 2826, 2011. View at: Google Scholar
  5. A. N. M. Idriss, S. Mridha, and T. N. Baker, “Laser and gtaw torch processing of Fe-Cr-B coatings on steel,” Materials Science and Technology (United Kingdom), vol. 31, no. 3, pp. 355–360, 2015. View at: Publisher Site | Google Scholar
  6. J. Ptačinová, M. Drienovský, M. Palcut, R. Čička, M. Kusý, and M. Hudáková, “Oxidation stability of boride coatings,” Kovove Materialy, vol. 53, no. 3, pp. 175–186, 2015. View at: Publisher Site | Google Scholar
  7. M. Zhong, C. Huang, and C. Tian, “The structural stabilities, mechanical properties and hardness of chromium tetraboride: compared with low-B borides,” International Journal of Modern Physics B, vol. 30, no. 30, Article ID 1650201, 2016. View at: Publisher Site | Google Scholar
  8. S. Wang, X. Yu, J. Zhang et al., “Crystal structures, elastic properties, and hardness of high-pressure synthesized CrB2 and CrB4,” Journal of Superhard Materials, vol. 36, no. 4, pp. 279–287, 2014. View at: Publisher Site | Google Scholar
  9. E. Gorbunov and F. M. Bodurjan, “Phase equilibria in ternary Cr-B-Fe system,” Metalurgija Tverdych Splavov, vol. 16, pp. 172–178, 1976 (Russian). View at: Google Scholar
  10. M. B. Chepiga and J. B. Kuzma, “Fazovyje ravnovesia v sisteme Cr-Fe-B,” Izvestija Vyssich Ucebnych Zavedenij, Chernaja Metalurgija, vol. 3, pp. 127–130, 1970. View at: Google Scholar
  11. P. Rogl, “Cr-B-C (Chromium-Boron-Carbon),” in Phase Diagrams of ternary Metal-Boron-Carbon Systems, G. Effenberg, Ed., pp. 36–52, ASM international, 1998. View at: Google Scholar
  12. E. Campbell and U. R. Kattner, “Assessment of the Cr-B system and extrapolation to the Ni-Al-Cr-B quaternary system,” Calphad, vol. 26, pp. 477–490, 2002. View at: Google Scholar
  13. D. Kotzott, M. Ade, and H. Hillebrecht, “Synthesis and crystal structures of α – and β- modifications of Cr2IrB2 containing 4-membered B4chain fragments, the τ-boride Cr7.9 Ir14.1B6 and orthorhombic Cr2B,” Solid State Sciences, vol. 10, no. 3, pp. 291–302, 2008. View at: Publisher Site | Google Scholar
  14. C. Gianoglio, G. Pradelli, and M. Vallino, “Solid state equilibria in the Cr-Fe-B system at the temperature of 1373K,” Metallurgical Science and Technology, vol. 1-2, pp. 51–57, 1983. View at: Google Scholar
  15. P. Villars, Pearson’s Handbook, The Materials Information Society, Materials Park Ohio, USA, 1997.

Copyright © 2017 Viera Homolová and Lucia Čiripová. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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