Enhancement of impact resistance of Fe-based amorphous coating by Al2O3 dispersion

doi:10.1016/j.matlet.2016.02.060

Materials Letters

Volume 171, 15 May 2016, Pages 112-116

https://doi.org/10.1016/j.matlet.2016.02.060 Get rights and content

Highlights

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20% Al₂O₃ particle addition remarkably improves the impact resistance of amorphous coating.
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Al₂O₃ particles absorb impact energy by crack deflection and micro-crack mechanisms.
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Al₂O₃ particles alleviate the stress concentration upon impacting revealed by FEM.
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The composite coating is more corrosion resistant than the monolithic coating after impact.

Abstract

The load-bearing applications of Fe based amorphous coatings are limited due to their poor impact resistance. Here, we have designed an amorphous composite coating reinforced with 20 wt% Al₂O₃ particles that is tougher and more impact resistant than the monolithic amorphous coating. Impact resistance of the coatings was systematically studied by drop-weight impact tests and finite element modelling (FEM). It was found that the hard Al₂O₃ particles in the composite coatings could effectively hinder crack propagation via the formation of micro-cracks inside the Al₂O₃ particles, which absorbs the impact energy. FEM indicates that the Al₂O₃ dispersion acts as the main loading-bearing phase and alleviates the stress concentration in the composite coating, thus suppresses crack initiation and propagation. Furthermore, electrochemical polarization test shows that composite coating remains good corrosion resistance in a 3.5% NaCl solution after impact.

Graphical abstract

Introduction

Fe-based amorphous coatings have currently attracted great attentions due to their high hardness, hydrophobicity, excellent wear- and corrosion-resistance [1], [2], [3], [4], [5], [6], [7], [8], [9]. The unique surface properties make the amorphous coatings good candidates for many applications in industries. However, recent studies revealed that the amorphous coatings exhibited low adhesion and toughness upon dynamic impact due to the intrinsic brittleness of amorphous solid, which has severely restricted their load-bearing applications [10], [11], [12], [13], [14].

To increase the toughness of the amorphous coatings, one promising approach is to introduce a second crystalline phase into amorphous coating and to form amorphous matrix composite coatings. In recent years, designing composite structure has been a hot research topic. Zhou et al. [13] observed that the amorphous composite coating reinforced by stainless steel (SS) particles had a higher fracture resistance as compared to monolithic amorphous coating due to enhanced bonding strength and good deformability of the soft SS particles. However, one problem caused by composite coating is that the addition of metallic reinforcements normally deteriorates the corrosion resistance of amorphous coating. On the other hand, Zhang et al. [14] found that the multilayer structures of Fe-based amorphous coating consisting of alternative amorphous layer and NiCrAl layer exhibits much higher impact resistance. However, such a processing method for the multilayered coatings is complicated and may not be practically applicable to industry. In addition to metallic reinforcements, researchers have attempted to add ceramic phases into the amorphous coatings as the later might not reduce the corrosion resistance of coatings owing to insulation. It has been shown that amorphous composite coatings reinforced with WC-12Co, TiN and B₄C particles have higher bonding strength, friction and wear resistance over the unreinforced amorphous coatings [15], [16], [17], [18]. However, to date, impact behavior as well as the effect of impact on the properties of the amorphous coatings reinforced with ceramic particles has not been well understood.

In this paper, we investigate the impact resistance and corrosion behavior after impact of a newly designed Fe-based amorphous coating reinforced with 20 wt% Al₂O₃ particles. The composite coating exhibits significantly improved impact resistance and corrosion resistance as compared to the monolithic amorphous coating. The finite element modelling was employed to disclose the toughening mechanism of the amorphous composite coating.

Section snippets

Experimental procedure

Gas-atomized amorphous powders (with a size of 33–55 µm) with a nominal composition of Fe₄₈Mo₁₄Cr₁₅Y₂C₁₅B₆ were blended with 20 wt% commercial Al₂O₃ powders (99.9% pure, 33–55 µm) [20] by low energy ball milling and the mixture was used as the feedstock powders. The powders were then deposited on NiCrAl bond layer coated AISI 1045 mild steel substrates by a high velocity oxygen fuel (HVOF) thermal spraying system (the processing parameters were described elsewhere [19]). The structural and

Results and discussion

The structure of as-sprayed coatings was characterized by XRD. As shown in Fig. 1(a), only broad scattering peaks without any evidence of crystalline phases were observed in the coatings with and without addition of Al₂O₃ particles, indicating that the two coatings are of amorphous structure. The disappearance of the crystalline peaks in the composite coating is probably due to the weak x-ray diffraction of Al₂O₃ phase and wrapping effect of amorphous phase [20]. Fig. 1(b) shows the cross

Conclusions

In summary, improving the impact resistance of Fe-based amorphous coating via the addition of Al₂O₃ particles is reported. It was found that the composite coating reinforced with 20 wt% Al₂O₃ is tougher and more impact resistant than the monolithic amorphous coating. This was evidenced by no visible damage in the composite coating after being impacted at the maximum impact energy of 21.2 J. In contrast, clear interface delamination and penetrating cracks occurred in the amorphous coating at the

Acknowledgements

This work was financially supported by the National Nature Science Foundation of China (Grant nos. 51271081, 51301072, 51471074). The authors are also grateful to the Analytical and Testing Center, Huazhong University of Science and Technology for technical assistance.

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Enhancement of impact resistance of Fe-based amorphous coating by Al2O3 dispersion

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgements

Acta Mater.

Intermetallics

J. Non-Cryst. Solids

Corros. Sci.

Surf. Coat. Technol.

J. Mater. Sci. Technol.

Acta Mater.

J. Alloy. Compd.

Surf. Coat. Technol.

J. Alloy. Compd.

Enhancement of impact resistance of Fe-based amorphous coating by Al₂O₃ dispersion