Simultaneously enhancing wear and corrosion resistance of HVAF-sprayed Fe-based amorphous coating from Mo clad feedstock

https://doi.org/10.1016/j.jmatprotec.2021.117465Get rights and content

Abstract

High-performance Fe-based amorphous (FA) composite coating was successfully fabricated on 304 stainless steels via employing a novel feedstock of FA powders partially clad with molybdenum (Mo). The microstructure, tribological and corrosion behavior of FA/Mo composite and pure FA coating coating were comparatively investigated. Experimental results show that with 20 vol. % Mo incorporation, FA/Mo composite coating became remarkably denser with porosity of 0.46 ± 0.12 % and attained a 35 % increase in fracture toughness. As a result, compared to the pure FA coating, superior wear resistance including lower specific wear rate and coefficient of friction (COF) were achieved in the composite coating. In addition, the dominant wear mechanism of coating changed from abrasive wear to oxidative wear. Furthermore, due to its favorable amorphous composite microstructure with less pores and more hydrophobic surface, the FA/Mo coating simultaneously obtained better corrosion resistance. The present findings may provide a valuable strategy to prepare FA protective coating for industrial application.

Introduction

Till now, numerous thermal sprayed coatings based on alloys of metal (Feizabadi et al., 2018), amorphous (Zhang et al., 2012) or high-entropy (Liu et al., 2021a, 2021b), ceramics (Qin et al., 2018), cermets (Thakur and Arora, 2020) and quasicrystalline (Xiao et al., 2021) were exploited to prolong the service life of components from severe wear, corrosion and cyclic oxidation environments. Among them, owing to the long range disorder of atom, Guo et al. (2020) proposed that Fe-based amorphous alloys possess prominent advantages in strength, hardness, chemical properties, material cost and corrosion resistance, which render them broad prospect in ocean engineering. Nowadays, some researchers such as Wang et al. (2020) developed Fe-based amorphous (FA) coating with thickness in micrometre range to overcome the intrinsic brittleness at room temperature and broaden their industrial application.

High velocity air fuel (HVAF) spraying is a newly emerged deposition process which combusts a mixture of compressed air and fuel gas. Besides, it has relatively low temperature (<1900 °C) and superhigh velocity (>1000 m/s) for the in-flight particle. Thus, HVAF was demonstrated to be an effective technique in fabricating Fe-based coatings with denser microstructure (Liu et al., 2021a, 2021b), less oxide contents (Guo et al., 2011), higher level of compressive residual stress (Sadeghimeresht et al., 2017) and bonding strength (Wang et al., 2016).

So far, extensive researches have investigated the effects of deposition methods, size of spraying powders (Zhang et al., 2014), spray distance (Liang et al., 2018), kerosene flux (Zhang et al., 2017), heat input (Kumar et al., 2019), surface modification of feedstock (Wang et al., 2015), second phase addition and subsequent processing (Liu et al., 2019) on the tribological and corrosion behavior of FA coatings. Among them, introducing second phase has been proved to be promising in enhancing the coating properties. For example, Zhou et al. (2015) reported that reinforcing FA matrix with 4−16 vol. % 316 L stainless steel powders could attain a 73 % increase in bonding strength and maximum fracture work of 310 J/m2. Besides, incorporating ceramics like B4C (Movahedi, 2017), WC/12Co (Terajima et al., 2010), TiN (Chu et al., 2019a, 2019b) or Al2O3-TiO2 (Chu et al., 2019a, 2019b) into the FA coating could significantly improve their tribological performance. Nevertheless, the strengthening effect of above methods is greatly determined by the size, amount, and distribution of reinforced phases. And added ceramics could lead to large-scale incompatible phase interfaces, which poses great challenge to obtain dense and uniform microstructure. Therefore, novel type of reinforced phases needs to be developed for future requirements.

Enlighten by the literature review, molybdenum (Mo) with high toughness and favorable thermal conductivity may be potential to improve the microstructure and fracture toughness of FA coating. Jiang et al. (2012) have sprayed feedstock of FA powders mixed with 9−23 wt.% Mo-based alloy, and reported a better corrosion resistance due to the porosity reduction and high stability of passive film. However, up to now, a microstructural design that integrating pure Mo into FA coating has not been attempted. And the influence of Mo on the microstructure, tribological and corrosion behavior of FA coating is not comprehensively investigated.

Thus, in this work, Mo were initially clad on FA powders via two mixing process, and then this composite feedstock were deposited on 304 stainless steels via HVAF technique. Along with pure FA coating, the microstructure, tribological and corrosion behavior of as-prepared coatings were comparatively investigated. In addition, the underlying wear and corrosion mechanisms were further discussed.

Section snippets

Coatings preparation

Gas atomized Fe-based amorphous powders with the composition of Fe52Cr26Mo17C2.5B2.1Si0.4 (13−55 μm, Guangzhou WanDun Co. Ltd.) and commercial Mo powders (1−3 μm, Shanghai NaiOu Co. Ltd.) were employed as the starting materials. To clad the Mo on the FA powders, the raw amorphous powders were firstly blended with 20 vol. % (equal to 24.5 wt. %) Mo powders by an automatic mixer for 2 h, followed by milling in a planetary ball mill (KXQM-4 L, Nanjing) with GCr15 steel balls in argon atmosphere to

Starting materials

The SEM micrograph, PSD result or XRD pattern of the FA and Mo powders is shown in Fig. 1. Fig. 1a displays that most FA powders had a roundish shape and smooth surface, and their average particle size (see Fig. 1b) was 38.19 μm. As for the raw Mo powders shown in Fig. 1c and d, they were agglomerated with each other with phase composition of pure Mo.

Microstructure of as-milled composite powders

Fig. 2 shows the backscattered SEM micrographs and PSD result of FA/Mo composite powders after mechanical mixing and BM process. Observed from

Discussions

In this study, the wear resistance of FA and FA/Mo coating was dependent on their microhardness, fracture toughness and lubrication state, while the corrosion resistance of the coatings was mainly governed by the coatings defects (such as pore or splat interface), phase composition and wetting behavior.

At the same spraying parameters, the thermal energy of the flame is fixed. Thus, differed from the raw FA feedstocks, the in-flight FA composite feedstocks were clad with high heat-conducted and

Conclusions

High-performance Fe-based amorphous composite coating reinforced with Mo was fabricated on 304 stainless steels via combined two mixing processes and HVAF spraying. The microstructure, tribological and corrosion behavior of pure FA coating and FA/Mo composite coating were comparatively investigated. The main findings are concluded as follows:

  • 1)

    A novel feedstock of FA powders partially clad Mo was successfully prepared to satisfy the requirement of HVAF technique.

  • 2)

    With 20 vol. % Mo incorporation,

CRediT authorship contribution statement

Xiaoqing Liu: Conceptualization, Experiments, Investigation, Formal analysis & Discussion, Writing - original draft; Writing - review & editing, Yaosha Wu: Data curation, Software and Methodology, Zhaoguo Qiu: Supervision, Project Administration, Writing and Editing, Zhengyi Lu: Resources, Visualization and Validation, Shunqiang Yao: Funding, Shiye Zhuo: Experiments, Dechang Zeng: Conceptualization, Funding, Project Administration.

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.

Acknowledgments

This work was supported by the Fundamental Research Funds for the Central Universities, the Natural Science Foundation of Guangdong Province (No. 2018A030313615, 2020A1515010736), the Zhongshan Municipal Science and Technology Program (Platform Construction and innovation Team) (2016F2FC0005), the Research and industrialization of key technology of high efficiency non-oriented electrical steel (191007102629094) and Zhongshan Collaborative Innovation Fund (2018C1001).

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