Rietveld-Based Quantitative Phase Analysis of Sherardizing Coatings
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ORIGINAL ARTICLE
Rietveld-Based Quantitative Phase Analysis of Sherardizing Coatings Yuncong Zhong1 • Xiaobo Li1,2
•
Junbi Long1
Received: 31 August 2019 / Accepted: 25 August 2020 Ó The Indian Institute of Metals - IIM 2020
Abstract The zinc coatings obtained by sherardizing consist of three zinc-rich Fe–Zn phases (c, d and f) and the properties of coatings are influenced by the contents of three phases. The quantitative phase analysis of coatings is generally characterized by the metallographic method. Because this method is a destructive testing. So a nondestructive testing method is required to quantify the zinc coating. X-ray diffraction in combination with the Rietveld method was used to quantify their proportion in the zinc coatings. The quantitative phase analysis of sherardizing coatings under heat treatment of 360 °C and 375 °C for 2 h was carried out by GSAS software. The results show that the values of Rp and Rwp are below 5%. The quantitative results obtained by the Rietveld method are almost consistent with the experimental values, and the errors are less than 8.2%. In order to improve the success rate of quantitative refinement, the c, d and f phases were successfully prepared separately by the sintering process and their structural models were refined by the Rietveld method. The acquired crystallographic parameters were used as the initial structural model for quantitative refinement of coatings. Keywords Quantitative analysis X-ray diffraction Fe–Zn phase Sherardizing Rietveld method
& Xiaobo Li [email protected] 1
School of Materials Science and Engineering, Xiangtan University, Xiangtan 411100, China
2
Key Laboratory of Materials Design and Preparation Technology of Hunan Province, Xiangtan 411100, China
1 Introduction Zinc coatings act as barrier protection and galvanic protection to steel against corrosion. There are a variety of zinc coating technologies, such as hot dip galvanizing, electroplating, sherardizing or thermal spraying. The sherardizing has great advantages such as process simplification, low zinc consumption and energy saving. The zinc coating obtained by sherardizing has strong bonding strength and high corrosion resistance [1]. Contrast to hot dip galvanizing, sherardizing can obtain a uniform diffusion bonded coating [2]. The zinc coating by sherardizing consists of three Fe–Zn intermetallic phases such as the c phase, d phase and the f phase, without g, pure zinc phase. It can serve as a better sacrificial anode protection layer since the potential difference between the coating by sherardizing and the substrate is lower than the potential difference between the pure zinc and the substrate [3–6]. The c phase next to the substrate is Fe/Zn alloy (Fe11Zn40) containing 17–19.5 wt% Fe, the d phase in the middle of the coating is Fe/Zn alloy (FeZn10) containing 7–11.5 wt% Fe, and the outermost f phase is Fe/Zn alloy (FeZn13) containing 5–6.2 wt% Fe [7]. Theses intermetallic phases vary not only in composition and morphology of the crystals, but also significant
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