Resistance of different Zn coatings at elevated temperature air environments

Abstract

In this work, the structure and oxidation behaviour of three different zinc coatings were examined. The coatings were formed with hot dip galvanizing, pack cementation and thermal spray methods. Three different oxidation conditions were selected for the tests, which correspond to low, medium and intensive oxidation conditions. The oxidized samples were examined by scanning electron microscopy and X-ray diffraction. Results showed that the thermal spray coatings are far more susceptible than the others and suffer from extreme oxidation because of the porous net existing in the coating, which provides diffusion paths to oxygen. Hot dip and pack coatings were proved more resistant under the same exposure conditions, mainly due to the presence of different Fe-Zn phases in their structure and their morphological homogeneity.

Application of X-rays Diffraction for Identifying Thin Oxide Surface Layers on Zinc Coatings

“…The GI-XRD diffractograms for both 5 • and 1.5 • were similar (Figure 8b,c). This is attributed to the characteristic rough surface morphology of such coatings [13,14,16]. It also important to mention that as the Zn diffraction peaks are very strong, low intensity peaks arising from very small concentrations of Zn compounds could not be identified in the pattern.…”

“…The crucibles were then inserted in an Ar purged electric furnace at 400 • C for 60 min. As a result, the formed coating had a similar thickness to the galvanized coating but different chemical composition-Consisting only of Fe-Zn phases [16,41,43]. Finally, for the wire flame thermal spraying, the substrates were previously degreased with a 10% HCl solution and then sandblasted in order to create the necessary roughness for coating adhesion.…”

“…The penetration depth can be narrowed to the top surface layers using grazing incidence X-ray geometry (GI-XRD). Thus, controlling the incidence angle of the X-ray beam enables the overall identification of the composition of the coating as well as the precise stoichiometry of the surface layers [16,17].…”

“…This work presents the results of a detailed theoretical analysis of zinc coatings based on grazing incidence X-ray diffraction technique. The samples grown using the hot-dip galvanizing process [1][2][3][4]8,13,14,16,[18][19][20], chemical vapor deposition by pack cementation [5][6][7][8]13,14,16,[21][22][23][24][25] and wire flame thermal spray [9][10][11][12][13][14]16,[26][27][28] were examined using scanning electron microscopy (SEM), Bragg-Brentano and grazing incidence XRD, with specific interest in the composition of the thin zinc oxide layer formed on the surface. The X-rays theoretical penetration depth for all three types of sample was also calculated and compared to the experimental results.…”

Fabrication of High Temperature Oxidation Resistance Nanocomposite Coatings on PEO Treated TC21 Alloy

“…However, its widespread application in high temperature parts of the aircraft are still limited due to poor high temperature oxidation resistance. To date, various coating methods have been studied to improve the high temperature oxidation resistance, including electron-beam physical vapor deposition [6], plasma spraying [7], hot dipping [8], laser cladding [9], arc ion plating [10], magnetron sputtering [11], sol-gel [12], and plasma electrolytic oxidation (PEO) [13].…”