Fabrication and Characterization of Zirconia Coating on the API5L Steel
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Fabrication and Characterization of Zirconia Coating on the API5L Steel M. Jafaria and M. Kalantara, * aDepartment
of Material Engineering, Yazd University, Yazd, Iran *e-mail: [email protected]
Received May 25, 2019; revised March 29, 2020; accepted April 3, 2020
Abstract—Four layers of zirconia coating were applied on surface of API5 steel samples by sol-gel processing using zirconium isopropoxide precursor. In the first group of samples, after each layer of coating and for the second group after four layer coating, heat treatment of calcination and sintering is carried out at the desired temperature (350–550°C). X-ray diffraction and differential thermal analysis were used to evaluate the physicochemical reaction and phase changes caused by heat treatment of obtained gel. Microstructural features and corrosion resistance of coated samples were determined by SEM observation, microhardness and electrochemical corrosion testing respectively. The results show that by increasing of sintering temperature from 350 to 550°C, structure evolve from amorphous to crystalline state. For the first group of samples, sintering at 450°C and for the second group, sintering at 550°C, offer a more homogenous microstructure and higher resistance of corrosion. Keywords: sol-gel, zirconia coating, sintering temperature, resistance corrosion, microstructural characterization, composition phase DOI: 10.1134/S2070205120050159
1. INTRODUCTION The protection of metals in corrosive environments by ceramic coatings was promised by increasing of refractoriness and corrosion, wear and oxidation resistance [1]. Zirconia, borosilicate, alumino-silicate and ceria coatings have been extensively studied as barriers against oxidation on metal substrates. Zirconia has the advantage of a high toughness, mechanical strength, chemical inertness and high thermal stability and low thermal expansion coefficient 12–14 × 10−6 K−1, which is very close to that of many metals and high temperature alloys) [2, 3]. The stable crystalline form of zirconium oxide at room temperature is monoclinic which changes to tetragonal structure between 950 and 1250°C and cubic at 2370°C [4]. Several techniques including physical vapor deposition (PVD) [5], chemical vapor deposition (CVD) [6], electro-deposition [7], pyrolysis spraying [8], plasma spraying [9] and sol–gel process [10–14] have been used for applying of ZrO2 coatings layer on different metallic substrates such as magnesium alloys, brass, carbon steels and stainless steels. The sol–gel process is one of the most promising methods, because it offers many advantages for the fabrication of coatings, including excellent control of compositional modification and microstructural characterization, a process of low temperature, simplicity and being inexpensive method [1].
Baron et al. [13] obtained ZrO2 coating on 1.25Cr0.5Mo steel surface by sol–gel method and observed fragments of the coating on the surface increasing the oxidation rate of the substrate. By using of basic cata
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