Thermal Spray Coatings of Al, ZnAl and Inconel 625 Alloys on SS304L for Anti-Saline Corrosion

Abstract

Stainless steel 304L (SS304L) has been selected as the material for canisters for spent fuel storage from three nuclear power plants in Taiwan. A crucial issue is extending the spent fuel storage safety standards of the canisters. The anti-saline corrosion abilities of three thermal spray coatings (i.e., Al, ZnAl, and 625 Inconel alloys) on the SS304L were evaluated by immersion in 3.5 wt % aqueous NaCl and with 0.025 g/cm2 NaCl deposition at 80 °C and 80% relative humidity (RH) for 1000 h. The pristine thermal spray coatings were examined using the pull-off adhesion test to understand the adhesion strength, and Vickers hardness was measured for the mechanical properties of the three coatings. Confocal laser scanning microscopy (CLSM) was used to identify the porosities of the coatings. Furthermore, the surfaces of the specimens before and after corrosion were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The composition and distribution of the oxide layers formed on the coating surfaces during corrosion were evaluated. Electrochemical measurement was also performed with the polarization method to quantify the corrosion property of the three thermal spray coatings. The results showed that the corrosion rate of Al coating was lowest from the Tafel analysis after the 1000 h corrosion test in 3.5% aqueous NaCl. In contrast, the corrosion rate of Inconel 625 was lowest after 1000 h of the NaCl deposition corrosion test in a controlled environment. Therefore, the ZnAl thermal spray coating is a potential protection layer, keeping in mind economic considerations, of SS304L for anti-corrosion in saline environments.

Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

“…The average thickness of AC and SPCN1 was found to be 100 ± 5 µm whereas SPCN2 and SPCN3 were found to be 110 and 140 ± 5 µm, respectively, attributed to the deposition of composite oxide after treatment. The average bond adhesion value of the coatings was 4.86 ± 0.08 MPa for four consecutive samples [19,31,[33][34][35].…”

“…The arc thermal spray coating process can be used to protect the steel substrate from corrosion [17]. Moreover, Al, Zn, and Mg are anodic metals which can be deposited by an arc thermal spray process and provide sacrificial protection to the steel substrate at a longer duration of exposure in an aggressive environment [18,19].The thermal spray coating process suffers from a limitation such as formation of defects/pores onto the coating surface which cannot be ignored during the deposition [20,21]. However, it can be minimized by optimizing parameters and pore sealing agents.…”

“…The arc thermal spray coating process can be used to protect the steel substrate from corrosion [17]. Moreover, Al, Zn, and Mg are anodic metals which can be deposited by an arc thermal spray process and provide sacrificial protection to the steel substrate at a longer duration of exposure in an aggressive environment [18,19].…”

The Effect of Zn and Zn–WO3 Composites Nano-Coatings Deposition on Hardness and Corrosion Resistance in Steel Substrate

“…In recent years, surface coating methods (electro-spark deposition, laser cladding, magnetron sputtering, thermal spray process and chemical-vapor deposition) have become practiced widely in industries [ 26 , 27 ]. Thermal spraying and electroplating techniques are widely applied coating techniques to protect or repair the metallic surfaces of mechanical parts [ 28 , 29 ]. The combination of Mo–Ni–Cr coatings is applied on the substrate surfaces of super duplex stainless steel by applying plasma spray coating techniques [ 30 ].…”

Ultrasonic Sensors-Assisted Corrosion Studies on Surface Coated AlSi9Cu3 Alloy Die Castings

“…The work [23] elucidated on the fabrication of photo catalysis-enhanced surface deposition on titanium surfaces. Moreover, the authors in [24] investigated the pristine thermal spray coatings using the pull-off adhesion test to understand the adhesion strength, and Vickers hardness was measured for the mechanical properties of the three coatings.…”