Influence of sealing treatment on the corrosion resistance of Fe-based amorphous coatings in HCl solution

Influence of Ultrasonic Excitation Sealing on the Corrosion Resistance of HVOF-Sprayed Nanostructured WC-CoCr Coatings under Different Corrosive Environments

“…The as-sprayed coatings were immersed in the sealant under ultrasonic excitation with the frequency of 40 kHz at atmospheric pressure and room temperature. After immersion for 4 h, the sealed coatings were taken out, heat-treated from room temperature to 100 • C for 2 h, 200 • C for 2 h, and 250 • C for 1 h in sequence, and then cooled down to room temperature slowly inside the furnace [21]. Subsequently, the coating specimens were ground and polished in order to remove excess sealant and ensure surface roughness of the sealed coating for electrochemical corrosion testing.…”

“…For 1 mol•L −1 HCl solution, the i corr value decreases from 43.75 µA•cm −2 for unsealed coating to 4.12 µA•cm −2 for sealed coating and the reduction is by more than one order of magnitude, indicating an obvious enhancement of kinetic resistance to corrosion. This can be attributed to the superior protection behavior and the stability of aluminum phosphate sealant in HCl solution, although HCl solution is particularly aggressive as a result of the continuous attack of chloride ions and the removal of oxide films [21,32]. As it can be seen, ultrasonic excitation sealing has changed both the anodic and cathodic slopes of the polarization curves and, in turn, the corrosion rate of unsealed coating.…”

“…Nonetheless, additional improvement in quality of HVOF-sprayed coatings is incessantly sought in order to further enhance the durability and performance, which can be achieved through post-treatments such as sealing, annealing and remelting [15][16][17]. Recently, it has been accepted that the anti-corrosion properties of the coatings can be improved by inorganic sealants with the help of different sealing techniques [18][19][20][21]. Aluminum phosphate sealant has been used not only to prevent the penetration of corrosive media, but also to enhance the cohesion strength of the coating by combining conventional impregnation sealing treatment with ultrasonic excitation [22].…”

Study of alumina sealing of HVOF thermally sprayed WC-Co coatings by sol-gel method

“…Aluminum phosphate (AlPO 4 ), sodium orthosilicate (Na 3 SiO 4 ), cerium salts (Ce(NO 3 ) 3 , CeCl 3 ), nickel salts (Ni(CH 3 COO) 2 , NiF 2 ) and dichromate (K 2 Cr 2 O 7 ) are common sealants used in various spraying coatings including amorphous/nanocrystalline coatings [4][5][6][7][8][9][10]. Wang et al [6] investigated the effect of sealing treatment on the corrosion behavior of high velocity oxygen fuel (HVOF) Fe-based amorphous/nanocrystalline coatings and found that sealing treatment obviously enhanced the corrosion resistance of coatings and AlPO4 sealant exhibited the best sealing effect.…”

THE EFFECT OF SEALING PROCESSES ON THE CORROSION BEHAVIOUR OF Al₂O₃-13 WT.%TiO₂ COATING

“…Although the optimisation of the spraying parameters has brought a decrease in the porosity, it is hard to obtain a completely dense ceramic coating without any cracks [6], which means the transportation of corrosive medium to the substrate cannot be prevented still. Therefore, a number of posttreatments have been adopted to the plasma sprayed ceramic coating to reduce the pores and cracks, such as laser remelting, inorganic sealing treatment [16,20,21]. Laser remelting process can make it possible to obtain a perfectly cohesive coating; however, some micro-cracks may still exist in the coatings due to the thermal shrinking and rapid cooling rate [16,22].…”