Laser surface modification of plasma sprayed yttria stabilised zirconia coatings on type 316L stainless steel

Abstract

Plasma sprayed yttria stabilised zirconia/NiCrAlY thermal barrier coatings proposed for molten LiCl-KCl salt environments contain pores and microcracks that may cause corrosion of the substrate on prolonged exposure. In the present work the as sprayed samples were laser remelted with various scan speeds of 1, 2?5 and 5 mm s 21 to reduce the segmented cracks. Microstructural inhomogeneities like pores and voids have been eliminated on laser remelting, however, segmented cracks were formed irrespective of scan speed. Distinct interface separating fine and coarse grains were observed at all scan speeds. The microhardness of the glazed surface improved and surface roughness was reduced. The beneficial non-transformable tetragonal phase was formed after laser remelting while the as sprayed coating consisted of insignificant monoclinic phase. An attempt was made to seal the pores of the zirconia coating by applying ZrO 2 and ZrO 2 z SiO 2 powder.

Effects of sealing on corrosion behaviour of plasma-sprayed Cr2O3–8TiO2 coating

“…The procedure can be performed using several techniques such as laser remelting, sealing treatment and annealing. [17][18][19][20] Among these methods, sealing treatment is widely used because of its advantages from the economic and technical points of view. The object of sealing is to make the sealant penetrate as deep as possible into the coating and fill the coating flaws that are connected to the substrate and surface.…”

Effects of cyclonic plasma deposited organosilicon nano‐coating on 316 stainless steel and its surface characterization

“…At cyclonic plasma deposition, the relatively low monomer gas input in association with plasma species residual time results the sphere formation and the film growth on SS316 surface. Therefore, a coating with cracks and pores not only does not act as a barrier to reduce corrosion rate but also increases the corrosion rate of the metallic substrate . On the other hand, a dense and crack‐free coating can perform as an appropriate barrier in order to reduce corrosion rate of metals .…”

Laser treatment of carbon film coated steel surface

“…13 The findings revealed that laser glazing and alloying improved the resistance of the steel surface to both corrosion and erosion; however, a marked improvement occurred in the specimens alloyed with nanocrystalline powders. Laser treatment of a steel surface through nanocomposite particle injection was carried out by Verezub et al, 14 demonstrating that a large number of nanosized (Fe,W) 6 C particles precipitated from the oversaturated steel matrix. Laser nitriding of stainless steel and plain carbon steel was investigated by Schaaf et al 15 The carbon steel was found to be better suited for the laser nitriding process than pure iron and the laser nitriding worked efficiently for the stainless steel.…”