improving the hot corrosion behavior of plasma-sprayed mcraly by rf sputtering of tio2 nano-coating and laser remelting treatment

Nanostructured tio2 coatings were deposited on nicraly coating by rf magnetron sputtering. nicraly coating was deposited by sprayed-plasma method on the ni-base superalloy substrate. nicraly layer work as the first protection layer while tio2 nanocoatings as the second protection layer. laser surface re-melting for coating layers by nd-yag laser was done. hot corrosion test conducted for substrate after coating with both nicraly and tio2 nanocoating with and without laser surface remelting. hot corrosion was tested by using a molten salt of na2so4–55 %v2o5 at 800 and 900 °c for 60 hours. the weight change measurements were performed to determine the cyclic hot corrosion kinetics of the coatings at a temperature of 800 and 900 °c. the microstructural features, surface topography, and phase composition were characterized by fe-sem, eds, afm, and xrd. the results of fe-sem indicate that some porosities, cracks, and unmelted powder can be seen on the surface of samples for plasma spraying and rf sputtering of nicraly coatings. after the laser surface remelting of coatings, it can be observed the absence of porosity and crack with enhanced surface properties. the roughness decreases after laser remelting. hot corrosion tests indicate that the plasma-sprayed nicraly coating can significantly lower the hot corrosion resistance than coating two layers by nanocoating of tio2 by rf sputtering with laser remelting. the improvement owing to the formation of extensive amounts of the protective oxide of nio, al2o3, cr2o3, y2o3, and nicr2o4 spinal generated on the surface.