Oxidation and hot corrosion behavior of sputtered nanocrystalline coating of superalloy K52

Performance of NiCrAlY Coatings Deposited by Oxyfuel Thermal Spraying in High Temperature Chlorine Environment

“…AISI 304 stainless steel, specimens of 20 9 10 9 1.2 mm 3 , was used as substrates. Specimens were grit blasted with corundum particle of 99.6 wt.% purity and 0.53-mm mean particle size, using an air pressure of 0.4 MPa, incidence angle of approximately 45°, and a gun-to-substrate distance of 130 mm.…”

“…At the coating-metal interface, a very low oxygen potential exists (O 2 is consumed to produce metal oxides), at which volatile metal chlorides such as FeCl 3 and CrCl 2 are thermodynamically stable. The Cl 2 may react with metal according to the Reactions 1 to form metal chlorides:…”

“…With this comparison, chromium chlorides and nickel chlorides are shown to be the fastest species among the metal chlorides, followed by the aluminum chlorides, and finally the iron chlorides. At 727°C, the diffusion coefficients range from 0.823 cm 2 /s for CrO 2 Cl 2 to 0.451 cm 2 /s for FeCl 3 . It should be noted that the difference in the diffusivities of the species is accentuated by increasing the temperature.…”

“…The protective feature is so important that about 75% of all hot components in industrial and aircraft engines are coated (Ref 2,3).Due to the requirement of enhanced power-out of energy plants (Ref 4), there is urgent demand for stable MCrAlY coating with improved longterm performance, as the inlet temperature is increased.…”

Oxidation Resistance of Nanocrystalline Alloys

“…Improved oxidation resistance of FeBSi [87], Ni-based alloys [88][89][90][91][92][93], Zr and its alloys [40][41][42][43], Cr-33Nb [94], Fe-Co based alloys [95,96] and Cu-Ni-Cr alloys [97] is reported in their nanocrystalline form (in comparison to their microcrystalline counterparts). The mechanistic role of a nanocrystalline structure leading to the improved oxidation resistance is discussed below:…”