Investigation of Na₂SO₄Deposit Induced Corrosion of Cr, Al, C Binary and Ternary Thin Film Coatings on Ni-201

Abstract

Al-C, Cr-C, Al-Cr and Al-Cr-C thin film coatings were sputtered onto Ni-201 substrates. Samples were deposited with 1.0 ± 0.3 mg cm −2 Na 2 SO 4 and exposed to dry air/2 ppm SO 2 gas atmosphere, at 700 • C for 250 hours. Coated samples had reduced corrosion rates relative to uncoated samples. Al-C and Cr-C coatings were not effective since NiO was the only compound detected on the surfaces; in contrast Cr-Al and Cr-Al-C developed protective layers of Al 2 O 3 and Cr 2 O 3 with Cr-Al-C coated samples having the least corrosion rate.

Type II Hot Corrosion Screening Tests of a Cr2AlC MAX Phase Compound

“…Although testing at 700°C, under a p(SO2) of 2 ppm for 250 h, diffused the coating into the Ni surface layer, it was more resistant to oxidation under Na2SO4 salt deposits than Al-C, Cr-C, Al-Cr binary films or the bare substrate. [10] A diffusion bonded hybrid Cr2AlCsuperalloy couple was found to be mechanically and environmentally stable after multiple cycles and thermal exposure to 800°C for 1000 h. While little additional interdiffusion occurred at 800°C, bonding at 1100°C for 2 h had already produced appreciable 50 µm layers of NiAl and Cr7C3. [11] Finally, a 760°C low cycle fatigue study demonstrated no additional detriment of hot corrosion to LCF life for a Cr2AlC-coated LSHR (low solvus, high refractory) disk superalloy.…”

The correlation between structure, multifunctional properties and application of PVD MAX phase coatings. Part III. Multifunctional applications

“…Cr 2 AlC also has excellent resistance to Type I molten salt (Na 2 SO 4 ) hot corrosion at 900-1000°C [141,142] and shows promising Type II low-temperature hot corrosion behaviour [152,245]. Molten ash can penetrate the YSZ hot surface and cause fracturing or delamination upon cooling.…”

The correlation between structure, multifunctional properties and applications of PVD MAX phase coatings. Part II. Texture and high-temperature properties

“…Lin et al [90,99] demonstrated that bulk Cr 2 AlC exhibits excellent resistance to Type I molten salt (Na 2-SO 4 ) hot corrosion at 900-1000°C, which can be attributed to the formation of a protective Al 2 O 3 -rich scale during the hot corrosion processes. Furthermore, Aw et al [273] reported improved Type II low-temperature hot corrosion behaviour of the Ni-superalloy coated with sputtered Cr-Al-C films relative to uncoated samples.…”