Poonam Yadav

Corrosion of Inconel 690 in N2-0.1%H2S gas at 700-800 °C

Inconel 690 superalloy was corroded at 700 °C and 800 °C for up to 70 h in N2-0.1% H2S gas. It corroded almost linearly with large weight gains, displaying little protectiveness. Its corrosion rates were quite fast when compared with its corrosion in air or Ar-1%SO2 gas. The formed scales were thick, fragile, and nonadherent. They consisted primarily of Cr2O3 with some NiCr2O4, Ni3S2, CrS, and Cr2S3. The H2S gas accelerated the corrosion significantly by forming nonprotective sulfides and dissolving hydrogen in the scale and in the internal corrosion zone that consisted of discrete chromium-sulfides and some oxide particles. The marker test indicated that the scales grew by the outward diffusion of metallic ions such as Ni, Cr, Fe, and Mn, whilst the internal corrosion zone thickened by the inward migration of oxygen and sulfur through the lattice, grain boundaries, and microcracks.

High-Temperature Corrosion of Ni3Al+ 2.9%Cr Alloy in Ar-0.2%SO2 Gas

The high-temperature corrosion behavior of Ni3Al+2.9 wt% Cr alloy was studied in SO2-containing environment. Corrosion tests were carried out at 900, 1000, and 1100 °C for 100 h in atmospheric Ar-0.2% SO2 gas. The alloy corroded relatively slowly due mainly to formation of Al2O3 in the scale. Its corrosion kinetics deviated from the parabolic corrosion rate law to a certain extent owing to ensuing scale spallation. This was attributed to (1) stress generated during scaling and the subsequent cooling period, (2) voids that formed due to the Kirkendall effect, and (3) incorporation of sulfur in the scale. The scale that formed after corrosion at 900 °C consisted of the outer NiO scale, middle NiAl2O4 scale, and inner Al2O3 scale. The increased corrosion rate at 1000 and 1100 °C led to formation of the outer NiO scale, and inner Al2O3 scale.

High-Temperature Corrosion of NiCrAlY/YSZ Coatings in Ar-1%SO2 Gas

The thermal barrier coating that consisted of ZrO2-8Y2O3 top-coat and Ni-22Cr-10Al-1Y bond-coat corroded in Ar-1%SO2 gas at 1000-1200°C for up to 300 h. The top-coat and bond-coat consisted primarily of β-ZrO2 and (γ-Ni, α-Al2O3), respectively. During corrosion, Al oxidized preferentially to α-Al2O3 to protect TBC, and sulfidation occurred to a small extent.

Corrosion of Fe-9%Cr-1%Mo Steel at 600 and 700℃ in N₂/(0.5, 2.5)%H₂S-mixed Gas

The T91 steel (Fe-9%Cr-1%Mo) was corroded at 600 and 700℃ for 5 - 70 h in the N₂/(0.5, 2.5)%H₂Smixed gas at one atm. It was corroded fast, forming the outer FeS layer and the inner (FeS, FeCr₂O₄)-mixed layer. The formation of the outer FeS layer facilitated the oxidation of Cr to FeCr₂O₄ in the inner layer. Since the nonprotective FeS scale was present over the whole scale, T91 steel displayed poor corrosion resistance.

High Temperature Oxidation Behavior of High Strength Steel Plates

Three kinds of high-strength steel plates containing (less than 0.07%, or 0.024%, or 0.057%)-Si were oxidized at 700-900 °C isothermally and cyclically in atmospheric air, and their oxidation behavior was compared. The composition of the steels significantly affected the scaling rates, thickness, and adherence of the formed scales. The most important element in terms of oxidation was Si because Si affected the oxidation rates and scale adherence much. Silicon formed quite slowly a growing SiO2–containing scale around the scale/matrix interface. In the Si-deficient steel, quite thick oxide scales formed, and their adherence was poor. An optimum amount of Si was necessary in order to decrease the oxidation rate, and improve the scale adherence.

Isothermal and Cyclic Oxidation of Ti-6Al-4V Alloy

The Ti-6Al-4V alloy was oxidized isothermally and cyclically in air, and its oxidation behavior was compared with that of Ti metal. The isothermal oxidation at 800°C indicated that Ti-6Al-4V and Ti oxidized fast almost linearly, and the oxide scales that formed on Ti-6Al-4V and Ti were non-adherent. The cyclic oxidation indicated that Ti-6Al-4V oxidized faster than Ti at 600°C, and serious scale spallation occurred in Ti-6Al-4V compared to Ti at 800°C. The oxide scales that formed on Ti-6Al-4V and Ti after cyclic oxidation at 800°C delaminated into several pieces owing to excessive stress aroused by the repetitive thermal shock.

Corrosion of Fe-2.25Cr-1.6W-0.1Mo Steels in Na2SO4 Salts at 800 and 900°C

The ASTM T23 steel with a composition of Fe-2.25Cr-1.6W-0.1Mo in wt.% was corroded in the Na2SO4 salt at 800 and at 900°C, and its corrosion behavior was studied. It formed thick, porous oxide scales that consisted primarily of outer Fe-rich oxides and inner (Fe, Cr)-rich oxides. The corrosion of the T23 steel progressed mainly via oxidation.