The Effect of Rare-Earth Metal Addition on the Oxidation and Hot Corrosion Resistance of Chromo-aluminized Nickel-Base Super Alloy
Mohamed Ali Mahmoud;
Abstract
Nimonic 75 alloy was coated with two different types of coatings; Chromoaluminized
coating and Zr-doped Cr-Al coating. Diffusion coating was
carried out by pack cementation process at 1000 oC for 8 h. Cyclic oxidation
tests of Nimonic 75 and its coated specimens were conducted at 900 oC,
1000oC and 1100oC in air for a total period of 100 h. The structures of the
coated Nimonic 75 alloy before and after high temperature oxidation were
investigated using light microscopy LM, scanning electron microscopy/energy
dispersive spectroscopy SEM/EDS, and X-ray diffraction XRD
characterization techniques.Cyclic hot corrosion tests of Nimonic 75 and its
coated system deposited with 2-4 mg / cm2 Na2SO4 were conducted at 900 oC
in air for 150 h at 10 h cycle. The results indicated that Zr-doped Cr-Al
coating is expected to be more effective in increasing the oxidation and hot
corrosion resistance of Nimonic 75 alloy. The role of zirconium can be
attributed to an improvement of the adherence of the oxide scales and
reducing voids formation at the coating/metal interface during cyclic
oxidation. The parabolic oxidation rate constants KP for cyclic oxidation of
uncoated alloy, Cr-Al coated and Zr/Cr-Al coated are (1.7, 0.77, 0.61) 10-6
mg2.cm-4.s-1 at 900oC, (10.08, 5.2, 3.91) 10-6 mg2.cm-4.s-1 at 1000 oC and
(41.27, 26.69, 18.13) 10-6 mg2.cm-4.s-1 at 1100 oC. XRD analysis of the
surface of uncoated Nimonic-75 alloy specimen after cyclic oxidation in air at
1000 oC for total period of 100 h identified the presence of Cr2O3 and nonprotective
oxide scale containing NiO and Ni(Cr2O4) phases. On the other
hand, the XRD analysis of the surface of Cr-Al coated specimen after cyclic
oxidation at 1000 oC, for 100 h identified the presence of protective oxide
scale containing α-Al2O3 and β-NiAl phases. XRD analysis of the surface of
Cr-Al-Zr coated specimen after hot corrosion at 900 oC, for 150 h identified
the presence of protective oxide scale containing α-Al2O3 and β-NiAl phases
but Al completely consumed in Cr-Al coating and not appeared Al phases in
its XRD analysis.
Keywords: superalloys, diffusion coating, pack cementation, Zr-doped, oxidation,
hot corrosion
coating and Zr-doped Cr-Al coating. Diffusion coating was
carried out by pack cementation process at 1000 oC for 8 h. Cyclic oxidation
tests of Nimonic 75 and its coated specimens were conducted at 900 oC,
1000oC and 1100oC in air for a total period of 100 h. The structures of the
coated Nimonic 75 alloy before and after high temperature oxidation were
investigated using light microscopy LM, scanning electron microscopy/energy
dispersive spectroscopy SEM/EDS, and X-ray diffraction XRD
characterization techniques.Cyclic hot corrosion tests of Nimonic 75 and its
coated system deposited with 2-4 mg / cm2 Na2SO4 were conducted at 900 oC
in air for 150 h at 10 h cycle. The results indicated that Zr-doped Cr-Al
coating is expected to be more effective in increasing the oxidation and hot
corrosion resistance of Nimonic 75 alloy. The role of zirconium can be
attributed to an improvement of the adherence of the oxide scales and
reducing voids formation at the coating/metal interface during cyclic
oxidation. The parabolic oxidation rate constants KP for cyclic oxidation of
uncoated alloy, Cr-Al coated and Zr/Cr-Al coated are (1.7, 0.77, 0.61) 10-6
mg2.cm-4.s-1 at 900oC, (10.08, 5.2, 3.91) 10-6 mg2.cm-4.s-1 at 1000 oC and
(41.27, 26.69, 18.13) 10-6 mg2.cm-4.s-1 at 1100 oC. XRD analysis of the
surface of uncoated Nimonic-75 alloy specimen after cyclic oxidation in air at
1000 oC for total period of 100 h identified the presence of Cr2O3 and nonprotective
oxide scale containing NiO and Ni(Cr2O4) phases. On the other
hand, the XRD analysis of the surface of Cr-Al coated specimen after cyclic
oxidation at 1000 oC, for 100 h identified the presence of protective oxide
scale containing α-Al2O3 and β-NiAl phases. XRD analysis of the surface of
Cr-Al-Zr coated specimen after hot corrosion at 900 oC, for 150 h identified
the presence of protective oxide scale containing α-Al2O3 and β-NiAl phases
but Al completely consumed in Cr-Al coating and not appeared Al phases in
its XRD analysis.
Keywords: superalloys, diffusion coating, pack cementation, Zr-doped, oxidation,
hot corrosion
Other data
| Title | The Effect of Rare-Earth Metal Addition on the Oxidation and Hot Corrosion Resistance of Chromo-aluminized Nickel-Base Super Alloy | Authors | Mohamed Ali Mahmoud | Issue Date | 2016 |
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