Title :
The mechanism of electrolytic Al2O3 coating on MAR-M247 superalloy
Author :
Yen, S.K. ; Chang, C.C.
Author_Institution :
Inst. of Mater. Eng., Nat. Chung-Hsing Univ., Taichung, Taiwan
Abstract :
Through an analysis of cathodic polarization experiments in H2O, NaNO3, HCl and a mixture of HCl and NaNO3, solutions respectively, the mechanism of coating electrolytic Al2O3 on MAR-M247 superalloy was investigated. We suggest that the cathodic polarization curves in Al(NO 3)3 can be comminuted into 4 steps: 1. H+ +e-→H2 (-0.1 V~-0.35 V), 2. reduction of Al3+(H2O)3 complex ion: 2Al3+ (H2O)3·xH2O+6e- →2Al(OH)3·xH2O+3H2 (-0.35 V~-0.65 V), 3. diffusion of +(H2O)3 complex ion (-0.65 V~-0.9 V), and 4. reduction of H2O: 2H2O+2e-→H2+2OH- (-0.9 V~-4 V). X-ray diffraction diagrams show the Al(OH3) gel transforms into amorphous-Al2O3→623 K γ-Al2O3→973 Kδ-Al2O3→1123 Kθ-Al2O3
Keywords :
X-ray diffraction; alumina; cobalt alloys; corrosion protective coatings; electrodeposition; electrodeposits; nickel alloys; reduction (chemical); superalloys; tungsten alloys; Al2O3; Al3+(H2O)3 complex ion reduction; MAR-M247 superalloy; NiCoW; X-ray diffraction diagrams; annealing; cathodic polarization curves; ceramic coatings; dissociation; electrolytic alumina coating mechanism; gel transformation; Annealing; Ceramics; Chemical vapor deposition; Coatings; Human computer interaction; Nickel; Polarization; Scanning electron microscopy; Testing; Voltage;
Conference_Titel :
Intelligent Processing and Manufacturing of Materials, 1999. IPMM '99. Proceedings of the Second International Conference on
Conference_Location :
Honolulu, HI
Print_ISBN :
0-7803-5489-3
DOI :
10.1109/IPMM.1999.791485
