| Co-Investigator(Kenkyū-buntansha) |
J-CZACHOR M. Institute of Physical Chemistry, Polish Academy of Science, Group leader, 物理化学研究所, 室長
MROWEC S. Univ.of Mining and Metallurgy, Facalty of Materials Science and Ceramics, Dep.of, 材料科学研究所, 教授
AKIYAMA Eiji Inst.for Mater.Res., Tohoku University, Res.Associate, 金属材料研究所, 助手 (70231834)
KAWASHIMA Asahi Inst.for Mater.Res., Tohoku University, Res.Associate, 金属材料研究所, 助手 (50005964)
ASAMI Katsuhiko Inst.for Mater.Res., Tohoku University, Assis.Professor, 金属材料研究所, 助教授 (20005929)
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| Research Abstract |
High temperature corrosion of sputter-deposited amorphous Al- (34-46) Mo and Al-31Mo- (6-16) Si alloys has been studies as a function of temperature in sulfur vapor, as well as in oxygen and air. The sulfidation process follows parabolic kinetics. The alloys showed excellent resistance to sulfide corrosion, their sulfidation rates being comparable with oxidation rates of chromia-forming materials. The oxidation resistance of binary Al-Mo alloys has been found to be satisfactory, but only at temperatures not exceeding 1073K.Above the melting point of MoO_3 (1069K), the scale, consisting mainly of Al_2O_3 with 5% MoO_3, becomes unprotectable because of evaporation of MoO_3. However, ternary Al-Mo-Si alloys show excellent resistance to oxidizing environment up to about 1200K,their oxidation rates being comparable with those of Al_2O_3 formers. This resulted from the fact that during heating of the ternary alloys, Mo_5Si_3 scale was formed instead of AlMo_3 formed.
The beneficial effect of alloying with aluminum enhancing the sulfidation resistance of molybdenum has been studied as a function of aluminum content. The reaction rate of Mo-Al alloys with low aluminum contents is lower than that of pure molybdenum and decreases with increasing aluminum content. The lower sulfidation rate is explained in terms of the aluminum doping effect in the MoS_2 scale.
Sputter-deposited Al-Nb alloys have excellent sulfidation resistance, their sulfidation rates being lower than that of niobium. Although their initial sulfidation rate is high due to the preferential sulfidation of aluminum, which leads to the enrichment of niobium at metal/scale interface, and consequently, the protective NbS_2 scale formed on the Al-Nb alloys.
The resistance of these alloys to high temperature oxidation is higher than that of niobium. The oxide scale is composed of a double aluminum-niobium oxide and alumina, which lead to high oxidation resistance.
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