Abstract
Abstract AlNbMo ternary alloys of about 5 μm thickness have been deposited on quartz substrates using a sputter deposition technique, and their sulfidation and oxidation behavior has been compared with the AlNb, AlMo and NbMo binary alloys. The sulfidation of the ternary alloys follows two-stage parabolic kinetics at temperatures of 1073–1273 K in sulfur pressure of 10 3 Pa. The steady-state sulfidation is significantly slower than the initial sulfidation. An interesting fact is that the steady-state sulfidation rates of the ternary alloys are further lower than those of the AlNb and AlMo binary alloys. In particular, an increase in niobium content in the ternary alloys leads to a decrease in the sulfidation rate. Similarly to the AlNb and AlMo binary alloys, apparently two-layered scales are formed on the ternary alloys, consisting of an outer Al 2 S 3 layer and an inner refractory metal sulfide layer. The detailed analysis of the inner layer reveals that the inner barrier layer is not a single layer but consisting of an outer thin NbS 2 layer and inner major layer of MoS 2 containing Nb 3 S 4 . The formation of the inner barrier layer consisting of two layers in which diffusing matters and directions are different is attributed to the higher sulfidation resistance of the ternary alloys than those of AlNb and AlMo binary alloys. The steady-state sulfidation rates of the ternary alloys are also lower than those of the NbMo binary alloys, because the two layered niobium sulfide-molybdenum sulfide doped with Al 3+ ions is more protective than the individual NbS 2 and MoS 2 sulfides doped with Al 3+ ions. The oxidation resistance of the aluminum-rich AlNbMo alloys is better than the AlNb and AlMo alloys, although the resistance of the former alloys is still not sufficient.
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