HOT SULFIDATION-AND OXIDATION-RESISTANT NEW ALLOYS

本文研究了溅射沉积的非晶态Al-(34-46)Mo和Al-31Mo-(6-16)Si合金在硫蒸气、氧气和空气中的高温腐蚀行为。硫化过程遵循抛物线动力学。该合金具有优异的抗硫化物腐蚀性能，其硫化速率可与铬形成材料的氧化速率相媲美。二元Al-Mo合金的抗氧化性较好，但仅在1073K以下。在MoO_3的熔点(1069K)，主要由Al_2O_3和5%MoO_3组成的氧化膜由于MoO_3的蒸发而失去保护。然而，三元Al-Mo-Si合金在1200K左右表现出良好的抗氧化性，其氧化速率与Al_2O_3的氧化速率相当。这是由于三元合金在加热过程中形成了Mo5Si3氧化膜而不是AlMo3。研究了铝合金化对提高钼的抗硫化性能的有利作用。低铝钼铝合金的反应速率低于纯钼合金，且随铝含量的增加而降低。溅射沉积Al-Nb合金具有良好的抗硫化性能，其硫化速率低于Nb。尽管由于铝的优先硫化，导致Nb在金属/鳞片界面上的富集，从而在Al-Nb合金上形成了保护性的NbS_2膜，但由于Al-Nb合金的初始硫化速率较高，其抗高温氧化性能高于Nb。氧化膜由双层铝-铌氧化物和氧化铝组成，具有较高的抗氧化性。

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.