HOT SULFIDATION-AND OXIDATION-RESISTANT NEW ALLOYS

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。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，其硫化速率与铬形成材料的氧化速率相当。二元Al-Mo合金的抗氧化性能令人满意，但仅在不超过1073K的温度下。在MoO_3的熔点（1069K）以上，由于MoO_3的蒸发，以Al_2O_3为主、MoO_3含量为5%的水垢变得无法保护。然而，三元Al-Mo-Si合金在1200K左右的氧化环境中表现出优异的抗氧化性，其氧化速率与Al_2O_3形成物相当。这是由于三元合金在加热过程中形成Mo_5Si_3结垢，而不是形成AlMo_3。研究了铝合金增强钼抗硫化性能的有利作用与铝含量的关系。低铝含量Mo-Al合金的反应速率低于纯钼，且随铝含量的增加而降低。较低的硫化速率可以用铝掺杂效应来解释。溅射镀铝铌合金具有优异的抗硫化性能，其硫化速率低于铌合金。但由于铝的优先硫化导致初始硫化速率较高，导致铌在金属/垢界面富集，从而在Al-Nb合金表面形成保护性NbS_2垢。这些合金的耐高温氧化性高于铌合金。氧化垢由双氧化铝铌和氧化铝组成，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.