HOT SULFIDATION-AND OXIDATION-RESISTANT NEW ALLOYS

本文研究了电沉积非晶Al-（34-46）Mo和Al-31 Mo-（6-16）Si合金在硫蒸气、氧气和空气中的高温腐蚀与温度的关系。硫化过程遵循抛物线动力学。合金表现出优异的抗硫化物腐蚀，其硫化速率与氧化铬形成材料的氧化速率相当。Al-Mo二元合金的抗氧化性能是令人满意的，但仅在不超过1073 K的温度范围内。在MoO_3的熔点以上（1069 K），由于MoO_3的蒸发，主要由Al_2O_3和5%MoO_3组成的氧化膜变得不受保护。而Al-Mo-Si三元合金在1200 K以下仍表现出良好的抗氧化性能，其氧化速率与Al_2O_3型合金相当。这是由于在加热过程中生成的是Mo_5Si_3氧化膜而不是AlMo_3氧化膜。低铝含量的钼铝合金的反应速率低于纯钼，且随铝含量的增加而降低。溅射沉积的Al-Nb合金具有优良的抗硫化性能，其硫化速率低于Nb。由于Al的优先硫化，使其初始硫化速度快，导致Nb在金属/氧化膜界面富集，形成NbS_2保护膜，使Al-Nb合金的抗高温氧化性能高于Nb。氧化皮由双铝铌氧化物和氧化铝组成，这导致高抗氧化性。

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.