NEW AMORPHOUS-ALLOYS RESISTANT TO HIGH-TEMPERATURE CORROSION

High temperature corrosion of sputter-deposited amorphous Al-(34-46)Mo and Al-31Mo-(6-16)Si alloys has been studied as a function of tempera ture (973-1273 K) in sulfur vapor (10(3) Pa), as well as in oxygen and air. The sulfidation process follows parabolic kinetics, so is diffus ion controlled. Over the whole temperature range studied, the discusse d alloys showed excellent resistance to sulfide corrosion, their sulfi dation rates being comparable with the oxidation rates of chromia-form ing materials. The oxidation resistance of binary Al-Mo alloys has bee n found to be satisfactory, but only at temperatures not exceeding 107 3 K. Above the melting point of MoO3 (1069 K), the scale, consisting m ainly of Al2O3 with about 5% MoO3, becomes unprotective because of the evaporation Of MoO3. However, ternary Al-Mo-Si alloys show excellent resistance to oxidizing environment up to about 1200 K, their oxidatio n rates being comparable with those of Al2O3 formers. No traces of mol ybdenum have been found in the Al2O3 scale on these alloys.