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研究了纯Ni,Ni-20％Cr和K3合金上渗铝层在含硫气氛中的退化机理。采用燃烧装置热腐蚀实验和改进的坩埚法实验。实验温度为900℃。同时,还进行了同样温度下的氧化实验。对热腐蚀试样和氧化试样分别进行了表面形貌观察。X射线衍射分析和电子探针成份分析。结果表明,在燃烧装置热腐蚀实验中,试样表面首先出现须状氧化铝,然后成为热腐蚀小孔的诱发点。随着小孔尺寸和数量的增加,渗层整体出现局部的剥落和破坏。在改进的坩埚法实验中,试样首先出现氧化物保护膜的大量剥落,使渗层表面出现铝的贫化,继尔β-NiAl相蜕变为γ′-Ni_3Al相,最终导致渗层局部点蚀剥落和破坏。 实验结果还表明,基体中的Cr可以提高渗铝层的抗热腐蚀性能。但在改进的坩埚法实验中。由于气氛中存在高浓度的NaCl,从而严重削弱了Cr的有益作用。

In the present paper, a study of degradation of aluminide coatings on Ni, Ni-20％Cr and K3 superalloy(Cr10～12％, Co4.5～6.0％, Al5.3～5.9％, Mo3.8～4.5％, W 4.8～5.5％, Ti 2.3～2.9％, Ni Bal.) has been conducted by two test methods at 900℃, one is the burner rig test with 20ppm NaCl injected,and the other is the modified crucible test with evaporation of a mixture of 25％ NaCl+75％Na_2SO_4. Oxidation test at the same temperature was carried out for comparison. The tested samples were analyzed by SEM, X-ray diffraction,and EPMA. It was found that alumina whiskers appeared on the surface of the samples in the burner rig test. The zones having the alumina whiskers became the initiation of pits. The number and size of pits increased with time. When the pits reached the interface between coating andsubstrate,the coating cracked and became unprotective. In the modified crucible test,β-NiAl phase disappeared earlier than in the burner rig test due to stripping of oxide scale and depletion of Al. Then pits appeared and the coatings cracked. The results indicated that Cr greatly increased the resistance of coating to hot corrosion. However, the extent of the improvement is different in both tests. The effect is more pronounced in the burner rig test than in the modified crucible test. This is probably because the higher NaCl concentration in the modified crucible test offsets the beneficial effect of Cr.