<正> 一、引言 高温合金在一定的工作环境下,会因含有一定量碱金属硫酸盐(Na_2SO_4,K_2SO_4)的燃煤灰粉沉积于合金表面而发生热腐蚀。为模拟上述条件,本工作在Na_2SO_4-K_2SO_4混合盐中测定了五种合金(铁基及镍基)的热腐蚀行为。本文报导实验结果。
Specimens of three chromia-forming alloys,Fe-25Cr-2Mo,Fe-25Cr-20Ni,Ni-28Cr-2Cu-RE,and of two alumina-forming alloys, Fe-25Cr-6Al-0. 4Y, Fe-40Ni-21Cr-6Al-0. 1 Y,were exposed to the ambient atmosphere at 900℃ in the mixed salts of 25Na_2 SO_4-75K_2SO_4 (wt. %). Corrosion products were analysed by X-ray diffraction and electron microscopy. Sulfate salts tagged with. ~(35)S were used; sulfur penetration profiles were then determined,and the lateral distribution of sulfur within the alloy matrix was observed by autoradiography. Internal sulfidation/internal oxidation was found to be the major mode of attack, preferably along grain boundaries. The chromia scale was rather thick, permitted rapid inward penetration of sulfur to form chromium sulfide along the grain boundaries. Alumina scale offered better protection than did chromia scale. By comparison, the two alumina-forming alloys were found to be more resistant than the other three chromiaforming alloys under the experimental conditions.
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