新型镍基高温合金在模拟燃煤锅炉环境中的腐蚀

CORROSION OF A NEW NICKEL BASE SUPERALLOY IN COAL-FIRED BOILER ENVIRONMENTS

在人工合成的煤灰/烟气环境中研究了一种新型镍基高温合金550℃和700℃的腐蚀行为和腐蚀机理.结果表明,合金在550℃发生了不均匀的点蚀,表面形成了一层很薄的Cr_2O_3膜,腐蚀按照硫化机制发展.合金在700℃腐蚀时,初期发生了氧化和硫化腐蚀,表面生成了保护性的氧化膜,并有内硫化物析出.由于合金表面生成CoO并在表面形成熔融态硫酸盐而逐渐进入加速腐蚀阶段,使合金遭受严重的低温热腐蚀.腐蚀产物外层为疏松的混合尖晶石化合物,内层为致密的氧化物层,在腐蚀层、腐蚀层与基体界面和Cr元素贫化区内分布着硫化物.合金耐腐蚀性能的迅速退化是合金表面Co及其氧化物在混合熔盐中的溶解所致.

The corrosion behavior and mechanism of a new nickel base superalloy have been studied at 550degreesC and 700degreesC in the synthetic coal ash/flue gas environments. The results indicate that low temperature hot corrosion of the alloy occurs at 550degreesC and develops as pitting attack resulted from sulfidation mechanism. The frontal attack at 700degreesC consists of two successive stages. The corrosion of specimen follows the oxidation and sulfidation mechanism during the initial stage. The protective Cr2O3 film forms on the surface of the alloy and the internal sulfidation takes place. The severe low temperature hot corrosion happens due to the presence of molten CoSO4 during the accelerated stage. The porous and loose external scale and the compact internal scale consist of spinels and oxides, respectively. The sulfides of Cr, Ti and Nb precipitate at the front of oxides and in Cr-depletion zone. The rapid degradation of corrosion resistance of the alloy is attributed to the dissolution of both cobalt and cobalt oxide on the surface.