Smialek James L, Gray Simon
NASA Glenn Research Center, Cleveland, OH 44135, USA.
Surface Engineering & Nanotechnology Institute, Cranfield University, Bedfordshire MK43 0AL, UK.
Materials (Basel). 2018 Oct 25;11(11):2098. doi: 10.3390/ma11112098.
Single crystal superalloys were screened in Type II molten (Na,K)-sulfate hot corrosion re-coat tests in air +300 ppm SO₂ at 700 °C. They exhibited large 20⁻40 mg/cm² weight changes, repeated spallation, and non-protective, 25⁻50 μm thick corrosion layers after 300 h of testing. Scale cross sections revealed dual outer Ni(Co)O and inner Al(Cr)S-rich corrosion layers. This chemical differentiation was partially consistent with previous models of oxide fluxing, alloy sulfidation, NiO micro-channel diffusion, and synergistic dissolution mechanisms. Broad shallow pits or uniform attack morphologies were consistent with prior studies performed in high >100 ppm pSO₂ environments. Higher Mo experimental alloys trended toward more degradation, producing 100 μm thick scales with distinct Al(Cr)S-rich inner layers or 500 μm thick NiO. The aggressive behavior in these environments supports the need for LTHC-resistant coatings for single crystal superalloys.
在700℃、空气+300 ppm SO₂环境下的II型熔融（Na，K）-硫酸盐热腐蚀再涂覆试验中对单晶高温合金进行了筛选。经过300小时的测试后，它们的重量变化为20⁻40 mg/cm²，出现反复剥落，并且腐蚀层厚度为25⁻50μm，无保护作用。氧化皮横截面显示出双层外层Ni(Co)O和内层富含Al(Cr)S的腐蚀层。这种化学差异与先前的氧化物助熔、合金硫化、NiO微通道扩散和协同溶解机制模型部分一致。宽浅坑或均匀侵蚀形态与先前在高>100 ppm pSO₂环境中进行的研究一致。含钼量更高的实验合金有更严重的退化趋势，形成了100μm厚且内层富含Al(Cr)S的氧化皮，或500μm厚的NiO。这些环境中的侵蚀行为表明需要为单晶高温合金提供抗低周热疲劳涂层。
