Morphology and Growth Mechanism of Sulfide Subscale in Superalloys

在1173K ~ 1273K的温度范围内，研究了含沃斯帕洛伊合金在内的Ni-Cr基合金在熔融硫酸钠中的硫化行为。对高温硫化形成的硫化物鳞片的光学显微镜、x射线衍射测量和电子探针显微分析表明，高温硫化形成的硫化物鳞片由合金表面的外部鳞片和具有较大亲和力的元素选择性硫化形成的合金内部的亚鳞片组成。在所有温度下，Ni-Cr合金和Waspaloy合金的亚鳞片均按抛物线速率规律生长。以往有关亚标度的论文几乎都是基于对硫化试样横截面的二维观察。然而，由于其形态的特殊性，难以准确估计其三维形态的发展。为了直接检测镍铬基合金的三维形貌，我们开发了一种不溶解构成亚尺度的金属硫化物相的金属基体溶解技术。研制了由溴、十六烷基溴化吡啶和乙腈组成的有机溶剂体系溶液。在Ni-Cr基合金中形成的晶间和晶内硫化物的三维形貌清楚地表明了每种生长机制的差异。新开发的使用有机溶剂体系的溶解技术证明是有用的

The sulfidation behavior of Ni-Cr based alloys including Waspaloy has been investigated in the temperature range of 1173K to 1273K in a molten sodium sulfate. Optical microscopy, X-ray diffraction measurements and electron probe microanalysis on the sulfide scales formed by high-temperature sulfidation indicate that the scale consist of an external scale on the, alloy surface and a subscale in the alloy interior by selective sulfidation of elements having a large affinity of sulfurAt all the temperatures the subscales in a Ni-Cr alloy and Waspaloy grew according to a parabolic rate law, and the apparent activation energies far their processes were estimatedAlmost of all the previous papers concerning with subscale have been on the basis of the wo-dimensional observation on the cross-sections of sulfidized specimens. However, it is difficult to estimate exactly the three-dimensional morphology development of the subscale because its morphology is peculiar. In order to examine directly the three-dimensional morphology, we have developed a metal matrix dissolution, technique for the sulfidized Ni-Cr based alloys without dissolving the metallic sulfide phases constituting the subscale by using an organic solvent system solution. The organic solvent system solution, we developed, consists of bromine, cetylpyridinium bromide and acetonitrile. The three-dimensional morphology of the intergranular and intragranular sulfides foamed in the Ni-Cr based alloys suggests clearly the difference of each growth mechanism. The newly developed dissolution technique using an organic solvents system proved useful