不同晶界形态高温合金在含硫环境中的蠕变和断裂特性

本文应用扫描电镜、剖面分析及EDAX能谱分析,研究了具有平直晶界和曲折晶界两种不同组织的GH302合金,及Rene 80合金在空气、含硫环境中的高温蠕变及断裂行为。试验结果表明,具有曲折晶界的GH302合金试样,虽然在空气环境中蠕变和持久性能明显地高于通常平直晶界试样,但在10%SO_2-空气环境中,二者的性能皆剧烈下降;定向凝固Rene80合金不仅在空气环境中性能显著优于普通铸造的合金,在含硫环境中仍保持原先水平。在含硫环境中蠕变与腐蚀的交互作用下,蠕变裂纹的扩展是以硫化-氧化腐蚀在应力促进下沿晶侵入并形成低熔点共晶,导致早期破坏。

CREEP AND FRACTURE FEATURE OF SUPERALLOYS WITH DIFFERENT BOUNDARY MICROSTRUCTURES IN SULPHUR CONTAMINATED ENVIRONMENT

Studies by SEM and EDAX were carried out on the high temperaturecreep and fracture behaviour undergone tests in air or in SO_2 contaminated enviro-nment for both Fe-base wrought superalloy GH302 and Ni-base superalloy Rene 80,with two different microstructures: i. e., flat and zig-zag grain boundary or equi-exed and Columnar grain boundary respectively. Although the creep rupture strenqthof the superalloy GH302 of zig-zag GB was remarkably superior to that of flat GBin air, the properties of both dropped suddenly in 10% SO_2 contaminated air. Thecreep rupture properties of the directional solidification superalloy Rene 80 weremuch better than that of the conventionally casted alloy in air, and also remainedthe former ones in SO_2 contaminated air. Owing to the interaction between creepand sulphidation, the damage mechanism seems to be that the creep cracking ispropagated intergranularly by suffering sulphidation-oxidation corrosion under stress,and formation of a low melting point NiN_3S_2 eutectic leads to premature failure ofthe alloy.