定向凝固镍基DZ792及DZ792G合金的高温热腐蚀行为

采用涂盐法研究了DZ792与DZ792G合金涂覆75%Na2SO4+25%NaCl混合盐后在900℃下的热腐蚀行为与机理.结果表明，900℃涂盐腐蚀条件下DZ792与DZ792G合金的热腐蚀机制为“酸/碱盐溶-内硫化氧化”.DZ792G合金在热腐蚀70~150h，腐蚀机制由碱性盐溶机制转化为酸性盐溶机制，最终导致灾难性腐蚀.DZ792G合金因具有较高的Ti含量，合金表面氧化膜的外侧形成富Ti氧化物层，TiO2与熔盐反应消耗其中的O2-，促进热腐蚀由碱性向酸性盐溶机制转变.而DZ792合金Ti含量较低，TiO2层在氧化膜内侧形成，外侧少量Ti氧化物形成稳定的NiTiO3尖晶石层.DZ792合金氧化膜外侧的富Cr2O3层与熔盐直接反应，抑制了热腐蚀反应，因而具有优异的抗热腐蚀能力.

High Temperature Hot Corrosion Behaviors of Directional Solidification Ni-Base Superalloy DZ792 and DZ729G

The hot corrosion behaviors and mechanisms of DZ792 and DZ792G alloys through 75%Na2SO4+25%NaCl salt deposit were investigated. The results show that the hot corrosion mechanisms of DZ792 and DZ792G alloys are “acidic-alkali dissolution/inter sulfide-oxide”. During testing 70-150h, the corrosion mechanism of DZ792G alloy changes from alkali to acidic dissolution mechanism, finally resulting in the catastrophic corrosion. While，for DZ792G alloy, the O2- in molten salt can be preferential to react with the outside Ti-rich layer than that with inner Cr2O3 layer owing to the high Ti content, thus, the mechanism changes from alkali to acidic. However, as Ti content of DZ792 alloy is lower than that of DZ792G, the Ti-rich layer forms in the middle of the multilayered oxide, and the outer Ti-rich oxide formed stable spinel NiTiO3. The outer Cr2O3 layer reacts with the salt directly, therefore, the further corrosion of DZ792 alloy enable to be inhibited.