An investigation of oxidation/hot corrosion-creep interaction at 800 ℃ in a Ni-base superalloy coated with salt mixture deposits of Na_2SO_4-NaCl-NaVO_3

摘要

Creep-rupture behaviour of Nimonic263 alloy coated with 87.5 wt.%Na2SO4+5 wt.%NaCl + 7.5 wt.% NaVO3(3SM) and 74 wt.%Na2SO4 + 21.7 wt.%NaCl+4.3 wt.%NaVO3(3SM-A) was investigated in the stress range of 180-350 MPa at 800 degrees C. The 3SMs are responsible for the reduction in creep-rupture life. Hot corrosion products found in the crack regions of the crept specimens deformed under the influence of 3SMs. Sulphidation followed by oxidation was dominant at 250 MPa, whereas oxidation was dominant at 215 and 180 MPa. Comprehensive microstructural characterization and analysis suggest that three-salt mixtures(3SMs) accelerate oxygen and sulphur penetration along the grain boundaries during creep, and enhance the stress assisted grain boundary oxidation resulting in a reduction in creep-rupture life.