Hot corrosion behavior and mechanical properties degradation of a Ni–Cr–W-based superalloy

Abstract: The effect of molten salts on the mechanical properties of a Ni–20Cr–18W (wt%)-based superalloy was investigated in this work. The hot corrosion characteristics and the microstructural evolution during the hot corrosion process were analyzed. The corrosion scale forms on the surface of the substrate, and its thickness increases gradually during the process. The element of S invades the substrate. The corrosion products mainly include NiO, Ni₃S₂ and Cr₂O₃. The hot corrosion in molten salt makes the specimens rough and flawed. The serration grain boundaries are observed in the hot corroded specimens. The tensile strength and elongation of the original alloy are ~1023 MPa and ~15 %, respectively. After corroded for 5 h, the tensile strength and elongation of the specimen decrease to ~771 MPa and ~7 % and diminish to ~814 MPa and ~9 % for the specimen corroded for 10 h. The hot corrosion process deteriorates the mechanical properties of the alloys. And the tensile strength and elongation of the specimen corroded for 20 h sharply decrease to ~539 MPa and ~3 %, respectively. The nonmonotonic variation of the mechanical properties of the specimen occurs for the specimens corroded for 10 h, which is related to the competition between the depredation of the molten salts and the strengthening process by carbides and the serrated grain boundaries. Graphical Abstract: The corrosion characteristics and microstructural evolution of a Ni–20Cr–18W-based superalloy were investigated during the hot corrosion process. It is found that the attack of molten salts makes the tensile strength of the specimens deteriorate significantly. The nonmonotonic variation of mechanical properties is related to the competition between the destruction of molten salts and the strengthening process during the hot corrosion process.[Figure not available: see fulltext.]