Improved creep-fatigue and remnant tensile/creep properties of 321 stainless steel by self-healing coating

AISI 321 steels used as intake valves in turbines are frequently subjected to creep-fatigue (C-F) exposure during service. Improving C-F resistance and assessing remnant creep/tensile properties are therefore required for their safe service. In this work, the self-healing coating consisting of Al2O3-13TiO(2) layer, TiC layer, and NiCrAlY layer was prepared for 321 steel. The effects of such self-healing coating on the C-F and remnant creep/tensile properties were studied. The results showed that the initial hardening phenomena of the studied steel during C-F exposure was mainly attributed to the dislocation strengthening and a certain level of carbides precipitation strengthening, while the subsequent softening behaviors were resulted from dynamic recovery and coarsening of carbides. Moreover, as compared to other coatings, the self-healing coating is able to improve the mechanical properties of steels due to dislocation strengthening, precipitation strengthening, and the self-healing behavior resulting from the reaction between the TiC layer and oxygen.