Influence of NiCrAlY Content in TiC-Based Self-Healing Coating and Laser Remelting on Creep–Fatigue and Remnant Properties of 321 Stainless Steel

Abstract

The remnant creep and tensile properties of AISI 321 steels after creep–fatigue exposure are crucial to their remnant service life. Therefore, based on our recently reported plasma-sprayed TiC-based self-healing coating, an improved self-healing coating consisting of a NiCrAlY layer, a TiC–50-wt.% NiCrAlY layer, and an Al₂O₃–13% TiO₂ (AT13)–25-wt.% NiCrAlY layer was designed and prepared for AISI 321 steel by plasma spraying and further laser remelting treatment. The results indicated that such laser remelting self-healing coatings could further simultaneously improve the creep–fatigue resistance and remnant creep/tensile properties compared with the counterpart plasma-sprayed self-healing coating. This improvement is attributed to enhanced interlayer bonding, reduced porosity, and the introduction of dislocations due to thermal stresses during laser remelting treatment. Furthermore, the initial hardening observed during creep–fatigue exposure is due to dislocation strengthening, twin strengthening, and carbide strengthening, while the subsequent softening occurred due to dynamic recovery and coarsening of carbides as well as twin degradation.