Experimental and chemo-mechanical analysis of hot corrosion influence on creep properties of DD6 single crystal superalloy in molten NaCl salt

The creep tests of specimens coated with NaCl salt were carried out to investigate the influence of hot corrosion on the creep properties of DD6 under 980 °C and 275 MPa. Bared specimens were also studied to make comparison. Creep lives of the salt-coated specimens are much lower than those of the bared specimens. Metallographic analysis of the fracture surface shows that creep-rupture of the salt-coated specimens is caused by a main tearing ridge rather than the connection of dimples in the bared specimens. Directional diffusion of metallic elements, i.e. Cr, Ta, and W, happens in hot corrosion-creep test due to the chemical gradient. The location of Al-rich region in the salt-coated specimen is found along the path of crack propagation. The microstructure evolution of γ/γ′ is different between the salt-coated specimens and the bared specimens. A chemo-mechanical coupling model was used to assist the understanding of the failure mechanism of the salt-coated specimen. The simulation results prove that the anodic concentration is a basic factor for the appearance of the main tearing ridge and Al-rich region in the salt-coated specimen. These findings can be helpful to understand the mechanical properties of Nickel-based single crystal superalloys in marine environment.