Mechanical and microstructural characterization of 9Cr-1Mo steel with Inconel 625 thick coating

The use of coated structural materials in Molten Salt Reactors (MSR) enables surfaces to be functionalized. This would allow to obtain a corrosion and irradiation resistant component. This study explores the mechanical and microstructural properties of a 9Cr-1Mo (grade 91) martensitic steel substrate coated with Inconel 625. Tensile tests were conducted at ambient (20 °C) and high temperatures (400 °C, 600 °C, and 700 °C). The interface’s tensile strength was evaluated, revealing that failures consistently occurred within the substrate rather than at the interface. This indicates strong adhesion between the coating and substrate. Microstructural analyses were performed, identifying five distinct regions within the Heat Affected Zone (HAZ). These regions included rapidly quenched martensite and residual δ ferrite, which influenced the mechanical properties observed during testing. Additionally, the solidification of the Inconel 625 coating is discussed. It is proposed that Inconel 625 grows epitaxially on the substrate (P91) while it is still in the austenitic phase during cooling of the molten zone. This could explain the good mechanical strength of the bond. • Functionalization of surfaces for molten salt reactors by TIG deposition. • Epitaxial growth of Inconel 625 on the substrate (P91). • Understanding the integrity of the junction by microstructural characterization.