Effect of Inconel 625 coating via high-speed laser direct energy deposition on the fatigue characteristics of Q235 steel

Single-layer and double-layer Inconel 625 coatings were deposited on the Q235 steel using high-speed laser direct energy deposition (HL-DED). Steel grains in heat-affected zone (HAZ) coarsened due to the heat generated during the single-layer coating deposition. In contrast, double-layer coating specimens exhibited fine-grain regions in the HAZ due to repeated laser treatment reaching the solid-state phase transition temperature. Compared to bare Q235 steel, the yield and ultimate tensile strength of the single-layer coated specimens increased by 25% and 21%, respectively, while their elongation decreased by 32%. Tensile strength increased, while elongation decreased with the coating thickness. Although fatigue performance of bulk HL-DED Inconel 625 and as-deposited coating specimens was lower than bare Q235 steel, polished coated specimens exhibited better fatigue performance than bare Q235 steel. The coating thickness in the as-deposited condition had minimal impact on fatigue performance, but the fatigue performance of the polished coated specimens decreased with coating thickness. Corrosion fatigue life of the single-layer coated specimens in a 3.5% NaCl solution was three times better than bare Q235, and the fatigue life of double-layer coated specimens is not affected by the corrosive environment.