Effect of laser-induced protective materials/rare earth boride double protection structure on the microstructure and properties of multi-pass ER2209 underwater direct laser energy deposition coating

Abstract

Underwater direct laser energy deposition technology has emerged as a prominent research focus in the field of underwater in-situ restoration due to its ease of operation and high precision in repairs. This study successfully prepared an ER2209 underwater in-situ cladding layer using a self-designed underwater laser-induced self-protection material. However, achieving a balance between the forming quality of the underwater repair layer and its critical service performance remains a significant research challenge. In this investigation, we introduced rare earth boride (LaB₆) into the underwater self-protective material, thereby constructing a double-layer composite protection structure. The results indicate that the incorporation of rare earth elements from the LaB₆ protective layer enhances the purification of the molten pool, leading to a more uniform internal structure of the underwater repair coating. The solution strengthening provided by the small atomic radius of the B element, combined with the lattice distortion effect of the larger atomic radius La element, contributed to improvements in microhardness and abrasion resistance of the underwater repair layer. In summary, the underwater in-situ cladding coating, characterized by superior forming quality and optimal properties, has been successfully prepared using an underwater self-purification/rare earth boride double-layer protective material structure. This advancement offers significant insights for the field of underwater in-situ laser repair.