In-situ fabrication of repairing layers for large structures using follow-up hot-hammering-assisted wire arc additive manufacturing

Abstract

The development of a spherical hammer head follow-up hot-hammering-assisted (FH) hybrid wire arc additive manufacturing enables the application of the hammering-assisted process to the in-situ repair of large-scale structural parts. This process allows for large deformation in the deposited weld bead with lower energy input at higher temperatures, resulting in less work hardening. A thermal, mechanical and plastic deformation coupled finite element model is established to analyze the plastic strain distribution with different shapes of hammer heads and different deformation history. Compared with the flat hammer head, the spherical hammer head is more likely to produce large plastic deformation in deposited weld bead under the same force and energy conditions, and obtain more uniform microstructure. Different hammering temperatures higher than austenite recrystallization temperature with the spherical hammer head, are selected to study the effect on grain refinement of repairing layers. The OM, XRD, SEM and EBSD are used for grain, texture evolution and strengthening mechanism analysis. The results show that by introducing the spherical hammer head FH process at 980 °C slightly higher than the austenite recrystallization temperature, the grain size decreases gradually from the bottom repairing layer to the top one, showing a genetic evolution law. The topmost repairing layer grain size is refined from 353 μm to 30 μm, the average grain size of repairing layers is refined from 361 μm to 62 μm, and the strong {100} texture of the topmost repairing layer is reduced to be approximately random. The grain refinement is attributed to the combined influence of recrystallization and co-generation crystallization. Meanwhile, the yield strength is significantly improved, and the main strengthening mechanisms are grain refinement strengthening and dislocation strengthening, and the contributions are 42.0 MPa and 101.4 MPa.