Optimization for achieving robust metallurgical bonding interfaces in the integrated laser additive manufacturing of extremely property-mismatched materials

Abstract

High-strength bonded interfaces of additive manufacturing (AM) multi-material structures are usually obtained through extensive trial-and-error experiments, leading to increased manufacturing costs. In this study, a three-way optimization method is proposed based on thermodynamic calculations, which combines joining methods, deposition strategies, and post-heat treatment to achieve robust metallurgical bonding interfaces in the integrated laser additive manufacturing of extremely property-mismatched materials. The integrated forming of ultra-high strength steel (UHSS) and Ti6Al4V (TC4) was achieved with Ni-Cr-V interlayers via laser-directed energy deposition (LDED). The introduction of Ni-Cr-V interlayers emerged as a pivotal solution for addressing material compatibility between UHSS and TC4. By optimizing deposition strategies, high-quality UHSS-Ni, NiCr, CrV, and V-TC4 bonded interfaces were obtained without cracks or intermetallics. Furthermore, a customized post-heat treatment significantly enhanced the performance of LDED UHSS-Ni-Cr-V-TC4 sample (UTS: 120.9 MPa → 298.3 MPa), surpassing the UTS of the weakest material, Cr. The 3D-DIC results revealed distinct locations where plastic deformation (V region) and ultimate fracture (Cr region) occurred in the heat-treated sample, presenting a novel phenomenon that sharply contrasts with the behaviors displayed by homogeneous materials such as UHSS and TC4. This disparity primarily arises from the properties of materials (elastic modulus/strength). Finally, strategic approaches for fabricating high-quality AM multi-material structures were discussed. These findings enrich and advance the innovative theory of “material-structure-performance/function integrated laser additive manufacturing”, which holds important reference and guiding significance for the subsequent high-quality forming of other AM multi-material structures.