Thermo-mechanical evolution and control of residual stress and distortion in hybrid investment casting-additive manufactured Ti6Al4V components

Hybrid investment casting (IC)-additive manufacturing (AM) combines the geometric precision of casting with the design flexibility of AM, offering a promising route for fabricating complex, high-performance metallic components. However, residual stress and distortion remain major challenges that limit dimensional accuracy and structural reliability. In this study, the thermo-mechanical behavior of Ti6Al4V components fabricated by laser directed energy deposition (LDED) on IC substrates is systematically investigated through combined in-situ thermo-mechanical measurements and finite element simulations. By maintaining identical laser input parameters, the effects of IC substrate thickness, thermal boundary conditions, cooling strategies, and scanning paths on heat accumulation, distortion, interfacial residual stress, and microstructural evolution are isolated and analyzed. Flat, annular, and beveled IC substrates are employed to represent both geometrically simple and application-relevant complex IC-AM configurations. The results show that moderate heat accumulation promotes stress relaxation and reduces distortion, whereas excessive thermal input induces prior-β grain coarsening and degrades mechanical performance. Increasing substrate thickness effectively suppresses part distortions but elevates residual stresses at the IC-AM interface, highlighting the necessity of coordinated thermal management. Furthermore, partitioned scanning strategies are found to significantly affect local stress superposition and deformation in complex geometries. By elucidating the coupled relationships among thermal history, mechanical response, microstructural and property, this work provides engineering-oriented insights into the coordinated regulation of residual stress, distortion, and metallurgical quality in hybrid IC-AM Ti6Al4V components, offering practical guidance for process optimization and structural design of complex hybrid-manufactured parts.