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Current methods for modeling hybrid additive manufacturing are computationally inefficient for use in optimization algorithms. An analytical tool is needed to understand how cycling thermal and mechanical loads via 3D printing and cold working reshapes cumulative residual stress within a build volume. A novel analytical model was developed that couples beam theory and superposition to rapidly predict cumulative residual stress. Modeling results were experimentally validated on AlSi10Mg after laser shock peening prescribed layers during powder bed fusion. Results demonstrated a vertically translating heat-affected zone, and the use of beam-based superposition accurately accounted for residual stress redistribution from cyclic printing and peening. 

The objective of this research was to quantify the change in magnitude and depth of compressive residual stress (CRS) retained in the subsurface by interlayer coldworking when subjected to localized annealing that superimposed tensile stress. The approach was to hybridize additive manufacturing of AlSi10Mg alloy by coupling powder bed fusion (PBF) with laser shock peening (LSP) and characterize the resultant residual stress state by the hole-drilling method. The research found localized annealing from layer deposition formed two distinct regions in the subsurface, which was driven by localized and bulk stress redistribution. The experiments also showed that residual stress redistribution from LSP reached 550 µm into the subsurface, whereas local annealing from the deposition of layers extended only to a depth of 160 µm. Hence, compressive stress imparted by LSP was not entirely canceled by local annealing from PBF. This work provides the first quantification of the stress state response of hybrid additively manufactured parts to thermal loads and is fundamental to improving part performance through increased functional reliability, fatigue life, and corrosion resistance. 

Additive manufacturing (AM) often results in high strength but poor ductility in titanium alloys. Hybrid AM is a solution capable of improving both ductility and strength. In this study, hybrid AM of Ti-6Al-4 V was achieved by coupling directed energy deposition with interlayer machining. The microstructure, residual stress, and microhardness were examined to explain how interlayer machining caused a 63% improvement in ductility while retaining an equivalent strength to as-printed samples. Interlayer machining introduced recurrent interruptions in printing that allowed for slow cooling-induced coarsening of acicular α laths at the machined interfaces. The coarse α laths on the selectively machined layers increased dislocation motion under tensile loads and improved bulk ductility. The results highlighted in this publication demonstrate the feasibility of hybrid AM to enhance the toughness of titanium alloys.