UCLA

Advances in metal additive manufacturing (AM) are reshaping the design of structural alloys with exceptional performance. This dissertation investigates the deformation behavior of laser powder-bed-fusion (L-PBF) metals through in-situ synchrotron X-ray diffraction (SXRD) and electron microscopy, establishing a mechanistic framework that connects AM-induced microstructures to strength and ductility.The first part of this work addresses the printability barrier in refractory metals. To our current knowledge, we demonstrate the first near-fully dense, crack-free L-PBF tungsten-based alloy by introducing a small boron addition (0.3 wt.%). This modification disrupts solidification-cracking pathways and enables unprecedented tensile ductility at 800 °C in a material historically viewed as unprintable and intrinsically brittle. These findings establish a new foundation for refractory AM alloys in fusion and extreme-environment applications.The second part focuses on a TiC-inoculated Al-Mg-Zn-Cu alloy designed for high performance. TiC nanoparticles provide solidification control, producing an equiaxed fine-grained structure that remains stable through post-processing. Hot isostatic pressing (HIP) and T6 aging create a hierarchical precipitation architecture consisting of a grain-boundary MgZn₂ cage and dense intragranular η′/cluster networks. In-situ SXRD measurements of lattice-strain deviation, peak broadening, and diffraction-intensity changes reveal how plasticity initiates and load progressively transfers between the matrix and its precipitates. These mechanisms yield a rare strength–ductility synergy, resulting in the highest specific ultimate tensile strength (SUTS) reported for any aluminum alloy (269MPa/g/cm3)—exceeding even conventional Ti-6Al-4V.Complementary SXRD studies of pure Cu, equiatomic CoCrNi, and 316L stainless steel provide a reference framework for interpreting defect evolution in face-centered cubic (FCC) AM metals. Cu enables unambiguous quantification of dislocation-controlled hardening, whereas CoCrNi and 316L illustrate the influence of stacking-fault energy (SFE) on lattice-strain deviation and reflection-dependent behavior. Together with Al, these comparisons show that SXRD response cannot be universally interpreted without accounting for intrinsic elastic properties, SFE, slip-system accessibility, and defect character.Overall, this dissertation demonstrates that in-situ SXRD is uniquely capable of revealing microstructural load sharing and defect evolution under realistic operating conditions. Coupled with AM-specific microstructure design strategies—from nanoparticle-stabilized grain refinement in Al to boron-driven solidification control in W-B—these results define a pathway for engineering the next generation of lightweight and extreme-environment structural materials.