UC San Diego

FeAl-based Metallic-Intermetallic Laminate (MIL) composites and FeAl/FeAl2 eutectoid MIL composites of various iron alloys were fabricated with an innovative “multiple-thin-foil” configuration and “two-stage reaction” strategy. Alternating stacked metal foils were reactive sintered via spark plasma sintering (SPS) (a.k.a. field assisted sintering) to grow intermetallics. The “multiple-thin-foil” configuration reduces reaction time, enables local chemical composition control and allows metal/intermetallic combinations, which cannot be produced via the conventional methods. Fe-FeAl, 430SS-FeAl, and 304SS-FeAl MIL composites can be synthesized with desired metallic/intermetallic ratios, where FeAl is the single intermetallic phase present in the composites. The deformation and fracture evolution of the FeAl-based MIL composites is investigated here via incremental compression testing. Geometrically necessary dislocation (GND) analysis indicates the FeAl regions deform in similar manners for the three MIL composites, and each fails in a similar mode. Single-phase intermetallic FeAl layered material is also synthesized using a similar approach to study the fracture mechanisms of FeAl-based MIL composites. Mesoscale hetero-deformation induced (HDI) stress, which is tensile on the FeAl layers of MIL composites, accelerates crack nucleation and crack propagation, eventually inducing failure. The HDI stress evaluated via finite element analysis (FEA) simulation explains the difference between 430SS-FeAl and 304SS-FeAl MIL composites, which possess similar microstructure and composition, but very different strengths. Meanwhile, the electromigration effect in SPS is quantitively analyzed in the Fe-Al diffusion couple system. In SPS, the samples are heated by the applied voltage and a high electric current, which can lead to an electromigration effect. FEA simulation is utilized to determine the voltage applied to the Fe-Al diffusion couple, which is found to be extremely small to induce any voltage effect. Additionally, the simulation suggests the temperature and current density distribution is uniform across the metallic diffusion couple, which makes quantitative measurement feasible. For the first time, a mathematic algorithm, which allows diffusivity and electromigration coefficients to be solved, is developed for the system with multiple reactive layers.