<b>IMPROVING PLASTICITY IN B2 COAL INTERMETALLICS AT ROOM TEMPERATURE AND STABILIZATION OF L12 CO3AL INTERMETALLICS</b>

<p dir="ltr">Co-Al based intermetallics (L1₂ Co₃Al and B2 CoAl) and alloys have attracted significant interest for advanced structural materials, because of high melting point and high strength. Nonetheless, two major challenges, i.e., stabilization of binary L1₂ Co₃Al and limited plasticity of B2 CoAl at room temperature, severely hindered their practical applications. Here we firstly report the synthesis/stabilization of stoichiometric L1₂ Co₃Al embedded within HCP supersaturation via magnetron sputtering, which provides new insights on the crystal structures of stoichiometric Co₃Al and the design of novel Co-Al based alloy systems. Then we utilized B2 CoAl intermetallic as a prototype to investigate several strategies of improving plasticity in brittle B2 intermetallics at room temperature. Three types of CoAl 100 nm/X 10 nm nanolaminate systems are constructed. In the first case, we examined CoAl/Fe nanolaminate with coherent interface. In the second case, we evaluated CoAl/Ni nanolaminate with incoherent interface and pre-existing dislocations in CoAl. In the third case, we investigated CoAl/Al-Co with amorphous intergranular film network and pre-existing dislocations in CoAl. <i>In situ</i> micropillar compression tests show significant synergy of high strength and room temperature plasticity in these nanolaminate systems. Transmission electron microscopy (TEM) studies coupled with molecular dynamics (MD) simulations reveal the effects of different types of interfaces and pre-existing dislocations on deformation mechanisms and work hardening capability in B2 CoAl intermetallics. The findings presented in this thesis provide a new perspective on improving room temperature plasticity in a wide range of brittle materials.</p>