Microstructural evolution and mechanical properties of Ni/Al reactive nanolaminates with different NixAly intermetallic phases

Nanolaminates made up by alternative Ni and Al nanolayers are widely applied to solder structural materials, due to abundant heat releases when supplied with an energetic input. This work studies the microstructural evolution and mechanical properties of Ni/Al nanolaminates with a wide mole ratio of Ni (MNi, 0.18-0.53), to ascertain the role of NixAly intermetallic phases during heat-treatment. To this end, 3 nanolaminates with Al thickness fixed at X110 nm and Ni thickness varying 15-75 nm are fabricated and are heat-treated at 400 degrees C, to trigger formations of NiAl3, Ni2Al3 and NiAl intermetallic phases. The results suggest an enhanced strength of Ni/ Al after heat-treatment. However, their evolution with MNi is complex. The nanolaminate with MNi X0.18 is the softest after heat-treatment, due to the dominant plasticity of residual Al phases. The maximized strength is achieved when MNi X0.40, in which a novel NiAl3/Ni2Al3 nanolaminate structure is formed. Owing to the brittleness of both phases, the nanolaminate after heat-treatment is fractured by shearing upon uniaxial compression. The best strength-ductility synergy is achieved when Ni mole ratio X0.53. In the heat-treated nanolaminate a homogenous nanocrystalline NiAl phase is formed. As a result, the nanolaminate exhibits excellent ductility and intermediate strength among the 3 nanolaminates.