TEM observations of reactive bonded Ti6Al4V alloy

Ni(V)/Al multilayer covered with Ag-based braze alloy (NanoFoil®) was applied for joining parts made of Ti6Al4V alloy. The reaction of multilayers was started with electric current pulse (0.5 A, 9 V). The transmission electron microscopy (TEM) observations of joint area, backed by analysis of the electron diffractions, showed that the initial Ni(V)/Al multilayer transformed into fine grain (~150 nm) of B2-NiAl intermetallic phase. The silver-based braze alloy layer from top and bottom of Ni(V)/Al multilayer, located itself mostly at the B2-NiAl/Ti6Al4V interface as Ag-rich precipitates, but small amounts out-diffused into B2-NiAl as intergranular veins. The Ti6Al4V close to the B2-NiAl is subject to strain high enough to fill it with platelets of α″-Ti martensite.