A physical phenomenon where the interface between two bonded metals moves when heated because atoms of one metal diffuse into the other faster than the reverse. This unequal flow leaves behind vacancies that coalesce into microscopic pores on the faster-diffusing side. Metallurgists monitor this during welding, brazing, and alloy bonding to prevent joint failure from internal void formation.
Heard on the job
The bond failed during thermal cycling because the Kirkendall effect created a layer of voids right at the interface.