Effect of thickness ratio on toughening mechanisms of Ta/W multilayers

Abstract

In the present work, effect of Ta/W thickness ratio on toughening mechanisms of Ta/W multilayers was investigated. Ta/W multilayers exhibit appreciable toughness and the toughness increase with increasing thickness ratio of Ta/W. Ta/W multilayers with thickness ratio tTa/W < 0.62 exhibit macroscopic crack propagation, higher tTa/W lead to more titled crack propagation and dissipates more energy by increased interface debonding during fracture. Crack propagation in Ta also changes from bidirectional crack propagation to unidirectional crack propagation as tTa/W increasing. Ta/W multilayers with tTa/W ≥ 0.62 exhibit multiple crack propagation. Formation of multiple cracking distributes damage and remarkably enhance the toughness. Crack propagation along interface to link the cracks which separated by the bridging effect of Ta, and crack propagation in Ta followed by plastic fracture of Ta mainly contributed to toughening. Smaller stress concentrations at crack tips due to multiple cracks, weakened driving force of each crack and increased interface debonding due to much more propagation directions, and crack propagation in Ta followed by plastic fracture of Ta contributed to much higher toughness of Ta/W multilayers with tTa/W ≥ 0.62 compared with those with tTa/W < 0.62.