Thickness effect on microstructural and mechanical properties of pulse-laser treated Ti/Ni multilayer thin films

Previous work showed that pulse-laser irradiation can strengthen metal multilayer thin films through intermetallic formation and the degree of strengthening is a function of laser pulse energy.In this work,the effect of individual layer thickness(λ)and total multilayer thickness(h)on the resulting microstructure and mechanical strength of laser-treated Ti/Ni multilayers was further investigated.Experiments were carried out on fourλ/hcombinations using individual layer thickness of 20 nm and 50 nm,and total multilayer thickness of 500 nm and1μm,respectively.Obvious intermetallic strengthening was observed in the 500 nm thick multilayers,especially with the 20 nm layer thickness,but not in the 1μm thick multilayers.Further,the multilayer surface morphology after laser treatment was observed to be dominated by competition between laser-induced optical interference and thermal melting,with the former leading to ripple or cross-hatched patterns and the latter leading to melted surfaces with pores and cracks.