||In this study, to solve the delamination behavior along the interface, graded regions were fabricated to erase the sharp interface. Three kinds of the amorphous ZrCu/ nanocrystalline Cu multilayered structures, namely, without graded region (ZCC-G0), with 50 nm graded region (ZCC-G50) and with 100 nm graded region (ZCC-G100), are manufactured by the magnetron co-sputter system. In the graded region, there are Cu nanoparticles distributed in the amorphous matrix. The graded region possesses the gradient nature in terms of composition, nanocrystalline phase size, nanocrystalline volume fraction, and cross sectional modulus distribution from the amorphous ZrCu to the nanocrystalline Cu. To figure out the mechanical properties enhancement by the graded region, nano-scratch, nano-tension, and nano-bending tests were applied in this study. |
For the nano-scratch testing, we first used the variation of fracture toughness as a function of normal force to determine the delamination point. And this method is considered not to be influenced by the loading rate. ZrCu/Cu interface delaminated when the applied normal force reached to 1460 μN for ZCC-G0, and no obvious interface delaminated behavior could be found for both ZCC-G50 and ZCC-G100.
For thenano-tension testing, nano-scaled tension samples are designed and fabricated by focus ion beam. The nano-scaled tension tes is performed by the nanoindentation system equipped a conical tip with scratch mode. Although this test failed due to the limitation of the film thickness, the tip could not drag the tension sample successfully, but it brings many possible ways for the nano-scaled tensile testing with scratch mode.
For the nano-bending testing, T-shaped cantilevers are designed and fabricated by focus ion beam to let the applied force concentrate on the interface region during testing. The nano-bending test is performed by an in-situ nanoindentation system. For the ZCC-G0 samples interface bending fracture stress is 1.9 ± 0.1 GPa, and the bending strain is about 11 ± 1%. The interface bending fracture stress, for the ZCC-G50 and ZCC-G100 samples is 2.8 ± 0.2 GPa, and the bending strain is about 18 ± 1%. These results demonstrated that multilayered thin films with graded structure would be inherited with a much higher interface strength/strain/modulus, with an overall improvement upgrade of more than 50% and a ductile failure manner.