Mechanical Behavior of Nanoscale Multi layer Metallic Composites-Dynamic Crack Propagation in Nanoscale Ni-Al Bilayer Composite
R Mohan and Y Purohit and A Kelkar, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 12, 60-69 (2015).
Nanoscale multilayer metallic composites (NMMCs) contain significantly high volume fraction of interfaces and exhibit strengths much higher than that of bulk materials composing the structures. This strengthening has been attributed to the presence of interfaces between materials that differ in properties such as elastic modulus, lattice parameters, slip plane orientations and act as barriers to propagating dislocations. This paper presents a review of two major factors that influence the properties and behavior of the NMMCs: Interface structure, Strengthening/Deformation mechanisms. The influence of semi-coherent Ni (nickel)-Al (aluminum) interface on Mode-I crack propagation in nanoscale Ni-Al bilayer composite under tensile and cyclic loading conditions analyzed through computational modeling is discussed. Results for nanoscale Ni-Al bilayer composite showed initial brittle crack propagation with planar cleavage of atoms followed by crack surfaces getting roughened when crack propagation speed is about one-third of Rayleigh wave speed. In case of Mode-I tensile cyclic loading, crack was found to propagate either by fatigue cleavage of the atoms or by void nucleation in the regions near the crack tip, depending on the value of maximum strain applied. In Ni-Al bilayer composite studied, as crack approached the interface, dislocations start emanating from the interfacial layer. The creation of voids was found to slow down crack growth in both the Ni and Ni-Al at higher maximum applied strain during cyclic loading. Plastic deformation was found to dominate crack propagation during tensile loading that resulted in a slower crack growth than cyclic loading. In all cases, presence of semi-coherent interface in the nanoscale Ni-Al bilayer composite was found to prohibit crack from propagating beyond the interface.
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