Interface Effects on the Mechanical Properties of Nanocrystalline Nanolaminates

Nanocrystalline nanolaminate (ncnl) structures are widely used in the study of physical properties in order to engineer materials for a variety of industrial applications. Often, novel and interesting mechanical behaviours that are found in nanolaminate materials can be linked with two characteristic features of structure. These are the layer pair spacing and the grain size. For the case of nanolaminates synthesized by physical vapor deposition processes, the layer spacing corresponds with the repeating sequence of layer pairs and can be referred to as composition wavelength. The grain size is the average width of the tapered columnar structure along the growth direction. Since the mechanical properties of strength and hardness are known to functionally vary with the separation between dislocations in crystalline materials, both structural features can potentially contribute to the total interfacial area and the characteristic separation of interfaces that mitigate dislocation motion. In this investigation, the individual contribution of layer pair spacing and grain size to the total interfacial structure are each quantified in an assessment of strength and hardness. A model is proposed for the total interfacial area of the material volume under plastic deformation that can quantify the interfacial area contribution from the layer pairs and the grain size. It is anticipated that each structural feature can potentially dominate the plastic deformation of the nanolaminate as dependent upon the specific layer pair spacing, the grain size, and the extent of plastic deformation.