Revealing multiple strengthening transitions in crystalline-amorphous nanolaminates through molecular dynamics

Crystalline-amorphous nanolaminates allow for a unique combination of high strength and good ductility. This promising mechanical behavior is attributed to the different deformation mechanisms that occur in the crystalline and amorphous layers, however, a mechanistic understanding of the plastic strain transmission among these layers does not exist. In the present study a new nanoindentation configuration is employed that allows for the continuous emission of a pair of edge dislocations in the same slip planes as plastic sources, revealing the different interaction mechanisms between dislocations and amorphous layers of varying thickness. This allows to study the transmission of plastic strain from the crystalline to amorphous, and amorphous to crystalline layers. It is shown that the thickness of the amorphous layer controls the deformation mechanism, since thin amorphous layers act as obstacles to dislocation motion, while thick ones as dislocation sinks. As a result, more shear transformation zones and mature shear bands form in the amorphous layer, but less dislocations are nucleated in the lower crystalline layer as its thickness increases. These findings can be used to guide the design of crystalline-amorphous nanolaminates with desirable mechanical properties by precisely controlling the thickness of the amorphous layer.