Morphological Stability of Ni(Al)/Ni₃Al Nanolaminate Composites

Abstract

This manuscript discusses the morphological instability observed when multilayered samples with alternating layers of Γ-Ni(Al)/γ-Ni3Al are exposed to 800C for approximately 100 hours. Samples with 20nm/20nm or 120nm/120nm layer thickness and <001> or <Ill> crystal orientation to the interface normal were tested. Pinching off of layers is strongly affected by crystal orientation and layer thickness. Corresponding modeling suggests that the stability of this system is sensitive to fluctuations in the volume fraction of the two phases, the aspect ratio of columnar grains in the layers, and whether coherent or semi-coherent interfaces are present.

Correlation of stress state and nanohardness via heat treatment of nickel-aluminide multilayer thin films

“…The breakdown occurs due to thermal grooving along columnar grain boundaries in ␥Ј layers, due to a large value of ␥Ј grain boundary energy compared to ␥/␥Ј interfacial energy. 33 Apparently, the compressive biaxial stress state present initially in the ␥Ј phase is not sufficient to offset the driving force to reduce the area of high energy ␥Ј grain boundaries. Further, the long-range diffusional transport present in this instability requires a larger temperature than the strengthening mechanism produced by a 673 K heat treatment.…”