  The fracture toughness of Al/SiC nanolaminates with different layer
thicknesses (in the range 10 to 100 nm) was measured by means of micropillar
splitting and bending of a notched beam. The crack plane was perpendicular to
the layers in the former while notched beams with the notch parallel and
perpendicular to the layers were milled in the latter. It was found that crack
propagation parallel to the layers took place along the metal-ceramic
interfaces and the toughness increased with the layer thickness due to the
contribution of the plastic deformation of the Al layers. Crack propagation
perpendicular to the layers showed evidence of crack deflection/arrest at the
interface. The toughness in this orientation increased as the layer thickness
decreased due to the higher density of interfaces except for the nanolaminates
with 10 nm layer thickness. In the latter case, crack propagation took place
along the weak columnar grain boundaries, leading to a marked reduction in
toughness.

Materials Science