Figure 4

Structural characterization of samples. (a) SEM image of Al-BNNT (3 wt.%) composite pellet before melt casting. (b) A morphology formed in the melt cast ribbon; the inset in (b) is an optical image of the cast ribbon after polishing and etching; this reveals an approximately 1.5- to 3-μm Al grain size. (c, d) Representative fracture surfaces of the tensile-tested sample (3 wt.% BNNT) at various magnifications; individual BNNTs are seen at those surfaces (arrowed); thus they, at least partially, carry the applied tensile load and participated in the deformation process. A framed area shows a tube presumably broken into two halves under tension; this area is specially enlarged in the upper-right inset.