The effect of the temperature on the compressive stress-strain behavior of Al/SiC nanoscale multilayers was studied by means of micropillar compression tests at 23 °C and 100 °C. The multilayers (composed of alternating layers of 60 nm in thickness of nanocrystalline A1 and amorphous SiC) showed a very large hardening rate at 23 °C, which led to a flow stress of 3.1 ± 0.2 GPa at 8% strain. However, the flow stress (and the hardening rate) was reduced by 50% at 100 °C. Plastic deformation of the A1 layers was the dominant deformation mechanism at both temperatures, but the A1 layers were extruded out of the micropillar at 100 °C, while A1 plastic flow was constrained by the SiC elastic layers at 23 °C. Finite element simulations of the micropillar compression test indicated the role played by different factors (flow stress of Al, interface strength and friction coefficient) on the mechanical behavior and were able to rationalize the differences in the stress-strain curves between 23 °C and 100 °C.

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In situ three-dimensional (3-D) X-ray synchrotron tomography of fatigue crack growth was conducted in a 7075-T6 aluminum alloy. Local measurements of da/dN were possible with the 3-D data sets obtained from tomography. A comparison with fatigue striation spacings obtained from scanning electron microscopy of the fracture surfaces yielded excellent correlation with da/ dN obtained from tomography. The X-ray tomography technique can be used to obtain a highly accurate and representative measurements of crack growth locally in the microstructure of the material.

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