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Methods to strengthen aluminum alloys have been employed since the discovery of the age-hardening phenomenon in 1901. The upper strength limit of bulk Al alloys is~0.7 GPa by conventional precipitation strengthening and increases to 41 GPa through grain refinement and amorphization. Here we report a bulk hybrid nanostructured Al alloy with high strength at both room temperature and elevated temperatures. In addition, based on high-resolution transmission electron microscopic observations and theoretical analysis, we attribute the strengthening mechanism to the composite effect of the high-strength nanocrystalline fcc-Al and nano-sized intermetallics as well as to the confinement effect between these nano phases. We also report the plastic deformation of nano-sized intermetallics and the occurrence of a high density of stacking faults and twins in fcc-Al after low-strain-rate deformation at room and high temperatures. Our findings may be beneficial for designing highstrength materials for advanced structural applications.

As two important mechanical properties, strength and ductility generally tend to be muturally exclusive in conventional engineering materials. The breakthrough of such a trade-off has been potentiated by the recently developed CuZr-based bulk metallic glass (BMG) composites ductilized by a shape memory CuZr(B2) phase. Here the microstructural dependences of tensile properties for the CuZr-based BMG composites were elucidated qualitatively and modeled quantitatively, and the underlying mechanisms were unraveled. Through the microstructural percolation induced by matching the length scales of particle size and interparticle spacing, a notable breakthrough was achieved in the composites that the general conflicts between strength and ductility can be defeated. This study is expected to greatly aid in the microstructural design and tailoring for improved properties of BMG composites. It also has implications for the development of strong and ductile materials in the future.

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The fracture criterion of metallic glass (MG) is still under debate so far. On the issue of describing the normal stress effect on the tensile fracture behaviors of MGs, there are two fracture criteria: the Mohr-Coulomb (M-C) criterion and the Ellipse criterion. In this study, the normal stress acting on the tensile fracture planes was controlled and varied in a wide range by introducing inclined notches with different inclination angles to a series of Zr-based MG specimens. Based on the experimental results, both the Ellipse criterion and the M-C criterion are compared and analyzed. The experimental results reveal that the Ellipse criterion gives a better prediction than the M-C criterion for the tensile fracture behavior of the investigated Zr-based MG in a wide normal stress range. Moreover, the pressure and normal stress effects were separately considered and some other criteria were further discussed. It is found that under tensile loading, the pressure effect is weak while the normal stress effect is strong. Combined with previously reported results for a variety of MGs, the Ellipse criterion is found to have the capability to describe all the different contributions of the normal stress effect and thus may be suitable as a unified tensile fracture criterion for all MGs with different fracture behaviors.

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