Recently, effective strategies for enhancing the mechanical properties of eutectic alloys have been suggested. By modulating the structural heterogeneity, e.g. length scale, morphology of eutectic phase, mechanical properties can be optimized. The growth tendency and morphology stability of eutectic phase have been effectively changed to destabilize the plastic instability by the addition of minor elements, resulting in the generation of a number of shear bands at the eutectic colony interface and encouraging the rotational motion of spherical eutectic colony. Moreover, systematic investigations on deformation mechanisms demonstrated that the rotational motion of the eutectic colonies including the structural heterogeneities (i.e. lamellar spacing, morphology, etc.) effectively accommodate and dissipates the localization of shear strain, resulting in improving the macroscopic plasticity. However, there have been only a few reports on the detailed investigation for the role of individual phase composed of multi-phase composites during deformation. Moreover, in more recently, there are researches to be described for deformation mechanisms using nano- and/or micro-scale deformation mechanisms such as dislocation, slip, etc.

In this presentation, the micro- to nano-scale deformation mechanisms of ultrafine eutectic composites successfully synthesized in Fe-Nb-B, and Co-Cr-Mo-(Cu) eutectic composites have systematically scrutinized.

First, we explore the microstructural modulation and mechanical properties of Fe-Nb-B ultrafine composites by the addition of boron. To understand the origin of critically changed macroscopic mechanical properties, the values of hardness and elastic modulus obtained from nanoindentation test were plotted and demonstrated as a contour map. The structural characterization and nano-scale mechanical analysis are capable of providing the clear evidence to understand the relationship between microstructure and mechanical properties of the ultrafine multi-phase composites.

  Second, the outstanding mechanical properties of Al-Cu-Si based bimodal ultrafine eutectic composites containing length scale hierarchy in the eutectic structure were demonstrated by using AFM observation of surface topography with quantitative height measurements and were interpreted in light of the details of the deformation mechanisms by three different interface modes. A strain accommodated microstructure characterized by the surface topology gives a hint to design novel ultrafine eutectic alloys with excellent mechanical properties.

Third, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

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