Formation of Cu-rich crystalline/NiNb-rich amorphous composite induced by liquid phase separation

Liquid phase separation phenomena give rise to a unique opportunity in developing the crystalline/amorphous composites using melt-spinning method. In this study, a new crystalline/amorphous composite with a droplet-type microstructure is investigated in Cu-Ni-Nb immiscible system. It is found that the Cu-30(Ni38Nb62)(70) alloy undergoes liquid-liquid phase separation in the undercooled liquid state, and then solidifies into Cu-rich crystalline phase and NiNb-based amorphous phase. The fcc Cu-rich crystalline droplets are dispersed in the NiNb-based amorphous matrix. The grain size of Cu-rich droplets is in the range between nanometer dimension order and micrometer order. On the other hand, an obvious layer without Cu-rich nanoparticles is observed near the wheel side. The indentation testing of Cu-30(Ni38Nb62)(70) ribbon shows a larger elastic-plastic deformation area and much smaller Vickers hardness, due to the formation of softer Cu-rich particles. Further results indicate that the formation of droplet-type microstructure could be attributed to the liquid phase separation and amorphous phase formation. (C) 2013 Elsevier B.V. All rights reserved.