Departing from the volume-averaging method,an overall solidification kinetic model for undercooled single-phase solid-solution alloys was developed to study the effect of back diffusion on the solidification kinetics.Application to rapid solidification of undercooled Ni-15%Cu（mole fraction） alloy shows that back diffusion effect has significant influence on the solidification ending temperature but possesses almost no effect on the volume fraction solidified during recalescence.Inconsistent with the widely accepted viewpoint of Herlach,solidification ends at a temperature between the predictions of Lever rule and Scheil＇s equation,and the exact value is determined by the effect of back diffusion,the initial undercooling and the cooling rate.
In-situ formed （Cu0.6Zr0.3Ti0.1）95Nb5 bulk metallic glass （BMG） composite with Nb-rich dendrite randomly dispersed in hard glassy matrix was prepared by casting into a water-cooled copper mold. The dendrite has much smaller hardness and elastic modulus than glassy matrix, and the stress concentration at interface provides a channel for the initiating and branching of shear bands upon loading, thus leading to a high compressive fracture strain of 6.08% and fracture strength about 2200 MPa. Comparing with other Cu-based BMG composite, the fracture strength of present （Cu0.6Zr0.3Ti0.1）95Nb5 composite is not significantly reduced, indicating that the addition of Nb in the current work is an effective and effortless way to fabricate new practical BMG composites with enhanced strength and good plasticity.
