2003 Volume 44 Issue 1 Pages 188-196
By incorporating small amounts (0≤5 at%) of transition metals (TM) of Cr, Mo, Fe and Ta into Pd40Cu30Ni10P20 alloy that has been considered to be the best glass former so far, in-situ composites consisting of a glassy phase and nano- and/or micro-sized crystalline particles were prepared by copper-mold casting. The nano- and micro-sized particles identified to be phosphides are homogeneously dispersed in a glassy matrix. The formation of such a characteristic structure is attributed to a primary crystallization reaction with high nucleation rate and limited growth rate in the undercooled Pd40Cu30−xNi10P20TMx melt. The TM atoms interact preferentially with the clusters of Pd–Ni–P, one kind of atomic units in the deeply undercooled Pd–Cu–Ni–P liquid, and result in the formation of the TM–Ni–P or TM–Ni–P–Pd clustered units in the undercooled melt, which act as nucleation sites during solidification. With the addition of Cr, Mo, Fe and Ta atoms into Pd40Cu30Ni10P20 alloy, the first phosphide phases precipitated from these melts are Ni33Cr33P34, MoNiP, Fe33Ni33P34, and (Pd,Ta)NiP, respectively. These phases possess the same hexagonal structure as Fe2P (hP9). The dispersed particles have a volume fraction ranging from 9 to 18% for the alloys investigated. The compressive strength and ductility of these glassy composites are not significantly improved by the dispersion of the nano- and micro-sized particles. These glassy composites deformed by an inhomogeneous shear slip mode and fractured by an adiabatic shear mechanism. The nucleation behavior and the effect of dispersed particles on the deformation and fracture behavior are discussed.