Microstructure and Mechanical Properties of Cr, Mo, Fe, Ta Modified Pd-Ni-Cu-P Glassy Alloys Prepared by Copper-Mold Casting

抄録

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 Pd₄₀Cu_30−xNi₁₀P₂₀TM_x 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.