Interaction of Dispersed Cobalt with Molten Copper under Low-Frequency Vibration

The possibility of increasing the hardness of a Co–Cu binder in single-stage production of WC–Cu–Co composites using pre-solidification low-frequency vibration (LFV) is investigated. Cu–Co and WC–Cu–Co alloys are fabricated by reactive infiltration of liquid copper into uncompacted WC and Co powders under LFV of their compositions (80 Hz for 10 min at 1300–1350°C). Their phase and chemical compositions, structure, and hardness have been studied. We are the first to experimentally show that metastable formations (frozen immiscibility regions of two liquids) are the precursors of (Co) dendrites and have the same composition with them. The cobalt distribution over the height of Cu–Co alloy ingots and over phase components is shown to depend on the cobalt content, the effect of vibration, the geometric arrangement of initial component layers, and the temperature. The optimum conditions for achieving a uniform cobalt distribution over the melt have been determined. Cobalt is shown to ensure precipitation hardening of the Cu–Co metal binder due to the formation of (Cu) solid solutions already at the stage of synthesis of Cu–Co and WC–Cu–Co alloys. Moreover, the potential for additional hardening by subsequent heat treatment or by changing cooling conditions is still incompletely fulfilled.