Regularities of sintering of zirconium diboride-molybenum alloys

Summary

In the process of sintering of mixtures of zirconium diboride with 5, 10, and 15% Mo, specimen growth resulting from heterodiffusion is observed at the instant of formation of solid solution of Mo in ZrB₂ during slow heating to high temperatures or during the initial period of isothermal holding in the case of very rapid heating. At temperatures of up to 1700–1750°C, growth predominates over shrinkage, and specimen dimensions increase with increasing holding time; at temperatures above 1800°C, positive shrinkage takes place, but is very slight in the case of rapid heating to the isothermal holding temperature.

During isothermal holding in the temperature range 1800–2200°C, very intensive shrinkage is observed during the initial period (20–30 min). Subsequently, this shrinkage slows down, and may be described as viscous flow caused by diffusional processes. The energy of activation of the densification process, calculated from the shear viscosity values obtained, was found to be 367±48, 352±28, and 379±46 kJ/mole for alloys of ZrB₂ with 5, 10, and 15% Mo, respectively, i.e., less than the energy of activation of densification of zirconium diboride (678±55 kJ/mole).

Thus, the presence of molybdenum activates diffusion processes during sintering.