2018 Volume 59 Issue 2 Pages 265-271
This article reports the pulsed electric current bulk synthesis and high-temperature X-ray diffraction structure of the amorphous B4C powder prepared by planetary ball milling. Solid state synthesized amorphous B4C shows two-stage structural relaxation characterized by a significant increase to 2.1 in relative integrated X-ray intensity of first amorphous diffraction peak with increasing temperature to 1573 K. Amorphous B4C can be consolidated, avoiding visible submicron sized pore without the need for additives; its temperature decreases 1473 to 1073 K by decreasing 2.5 to 1.0 mm in final sample height in combination with an increasing applied stress 100 to 120 MPa. For the amorphous B4C, subjected to full structural relaxation; the rapid densification in heating can be fairly well expressed by an Arrhenius-type equation of Newtonian viscous flow, η = ηoexp(420 kJmol−1/RT) where η is the consolidation process viscosity. Progressive structural relaxation of amorphous B4C then is described as increase in viscosity constant (ηo) having a relationship of the form, ηo = ηooexp(−335 kJmol−1/RT). The density of the consolidated amorphous B4C is estimated at 2.02 Mgm−3 at the minimum, which is 0.8 of theoretical one for stoichiometric compound. The strain rate sensitivity for bulk amorphous B4C is determined to be a significantly low value of 0.043, characteristic of inhomogeneous plastic flow in Berkovich dynamic indentation testing.
