EFFECT OF DISPERSITY OF POWDER, PRESSURE AND SINTERING TEMPERATURES FOR MICROSTRUCTURE AND PHYSICO-MECHANICAL PROPERTIES OF BORON CARBIDE CERAMICS

Abstract

The main purpose of this work was to obtain a high-density superhard ceramic material based on boron carbide by sintering under high pressure without the use of activating additives. The microstructure, density and Vickers hardness of samples sintered from boron carbide powders of various dispersities at a pressure of 4 GPa in the temperature interval 1200–2000 °C were investigated. The powder with a bimodal particle distribution exhibits the best sinterability at this pressure. It was established that with an increase in the dispersion of the powder, the maximum on the curves of the dependence of the hardness of the samples on the sintering temperature shifts toward more low temperatures. Samples with the highest hardness were obtained from a micron powder with particles of fragment size ranging from 3.0 to 12.0 μm, and containing a significant number of fine fragments with an average size of ~ 0.2 μm. It was found that with increasing sintering pressure to 7.7 GPa, the density and hardness of boron carbide samples increase without significant grain growth in the material structure. This is achieved by a high heating rate and a short sintering time. A highly density superhard ceramic material made of boron carbide with a fine-grained structure (D ~ 0,5–1,3 μm), a relative density of 99.6 %, and a Vickers hardness HV1 47 GPa was obtained. The obtained results will be used in the development of new composite materials for various applications with usage of high pressure sintering with free of activating additives