Effect of impurities introduced by ball milling on hot pressed boron carbide

Ball milling is commonly used refining process to improve sintering properties of boron carbide. However, this process often leads to the introduction of trace metal impurities into raw materials. It was found in this study that, with prolonged holding time and increased sintering temperature at 2000 degrees C, these metal impurities led to the recrystallization of boron carbide grains, which significantly affected mechanical properties of sintered boron carbide. Results showed that relative density of sample increased from 98.4%-98.9%, when sintering temperature was raised from 2000 degrees C to 2050 degrees C and holding time was extended from 30 min to 60 min. However, under these conditions, flexural strength of boron carbide decreased sharply from 403 MPa to 98 MPa and fracture toughness decreased from 4.4 MPa m(1/2) to 2.3 MPa m(1/2).