Room and high temperature flexural failure of spark plasma sintered boron carbide

Dense (95-98.6%) bulk boron carbide prepared by Spark Plasma Sintering (SPS) in Ar or N-2 atmospheres were subject to three-point flexural tests at room and at 1600 degrees C. Eight different consolidation conditions were used via SPS of commercially available B4C powder. Resulting specimens had similar grain size not exceeding 4 mu m and room-temperature bending strength (sigma(25) (degrees C)) of 300-600 MPa, suggesting that difference in sigma(25) (degrees C) m is due to development of secondary phases in monolithic boron carbide ceramics during SPS processing. To explain such difference the composition of boron carbide and secondary phases observed by XRD and Raman spectroscopy. The variation in intensity of the Raman peak at 490 cm(-1) of boron carbide suggests modification of the boron carbide composition and a higher intensity correlates with a higher room temperature bending strength (sigma(25) (degrees C)) and Vickers hardness (HV). Secondary phases can modify the level of mechanical characteristics within some general trends that are not dependent on additives (with some exceptions) or technologies. Namely, HV increases, sigma(25) (degrees C) decreases, and the ratio sigma(1600 degrees C)/sigma(25 degrees C) (sigma(1600 degrees C) - bending strength at 1600 degrees C) is lower when fracture toughness (K-IC) is higher. The ratio sigma(1600 degrees C)/sigma(25 degrees C) shows two regions of low and high K-IC delimited by K-IC=4.1 MPa m(0.5): in the low K-IC region, boron carbide specimens are produced in nitrogen. (c) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.