Reactive sintering of B_4C-TaB_2 ceramics via carbide boronizing:Reaction process,microstructure and mechanical properties

Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of B_xC-TaB₂ (x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense B_xC-TaB₂ ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800 °C/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB₂ grains in the B_xC matrix is favor of the densification process and restricting grain growth. Besides, planar defects with high density were observed from the as-formed B_7.1C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB₂ lattice and most of the B_7.1C/TaB₂ phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained B_xC-TaB₂ ceramics exhibit high Vickers hardness (33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.