Synthesis and growth mechanism of highly crystalized multi-branched HfB2 microrods with self-toughening effect

Abstract

Development of strategies to toughen HfB2 ceramic, improve their mechanical properties is the key to promote their applications in extreme thermal environments. This study explores a kind of self-toughening method of HfB2 ceramic by incorporation the highly crystalized multi-branched HfB2 microrods. The multi-branched HfB2 microrods were synthesized by sol–gel process and carbothermal reduction, exhibiting length of 6–13 μm and diameter of 0.60–1.50 μm, respectively. Detailed analysis of the formation mechanism of HfB2 microrods reveals that the HfB2 multi-branched structure is a collaborative consequence of orientation attachment mechanism and reactive templates growth, in which process monoclinic HfO2 crystals transform into crystalized HfO2 microrods at ∼1000 °C, and worked as template to induce one-dimensional HfB2 microrods. Furthermore, spark plasma sintering experiments show that the optimal mechanical properties were attained by 6 wt% addition of HfB2 microrods, comparing with HfB2 ceramics free of self-toughening agent, the hardness and fracture toughness of self-toughened HfB2 ceramic improved by 8.82 % and 81.91 % respectively, demonstrating the effectiveness of self-toughening of the microrods without sacrificing the hardness of HfB2 ceramic. Thus, it can be seen that the work has important reference value for the synthesis of HfB2 powder with different morphologies and the toughening of HfB2 ceramics.