Strengthening Hf0.95Ta0.05B2 ceramic with ultrafine grains and high-density dislocations

Abstract

Full densification and fine microstructures are the two key optimization targets of ceramic materials. Although fine Hf0.95Ta0.05B2 powder (~ 0.36 μm) has been synthesized, it was still difficult to obtain densified Hf0.95Ta0.05B2 ceramics with ultrafine grains (< 1 μm) using conventional high temperature sintering. Increasing sintering pressure could provided higher densification driving force, but it usually negatively promoted grain growth for nanoceramics. Our strategy was to gain the fully dense Hf0.95Ta0.05B2 ceramic under a high pressure at a selected temperature with retarded grain growth. In this work, fully dense Hf0.95Ta0.05B2 ceramic was prepared at 1700 °C under a high pressure of 200 MPa. The limited grain growth was achieved with the average grain size of 0.6 μm. Therefore, the mechanical properties were significantly improved, including Vickers hardness (24.8 GPa) and fracture toughness (4.2 MPa.m1/2), which were ascribed to Hall-Petch and dislocation strengthening mechanism.