Microstructure and properties of self-reinforced α-sialon ceramics doped with Lu₂O₃

Lu-α-sialon ceramics containing elongated grains embedded into fine α-sialon matrix were obtained by applying a two-step hot-press procedure. Incorporation of excess Lu₂O₃ could promote anisotropic growth of α-sialon grains, and the quantity and aspect ratio of elongated α-sialon grains increase with the amount of Lu₂O₃ addition. The elongated α-sialon grains nucleate and grow epitaxially on the α-Si₃N₄ core, and the initial precipitation on the core is richer in Lu and Al content than the subsequent precipitation. The obtained Lu-α-sialons possess improved mechanical properties, the Vickers hardness, flexural strength and fracture toughness of the materials with 4 wt%Lu₂O₃ could reach with value of 22 GPa, 620.4 MPa and 4.8 MPa m^1/2, respectively. The Lu-α-sialons also demonstrate excellent high-temperature strength due to the presence of the refractory intergranular phase. The strength of the material with 4 wt%Lu₂O₃ at 1400 °C could retain 87% of its room-temperature strength.