Liquid phase sintering of SiC with AIN and rare-earth oxide additives

Liquid phase sintering of SiC was performed using rare-earth oxide R ₂O₃ (R = Y, Yb, and Sm) and AlN sintering additives. The addition of 2 vol% β-SiC seeds or α-SiC platelets resulted in bimodal microstructure after annealing for 10 hours at 1850°C in mixed N ₂ + Ar atmosphere. Samples had a negligible weight loss after hot pressing. The bimodal microstructure contributed to the improvement of fracture toughness. Seeding by α-SiC seeds stimulated the β → α-SiC phase transformation and increased the hardness. Samples with α-SiC seeds and complex Yb₂O₃ + Sm₂O₃ + AlN additives had a Vickers hardness of 27.5 GPa. Seeding by β-SiC whiskers hindered the β → α-SiC phase transformation and increased the fracture toughness up to 6.5 MPa.m_1/2.