Optimised Si_3N_4 ceramics containing nitrogen woehlerite as a grain boundary phase

摘要

Sintering aids with the formulation of ytterbium woehlerite J(Yb), YB_4Si_2O_7N_2, and its solid solutions with Al_2O_3 J(Yb), Yb_4Si_2_xAl_xO_7+xN_2-x, were introduced into silicon nitride to obtain high density bodies by gas pressure sintering. Partial stabilisation of α-Si_3N_4 (up to ≈18/100) was achieved by controlled thermal oxidation of the initial powder mixtures. The resulting materials with J(Yb) as an intergranular phase showed good sinterability, invariably reproducible phase formation And excellent oxidation resistance up to 1400 deg.C in air. Overall, secondary phases with J(Yb) Formulation show promise as sintering aids that allow Si_3N_4-based ceramics to be sintered to high Density without compromising intrinsic mechanical and thermal properties.