Effect of nano-sized sintering additives on microstructure and mechanical properties of Si3N4 ceramics

Nano-sized sintering additives such as MgO, Al2O3, Y2O3 and La2O3 are added to process Si3N4 based ceramics. The effects of such sintering additives on the phase transformation, mechanical properties and microstructure of silicon nitride were investigated. XRD analysis of sintered silicon nitride with these sintering additives have shown the complete transformation of alpha-Si3N4 into beta-Si3N4. The silicon nitride ceramics sintered with nano-sized additives (4MgO-4Al(2)O(3)-5La(2)O(3)) have exhibited the highest fracture toughness. This is not only due to the weak glass' grain interface but also due to the formation of high aspect ratio grains (beta-Si3N4). Superior mechanical properties of Si3N4 can be obtained by way of adding small and large RE(3+ )radii RE2O3 (Y2O3 and La2O3) together than the addition of single RE2O3.