Spark plasma sintered β-phase silicon nitride with Sr and Ca as a sintering aid for load bearing medical applications

Due to its inherent good physical and chemical properties silicon nitride has high potential to be used for load bearing implants. However, the standard sintering additives alumina and rare earth oxides are limiting the biocompatibility of the material. The aim of the current project is to exchange the additives for more biologically beneficial additives. Spark plasma sintered silicon nitride was manufactured with strontium or calcium as sintering aids. The ability of forming high strength β-phase microstructure silicon nitride was investigated. Powders were prepared with 10 and 30 wt.% glass phase and sintered at 1600, 1650, 1700 and 1750 °C. X-ray diffraction demonstrated compositions with 10 wt.% glass phase with strontium as sintering aid to yield larger amount of β-phase. The highest amount of β-phase (96% of the crystalline structure) was obtained using SPS for strontium-doped silicon nitride at sintering temperature 1750 °C, resulting in the highest fracture toughness, 4.2 MPa m1/2.