Properties of silicon nitride for aluminum melts prepared by nitrided pressureless sintering

In this study, silicon nitride ceramics for aluminum melts were prepared by nitrided pressureless sintering (NPS) process, which process is the continuous process of nitridation reaction of Si metal combined with pressureless sintering. Mechanical, chemical and thermal properties of the NPS silicon nitride sintered with Al2O3, Y2O3 and Si additives were evaluated. Fully densed products show appropriate strength, ∼500 MPa, high hardness, ∼13 GPa, and superior damage tolerances with high fracture toughness, ∼9.8 MPa m1/2. Contact testing with spherical indenters is used to characterize the damage response. Examination of the indentation sites indicates a quasi-plastic damage modes are observed. Bend tests on specimens containing quasi-plastic contact damages reveal those materials to be not susceptible to strength degradation. And it has a low thermal expansion coefficient of 2.9 × 10−6 °C, and good thermal conductivity of 28 W/mK.