Mechanical and fatigue strengths of silicon nitride ceramics in liquid aluminum alloys

Although the silicon nitride ceramic (Si3N4) has a high mechanical strength even at high air temperature, much reduction in the material strength occurs in liquid aluminum alloys. The bending strength of the ceramic in molten Al alloys is about 20% lower than that obtained in an air temperature of 750 °C. Moreover, a significant reduction of the fatigue strength occurs in the Al alloy melt. The change of mechanical properties of Si3N4 ceramic in the melt also depends on the amount of iron in the molten aluminum alloy; a large amount of iron makes the fatigue strength low. The reduction in the material strength is attributed to the change of material properties caused by the chemical reaction between iron and silicon nitride. Details of the chemical reaction in Si3N4 ceramic are discussed in the present work.