Dense silicon nitride mouldings, esp. for gas turbine components - contg. yttrium oxide, alumina and ferric oxide; with excellent mechanical properties

摘要

The mouldings consist of sintered and/or pressed Si3N4, contg. Y2O3 and, by wt. 0.2-2.0% Al2O3, 0.2-2.0% Fe2O3, and max. 0.4% carbon. Alternatively, the mouldings pref. contain Si3N4, Y2O3 and 0.05-3.0% Li2O. One pref. mixt.used to make the mouldings contains by wt. 76-98.6% Si3N4, 1-20% Y2O3, 0.2-2% Al2O3, 0.2-2% Fe2O3, or corresp. cpd. which forms these oxides when heated, and where the finished moulding contains max. 0.4% C. The Si3N4 may be obtd. from Si powder, which is nitrided after adding the other oxides. Another pref.mixt. used to make the mouldings contains 79.95-98.95% Si3N4, 1-20% Y2O3, and 0.05-3.0% Li2O. The Si3N4 may be obtd. from Si powder, which is nitrided after adding the Y2O3 and Li2O. Good and reproducible properties can be obtd. at room temp. and at high temps., without the need to use high purity silicon nitride.