Abstract: Novel fine grained pyrolytic silicon nitride is produced by adding a substantial amount of methane to the normal reactant gases. Silicon tetrafluoride and ammonia in ratios of 60:40 to 10:90 may be employed with additions of methane in amounts equal to from 50 to 500% of the sum of silicon tetrafluoride and ammonia. When these reactant gases are passed over a heated substrate at a low pressure pyrolytic silicon nitride with a grain size of less than about 10 microns results.

Abstract: An interlayer for transient liquid phase diffusion bonding is provided by depositing a metallic coating on at least one of the superalloy surfaces to be bonded and boriding a portion of the metallic coating to form a working coating having an overall composition resembling that of an interlayer alloy and an overall melting temperature less than that of the superalloys. When the superalloy surfaces are placed in contact and heated to above said melting temperature, the partially borided metallic coating functions as an interlayer alloy to effect bonding.

Abstract: A method for producing a low reactivity tungsten impregnated ceramic mold for casting refractory metals such as titanium is described. The method involves impregnation of a standard ceramic shell mold with an aqueous solution of tungstic acid and ammonium hydroxide. The saturated mold is then dried and fired to convert the tungsten compound to metallic tungsten or tungsten oxides. The process may be repeated several times to achieve the desired tungsten concentration.