Abstract: A method is disclosed for hot pressing agglomerated materials in a pressing assembly having walls which can be reactive with the material to be pressed under the environmental, temperature, and pressure conditions to be experienced by the material at the interface with the pressing assembly walls. After a plurality of generally flat stackable billets (10-20) of the powdered material are formed and stacked in a pressing assembly (21) in a predetermined aligned order, a barrier wall (30) is interposed between the interface of the billets and pressing assembly along at least a zone (26) in which a temperature of 1600.degree.-1750.degree. C. and a pressure of at least 3000 psi will be experienced at the interface during hot pressing. The billets are then hot pressed to a desirable density and removed, leaving the assembly walls in a substantially unreacted condition.

Abstract: A method of making a heat fused silicon nitride comprising object is disclosed. A series of measured powder shots are containerized to be carried in the container between the nitriding and heat fusing steps. The containerization comprises lining the internal wall of a graphitic sleeve, treated for inertness, with a refractory metal foil essentially impervious to migration of carbon ions and having a thickness of 0.2 inches or less. A series of measured shots, of a powder mixture of silicon and oxygen carrying agents, is inserted into the assembly, each shot being separated by an inert spacer. The assembly is subjected to a nitriding treatment and subsequently hot pressed/or sintered.

Abstract: A method is disclosed of making a fully dense silicon nitride comprising object by heating a silicon nitride mixture containing yttrium silicon oxynitride (at least 75% Y.sub.10 Si.sub.6 O.sub.24 N.sub.2) to full density without the need for special atmospheres or packing mediums. A reaction bonded silicon nitride/yttrium silicon oxynitride comprising object is fabricated to have the oxynitride present in an amount of 5-17% by weight of the object, free silicon and other oxides in an amount up to 0.5%, and the remainder essentially silicon nitride. The object is heated in an ambient atmosphere to a temperature below the sublimation temperature of silicon nitride and for a period of time to fully densify the object as a result of solution of the silicon nitride into liquified oxynitride, the object being in direct contact with the ambient atmosphere during heating.

Abstract: A method is disclosed comprising placing in a hot pressing environment a controlled mixture of a first powder of Si.sub.3 N.sub.4 containing a controlled amount of SiO.sub.2 (with or without a limited amount of milling media) with a second powder consisting essentially of Y.sub.2 O.sub.3, hot pressing the controlled mixture, and cooling the resultant unitary object.A novel silicon nitride comprising a unitary object is disclosed which can be shaped to form a novel cutting tool useful for machining metal such as cast iron. The object has selected crystalline phases formed beta Si.sub.3 N.sub.4 and beta prime Si.sub.3 N.sub.4 and has intergranular crystalline secondary phases consisting essentially of YSiO.sub.2 N, Y.sub.10 Si.sub.17 N.sub.4 O.sub.23 and Y.sub.2 Si.sub.2 O.sub.7 with the YSiO.sub.2 N phase representing at least a 25% volume fraction of the secondary phases and comprising essentially all of the yittria-silicon oxide.

Abstract: A method is disclosed comprising placing in a hot pressing environment a controlled mixture of a first powder of Si.sub.3 N.sub.4 containing a controlled amount of SiO.sub.2 (with or without a limited amount of milling media) with a second powder consisting essentially of Y.sub.2 O.sub.3, hot pressing the controlled mixture, and cooling the resultant unitary object.A novel silicon nitride comprising a unitary object is disclosed which can be shaped to form a novel cutting tool useful for machining metal such as cast iron. The object has selected crystalline phases formed beta Si.sub.3 N.sub.4 and beta prime Si.sub.3 N.sub.4 and as intergranular crystalline secondary phases consisting essentially of YSiO.sub.2 N, y.sub.10 Si.sub.17 N.sub.4 O.sub.23 and Y.sub.2 Si.sub.2 O.sub.7 with the YSiO.sub.2 N phase representing at least a 25% volume fraction of the secondary phases and comprising essentially all of the yittria-silicon oxide.

Abstract: A method of machining cast iron by using a ceramic cutting tool of specific composition at specified removal rates which results in increased tool life.

Abstract: A process for machine cutting of cast iron with a shaped tool which is a ceramic having as constituent ingredients about 4 to about 12% by weight Y.sub.2 O.sub.3 and a balance consisting essentially of Si.sub.3 N.sub.4 and which has a density of at least 3.25 gm./cm.sup.3.

Abstract: A method of making a silicon nitride part is disclosed. In this method an article of silicon nitride is first made which has a density less than the theoretical density of silicon nitride. This article also contains a densification aid. The entire surface area of this article is coated with a thin silicon nitride skin which is gas impervious. The so coated article is heated to a temperature for a time sufficient so that some of the densification aid may diffuse into the silicon nitride skin. The so treated article is then subjected to a pressure sufficiently high, for a time sufficiently long and at a temperature which permits the silicon nitride article and skin thereon to be compacted to increase the density of the article to a density greater than it originally had and to form the silicon nitride skin about the article so that the skin becomes an integral of the finished part.

Abstract: A method of forming a slip cast article having at least one zone of cellular construction is disclosed. The method may be utilized to make articles having zones of different cellular size as well as articles having zones of cellular construction adjacent zones of noncellular construction. In its simplest form, the method is carried out by providing a slip casting mold which has a casting volume formed therein. A stabilized casting slip is poured into the casting volume. The pH of the stabilized casting slip is increased until a hydrolysis reaction takes place between the water forming the vehicle and an oxidizable metal forming the casting material. This hydrolysis reaction results in the evolution of gases, some of which are trapped within the slip to develop a zone of cellular construction. The greater the increase in pH, the more vigorous is the hydrolysis reaction and the resulting cellular construction has larger sized cells.

Abstract: A method of making a unitary silicon nitride comprising object and tool is disclosed. A uniform powder mixture of Si.sub.3 N.sub.4 containing SiO.sub.2 as an oxide coating, 4-12% by weight Y.sub.2 O.sub.3, and 0.50-2.5 Al.sub.2 O.sub.3 is prepared. The mixture is hot pressed at a temperature of 1,680.degree.-1,750.degree. C. under a pressure and for a period of time sufficient to produce at least 99.0% (preferably at least 99.5%) of full theoretical density in the mixture to form a pressed object. The heating and pressure is then relieved and the object cooled. The object is heat treated by holding at a temperature in the range of 1,000.degree.-1,400.degree. C. without mechanical pressure for at least 5 minutes but for a time sufficient to provide a nucleating reaction in secondary phases formed as a result of hot pressing. The heat treatment can take place either as an interruption of the cooling cycle or as a subsequent reheat cycle after cooling to room temperature.

Abstract: A method of making a unitary silicon nitride comprising object is disclosed. A uniform powder mixture is prepared of Si.sub.3 N.sub.4 containing SiO.sub.2 as an oxide surface coating, 4-12% by weight Y.sub.2 O.sub.3, and 0.50-2.5% Al.sub.2 O.sub.3. The mixture is heated to 1000.degree.-1400.degree. C. under a pressure of at least 2,000 psi for a time of at least one minute but sufficient to permit a nucleating reaction to take place in secondary phases. Heating is then increased to a temperature of 1680.degree.-1750.degree. C. under a pressure and for a period of time sufficient to produce 99.0% or more of full theoretical density in the pressed object.

Abstract: A process for continuous or interrupted machine cutting of solid cast iron by milling, turning or boring with a shaped tool, wherein said shaped tool is a ceramic consisting essentially of Si.sub.3 N.sub.4 and 4-12% by weight Y.sub.2 O.sub.3, produced by hot pressing at a pressure and a temperature of 1700.degree.-1750.degree. C. to achieve substantially full density.

Abstract: A method of forming a slip cast article is disclosed. The slip cast article is formed in a casting volume of a forming mold, which mold has a portion thereof formed of a meltable organic material. The vehicle of the casting slip used to form the article is drawn off to a level which provides a consolidated casting in the casting volume which contains sufficient vehicle that the casting is resistant to shrinkage. The consolidated casting and the organic mold portion are then surrounded with a porous, liquid drawing media. A high humidity of the vehicle of the casting slip is maintained about the consolidated casting surrounded by the porous, liquid drawing media. The consolidated casting and surrounding liquid drawing media are heated while the high humidity of the vehicle is maintained to a temperature which causes the meltable organic material to melt. The porous, liquid drawing media then draws the melted material away from the consolidated casting.

Abstract: A method for forming a silicon nitride article is set forth. An article having silicon particles therein is formed in a manner which provides a degree of porosity for the article. The silicon particles of the article are reactable with nitrogen to form silicon nitride. The article is heated to a temperature below a significant reaction temperature at which nitrogen gas reacts with the silicon particles at a measurable rate. The article is surrounded with an atmosphere containing nitrogen gas. A reaction zone is established on at least a portion of the surface area of the article. The reaction zone has a temperature above the significant reaction temperature whereby the silicon particles in the reaction zone are reacted at a measurable rate with the nitrogen gas to form silicon nitride. The reaction zone is moved in a controlled manner from the surface of the article into the interior of the article whereby the article is progressively nitrided inwardly into its bulk from the surface thereof.

Abstract: A method of forming a slip cast article is disclosed. The slip cast article is formed in a casting volume of a forming mold which has a portion thereof formed of a dissolvable organic material which has binder properties. A casting slip is cast into the casting volume. The vehicle of the casting slip is drawn off to a level which provides a consolidated casting in the casting volume containing sufficient vehicle that the casting is resistant to shrinkage. The consolidated casting and the organic mold portion are placed in a solvent for the mold portion so that it may be dissolved. The solvent for the mold portion is one which is miscible with the vehicle of the casting slip. The consolidated casting is maintained in the solvent after the organic mold portion has been dissolved so that the dissolved organic material previously forming the mold portion may penetrate into the consolidated casting.