Abstract: A method for preventing the discovery of military aircraft and missiles by enemy and infrared detectors. The method involves applying a coating of a ferrite containing glass composition to the surfaces of those metal or ceramic substrates that are susceptible to detection through their radar or infrared signature.

Abstract: A composite comprising a ceramic matrix having immersed ceramic reinforcing fibers is strengthened and toughened by providing a multi-layer ceramic coating surrounding each fiber. The multiple layers in the fiber coating are not bonded to one another. As a result, the multiple layers separate from one another in the presence of an advancing crack in the ceramic matrix, thereby permitting the fibers to pull out of the matrix and avoid premature fiber breakage. The choice of materials for the fiber coating is not limited by any requirement to establish a particular type of chemical bond between the coating and the fiber. Instead, the invention relies only upon the mechanical tendency of the unbonded multiple layers in the fiber coating to separate to promote fiber pull-out from the matrix in the wake of an advancing crack.

Abstract: A ceramic fiber/ceramic matrix composite has ceramic fibers and a porous coating on the fibers. A ceramic matrix contacts the porous coating, the fiber and coating being immersed in the ceramic matrix. The porous coating is selected from the group including Si.sub.3 N.sub.4, SiC, ZrO.sub.2, Al.sub.2 O.sub.3, SnO.sub.2 and Ta.sub.2 O.sub.5. The pores are generally empty so as to render the coating frangible to promote fiber de-bonding and pull-out in the wake of an advancing crack in the matrix. In order to keep the pores empty, a non-porous sealing layer is formed over the porous coating which closes the pores without filling them. The ceramic matrix remains generally outside of the pores, whereby said pores remain empty after the fiber and coating are immersed in the ceramic matrix.

Abstract: A method of toughening a fiber/matrix ceramic composite consisting of non-oxide based ceramic fibers immersed in a ceramic matrix. The method includes, prior to immersing the fibers in the matrix, applying a metallo-organic solution of a noble metal to the fibers to form a coating of the solution on the fibers, evaporating the solvent from the solution and oxidizing the residual organic compounds whereby the coating becomes a pure noble metal and immersing the coated fibers in the matrix. The applying, evaporating, oxidizing and immersing steps are characterized by a limited raising of the temperature of the fibers. The coating is ductile so as to blunt advancing cracks in the matrix.

Abstract: A method of producing a ceramic fiber/ceramic matrix composite having a precracked fiber coating includes depositing a metal coating or a metal nitride or metal carbide coating on each ceramic fiber in a preform of fibers, infiltrating the fiber preform with a ceramic matrix to form a ceramic fiber/ceramic matrix composite, after the formation of the composite is complete, oxidizing the coating so as to change the coating to an oxide thereof. This process forms microcracks throughout the oxidized coating because of the mismatch in characteristics between the precursor layer and the final oxidized layer. An alternative method of producing a ceramic fiber/ceramic matrix composite having a precracked fiber coating includes depositing an oxidation resistant oxide, carbide or nitride which undergoes a destructive phase transformation after the coating and matrix infiltration processes are complete by the use of thermal cycling.

Abstract: A tough Si.sub.3 N.sub.4 ceramic composite is provided by incorporating a ternary oxide additive containing hafnia, titania and zirconia. The ternary oxide additive consists essentially of 60 to 85 mole percent hafnia, 10 to 30 mole percent titania and 10 to 30 mole percent zirconia, and is added to the Si.sub.3 N.sub.4 in a proportion ranging from about 10 to about 50%, by volume of ternary oxide additive, based on the overall composition. The ceramic composites are prepared by providing a mixture of the Si.sub.3 N.sub.4 and the ternary oxide additive, forming the mixture into a predetermined shape, e.g. by cold pressing, and sintering the shape at an appropriate temperature, to solidify and densify the shape.

Abstract: A compact is surrounded by a compatible, nonsinterable powder within a container with a layer of sinterable powder disposed on top of the nonsinterable powder and placed in a sintering oven. During sintering, the sinterable powder forms a cover that retards decomposition of the compact and serves to enhance densification of the compact.