초록 ▼

Methods are disclosed for producing architectural preforms and high-temperature composite structures containing high-strength ceramic fibers with reduced preforming stresses within each fiber, with an in-situ grown coating on each fiber surface, with reduced boron within the bulk of each fiber, and

Methods are disclosed for producing architectural preforms and high-temperature composite structures containing high-strength ceramic fibers with reduced preforming stresses within each fiber, with an in-situ grown coating on each fiber surface, with reduced boron within the bulk of each fiber, and with improved tensile creep and rupture resistance properties for each fiber. The methods include the steps of preparing an original sample of a preform formed from a pre-selected high-strength silicon carbide ceramic fiber type, placing the original sample in a processing furnace under a pre-selected preforming stress state and thermally treating the sample in the processing furnace at a pre-selected processing temperature and hold time in a processing gas having a pre-selected composition, pressure, and flow rate. For the high-temperature composite structures, the method includes additional steps of depositing a thin interphase coating on the surface of each fiber and forming a ceramic or carbon-based matrix within the sample.

대표청구항 ▼

The invention claimed is: 1. A method for producing high-strength ceramic fibers and ceramic fiber architectural preforms with an in-situ grown coating on each fiber surface with a composition different than that of a bulk fiber, comprising: preparing an original sample composed of an architectural

The invention claimed is: 1. A method for producing high-strength ceramic fibers and ceramic fiber architectural preforms with an in-situ grown coating on each fiber surface with a composition different than that of a bulk fiber, comprising: preparing an original sample composed of an architectural preform formed from an as-produced high strength ceramic fiber type, wherein the fiber composition is based on silicon carbide, and wherein the architectural preform comprises at least one of a finite section of a continuous-length multi-fiber tow, a two-dimensional textile-formed fabric, and a three-dimensional textile-formed complex-shaped preform; placing the original sample in a processing furnace; and thermally treating the original sample in the processing furnace at a processing temperature and a hold time of five hours or less in a processing gas having a composition, a pressure that is greater than 1 and less than or equal to 40 atmospheres, and a flow rate, wherein the fiber composition, the processing temperature, the hold time, the gas composition, the pressure, and the flow rate are preselected to allow atomic decomposition from the surface of each fiber with reduced loss in an average tensile strength of the fibers within the thermally treated sample. 2. The method as recited in claim 1, wherein the fiber composition is based on silicon carbide (SiC), the gas composition is based on a chemically inert composition, and the in-situ grown coating on each fiber surface has a carbon-rich composition. 3. The method as recited in claim 2, wherein the fiber composition is based on silicon carbide (SiC) with boron additives, the processing temperature, the hold time, the gas composition is based on a chemically inert composition, the pressure, and the flow rate are preselected to also allow the removal of boron from the bulk of each fiber within the treated sample. 4. The method as recited in claim 3, wherein the thermal treatment also allows an improved tensile creep resistance and an improved tensile rupture resistance of each fiber in the thermally treated sample. 5. The method as recited in claim 4, wherein the thermal treatment comprises processing the original sample in the processing furnace at a processing temperature between 1700° C. and 1900° C. for a processing hold-time of five hours or less in an argon gas with a purity greater than 99.999% at a pressure that is greater than 1 and less than or equal to 40 atmospheres with a flow rate between zero and one cubic-foot/hr. 6. The method as recited in claim 5, wherein the thermal treatment comprises processing the original sample in the processing furnace at a processing temperature of 1800° C. for a processing hold-time of one hour at a pressure of 40 atmospheres with a flow rate of approximately zero cubic-foot/hr. 7. The method as recited in claim 1, wherein the fiber composition is based on silicon carbide (SiC) with boron additives and the gas composition is based on nitrogen. 8. The method as recited in claim 7, wherein the thermal treatment allows the in-situ growth of a coating on each fiber surface with a composition containing boron nitride (BN) and the properties of an improved tensile creep resistance and an improved tensile rupture resistance for each fiber in the thermally treated sample. 9. The method as recited in claim 8, wherein the thermal treatment comprises processing the original sample in the processing furnace at a processing temperature between 1700° C. and 1900° C. for a processing hold-time of five hours or less in a nitrogen gas with a purity greater than 99.999% at a pressure that is greater than 1 and less than or equal to 40 atmospheres with a flow rate between zero and one cubic-foot/hr. 10. The method as recited in claim 9, wherein the thermal treatment comprises processing the original sample in the processing furnace at a processing temperature of 1800° C. for a processing hold-time of one hour at a pressure of 40 atmospheres with a flow rate of approximately zero cubic-foot/hr. 11. The method as recited in claim 1, wherein during the placing of the original sample in a processing furnace, additional external reshaping stresses are applied to the sample so that during the treatment, these reshaping stresses are reduced by creep-relaxation within the ceramic fibers, thereby allowing the thermally treated sample to achieve a net preform shape. 12. The method as recited in claim 1, the method further comprising, after the thermally treating of the original sample: depositing a thin interphase coating on the treated fibers within the sample by chemical vapor infiltration; and forming a matrix within the coated sample with at least one of a ceramic and a carbon-based composition, thereby producing a final sample comprising a SiC fiber-reinforced composite material structure with improved properties. 13. The method as recited in claim 12, wherein the composition of the interphase fiber coating is based at least one of boron nitride and carbon, and the composition of the matrix is based on at least one of silicon carbide and silicon nitride. 14. The method as recited in claim 13, wherein the thermal treatment on the original sample is performed under a nitrogen gas with a purity greater than 99.999%, the fiber coating composition is based on boron nitride, and the final sample comprises a SiC fiber-reinforced ceramic matrix composite structure with properties including ultimate tensile strength, intrinsic strength retention at high temperatures, rupture strength after matrix pre-cracking, and long-term oxidation resistance that are greater than properties of final samples without the thermal treatment.