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Sikora, P. F.

Publications and source records attributed to Sikora, P. F..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Consolidation of Si3N4 by hot isostatic pressing

Silicon nitride (Si3N4) is being considered for gas turbine engine applications because present-day metallic alloys are rapidly approaching the limits of their temperature capabilities. The present investigation was undertaken to determine the feasibility of producing a sound, dense Si3N4 body without additives, using conventional gas hot-isostatic-pressing techniques and an uncommon hydraulic hot-isostatic-pressing technique. These two hot-isostatic-pressing (HIP) techniques produce much higher pressure (275-413 MN/sq m) than conventional hot-pressing techniques and have the potential of producing large bodies of desirable shapes. Evaluation was based on density measurement, microscopic examination, both optical and electron, and X-ray diffraction analysis.

Yeh, H. C.↗
NASA NTRS1977

Consolidation of silicon nitride without additives

The feasibility of producing a sound, dense Si3N4 body without additives was explored, using conventional gas hot isostatic pressing techniques and an uncommon hydraulic hot isostatic pressing technique. These two techniques produce much higher pressure 275-413 MN/m sq (40,000 - 60,000 psi) than hot-pressing techniques. Evaluation was based on density measurement, microscopic examination, both optical and electron, and X-ray diffraction analysis. The results are summarized as follows: (1) Si3N4 can be densified to high density, greater than 95% of theoretical, without additions. (2) The higher density Si3N4 specimens appear to be associated with a greater amount of alpha to beta transformation. (3) Under high pressure, the alpha to beta transformation can occur at a temperature as low as 1150 C. (4) Grain deformation and subsequent recrystallization and grain refinement result from hot isostatic pressing of Si3N4.

Sikora, P. F.↗
NASA NTRS1976

Consolidation of silicon nitride without additives

The use of ceramics for gas turbine engine construction might make it possible to increase engine efficiency by raising operational temperatures to values beyond those which can be tolerated by metallic alloys. The most promising ceramics being investigated in this connection are Si3N4 and SiC. A description is presented of a study which had the objective to produce dense Si3N4. The two most common methods of consolidating Si3N4 currently being used include hot pressing and reaction sintering. The feasibility was explored of producing a sound, dense Si3N4 body without additives by means of conventional gas hot isostatic pressing techniques and an uncommon hydraulic hot isostatic pressing technique. It was found that Si3N4 can be densified without additions to a density which exceeds 95% of the theoretical value

Sikora, P. F.↗
NASA NTRS1974

Dispersion strengthened nickel-yttria sheet alloy produced from comminuted powders

Report on initial efforts to dispersion-strengthen nickel with Y2O3 in an attempt to replace radioactive ThO2 as the strengthening phase in dispersion-strengthened alloys. Nickel-Y2O3 powders were processed by the NASA comminution and blending (NASCAB) method and subsequently thermomechanically worked. Experimental variables included volume per cent Y2O3 (2% and 4%), powder cleaning temperature (315, 371, and 426 C), a screening step in the process, and the number (up to 23) of cold-roll-anneal cycles. Tensile strengths, determined at 1093 C, as well as some stress-rupture life data, are presented.

Sikora, P. F.↗
NASA NTRS1973

Dispersion strengthened nickel-yttria sheet alloy produced from comminuted powders

An investigation was conducted to determine whether a nickel matrix with yttria as a dispersoid could be produced by a comminution and blending (wet attrition-NASCAB) approach. Concentration of yttria, powder cleaning temperature, screening (sieving) of the powders, and amount of thermomechanical working were major variables. Tensile strength and stress-rupture life at 1093 C were determined. A product containing 4v/o Y2O3, cleaned at 315 or 371 C with screening exhibited 1093 C tensile strength equivalent to NASCAB Ni-4ThO2 and to commercially produced thoriated nickel sheet.

Sikora, P. F.↗
NASA NTRS1972

Dispersion-strengthened nickel-alumina alloy produced from comminuted powders

An investigation was conducted to determine whether a nickel - 2-volume-percent alumina dispersion-strengthened material with a fine, uniformly distributed dispersoid could be produced, which was equivalent in short time tensile strength to commercially available thoriated sheet materials. Comminution and blending with a modified triple stirrer attritor and a hydrogen and vacuum precleaning treatment prior to consolidation were used. A product with a fine dispersoid with an average particle size of 0.04 micron and an interparticle spacing of 0.7 micron was achieved. This material has a 1093 C (2000 F) short time tensile strength of 117 MN/sq m (16 900 psi).

Sikora, P. F.↗
NASA NTRS1964

Apparatus facilitates high-temperature tensile testing in vacuum

An apparutus for heating refractory materials to high temperatures during tensile testing includes a water-cooled stainless steel vacuum chamber. This contains a resistance heater consisting of a slit tube of tantalum or tungsten to enclose the tensile test rod.

Sikora, P. F.↗