Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “sinter”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Crack barriers improve the mechanical and thermal properties of non-metallic sinter materials

Means of improving the tensile strength of ceramic composites by introducing ductile intermediate layers capable of absorbing the elastic energy at the rupture front are studied. Tests with an Al203 laminate with niobium inclusions showed that crack propagation could be successfully precluded by dissipation of the energy by deformation and/or delamination at the inclusion/matrix interface.

Gruenthaler, K. H.↗
NASA NTRS1982

Study of phenomena related to the sintering process of silicon nitride at atmospheric pressure

A procedure was perfected for the production of components used in engineering applications of silicon nitride. Particles of complex geometry that combine remarkable mechanical properties with a high density are obtained. The process developed, in contrast to the "hot pressing" method, does not use external pressures, and in contrast to the reaction bonding method, final densities close to the theoretical value are obtained.

Bertani, A.↗
NASA NTRS1982

Preliminary results on the abradability of porous, sintered seal material

Preliminary results are presented for the case of titanium blade specimens, with bare tips (or covered with wear resistant, plasma sprayed materials) rubbing at 100 m/s against specimens of abradable nickel-chromium seal material moving toward the rotating blades at 0.0125 mm/s or at 0.025 mm/s. Using a two component dynamometer, the normal force of the rub interaction was measured and the shear component estimated. The elastoplastic properties of the seal material have been determined and those parameters as well as the rigidity of the rub tester system are considered in conjunction with those affecting the accuracy of the measurement of the forces arising at the blade-seal interface. The average and the 'local instantaneous' temperatures of the seal specimen and the temperature of the blade tip surface during rubbing are presented as functions of time. A seal densification factor is defined and its functional relationships with contact force components, temperature, wear ratio and blade tip abrading capability are indicated.

Wolak, J.↗
NASA NTRS1982

Comparison of NDE techniques for sintered-SiC components

High frequency, bulk-wave ultrasonics detected defects in manufactured SiC components. In addition, gas-turbine blades and vanes were examined by scanning laser acoustic microscopy (SLAM). Comparative results obtained on simple shapes such as disks and bars by microfocus X-ray radiography, ultrasonics, scanning photoacoustic spectroscopy, and SLAM are discussed.

Srinivasan, M.↗
NASA NTRS1984

Gas pressure sintering of Beta-Sialon with Z=3

An experiment conducted on beta-sialon in atmospheric pressure, using a temperature of 2000 C and 4 MPa nitrogen atmosphere, is described. Thermal decomposition was inhibited by the increase of the nitrogen gas pressure.

Tani, E.↗
NASA NTRS1985

Metallurgical and mechanical phenomena due to rubbing of titanium against sintered powder Nichrome

Metallurgical and mechanical changes occurring during high-speed rubbing of Ti-6Al-4V blade specimens against an abradable Nichrome aircraft engine seal material were studied using optical microscopy, electron microscopy, and microhardness techniques. Evidence of temperatures above the beta transus of Ti-6Al-4V (1000 C) and of thermal hardening was found on blade tips that exhibited undesirable abrading characteristics resulting in high forces of interaction, high temperatures, and smearing. The material within the layer of the corresponding seals was found to be work-hardened to a depth of about 0.1 mm and showed evidence of densification extending to a depth of about 0.5 mm below the rubbed surface. Wear particles produced by rub interactions that generated cleanly abraded seal surfaces were found to be several times larger than those produced during interactions which showed evidence of surface smearing and seal densification.

Zenas, R.↗
NASA NTRS1984

Sintered plug flow modulation of a vapor-liquid phase separator for a helium II vessel

Presented is a system for modulation of a superfluid (helium II) flow in a vapor-liquid phase separator, for use in cryogenic storage tanks in future space missions. The system consists of a semicircular mechanically operated shutter, downstream of the separator plug, rotated at 0.1 rpm to control the operational surface area of the separator. The mass flow rate was varied from 10 to 22 mg/s. Pressure gradients across the plug are also discussed.

Frederking, T. H. K.↗
NASA NTRS1985

Effect of hot isostatic pressing on the properties of sintered alpha silicon carbide

Two lots of alpha silicon carbide were isostatically hot-pressed under 138 MPa for 2 h in Ar at temperatures up to 2200 C. Nearly theoretically dense specimens resulted. Hot isostatic pressing increased both room-temperature strength and 1200 C strength, and resulted in improved reliability. One lot of material which was pressed at 2200 C showed increases of about 20 percent in room-temperature strength and about 50 percent in 1200 C flexural strength; the Weibull modulus improved about 100 percent.

Watson, G. K.↗
NASA NTRS1986

Friction and wear of sintered Alpha SiC sliding against IN-718 alloy at 25 to 800 C in atmospheric air at ambient pressure

The sliding friction and wear of the SiC-nickel based alloy IN-718 couple under line contact test conditions in atmospheric air at a linear velocity of 0.18 m/sec and a load of 6.8 kg (67N) was investigated at temperatures of 25 to 800 C. It was found that the coefficient of friction was 0.6 up to 350 C then decreased to 0.3 at 500 and 800 C. It is suggested that the sharp decrease in the friction in the range of 350 to 550 C is due to the lubrication value of oxidation products. The wear rate reaches a minimum of 1 x 10 to the -10 to 2 x 10 to the -10 cu cm/cm/kg at 400 to 600 C.

Deadmore, Daniel L.↗
NASA NTRS1987

Flaw imaging and ultrasonic techniques for characterizing sintered silicon carbide

The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

Baaklini, George Y.↗
NASA NTRS1988

Characterization of sintered SiC by using NDE

Capabilities of projection microfocus X-radiography and of ultrasonic velocity and attenuation for characterizing silicon carbide specimens were assessed. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room-temperature, four-point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined. Radiography proved useful in detecting high-density inclusions and isolated voids, but failed in detecting surface and subsurface agglomerates and large grains as fracture origins. Ultrasonic velocity dependency on density was evident. Attenuation dependency on density and mean pore size was clearly demonstrated. Understanding attenuation as a function of toughness was limited by shortcomings in K sub IC determination.

Baaklini, George Y.↗
NASA NTRS1988

Radiographic and ultrasonic characterization of sintered silicon carbide

The capabilities were investigated of projection microfocus X-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

Baaklini, G. Y.↗
NASA NTRS1991

Grain growth kinetics in liquid-phase-sintered zinc oxide-barium oxide ceramics

Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300 to 1400 C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence 3D grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature. All regressions between G exp n and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol.

Yang, Sung-Chul↗