Engineering topics

Carruthers, W. D.

Publications and source records attributed to Carruthers, W. D..

6 records

NASA NTRS1987

Durability characterization of ceramic materials for gas turbines

The strength retention of ceramic materials during extended high-temperature cyclic exposure is critical to their widespread application in gas turbine engines. During a continuing NASA funded program initated in 1979, reaction bonded silicon nitride (RBSN), sintered silicon carbide (SSC), reaction sintered silicon carbide (RSSC), and sintered silicon nitride (SSN) materials were evaluated following simulated gas turbine engine exposures. Exposures were performed by cycling specimens five times per hour between a high velocity burner discharge and a rapid air quench. The retained flexural strengths were determined following up to 3500 hours of exposure at temperatures up to 1370 C. Post-exposure strengths have been correlated with fractography and surface examination using SEM. Results illustrate excellent strength retention of SSC materials after 3500 hours of exposure to 1370 C. At 1200 C, RBSN and RSSC also demonstrate significant strength retention. Although SSN materials typically suffer significant strength losses during exposures at 1200 C, a new composition, which has improved high-temperature strength, also shows improved durability. In the majority of the materials, strength loss is typically associated with flaw formation in the protective SiO2 layer.

Carruthers, W. D.↗

NASA NTRS1984

Ceramic component development for the AGT101 gas turbine engine

Under DOE/NASA sponsorship, a team is developing the AGT101, a highly efficient gas turbine engine for automotive application. The regenerated engine will operate at a maximum of 1370 C (2500 F) and 100,000 rpm, and will utilize a variety of Si3N4, SiC, lithium aluminum silicate and ceramic fiber insulation components. Engine design has been performed to consider the fabrication and material characteristics of these ceramic materials for both the static and rotating hot section components. Component fabrication has been performed, components have been screened in thermal and mechanical tests, and initial engine testing has been performed.

Carruthers, W. D.↗

NASA NTRS1982

Oxidation stability of advanced reaction-bonded Si3N4 materials

Four slip-cast, injection-molded and isostatically-pressed specimens of reaction-bonded silicon nitride (RBSN) were subjected to static oxidation tests at 900 C for 10 hours. Specimens containing 8-10% interconnected open porosity of size greater than one micron exhibited a 20-30% decrease in average room temperature four-point flexure strength, while those with 10% open porosity of magnitudes much smaller than one micron as well as those with 2-4% interconnected open porosity of about one micron did not decrease in strength after 900 C exposure. It was determined that preoxidation treatment at 1350 C prevents the 20-30% strength degradation due to internal oxidation, and evidence is presented which suggests that surface pit formation in some RBSN may result from contamination by the furnace environment rather than any intrinsic material properties.

Lindberg, L. J.↗

NASA NTRS1980

3500-hour durability testing of ceramic materials for automotive gas turbine engines

A two-year durability program was performed by AiResearch Phoenix to evaluate four commercially available ceramic materials under simulated automotive gas turbine combustor discharge conditions. These conditions included extended cyclic thermal exposures up to 2500 F and 3500 hr. The four materials selected for evaluation were Norton NCX-34 hot pressed silicon nitride, AiResearch RBN 101 reaction bonded silicon nitride, Carborundum pressureless sintered alpha-SiC and Pure Carbon Co. (British Nuclear Fuels, Ltd.) Refel reaction sintered silicon carbide. These materials were initially exposed to 350 hr/1750 cycles at 1200 and 1370 C. Subsequent exposures to 1050, 2100 and 3500 hr were performed on those materials maintaining 50% of baseline strength after the initial exposure. Additional evaluations of exposed bars included dimensional and weight changes, dye penetrant, specific damping capacity changes, SEM fractography, and X-ray diffraction.

Carruthers, W. D.↗

NASA NTRS1979

Combustion rig durability testing of turbine ceramics

A test facility for cyclic exposure of ceramic test bars to 1370 C has been designed as a means of the evaluation of the material durability under high-temperature cycling, particularly in heat-engine applications. The principal features of the test rig and test procedures are briefly discussed, and test results are presented for several commercial ceramics, including hot-pressed silicon nitride, carborundum sintered alpha-SiC, siliconized SiC, and reaction-bonded silicon nitride.

Carruthers, W. D.↗

NASA NTRS1978

Ceramic blade attachments

Studies under way on two concepts for producing a turbine rotor with ceramic blades and superalloy disks are discussed. One concept employs hot-pressed silicon nitride blades and a compliant interlayer at the blade root end fitting whereas the second concept relies on a superplastic plastic forging technique to attach ceramic blades to the metal disk. This latter concept has been hot spin tested at 2250 F and 45,000 RPM for 50 hours in a vacuum spin pit. The fully bladed (30 blades) rotor survived this major test.

Calvert, G. S.↗