Vacuum thermal-mechanical fatigue testing of two iron base high temperature alloys

Ultrahigh vacuum elevated temperature low cycle fatigue and thermal fatigue tests of 304 stainless steel and A-286 alloy have shown significant effects of frequency and combined temperature-strain cycling on fatigue life. At constant temperature, the cyclic life of both alloys was lower at lower frequencies. Combined temperature-strain cycling reduced fatigue life with respect to isothermal life at the maximum temperature of the thermal cycle. Life reductions with in-phase thermal cycling (tension at high temperature, compression at low temperature) were attributed to grain boundary cavitation caused by unreversed tensile grain boundary sliding. The proposed mechanism for out-of-phase cavity generation involved accumulation of unreversed compressive grain boundary displacements which could not be geometrically accomodated by intragranular deformation in the low-ductility A-286 alloy

The partitioned strainrange fatigue behavior of coated and uncoated MAR-M-302 at 1000 C (1832 F) in ultrahigh vacuum

Elevated temperature (1000 C (1832 F)) vacuum fatigue tests have been conducted on uncoated and aluminide (PWA 45) coated cobalt-base MAR-M-302 alloy with the four different types of thermalmechanical reversed inelastic strain cycles (wave shapes) defined by the method of strainrange partitioning. Results of these tests indicated two major conclusions. First, there was no significant influence of the aluminide coating on the thermal-mechanical fatigue life of the MAR-M-302 alloy. Second, variations in the type of thermal-mechanical fatigue cycle applied caused significant variations of fatigue life for both coated and uncoated material. The longest lives were achieved with sigma sub pp type cycling, while the sigma sub cc cycle caused a reduction of fatigue life of about 1/2 order of magnitude with respect to the sigma sub pp life. The sigma sub cp type cycle caused a life reduction of between 1-1/2 and 2 orders of magnitude relative to the sigma sub pp life, while the sigma sub pc type cycle provided a fatigue life which appeared to be comparable to that generated by the sigma sub cc cycle

Effect of long-time, elevated-temperature exposures to vacuum and lithium on the properties of a tantalum alloy, T-111

The effect of long-term, elevated-temperature vacuum and lithium exposures on the mechanical properties of T-111 (Ta-8W-2Hf) is determined. Exposure conditions were for 1000 hours at 980 or 1315 C, 5000 hours at 1315 C, and a duplex temperature exposure of 1000 hours at 980 C plus 4000 hours at 1040 C. The exposures resulted in reduced tensile and creep strengths of the T-111 in the 900 to 1100 C temperature range where a dynamic strain-age-strengthening mechanism is operative in this alloy. This strength reduction was attributed to the depletion of oxygen from solid solution in this alloy

Thermal barrier coating life prediction model development

The objective is to develop an integrated life prediction model accounting for all potential life-limiting thermal barrier coating (TBC) degradation and failure modes, including spallation resulting from cyclic thermal stress, oxidation degradation, hot corrosion, erosion and foreign object damage

Generation of long time creep data on refractory alloys at elevated temperatures Quarterly report, 28 Mar. - 13 Jun. 1968

Creep tests of molybdenum alloys, and tantalum alloy

Generation of long time creep data on refractory alloys at elevated temperatures Quarterly report, 14 Dec. 1967 - 27 Mar. 1968

Creep analysis of refractory metal alloys at high temperatures under ultrahigh vacuum condition

Development of strain tolerant thermal barrier coating systems, tasks 1 - 3

Insulating ceramic thermal barrier coatings can reduce gas turbine airfoil metal temperatures as much as 170 C (about 300 F), providing fuel efficiency improvements greater than one percent and durability improvements of 2 to 3X. The objective was to increase the spalling resistance of zirconia based ceramic turbine coatings. To accomplish this, two baseline and 30 candidate duplex (layered MCrAlY/zirconia based ceramic) coatings were iteratively evaluated microstructurally and in four series of laboratory burner rig tests. This led to the selection of two candidate optimized 0.25 mm (0.010 inch) thick plasma sprayed partially stabilized zirconia ceramics containing six weight percent yttria and applied with two different sets of process parameters over a 0.13 mm (0.005 inch) thick low pressure chamber sprayed MCrAlY bond coat. Both of these coatings demonstrated at least 3X laboratory cyclic spalling life improvement over the baseline systems, as well as cyclic oxidation life equivalent to 15,000 commercial engine flight hours

Progress toward determining the potential of ODS alloys for gas turbine applications

The Materials for Advanced Turbine Engine (MATE) Program managed by the NASA Lewis Research Center is supporting two projects to evaluate the potential of oxide dispersion strengthened (ODS) alloys for aircraft gas turbine applications. One project involves the evaluation of Incoloy (TM) MA-956 for application as a combustor liner material. An assessment of advanced engine potential will be conducted by means of a test in a P&WA 2037 turbofan engine. The other project involves the evaluation of Inconel (TM) MA 6000 for application as a high pressure turbine blade material and includes a test in a Garrett TFE 731 turbofan engine. Both projects are progressing toward these engine tests in 1984

Generation of long time creep data on refractory alloys at elevated temperatures Quarterly report, 20 Jun. - 18 Sep. 1969

Refractory alloy creep test data for molybdenum base alloy TZM, pure tantalum, and tantalum base alloys T-111 and ASTAR-811C at elevated temperatures in ultrahigh vacuu

Mechanical behavior of tantalum-base T-111 alloy at elevated temperature

Mechanical behavior of tantalum T-111 alloy at high temperatures and ultrahigh vacuu