Search NASA⌕ Search

Engineering topics

Lemkey, F. D.

Publications and source records attributed to Lemkey, F. D..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Identification of a cast iron alloy containing nonstrategic elements

A program was performed to address the mechanical and environmental needs of Stirling engine heater head and regenerator housing components, while reducing the dependence on strategic materials. An alloy was developed which contained no strategic elemental additions per se. The base is iron with additions of manganese, molybdenum, carbon, silicon, niobium, and ferro-chromium. Such an alloy should be producible on a large scale at very low cost. The resulting alloy, designated as NASAUT 4G-Al, contained 15 Mn, 15 Cr, 2 Mo, 1.5 C, 1.0 Si, 1.0 Nb (in weight percent) with a balance of Fe. This alloy was optimized for chemistry, based upon tensile strength, creep-rupture strength, fracture behavior, and fatigue resistance up to 800 C. Alloys were also tested for environmental compatibility. The microstructure and mechanic properties (including hardness) were assessed in the as-cast condition and following several heat treatments, including one designed to simulate a required braze cycle. The alloy was fabricated and characterized in the form of both equiaxed and columnar-grained castings. The columnar grains were produced by directional solidification, and the properties were characterized in both the longitudinal and transverse orientations. The NASAUT 4G-Al alloy was found to be good in cyclic-oxidation resistance and excellent in both hydrogen and hot-corrosion resistance, especially in comparison to the baseline XF-818 alloy. The mechanical properties of yield strength, stress-rupture life, high-cycle-fatigue resistance, and low-cycle-fatigue resistance were good to excellent in comparison to the current alloy for this application, HS-31 (X-40), with precise results depending in a complex manner on grain orientation and temperature. If required, the ductility could be improved by lowering the carbon content.

Cooper, C. V.↗
NASA NTRS1988

Iron-base superalloys - A phase analysis of the multicomponent system (Fe-Mn-Cr-Mo-Nb-Al-Si-C)

In the course of studies on the iron-rich multicomponent system Fe-Mn-Cr-Mo-Nb-Al-Si-C, work was concentrated on pertinent quinary and six-component combinations namely Fe-Mn-Al-Si-C, Fe-Cr-Al-Si-C and Fe-Mn-Cr-Al-Si-C which had been elaborated at 65, 72, and 80 wt pct Fe. Manganese acts as a strong stabilizer for the cementite carbide. Chromium seems to stabilize the iron aluminide Fe2Al5 which forms in a considerable amount within an alloy of nominal composition Fe(65)Mn(15)Cr(12)Al(5)Si(2)C(1) (percent by weight). Although the Mn3AlC carbide is, like Fe3AlC, a perovskite carbide, manganese does not appear to favor the formation of the perovskite carbide. Because of the relatively low sintering temperature (700 C), for al large portion of the samples equilibria conditions are not always reached.

Gupta, H.↗
NASA NTRS1987

High-temperature oxidation/corrosion of iron-based superalloys

The oxidation and sulfidation of several novel iron-base superalloys were evaluated in high-temperature cyclic tests. The experimental austenitic alloys examined were modifications of NASAUT-4GA which were developed for Stirling-engine application. The weight gains and resulting surface scales were measured and analyzed. Mixed oxide scales were found to form on all specimens exposed above 871 C. The build-up of these scales led to a depletion of Mn and Cr in a zone adjacent to the oxides. In addition, the initial oxidation of the Fe-rich alloy was inhibited by a thin but tenacious Si layer which formed at the interface between oxides and the parent layer. Sulfidation tests using Na2SO4 coatings resulted in the formation of a protective spinel and alpha-Fe2O3 phases. Preferential attack of the carbide phase by hydrogen was not observed after 350 h at 871 C.

Lemkey, F. D.↗
NASA NTRS1985

High temperature static strain gage alloy development program

The literature, applicable theory and finally an experimental program were used to identify new candidate alloy systems for use as the electrical resistance elements in static strain gages up to 1250K. The program goals were 50 hours of use in the environment of a test stand gas turbine engine with measurement accuracies equal to or better than 10 percent of full scale for strains up to + or - 2000 microstrain. As part of this effort, a computerized electrical resistance measurement system was constructed for use at temperatures between 300K and 1250K and heating and cooling rates of 250K/min and 10K/min. The two best alloys were an iron-chromium-aluminum alloy and a palladium base alloy. Although significant progress was made, it was concluded that a considerable additional effort would be needed to fully optimize and evaluate these candidate systems.

Hulse, C. O.↗
NASA NTRS1984

Carbides in iron-rich Fe-Mn-Cr-Mo-Al-Si-C systems

The optimization of high carbon iron-base superalloy properties with duplex microstructure gamma + M7C3 carbide requires analysis in the context of a seven-component system. Data are first provided here for the Fe-Mn-Cr-Mo-C quinary system, at 30 at. pct carbon. A characterization of competing carbides, according to a pseudoternary phase diagram at 35 wt pct iron, is made from isothermal sections. It is noted that while M7C3 and M3C carbides' occurrences are respectively favored at the Cr and Mn corners, the M2C carbide and molybdenum cementite are predominant with increasing amounts of Mo. Lattice parameters are reported for the various carbides.

Lemkey, F. D.↗
NASA NTRS1982

Elevated temperature properties of aligned ferrous eutectics

Iron base alloys containing aluminum and chromium together with smaller amounts of yttrium and silicon are of interest for high temperature applications. Strengthening an inherently weak but oxidation resistant solid solution matrix with aligned in situ chromium carbides represents an attractive approach to achieving both surface stability and creep resistance at elevated temperatures. Aligned microstructures were produced in alloys of approximately 30 wt % (Cr + Mn), about 3 wt % C and the balance Fe consisting of a gamma matrix and the hexagonal carbide (Cr, Mn, Fe)7C3. The tensile and stress rupture strength to 2000 F of aligned Fe-20 w/t % Cr-10 wt % Mn-3.2 wt % C measured parallel to the carbide reinforcement exceeded those of the strongest iron-nickel superalloys, e.g., CRM-6D developed by Chrysler for automotive turbine application. The cyclic oxidation and sulfidation response of these alloys at elevated temperatures can be markedly improved by aluminum additions.

Lemkey, F. D.↗
NASA NTRS1982

Development of cast ferrous alloys for Stirling engine application

Low cost cast ferrous base alloys that can be used for cylinder and regenerator housing components of the Stirling engine were investigated. The alloys must meet the requirements of high strength and thermal fatigue resistance to approximately 1500 F, compatibility and low permeability with hydrogen, good elevated temperature oxidation/corrosion resistance, and contain a minimum of strategic elements. The phase constituents of over twenty alloy iterations were examined by X-ray diffraction. These alloy candidates were further screened for their tensile and stress rupture strength and surface stability in air at 1450 and 1600 F, respectively. Two alloys, NASAUT 1G (Fe-10Mn-20Cr-1.5C-1.0Si) and NASAUT 4G (Fe-15Mn-12Cr-3Mo-1.5C-1.0Si-1.0Nb), were chosen for more extensive elevated temperature testing. These alloys were found to exhibit nearly equivalent elevated temperature creep strength and oxidation resistance. Silicon present in these alloys at the 1 w/o level permitted the achievement of oxide scale adherence to 1600 F without loss of strength (or ductility) as was noted for equivalent additions of aluminum.

Lemkey, F. D.↗
NASA NTRS1976

Conference on In Situ Composites, 2nd, Bolton Landing, N.Y., September 2-5, 1975, Proceedings

The present collection of papers deals with advances in several areas of interest in in-situ composites. Major areas discussed include solidification and structural control, physical properties, mechanical behavior, stability, environmental response, and development of new metallic and ceramic systems. New evidence about directional solidification in terms of temperature gradients is presented along with solidification rates for successful formation of in-situ composite structures. Much is learned about the factors that control structure in directionally solidified eutectic alloys and the relationship of properties to structure, especially the change in properties as a function of operating environment. Less progress is achieved in the area of physical properties than in the area of mechanical properties. Individual items are announced in this issue.

Jackson, M. R.↗
NASA NTRS1976

Quaternary and quinary modifications of the eutectic superalloy gamma/gamma prime-delta

Quaternary modifications and quinary additions from the elements Co, Ti, Mo, W, Re, B, Si, and Ta to the baseline quaternary alloy gamma/gamma prime-delta Ni-19.7 at.% Nb-6.0 at.% Cr-2.5 at.% Al are examined for various concentrations. From modification studies five alloys were chosen for detailed mechanical property characterization: Ni-19.7 Nb-6.0 Cr-2.5 Al-1.0 W; Ni-19.7 Nb-6.0 Cr-2.5 Al-1.0 Mo; Ni-18.6 Nb-6.0 Cr-2.5 Al-0.87 Ti; Ni-20.2 Nb-6.0 Cr-2.5 Al-2.0 Co; and Ni-17.9 Nb-6.0 Cr-2.5 Al-3.0 Ta. It is shown that extensive alloying of the baseline quaternary alloy is possible for elements exhibiting a wide solubility range in both phases, and that limited substitution of W, Mo, Re, Si, and B is possible for elements with restricted solid solubility especially in the delta phase. Improvement of creep rupture strength and cyclic oxidation resistance at 1100 C is discussed.

Lemkey, F. D.↗
NASA NTRS1975

Quaternary and quinary modifications of eutectic superalloys strengthened by delta Ni3Cb lamellae and gamma prime Ni3Al precipitates

By means of a compositional and heat treatment optimization program based on the quaternary gamma/gamma prime-delta, a tantalum modified gamma/gamma prime-delta alloy with improved shear and creep strength combined with better cyclic oxidation resistance was identified. Quinary additions, quaternary adjustments, and heat treatment were investigated. The tantalum modified gamma/gamma prime-delta alloy possessed a slightly higher liquidus temperature and exhibited rupture strength exceeding NASA VIA by approximately three and one-half Larson-Miller parameters (C = 20) above 1000 C. Although improvements in longitudinal mechanical properties were achieved, the shear and transverse strength property goals of the program were not met and present a continuing challenge to the alloy metallurgist.

Lemkey, F. D.↗
NASA NTRS1973

Eutectic superalloys strengthened by sigma, Ni3CB lamellae and gamma prime, Ni3Al precipitates

By means of a screening and solidification optimization study of certain alloys located on the gamma-sigma liquidus surface within the Ni-Cb-Cr-Al system, alloys with high temperature properties superior to those of all known superalloys were defined. One alloy, Ni - 19.7w/o Cb - 6.0w/o Cr - 2.5w/o Al, directionally solidified at 3 cm/hr met or exceeded each program goal. A second alloy, Ni-21.75 w/o Cb-2.55 w/o Al, although deficient in its inherent oxidation resistance, met the other program goals and combined a remarkable insensitivity of composite microstructure to solidification parameters with excellent low temperature toughness. This investigation demonstrated that useful properties for gas turbine airfoil application have been achieved by reinforcing a strong and tough gamma solid solution matrix containing precipitated gamma prime by a lamellar intermetallic compound Ni3 Cb having greater strength at elevated temperature.

Lemkey, F. D.↗
NASA NTRS1973

Eutectic superalloys strengthened by aligned delta, Ni3Cb lamellae, gamma-prime, Ni3Al precipitates and reduced interlamellar spacing.

Monovariant eutectic alloys, located on the liquidus trough between the binary eutectic gamma, Ni - delta, Ni3Cb and the ternary eutectic gamma, Ni - gamma-prime, Ni3Al - delta, Ni3Cb, were identified which permitted the production of aligned lamellae within a nickel solid solution matrix containing the precipitate gamma-prime. These alloys exhibited great insensitivity in their composite microstructures to solidification parameters such as growth rate temperature gradient, and were found to be remarkably uniform in composition along their length.

Lemkey, F. D.↗
NASA NTRS1972

Eutectic superalloys strengthened by delta Ni3Cb lamellae, and gamma prime, Ni3Al precipitates.

Bivariant eutectic alloys, located on a liquidus surface within the Ni-Cb-Cr-Al quaternary, were identified which permitted the production of aligned delta Ni3Cb lamellae within a nichrome matrix containing the fcc precipitate gamma prime Ni3Al. The volume fraction of delta and gamma prime could be varied significantly by compositional changes. After directional solidification certain alloys possessed improved ductility and corrosion resistance with respect to the Ni3Al-Ni3Cb eutectic, while their values of tensile and creep strength approached or exceeded those for the Ni3Al-Ni3Cb pseudobinary system. The mechanical properties of the directionally solidified alloy, Ni-19.7 wt % Cb-6.0 wt % Cr-2.5 wt % Al, were evaluated. Its longitudinal strength in tension and creep was found to be superior to all advanced nickel base superalloys. It is thus demonstrated that useful properties for gas turbine airfoil applications can be achieved by reinforcing a strong and tough gamma nichrome matrix containing precipitated gamma prime by a strong lamellar intermetallic compound having greater strength at elevated temperature.

Lemkey, F. D.↗