Selection of an alloy composition in the ternary Co-Cr-Al system for oxidation resistance
Ternary Co-Cr-Al alloy oxidation resistant composition selection, using oxide maps superimposed on phase diagram
Hed, A. Z.↗
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Development of dispersion-strengthened Ni-Cr-ThOz alloys for the space shuttle thermal protection system
Manufacturing processes were developed for TD-NiCr providing small sheet (45 x 90 cm), and larger sheet (60 x 150 cm) and foil. The alternate alloy, DS-NiCr, was produced by pack-chromizing Ni-ThO2 sheet. Formability criteria are being established for basic sheet forming processes, which are brake forming, corrugation forming, joggling, dimpling, and beading. Resistance spot welding (fusion and solid state), resistance seam welding, solid state diffusion welding, and brazing are included in the joining programs. Major emphasis is centered on an Al-modified Ni-Cr-ThO2 alloy development. These alloys, containing 3 to 5% Al, form the protective Al2O3 scale. This enhances oxidation resistance under reentry conditions. Both TD-NiCrAl and DS-NiCrAl alloys are included. A tentative composition of Ni-16Cr-3.5Al-2ThO2 was selected based on oxidation resistance and fabricability.
Blankenship, C. P.↗
Mechanisms of oxidation in the Co-Cr system.
Oxidation has been studied both as a function of temperature in the range from 900 to 1300 C and of the partial pressure of oxygen in the range from 0.05 to 760 torr. In addition, microstructures of oxide scales have been studied and characterized in more detail utilizing metallographic and X-ray techniques combined with electron microprobe analysis. The parabolic rate constants in 1100 C and at 100 and 10 torr oxygen are presented in a graph as a function of chromium content. Three main different mechanisms of oxidation in the Co-Cr system have been identified. In two of these, the rate determining process controlling the oxidation is the solid state diffusion of cobalt through the oxide CoO. The rate controlling process governing the oxidation for the third mechanism is chromium diffusion in dichromium trioxide.
Kofstad, P. K.↗
Evaporative segregation in 80 percent Ni-20 percent Cr and 60 percent Fe-40 percent Ni alloys
The phenomenon of evaporative segregation in binary alloys has been investigated through a study of some experimental evaporation data relating to the Ni-Cr and Ni-Fr systems. In normal evaporation it is assumed that (1) the evaporating alloy is always homogeneous, (2) the vapor is instantly removed, and (3) the alloy follows Raoult's law. The solutions of the evaporation equations for the two most important cases are presented and experimental data are analyzed with these equations. The difference between observed and calculated values of evaporation constants lies within one order of magnitude. This is surprising because of the major assumptions stated above. Experimental results have shown that the evaporation time and final solute concentration are logarithmically related, further supporting our evaporation equations. It is further shown that neglecting the nonlogarithmic term in these evaporation equations may introduce considerable errors in the analysis.
Mukherjee, J. L.↗
The effect of thermal cycling on the structure and properties of a Co, Cr, Ni-TaC directionally solidified eutectic composite
A Co, Cr, Ni-TaC directionally solidified eutectic composite was subjected to thermal fatigue between 427-1093°C. The material suffered degradation in microstructure and elevated temperature mechanical properties. The loss in properties varied with the maximum cycling temperature and number of cycles. This behavior is attributed to the increasing solubility of the TaC in the matrix with temperature from 0.4% at room temperature to 2.2% at 1200°C. During the thermal cycling, the TaC is subjected to solution and reprecipitation which form serrations on the fibers since the easy growth planes of the TaC are not coincident with the fiber faces exposed to the matrix.
Composites↗
Evaporative segregation in 80% Ni-20% Cr and 60% Fe-40% Ni alloys
An analytical approach is outlined to calculate the evaporative segregation behavior in metallic alloys. The theoretical predictions are based on a 'normal' evaporation model and have been examined for Fe-Ni and Ni-Cr alloys. A fairly good agreement has been found between the predicted values and the experimental results found in the literature.
Gupta, K. P.↗
Tough cryogenic alloys from the Fe-Mn and Fe-Mn-Cr systems
By adjusting composition, metastable gamma (austenite) and epsilon (hexagonal) martensite may be retained in Fe-Mn and Fe-Mn-Cr alloys and used to impact toughness through the TRIP mechanism. The resulting alloys have excellent toughness at cryogenic temperatures. The best alloys obtained to date are: Fe-20Mn, with sigma (sub y) = 79ksi and K sub IC = 275ksi square root of (in) at 77 K, and Fc-16Mn-8Cr, with sigma sub y = 85ksi and K sub IC = 72ksi square root of (in) at 77 K.
Schanfein, M. J.↗
Application of strainrange partitioning to the prediction of MPC creep-fatigue data for 2 1/4 Cr-1Mo steel
Strainrange partitioning is used to predict the long time cyclic lives of the metal properties council (MPC) creep-fatigue interspersion and cyclic creep-rupture tests conducted with annealed 2 1/4 Cr-1Mo steel. Observed lives agree with predicted lives within factors of two. The strainrange partitioning life relations used for the long time predictions were established from short time creep-fatigue data generated at NASA-Lewis on the same heat of material.
Saltsman, J. F.↗
Superalloy eutectic composites with the VI A refractory elements - Cr, Mo and W
The paper discusses the phase equilibria for the ternary systems NiAlCr, NiAlMo, and NiAlW, with emphasis on reactions from the liquid state, although some of the solid state reactions are mentioned. It is shown that eutectics in the Ni-Al-refractory element (Cr, Mo, W) systems offer the potential for high-temperature turbine blade and vane applications. In particular, it is shown that the phase diagrams of these ternary systems can be manipulated to alter the eutectic phases and morphologies by simple quaternary alloying modifications. The resultant combination of chemistry and structure can be controlled to ensure a behavior that is well-matched to hot section component materials requirements.
Jackson, M. R.↗
High temperature oxidation resistant coatings for the directionally solidified Ni-Nb-Cr-Al eutectic superalloy
Protective coatings required for the Ni-Nb-Cr-Al directionally solidified eutectic superalloy were developed and evaluated on the basis of oxidation resistance, diffusional stability, thermal fatigue, and creep resistance. NiCrAlY+Pt and NiCrAlY physical vapor-deposition coating systems exhibited the best combination of properties. Burner-rig testing indicated that the useful life of a 127-micron-thick NiCrAlY+Pt coating exceeds 1000 h at 1366 K. Eutectic-alloy creep lives at 1311 K and a stress of 151.7 MN/sq m were greater for NiCrAlY+Pt-coated specimens than for uncoated specimens by a factor of two.
Strangman, T. E.↗
Application of strainrange partitioning to the prediction of MPC creep-fatigue data for 2 1/4 Cr-1 Mo steel
Creep-fatigue tests were conducted on annealed 2.25Cr-1Mo steel in air at 538 C involving interspersion of rapid strain cycles (0 to 22 cycles) between constant tensile stress-hold periods (23 or 47 hours). Life predictions were made on the basis of the strain range-life relations obtained from short-time material characterization tests on tubular specimens taken from the same heat as the specimens for the creep-fatigue tests. The creep-fatigue tests lasted from about 500 to 5000 hours, while the short-time tests used as the prediction basis lasted from 0.1 to 100 hours. By partitioning the creep and plastic strains within every cycle and summing the damage on a cycle-by-cycle basis, the predicted lives agreed with the observed ones within factors of two.
Saltsman, J. F.↗
Oscillator strengths of Cr I lines lying between 200 and 541 nm from hook-method and absorption measurements in a furnace
Measurements of 148 oscillator strengths of neutral chromium transitions were made on Cr vapor in a high-temperature furnace by the hook and absorption methods for strong and weak lines, respectively. With the aid of a 5D-z 5F0 multiplet, the product of the oscillator strengths of the lines of this multiplet with the column densities of their respective lower levels could be determined, and by using estimated oscillator strengths for these lines, all data could be put on a common relative scale. This scale was altered so that the results were matched with relative emission intensities. Results are compared with other authors' results. A correction to the hook method constant was also determined.
Huber, M. C. E.↗
Method for producing thin sheets of proton-sensitive CR-39 plastic track detectors
Procedures for fabricating large sheets of CR-39 with uniform chemical reactivity and sensitivity and which retain a clear, smooth surface after prolonged etching were investigated. Very thin sheets for certain Spacelab applications were fabricated.
Kinoshita, K.↗
Structural and compositional characterization of RF sputter-deposited Ni-Cr + Cr2O3 films
An RF-sputtered chrome oxide coating with metallic binders was developed. The chrome oxide coating has high-temperature capabilities and is wear resistant, and has some self-lubricating properties. A nichrome metallic binder was added in the coating to improve its ductility without significant loss in the hardness. The sputtering parameters were optimized to obtain a smooth coating with the maximum adherence. The coatings were applied using bias-sputter and sputter-deposit modes on the heat treated and annealed foil substrates. The coating applied on annealed foils using the sputter-deposit mode was smooth and had the best adherence. Metallurgical examinations showed that the coating was Ni-Cr + Cr2O3. The coating as applied was amorphous and it crystallized during substrate heat treatment.
Bhushan, B.↗
Solute transport during the cyclic oxidation of Ni-Cr-Al alloys
Important requirements for protective coatings of Ni-Cr-Al alloys for gas turbine superalloys are resistance to oxidation accompanied by thermal cycling, resistance to thermal fatigue cracking. The resistance to oxidation accompanied by thermal cycling is discussed. The resistance to thermal fatigue cracking is also considered.
Nesbitt, J. A.↗
IUE observations of the 1981 outburst of nova Cr A
Low dispersion spectrum observations are analyzed. The light curve of nova Cr A, indicating a moderately fast nova, is presented. Flux calibrated, merged spectrum graphs of April 21, 1981 and September 13, 1981 are presented, demonstrating very strong lines of Al and Si. Additional strong C, Ni, O, and Ne emission lines were identified. Emission lines due to highly ionized species such as Mg VII and Al Vl were observed for short times in May and June 1981. Preliminary analysis of spectra obtained 200 days after maximum indicate that the nebula is still in transition and has not yet reached the nebula state. An over abundance of N and Ne are suggested.
Sparks, W. M.↗
The ultraviolet variability of T Cr B
Preliminary results of the ultraviolet variability monitoring of the recurrent nova T Cr B are presented. The star has shown striking changes of the continuum (both shape and integrated luminosity) and of the emission lines since 1979, with a maximum activity in early 1981. In the same period the visual luminosity remained practically constant. The data being studied that the UV variability is due to changes in the physical structure of the accretion disk around the secondary.
Cassatella, A.↗
Lunar highland rocks - Element partitioning among minerals. II - Electron microprobe analyses of Al, P, Ca, Ti, Cr, Mn and Fe in olivine
Lunar olivines from anorthosites, granulitic impactites, and rocks in the Mg-rich plutonic trend were subjected to electron probe measurements for Al, P, Ca, Ti, Cr and Mn, which show that the FeO/MnO ratio for lunar olivines lies between 80 and 110 with little difference among the rock types. The low values of Ca in lunar olivines indicate slow cooling to subsolidus temperatures, with blocking temperatures of about 750 C for 67667 and 1000 C for 60255,73-alpha determined by the Finnerty and Boyd (1978) experiments. An important paradox is noted in the low Ti content of Fe-rich olivines from anorthosites, although both Ti and Fe tend to become enriched in liquid during fractional distillation. Except for Ca and Mn, olivine from anorthosites has lower minor element values than other rock types. Formation from a chemically distinct system is therefore implied.
Smith, J. V.↗