Thermal fatigue and oxidation data for directionally solidified MAR-M 246 turbine blades

Thermal fatigue and oxidation data were obtained for 11 plasma spray coated and 13 uncoated directionally solidified and single crystal MAR-M 246 blades. Blade coatings on the airfoil included several metal-oxide thermal barrier layers based on Al2O3, Cr2O3, or ZrO2. The 24 turbine blades were tested simultaneously for 3000 cycles in fluidized beds maintained at 950 and 25 C using a symmetrical 360 set thermal cycle. In 3000 cycles, only uncoated turbine blades exhibited cracking on the trailing edge near the platform; 3 of the 13 uncoated blades did not crack. Cracking occurred over the range 400 to 2750 cycles, with single crystal blades indicating the poorest thermal fatigue resistance. Oxidation of the uncoated blades was limited in 3000 cycles. All coatings indicated microscopically visible spalling at the trailing edge radius after 3000 cycles. Severe general spalling on the airfoil was observed for two multilayered coatings

Thermal fatigue and oxidation data of oxide dispersion-strengthened alloys

Thermal fatigue and oxidation data were obtained 24 specimens representing 9 discrete oxide dispersion-strengthened alloy compositions or fabricating techniques. Double edge wedge specimens, both bare metal and coated for each systems, were cycled between fluidized beds maintained at 1130 C with a three minute immersion in each bed. The systems included alloys identified as 262 in hardness of HRC 38; 264 in hardness of HRC 38, 40 and 43; 265 HRC 39, 266 of HRC 37 and 40; 754; and 956. Specimens in the bare condition of 265 HRC 39 and 266 HRC 37 survived 6000 cycles without cracking on the small radius of the double edge wedge specimen. A coated specimen of 262 HRC 38, 266 HRC 37 and 266 HRC40 also survived 6000 cycles without cracking. A duplicate coated specimen of 262 HRC 38 alloy survived 5250 cycles before cracks appeared. All the alloys showed little weight change compared compared to alloys tested in prior programs

Thermal fatigue and oxidation data of superalloys including directionally solidified eutectics

Thermal fatigue and oxidation data were obtained on 61 specimens, representing 15 discrete alloy compositions or fabricating techniques and three coating systems. Conventionally fabricated alloys included V57, MM 200, Rene 77, Rene 125, MM 246, MM 509, IN-738, IN-792 + Hf, and MM 200 + Hf. The directionally solidified alloys were MM 200, MM 200 single crystal, MM 200 bicrystal, cellular gamma/gamma' - delta) and lamellar gamma/gamma' - delta. The coatings systems included NiCrAlY on IN-738, In-792 + Hf, MM 200 DS, MM 200 DS single crystal, and cellular gamma/gamma' - delta and NiCrAlY/Pt on lamellar gamma/gamma' - delta. Crack initiation survival rates were recorded for all alloys, with and without coatings. All uncoated alloys, except MM 509, exhibited significant oxidation weight loss in 75,000 to 15,000 cycles. MM 509 specimens had weight losses only slightly higher than coated specimens through 7,500 cycles. All coated specimens had low weight loss

Thermal fatigue and oxidation data for alloy/braze combinations

Thermal fatigue and oxidation data were obtained for 62 brazed specimens of 3 iron-, 3 nickel-, and 1 cobalt-base alloy. Fluidized bed thermal cycling was conducted over the range 740/25 C employing 10 cm long single-edge wedge specimens. Immersion time was always 4 minutes in each bed. Types of test specimens employed in the program include those with brazed overlays on the specimen radius, those butt brazed at midspan and those with a brazed foil overlay on the specimen radius. Of the 18 braze overlay specimens, 5 generated fatigue cracks by 7000 cycles. Thermal cracking of butt brazed specimens occurred exclusively through the butt braze. Of the 23 butt brazed specimens, 7 survived 11,000 thermal cycles without cracking. Only 2 of the 21 foil overlaid specimens exhibiting cracking in 7,000 cycles. Blistering of the foil did occur for 2 alloys by 500 cycles. Oxidation of the alloy/braze combination was limited at the test maximum test temperature of 740 C

Affine algebraic groups with periodic components

A connected component of an affine algebraic group is called periodic if all its elements have finite order. We give a characterization of periodic components in terms of automorphisms with finite number of fixed points. It is also discussed which connected groups have finite extensions with periodic components. The results are applied to the study of the normalizer of a maximal torus in a simple algebraic group.Comment: 20 page

Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-Frequency SiO Masers

We present Submillimeter Array observations of high frequency SiO masers around the supergiant VX Sgr and the semi-regular variable star W Hya. The J=5-4, v=1 28SiO and v=0 29SiO masers of VX Sgr are shown to be highly linearly polarized with a polarization from ~5-60%. Assuming the continuum emission peaks at the stellar position, the masers are found within ~60 mas of the star, corresponding to ~100 AU at a distance of 1.57 kpc. The linear polarization vectors are consistent with a large scale magnetic field, with position and inclination angles similar to that of the dipole magnetic field inferred in the H2O and OH maser regions at much larger distances from the star. We thus show for the first time that the magnetic field structure in a circumstellar envelope can remain stable from a few stellar radii out to ~1400 AU. This provides further evidence supporting the existence of large scale and dynamically important magnetic fields around evolved stars. Due to a lack of parallactic angle coverage, the linear polarization of masers around W Hya could not be determined. For both stars we observed the 28SiO and 29SiO isotopologues and find that they have a markedly different distribution and that they appear to avoid each other. Additionally, emission from the SO 5_5-4_4 line was imaged for both sources. Around W Hya we find a clear offset between the red- and blue-shifted SO emission. This indicates that W Hya is likely host to a slow bipolar outflow or a rotating disk-like structure.Comment: 8 pages, 7 figures, accepted for publication in ApJ. Online table will be available with published versio

Multidimensional Toda type systems

On the base of Lie algebraic and differential geometry methods, a wide class of multidimensional nonlinear systems is obtained, and the integration scheme for such equations is proposed.Comment: 29 pages, LaTeX fil

The rings of n-dimensional polytopes

Points of an orbit of a finite Coxeter group G, generated by n reflections starting from a single seed point, are considered as vertices of a polytope (G-polytope) centered at the origin of a real n-dimensional Euclidean space. A general efficient method is recalled for the geometric description of G- polytopes, their faces of all dimensions and their adjacencies. Products and symmetrized powers of G-polytopes are introduced and their decomposition into the sums of G-polytopes is described. Several invariants of G-polytopes are found, namely the analogs of Dynkin indices of degrees 2 and 4, anomaly numbers and congruence classes of the polytopes. The definitions apply to crystallographic and non-crystallographic Coxeter groups. Examples and applications are shown.Comment: 24 page

The structure of quantum Lie algebras for the classical series B_l, C_l and D_l

The structure constants of quantum Lie algebras depend on a quantum deformation parameter q and they reduce to the classical structure constants of a Lie algebra at $q=1$. We explain the relationship between the structure constants of quantum Lie algebras and quantum Clebsch-Gordan coefficients for adjoint x adjoint ---> adjoint. We present a practical method for the determination of these quantum Clebsch-Gordan coefficients and are thus able to give explicit expressions for the structure constants of the quantum Lie algebras associated to the classical Lie algebras B_l, C_l and D_l. In the quantum case also the structure constants of the Cartan subalgebra are non-zero and we observe that they are determined in terms of the simple quantum roots. We introduce an invariant Killing form on the quantum Lie algebras and find that it takes values which are simple q-deformations of the classical ones.Comment: 25 pages, amslatex, eepic. Final version for publication in J. Phys. A. Minor misprints in eqs. 5.11 and 5.12 correcte

Molecular beam epitaxy of free-standing bulk wurtzite AlxGa1-xN layers using a highly efficient RF plasma source

Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commer-cially viable deep ultra-violet light sources. Due to a sig-nificant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-ite AlxGa1-xN films were grown by PA-MBE on 2-inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. Growth rates of AlxGa1-xN up to 3 μm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free-standing bulk AlxGa1-xN layers in a single day’s growth, which makes our MBE bulk growth technique commercially vi-able