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[en] Nontraditional machining is a generic term for those material removal processes that differ drastically from the historic operations such as turning, milling, drilling, tapping, and grinding. The use of primary energy modes other than mechanical, such as thermal, electrical, and chemical, sets these operations apart and reinforces their nontraditional label. Several of these newer processes have been very successful in machining close tolerance parts from refractory materials. This paper provides a general overview of both traditional and nontraditional aspects of machining refractory materials. 11 figures, 7 tables
[en] A diffusion welding equipment with a view to multiple applicability was conceived, erected and put into operation; it has proved to be efficient and flexible according to the experiences gained in the acceptance tests and in practical operation. Pressing equipment, generator, and vacuum system are designed for the mastering of various welding problems and possess sufficient reserve sources of power. The possibilities for later expansion of the vacuum and measuring equipment are left open. (orig./LH)
[de]Unter dem Gesichtspunkt einer vielseitigen Einsetzbarkeit wurde eine Diffusionsschweissanlage konzipiert, erstellt und in Betrieb genommen, die sich nach den bei den Abnahmeversuchen und im praktischen Betrieb gewonnenen Erfahrungen als leistungsfaehig und flexibel erwiesen hat. Pressausruestung, Generator und Vakuumsystem sind ausgelegt fuer die Bewaeltigung unterschiedlichster Schweissprobleme und besitzen ausreichende Leistungsreserven. Die Moeglichkeiten fuer spaetere Erweiterung der Vakuum- und Messeinrichtungen wurden offengehalten. (orig.)
[en] The present work discusses the evolution of grain boundary structure during thermomechanical processing and its effect on sensitization behavior in a nickel-based superalloy. Alloy 600 was deformed to varied degrees of strain (4–25%) using hot rolling followed by annealing at 1000 °C for 10 min followed by water quenching. Structure of the grain boundary was analyzed with reference to various parameters, such as grain boundary character distribution, twin-related domains, misorientation, and triple junction distribution. Each thermomechanically processed sample was heat-treated at 650 °C for 24 h before studying its sensitization behavior. The effect of structure of the grain boundary on sensitization was assessed through double loop electrochemical potentiokinetic reactivation test and measured in terms of degree of sensitization (DOS). DOS was found to be in a direct relation with the fraction of random high-angle grain boundaries and their connectivity, while it was inversely related to the fraction of low-Σ coincidence site lattice boundaries and special triple junctions. Residual strain and the fraction of low-angle grain boundaries were found to be weakly related to DOS. We show that a simple parameter can be used to predict the combined effect of all these factors on sensitization behavior.
[en] At temperatures of 750 to 9500C the permeation of hydrogen through bare, heat resistant alloys was studied from 1 to 40 bar, the diffusion and permeation of tritium in the partial pressure range of 10-4 bar. Among the alloys studied were Incoloy 800, 800 H, 802, Inconel 617, 625, the Ni-based alloy Nimonic PE 13, and several non-commercial steels. At a given temperature, the permeation rate through samples with clean surfaces - substantially free of oxide films - was found to be proportional to the square root of the hydrogen pressure. The C and the Cr contents of the steels investigated proved to exert a strong influence on the activation energies of diffusion and permeation. In some alloys a reduction of the permeation rate was observed that can be attributed to the precipitation of intermetallic phases. In one case a decrease of the permeation rate occured during the measurements due to a phase transformation. (orig.)
[en] A method of preparing a charge of super alloy material for use in metal casting is disclosed. Thin wall tubes consisting of one of the metallic elements of the alloy material, or an alloy of such element are provided. If an alloy tube is selected, all elements in the tube alloy must also be materials included in the overall formulation of the alloy material. The type and quantity of the materials contained in the tubes is deducted from the quantities set forth in the overall formula and the balance of the formula is melted and poured under vacuum as a core in the tube using the tube as a mold. The resulting master charge is cut into unit charges each of a predetermined weight. These unit charges are then used in a subsequent casting operation by melting the entire unit charge under vacuum to cast precision products of an alloy which consists of the mixed and alloyed materials of both the tube and the core
[en] The one-dimensional behavior of single crystal superalloys at high temperatures under constant and cyclic creep conditions is described by means of a 4-parameter rheological model based on linear viscoelasticity. Tertiary creep is taken into account by reducing the effective cross section by means of an additional damage parameter. Tensile creep tests have been used for the identification of the material constants by a non-linear optimization procedure. For the generalization to threee dimensions, a complete tensor-representation of cubic material symmetry is given. It contains twelve (temperature dependent) material parameters. Some results by finite element analysis will be presented. (orig.)
[en] Atom probe tomography was used to quantitatively assess grain boundary phase compositions and determine local segregation along the grain boundary before and after a 1000 h thermal exposure at 800 °C on an experimental powder processed Ni-base superalloy containing elevated levels of Nb. Due to high levels of refractory alloying elements at the grain boundary, a complex network of σ phase precipitates formed and the interfacial segregation profiles were studied. Although elemental B segregates to grain boundaries and secondary phase interfaces, insufficient levels are present to result in boride formation due to an enhanced solubility of B in the matrix phase.
[en] 3D Zernike functions are defined and used for the reconstruction of precipitate shapes. These functions are orthogonal over the unit ball and allow for an arbitrary shape, scaled to fit inside an embedding sphere, to be decomposed into 3D harmonics. Explicit expressions are given for the general Zernike moments, correcting typographical errors in the literature. Explicit expressions of the Zernike moments for the ellipsoid and the cube are given. The 3D Zernike functions and moments are applied to the reconstruction of γ' precipitate shapes in two Ni-based superalloys, one with nearly cuboidal precipitate shapes, and one with more complex dendritic shapes
[en] The present work shows the effect of mean stress on high cycle fatigue behavior of the superalloy IN718 at 400, 500 and 600 °C, at stress ratios (R) −1, 0.5, and 0.7. Fatigue life is decreased with increase in tensile mean stress. At high mean stress, decrease in fatigue life is associated with multiple crack initiation sites at the specimen surface. Fatigue limit is highly affected by the tensile mean stress and stress ratio, R = 0.7, since the maximum stress approaches near yield stress and causes cyclic ratcheting. (paper)