Results 1 - 10 of 17064
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[en] The purpose of this investigation is to develop a model for prediction of topologically closed-packed (TCP) phases formation in superalloys. In this study, artificial neural networks (ANN), using several different network architectures, were used to investigate the complex relationships between TCP phases and chemical composition of superalloys. In order to develop an optimum ANN structure, more than 200 experimental data were used to train and test the neural network. The results of this investigation shows that a multilayer perceptron (MLP) form of the neural networks with one hidden layer and 10 nodes in the hidden layer has the lowest mean absolute error (MAE) and can be accurately used to predict the electron-hole number (Nv) and TCP phases formation in superalloys
[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] Serial sectioning methods continue to produce an abundant amount of image data for quantifying the three-dimensional nature of material microstructures. Here, we discuss a methodology to automate detecting and characterizing eutectic particles taken from serial images of a production turbine blade made of a heat-treated single crystal Ni-based superalloy (PWA 1484). This method includes two important steps for unassisted eutectic particle characterization: automatically identifying a seed point within each particle and segmenting the particle using a region growing algorithm with an automated stop point. Once detected, the segmented eutectic particles are used to calculate microstructural statistics for characterizing and reconstructing statistically representative synthetic microstructures for single crystal Ni-based superalloys. The significance of this work is its ability to automate characterization for analysing the 3D nature of eutectic particles
[en] Laser induced breakdown spectroscopy (LIBS) was performed on the CMSX-4 Ni-based superalloy using a femtosecond pulsed laser. An orthogonal double-pulse technique was used to minimize surface damage associated with LIBS. With this technique, the depth of ablation craters was reduced from 200 nm for single-pulse LIBS down to less than 60 nm using orthogonal double-pulse LIBS. The technique also allowed the average velocity of the ablated material to be determined, which ranged from 4720 ± 560 m/s at a pump laser fluence of 3.1 J/cm2 to 8150 ±1800 m/s at 10.1 J/cm2
[en] The specification discloses chromium-niobium alloys which exhibit improved mechanical properties at high temperatures in the range of 1250 C and improved room temperature ductility. The alloys contain a Cr2Nb-rich intermetallic phase and a Cr-rich phase with an overall niobium concentration in the range of from about 5 to about 18 at. %. The high temperature strength is substantially greater than that of state of the art nickel-based superalloys for enhanced high temperature service. Further improvements in the properties of the compositions are obtained by alloying with rhenium and aluminum; and additional rare-earth and other elements. 14 figures
[en] The effects of the alloying element Re on the ideal strength of γ'-Ni3Al under tensile and shear stresses are investigated using the first-principles method. Results for the stress-strain relationships, ideal tensile and shear strengthes with and without Re addition are presented and explained. Re is found to be effective in improving the strength of Ni3Al. The electronic mechanism underlying the strengthening effects of Re is also elucidated.
[en] Thermo-mechanical-physical properties of bulk metallic glasses (BMGs) depend strongly on the concentrations of each of the chemical elements in a given alloy. The proposed methodology for simultaneously optimizing these multiple properties by accurately determining proper concentrations of each of the alloying elements is based on the use of computational algorithms rather than on traditional experimentation, expert experience and intuition. Specifically, the proposed BMG design method combines an advanced stochastic multi-objective evolutionary optimization algorithm based on self-adapting response surface methodology and an existing database of experimentally evaluated BMG properties. During the iterative computational design procedure, a relatively small number of new BMGs need to be manufactured and experimentally evaluated for their properties in order to continuously verify the accuracy of the entire design methodology. Concentrations of the most important alloying elements can be predicted so that new BMGs have multiple properties optimized in a Pareto sense. This design concept was verified for superalloys using strictly experimental data. Thus, the key innovation here lies in arriving at the BMG compositions which will have the highest glass forming ability by utilizing an advanced multi-objective optimization algorithm while requiring a minimum number of BMGs to be manufactured and tested in order to verify the predicted performance of the predicted BMG compositions
[en] Arc ion plating was employed on a directionally solidified nickel-based superalloy to deposit a NiCrAlYSi coating. The failure behavior of the coated cylindrically specimens under thermomechanical fatigue loadings was experimentally investigated. The results show that the effect of coatings on TMF lives is dependent on the temperature ranges, and the TMF life with dwell time is reduced compared to the one without dwells. Through microstructure observation methods, the Al-rich areas in the coatings especially near the interfaces of the coating and superalloy are crack initiation sites. The combination of temperature dependent localized oxidation and stress concentration at the crack tip dominate the crack initiation and small crack propagation procedure.
[en] In metallic materials, phase transformation temperature is a critically important physical parameter, yet, in most cases is difficult to be measured in situ and full scale. In past decades, the measurement of phase transformation temperature primarily relies on the differential thermal analysis (DTA) and dilatometry analysis (DA) techniques. Recently, Single sensor DTA technique has been successfully developed to measure transformation starting and finishing temperatures based on one measured curve. In this research, we developed a method to generate a wide range of cooling rate within an individual nickel base superalloy specimen on the basis of end-quenching methodology. By means of recording the cooling history at different specimen positions, three different cooling curves were obtained and the self-developed code can clearly recognize the phase transformation starting and finishing temperatures. This method provides a promising means to measure continuous cooling transformation curve in a rapid and economic manner. (paper)