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[en] The use of locally developed high performance alloys in power plants has become essential in the past ten years. Application of these alloys has been difficult because of a shortage of field demonstration testing, and the lack of lab-based test data. In this work, three types of locally developed heat resistant alloys were demonstration tested in boiler tubes in a power plant. The test procedures included a pre-test, a field demonstration and a post-test. The pre-test revealed the quality of the local tubes was the same level as the originally imported tubes. This suggested the potential outcomes of further demonstration testing. The demonstration was carried out by replacing parts of the original components with newly manufactured test components, made of local and imported tubes. There were no failures in the test components after 13,000 h of operation. A portion of the tubes were sampled for a post-test, while the remaining parts were operated in the boiler for an even longer time. The post-test results revealed no significant degradation of the properties of the local tubes. The works no matter set up the properties database, but also set-up the performance and reliability, as well as test procedures for locally developed tubes.
[en] Generally, Ni based superalloys are used as combustor material owing to its high temperature resisting properties. These materials are also having high strength and hence, they are difficult-to-machine. Producing components of these materials with complex shapes employing traditional machining techniques is practically near to impossible. This problem can be addressed by using WEDM technique. The current research aims to study the effect of wire related parameters and servo feed on material removal rate (MRR) and wire wear rate (WWR) during WEDM of waspalloy. Experimentation has been conducted as per one-factor-at-a-time (OFAT) approach and optimum solution is obtained by graphical analysis. It is observed that wire feed rate of 4 m/min, wire tension of 11 machine unit, and servo feed of 2050 mm/min provide highest value of material removal rate. (paper)
[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] Highlights: • Isothermal two-pass hot compressive tests with stepped strain rates are performed on an aged Ni-based superalloy. • The primary DRX nucleation mechanism is the discontinuous DRX. • True stress of second stage increases with increasing strain rate/strain of first stage or strain rate of second stage. • The developed e-SVR model is feasible to depict the effects of variant strain rate on flow behaviors. The high-temperature flow characteristics and microstructural changes of alloys are usually investigated by isothermal compressive experiments at constant strain rates. However, during the practice industrial production of components, the strain rate is varying. In the present work, the microstructure changes and high-temperature flow characteristics of a Ni-based superalloy containing δ phases were researched by isothermal two-stage high-temperature compression experiments with stepped strain rates. It is revealed that the true stress of the later stage distinctly increases when the true strain/strain rate of the former stage or the strain rate of the later stage are raised. Meanwhile, the dynamic recrystallization (DRX) grains become finer, and the dissolution of δ phase is weakened. But, the coarsening of DRX grains and the dissolution of δ phase are enhanced as the deformation temperature is raised. The primary DRX nucleation mechanism is the discontinuous DRX. Based on the measured flow stress, an e-insensitive support vector regression (e-SVR) model is established for depicting the flow behavior of the researched alloy. The measured results are consistent with the forecasted ones, which illustrating that the developed e-SVR model is feasible to accurately describe the flow behaviors of the researched alloy during two-stage high-temperature deformation with stepped strain rates.
[en] Wire electrical discharge machining (WEDM) is a non traditional electro thermal machining process used for the manufacturing of 3D complex shape and geometry of the alloys or composites. Wire EDM capable of precisely machining parts with different Sizes or hardness which have keen edges that are very tough to be machined by the traditional manufacturing processes. There are many numbers of process parameters and performance measures. Lots of researchers have studied and investigated this machining process. This paper shows the reviews in the current research trends in wire electric discharge machining. There are many process parameters, such as pulse on time (TON), pulse off time (TOFF), servo voltage, peak current (IP), wire tension, wire speed for the improvement of different performance parameter such as material removal rate (MRR), surface roughness (SR), surface integrity factors, Kerf width and Tool wear ratio (TWR). The different optimization technique include Taguchi technique, GRA (Grey Relational Analysis), RSM (Response Surface Methodology) and analysed by ANOVA (Analysis of Variance), on different material like Alloys, Superalloys and MMC (Metal Matrix Composites). This literature survey gives the acceptable process parameters and its effect on different performance measure under normal or cryogenic treated tool electrode condition and their ranges in machining of different materials (paper)
[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] 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] 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] 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.