The effect of varying amounts of CoAl2O4 inoculant ranging from 0 to 2 wt pct on the microstructure evolution of Inconel 718(IN718) fabricated by selective laser melting (SLM) was evaluated. Characterization of the as-built microstructure revealed that addition of CoAl2O4 resulted in a modest degree of grain refinement with a slight increase in microstructural anisotropy. Increasing the total CoAl2O4 content beyond 0.2 wt pct resulted in severe agglomeration of the non-metallic particles and the formation of slag inclusions measuring up to 100 μm in size present in the as-built microstructure. In addition to large agglomerates, the inoculant was chemically reduced to form a fine dispersion of submicron-sized Al2O3 particles throughout the IN718 matrix. The fine dispersion of oxides significantly hindered grain recrystallization during the post-fabrication heat treatment due to a Zener pinning effect. The findings from this study indicate in order to effectively utilize CoAl2O4 as a grain refining inoculant for additive manufacturing, the process parameters need to be optimized to avoid agglomeration of the non-metallic particles and other process-related defects.
Abstract The convergence property of the lp‐norm algorithm for polynomial‐perceptron having different error signal distributions will be analyzed in this paper. To see the effect of error signal on the convergence rate, two types of activation functions are considered in the analysis: one is of a linear type and the other is of a sigmoidal type. Different activation functions yield different ranges of output signal and, in turn, yield different error signal distributions. Linear activation function causes the error signal to be distributed in an uncertain way, while sigmoidal activation function causes it to be distributed in a tightly bounded region. Based on this difference the convergence property of the lp‐norm algorithm, 1 ≤ p ≤ 2, is investigated in this paper. Expressions of average learning gains are obtained in terms of the power metric p, the error probability, and the upper bound of the error signal distribution. Analytic results indicate that it is of particular value in using the lp‐norm algorithm for the perceptron using sigmoidal activation functions. Computer simulation of an adaptive equalizer using this algorithm confirms the theoretical analysis. 相似文献
A series of experiments have been performed to investigate the effects of three electrolytes of different compositions (EO, EA and EM) on the electrochemical characteristics of MmNi3.55Co0.72Al0.3Mn0.43 hydrogen storage alloy electrode. Electrolytes EA and EM were obtained by adding appropriate amounts of Al2(SO4)3 and MnSO4 to the original electrolyte EO (6 M KOH + 1 wt% LiOH), respectively. Electrode activation, maximum capacity, cycle life, self-discharge and high-rate discharge characteristics have been studied. It was found that a maximum capacity of about 260 mA h/g has been obtained for the alloy electrodes in all these electrolytes after 5–7 cycles of charging/discharging. The alloy electrodes have a good durability in electrolytes EA and EM, especially after 175 cycles. Using the capacity retention as an indication of self-discharge resistance, almost identical degree of capacity retention (82% after 4 days and 45% after 16 days) has been observed at 298 K, regardless of the electrolytes used. When tested at higher temperature, however, a higher capacity retention (46% after 3 days) at 333 K has been observed for electrodes in electrolyte EA, and about 32% for electrodes in both electrolytes EO and EM. As to high-rate discharge behavior of the results of high-rate discharge tests indicated that about 50% of discharge efficiencies were obtained in the three electrolytes at 333 K by continuous-model high-rate discharge method, at a discharge rate of 7C, and 22% in 298 K. The alloy electrode in electrolyte EM has the best durability, in which about 50% of discharge efficiency at DC = 9C was obtained by step-model high-rate discharge method at 333 K, which was even higher than that at 298 K. 相似文献
In the current investigation, the effect of Cr on the solidification characteristics and as-cast microstructure of pseudobinary
γ-δ eutectic alloys based on a near-eutectic composition (Ni-5.5Al-13.5Nb at. pct) was investigated. It was found that Cr additions
promote the formation of a higher volume fraction of γ-δ eutectic microstructure in the interdendritic region. Increasing levels of Cr also triggered morphological changes in the
γ-δ eutectic and the formation of γ-γ′-δ ternary eutectic during the last stage of solidification. A detailed characterization of the as-cast alloys also revealed
that Cr additions suppressed the liquidus, solidus, and γ′ precipitation temperature of these γ/γ′-δ eutectic alloys. A comparison of the experimental results with thermodynamic calculations using the CompuTherm Pandat database
(CompuTherm LLC, Madison, WI) showed qualitative agreement. 相似文献
The cycle stability of La-Mg-Ni based alloys in a gas–solid reaction system was investigated in this work. Both partial substitutions of La and Ni by Ce and Al, respectively, improved the cycle stability of La(0.65?x)CexCa1.03Mg1.32Ni(9?y)Aly alloys. Although the addition of Al reduced the hydrogen storage capacity significantly, it is still important to be included in the system for its superior property in improving the cycle life. Hence, two optimized samples with a small addition of Al (y = 0.10) were used to compare with the cycle life of CaNi5. It was found that the Ce and Al added samples have a better hydrogen capacity retention than that of samples without element substitution; and their overall hydrogen storage capacity was still higher than that of CaNi5. We also found that heat treatment used in this study did not fully recover the hydrogen storage capability of La-Mg-Ni based alloy to its original storage capacity. A probable reason was the heat treatment used in this study could only recover the degradation caused by the disproportionation to some extent, but the treatment was unable to reverse the degradation caused by decrepitation. 相似文献
In order to overcome the existence of the local minimum in the multilayer perceptron (MLP) implemented with back-propagation (BP) algorithm, the evolutionary strategy (ES) is proposed. Introducing the factors of the chromosome and gene mutation rates, one can enhance the flexibility of the mutation. The bounds of the chromosome and gene mutation rates are derived. Simulation results are shown to verify the theoretical calculations and also suggest appropriate strategy parameter values. The theoretical results are studied using the MLP-based decision feedback equalizer (MLP DFE) scenarios. The results indicate that the evolutionary strategy outperforms the BP algorithm 相似文献
Two normal strength concretes and three high strength concretes, with 28-day compressive strengths of 28, 47, 76, 79 and 94 MPa respectively, were used to compare the effect of high temperatures on high strength concrete and normal strength concrete. After being heated to a series of maximum temperatures at 400, 600, 800, 1000 and 1200°C, and maintained for 1 hour, their compressive strengths and tensile splitting strengths were determined. The pore size distribution of hardened cement paste in high strength concrete and normal strength concrete was also investigated. Results show that high strength concrete lost its mechanical strength in a manner similar to or slightly better than that of NSC. The range between 400 and 800°C was critical to the strength loss of concrete with a large percentage of loss of strength. Microstructural study carried out revealed that high temperatures have a coarsening effect on the microstructure of both of high strength concrete and normal strength concrete. 相似文献