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21.
《中国有色金属学会会刊》2020,30(3):710-726
Cylindrical samples of Ni-based GH4037 alloy were compressed at solid temperatures (1200, 1250 and 1300 °C) and semi-solid temperatures (1340, 1350, 1360, 1370 and 1380 °C) with different strain rates of 0.01, 0.1 and 1 s−1. High temperature deformation behavior and microstructure evolution of GH4037 alloy were investigated. The results indicated that flow stress decreased rapidly at semi-solid temperatures compared to that at solid temperatures. Besides, the flow stress continued to increase after reaching the initial peak stress at semi-solid temperatures when the strain rate was 1 s−1. With increasing the deformation temperature, the size of initial solid grains and recrystallized grains increased. At semi-solid temperatures, the grains were equiaxed, and liquid phase existed at the grain boundaries and inside the grains. Discontinuous dynamic recrystallization (DDRX) characterized by grain boundary bulging was the main nucleation mechanism for GH4037 alloy. 相似文献
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23.
《Calphad》2019
MCrAlY (M = Ni, Co) coatings are commonly used on gas-turbine components as oxidation resistant overlay coatings and bondcoats for thermal barrier systems. The present work focuses on the effect of the aluminizing process on the CoNiCrAlY coating microstructure. In the as-received condition the outer part of the coating consisted mostly of β-(Ni,Co)Al with interspersed precipitates of Cr-rich carbide and Cr-rich boride precipitates. Formation of σ-CoCr was observed at the interface between the β-layer and the inner initial CoNiCrAlY microstructure. Scanning electron microscopy (SEM) combined with energy and wavelength-dispersive X-ray spectroscopy (EDX/WDX) was employed to characterize the aluminized CoNiCrAlY coating. Phases were then identified by electron backscatter diffraction (EBSD). Detailed microstructural studies of the coating were corroborated with the help of coupled thermodynamic-kinetic calculations to model the aluminizing process. The calculations were performed with the in-house developed code employing the commercially available thermodynamic and kinetic databases (ThermoCalc). The mechanisms of the observed microstructural changes were elucidated with the help of the modelling results. 相似文献
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25.
Hongyu Wu Dong Zhang Biaobiao Yang Chao Chen Yunping Li Kechao Zhou Liang Jiang Ruiping Liu 《材料科学技术学报》2020,(1):7-17
In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology. 相似文献
26.
电渣重熔凝固组织的控制直接关系到高温合金的品质与实际生产应用。针对电渣重熔GH984G的定向凝固过程,同时考虑传热和溶质扩散,基于CAFE法与C语言结合,建立了三维电渣重熔凝固过程组织演变的CAFE模型,并对凝固过程温度场和凝固组织演变进行模拟预测。结果表明,铸锭温度场和熔池深度都是首先为较浅平状态,然后不断加深至最后稳定;在电极熔化初始,金属熔池浅平,枝晶生长方向是竖直向上,之后金属熔池不断加深,底部竖直向上的柱状晶方向变为斜向上约26°。同时在铸锭的中心线上出现了等轴晶,等轴晶形核长大后与柱状晶镶嵌生长。此外,随着电极熔速变大,渣金界面上涨速度也随之变大,且熔池深度相应变宽变深。模拟结果与试验结果基本吻合,从而验证了模型与形核参数的适用性。 相似文献
27.
《International Journal of Hydrogen Energy》2021,46(60):30959-30975
The performance of Ni-based catalyst supported on γ-Al2O3 for glycerol dry reforming (GDR) reaction was investigated in the current study. γ-Al2O3 was prepared from aluminum dross (AD) before use as catalyst support. Al2O3 was extracted using three different techniques assisted with ultrasonication: acid leaching with ammonia precipitation, acid leaching with re-precipitation of HCl, and alkaline leaching with ammonium hydrogen carbonate. The results show that extracted γ-Al2O3 3 (EGA3) with the highest purity and the surface area of 267.5 m2 g−1 was produced from acid leaching with ammonia precipitation technique at a calcination temperature of 800 °C. A series of Ni/EGA3 (5%, 10%, 15% and 20%) catalysts were tested and it was found that the catalytic activity was increased in the order of 5%Ni/EGA3 < 10%Ni/EGA3 < 20%Ni/EGA3 < 15%Ni/EGA3. 15%Ni/EGA3 catalyst has the highest catalytic activity due to the excellent distribution of Ni on the EGA support, high specific surface area of the support and high catalyst's basicity. In addition, the strong Ni-EGA3 interaction of the 15%Ni/EGA3 catalyst suppressed the carbon formation with the catalyst having the lowest carbon deposition value of 25.51% during the GDR reaction carried out for 8 h. Studies on the GDR reaction catalytic activities revealed that 15%Ni/EGA3 achieved the maximum catalytic activity with 56.7% glycerol conversion, 44.7% H2 yield, and 40.6% CO yield at 800 °C and CGR of 1:1. The H2:CO ratio obtained in this study was approximately 1.2–1.5 throughout the reaction, depicting a relatively rich H2 syngas product. Overall, the strong interaction between Ni and EGA3 ensured stable Ni particles that can mitigate carbon deposits, thereby enhancing the catalytic activity. 相似文献
28.
Miao Guo Huiping Yuan Yuru Liu Lijun Jiang 《International Journal of Hydrogen Energy》2021,46(10):7432-7441
The LaY2Ni9.7Mn0.5Al0.3 and LaSm0.3Y1.7Ni9.7Mn0.5Al0.3 alloys have been synthesized to investigate the effect of Sm partial substitution for Y on the cyclic stability of A2B7-type La–Y–Ni-based alloys. Their cyclic properties were also compared with the A2B7-type (RE0.85Mg0.15)2(NiAl)7 (RE = Rare Earth) alloys. The gas-solid and electrochemical cycle lives were tested. The structural stability, pulverization, and oxidation/corrosion performances were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical methods. The partial substitution of Sm for Y improves anti-corrosion and anti-pulverization performances, thereby increasing the cycle life of A2B7-type La–Y–Ni-based hydrogen storage alloys. The A2B7-type RE–Y–Ni-based alloys exhibit better crystal structure stability, but the gas-solid and electrochemical cyclic stability is worse than A2B7-type (RE0.85Mg0.15)2(NiAl)7 alloys due to easier pulverization of particles and the oxidation of Y elements. 相似文献
29.
30.
《International Journal of Hydrogen Energy》2022,47(2):984-992
The rational design and preparation of bifunctional electrocatalysts with pleasant oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance is crucial for extensive commercial applications of rechargeable Zn–air batteries (ZABs). Herein, we report a simple method to obtain multi-metal (Fe, Ni, Zn) embedded in N-doped carbon sheets entangled with carbon nanotubes (CNTs) as superior oxygen electrocatalysts (FeNi-NCS-2). The resultant FeNi-NCS-2 exhibits an impressive electrochemical performance, providing a reversible oxygen overpotential as low as 0.758 V. The ZAB with FeNi-NCS-2 as the air cathode shows a promising capacity of 639.71 mAh g?1 at 20 mA cm?2, a power density of 109.8 mW cm?2 and cycling stability of over 130 cycles at 10 mA cm?2 with an energy efficiency of about 55%, superior to the ZAB based on Pt/C–IrO2. The satisfactory electrocatalytic performance is mainly due to the Fe, Ni-based nanoparticles protected by graphitic carbon layers, hierarchical porous lamellar structures that promote the accessibility between the active centers and the electrolyte as well as self-growing tangled carbon nanotubes that provide fast transmission channels. This study presents a facile way for the synthesis of highly efficient ORR/OER bifunctional electrocatalysts for high-performance rechargeable ZABs. 相似文献