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Study on tungsten sintering temperature field based on electromagnetic simulation and computational fluid dynamics

Tungsten 2024年第2期6卷 355-366页

作者： Lu-Yan Wang Yue-Guang Yu jian-xin dong Kai-Ping Du Shan-Yu Liu Cao-Bing Li University of Science and Technology Beijing Beijing 100083China BGRIMM Technology Group Beijing 100160China China Iron&Steel Research Institute Group Beijing 100081China

In order to study the influence of various sintering variables more intuitively and clearly,electromagnetic field analysis and computational fl uid dynamics are used to analyze the infl uence of gas flow,heating power and other process parameters on the temperature range of medium-frequency sintering in this *** results indicate that the uniformity of temperature fi eld is determined by the gas flow rate and heating *** the heating power is 50 kW,the stable temperature drops about 10 K for every 1 m^(3)·h^(−1)increase of hydrogen *** peak value of the maximum temperature diff erence on the tungsten rods gradually increases with the increase of the hydrogen flow rate,and it appears slightly *** temperature distribution of tungsten rods in furnace is similar with diff erent hydrogen flow *** the same time,the closer to the furnace wall,the higher the temperature of the tungsten *** temperature diff erence between tungsten rods mainly occurred within 1 h after the beginning of *** the heating power can improve the stable temperature,but has little eff ect on the heating *** heating power can increase the peak value of the maximum temperature diff erence on the tungsten rods,but has little eff ect on the occurrence time of the peak value of the maximum temperature diff erence on the tungsten *** the heating power will increase the temperature diff erence of a single tungsten rod,but the temperature diff erence of a single tungsten rod never exceeds 65 *** study can be used to guide the process optimization *** with numerical simulation calculation,the sintering parameters with low energy consumption and high temperature uniformity can be quickly and eff ectively found,thus improving the microstructure and properties of sintered tungsten products.

关键词： Tungsten products Sintering Hydrogen flow rate Heating power

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Nucleation mechanisms of dynamic recrystallization for G3 alloy during hot compression

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Rare Metals 2016年第7期35卷 543-550页

作者： Jue Wang jian-xin dong Mai-Cang Zhang jiangsu Key Laboratory of Advanced Structural Materials andApplication Technology Nanjing 211167China School of Materials Science and Engineering Nanjing Instituteof TechnologyNanjing 211167China School of Materials Science and Engineering University ofScience and Technology BeijingBeijing 100083China

Dynamic recrystallization （DRX） mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200 ℃ and strain rates from 0.1 to 5.0 s-1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction （EBSD） and transmission electron microscope （TEM）. Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dis- locations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate.

关键词： G3 alloy Dynamic recrystallization Nucleation mechanism Annealing twins

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Hot deformation behavior of uniform fine-grained GH4720Li alloy based on its processing map

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International Journal of Minerals,Metallurgy and Materials 2016年第1期23卷 83-91页

作者： Qiu-ying Yu Zhi-hao Yao jian-xin dong Beijing Institute of Aeronautical Materials Beijing 100095 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

The hot deformation behavior of uniform fine-grained GH4720Li alloy was studied in the temperature range from 1040 to 1130℃ and the strain-rate range from 0.005 to 0.5 s-1 using hot compression testing. Processing maps were constructed on the basis of compression data and a dynamic materials model. Considerable flow softening associated with superplasticity was observed at strain rates of 0.01 s 1 or lower. According to the processing map and observations of the microstructure, the uniform fine-grained microstructure remains intact at 1100℃ or lower because of easily activated dynamic recrystallization （DRX）, whereas obvious grain growth is observed at 1130℃. Metal- lurgical instabilities in the form of non-uniform microstrucmres under higher and lower Zener-Hollomon parameters are induced by local plastic flow and primary γ＇ local faster dissolution, respectively. The optimum processing conditions at all of the investigated strains are pro- posed as 1090-1130℃ with 0.084）.5 s-1 and 0.0054）.008 s-1 and 1040-1085℃ with 0.0054）.06 s-1.

关键词： superalloys hot deformation processing maps microstrucmre superplasticity

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A new insight into rapid oxidation of alloy 925 contaminated by oxide powder

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Rare Metals 2021年第7期40卷 1872-1880页

作者： He jiang jian-xin dong Mai-Cang Zhang jiang-Yang Li Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China

Rapid oxidation takes place both in the laboratory and in industrial conditions when alloy 925 is contaminated by oxide powder,and the oxidation rate is much higher than ***,the rapid oxidation behavior and mechanism of alloy 925 were investigated by a series of comparison tests at 1160℃.It is found that the oxide powder produced during the oxidation process is mainly composed of NiCr_(2)O_(4)spinel,accompanied by NiO and NiMoO_(4).The oxide powder plays a triggering role in the rapid oxidation of alloy 925,as NiO has a strong affinity with O.A composition adjustment experiment of alloy 925 shows that rapid oxidation is the synergetic effect of Mo and Cu in the *** and Cu easily combine to form low melting point *** formation and volatilization of MoO_(3)oxide can destroy the completeness of the protective oxide *** MoO_(3)flux can dissolve protective Cr_(2)O_(3)and prevent the repair of the oxide layer and also promote the formation of nonprotective and easy-spall NiCr_(2)O_(4)*** synergetic effect of Cu and Mo in accelerating oxidation should be considered in any nickel-based alloy with a high content of Cu and Mo.

关键词： Rapid oxidation Synergetic effect Nickelbased superalloy

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Mechanism of high-temperature oxidation effects in fatigue crack propagation and fracture mode for FGH97 superalloy

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Rare Metals 2019年第7期38卷 642-652页

作者： Chao Xu Zhi-Hao Yao jian-xin dong Yu-Kun jiang School of Materials Science and Engineering University of Science and Technology Beijing

The high-temperature fatigue crack growth behaviors in powder metallurgy (P/M) Ni-based superalloy FGH97 for turbine disk application were investigated at different temperatures (650, 700 and 800℃) in air using a combination a servohydraulic test system, fractographic and microanalytical investigations. It is found that there is a temperature-sensitive region in which the fatigue life of FGH97 alloy decreases sharply. To further evaluate the crack propagation mode and oxidation effects, interruption experiments were conducted at 700 and 300℃, respectively. The results indicate that the reduction of the fatigue lifetime for FGH97 takes place when the fracture mechanism transforms from a predominantly transgranular mode to an intergranular one as the temperature increases. Although the microstructures and mechanical properties may vary with the temperature, they are not the dominating factors contributing to the temperature sensitivity of fatigue property for FGH97. It is the oxidation that governs the fatigue crack growth behaviors in air at elevated temperature. The enhanced thermal activity of oxygen and certain active metal elements result in accelerated oxidation reaction. The brittle oxide intrusions formed at the crack tip and grain boundaries of crack frontier lead to grain boundary weakness, which is responsible for the transformation of crack growth mode and degradation of the fatigue property of FGH97 alloy.

关键词： FGH97 Fatigue crack growth Temperature sensitivity Fracture mode Oxidation

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Effect of cooling rate on the phase transformation and stability of the mushy zone during the solidification of Waspaloy

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International Journal of Minerals,Metallurgy and Materials 2010年第4期17卷 464-469页

作者： Ling Wang Yi-jun Yao Bin Liu Bo-ying Zhong jian-xin dong College of Mathematics and Physics Nanjing University of Information Science and Technology Nanjing 210044 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Scanning electron microscopy（SEM） and energy dispersive X-ray analysis（EDAX） were used to study the microstructure,microsegregation, and fluid flow tendency of the superalloy Waspaloy in the mushy zone,which had been solidified at different cooling rates. The investigation was accompanied with the calculation of Rayleigh *** is found that Ti is the main segregating element and the content of Ti is the highest in the final liquid at the cooling rates of 3-6℃/*** eta phase（η） precipitate presented in the residual liquid at the cooling rates higher than 6℃/min is responsible for the fluctuations in the curves of Ti *** dendrite arm spacing is found to markedly decrease with the increase of cooling *** maximum relative Rayleigh number occurs at 10-20℃below the liquidus temperature at a cooling rate of 1℃/min,where the mushy zone is most unstable and fluid flow is most prone to occur.

关键词： Waspaloy cooling rate solidification segregation stability mushy zone

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Hot corrosion behavior and mechanism of FGH96 P/M superalloy in molten NaCl–Na_2SO_4 salts

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Rare Metals 2019年第2期38卷 173-180页

作者： He jiang jian-xin dong Mai-Cang Zhang Lei Zheng Zhi-Hao Yao Materials Science and Engineering University of Science and Technology Beijing

Hot corrosion behavior of FGH96 powder metallurgy(P/M) superalloy in 25 % NaCl + 75 % Na_2SO_4 molten salts at 650, 700, and 750 ℃ was investigated in this paper. The methods of mass loss measurement, X-ray diffraction(XRD), scanning electron microscopy(SEM),and energy-dispersive spectroscopy(EDS) were used *** experimental results show that hot corrosion kinetics follows a square power law at 650 ℃, while a linear one at 700 and 750 ℃. The corrosion layer is detected to be composed of Cr_2O_3, NiO, and Ni2S_3 at each *** cross-sectional morphologies and corresponding elemental maps indicate that the corrosion layer is a stratified structure of oxide and sulfide. The results and analyses confirm that the hot corrosion mechanism of FGH96 P/M superalloy is a cooperate process of oxidation and sulfidation. Furthermore, the relatively higher concentrations of Cr, Co, and Ti provide better corrosion resistance to the attack of S and Cl^-.

关键词： Nickel-based superalloy FGH96 Hot corrosion Molten salts

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Microstructure and homogenization process of as-cast GH4169D alloy for novel turbine disk

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International Journal of Minerals,Metallurgy and Materials 2019年第7期26卷 889-900页

作者： Kai Chen Shu-yuan Rui Fa Wang jian-xin dong Zhi-hao Yao School of Materials Science and Engineering University of Science and Technology Beijing

To investigate the microstructure, segregation, and suitable homogenization process of as-cast GH4169D alloy, the microstructure, elements segregation, and precipitates of cast GH4169D ingots prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) were observed by optical microscopy (OM), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). According to the residual segregation model and simulation results of DICTRA thermodynamic software, the homogenization temperature and time range were set as 1120–1170°C and 5–20 h, respectively. The experimental results showed that microscopic dendrite and element segregation occurred in the interior of ingots and the main segregation elements were Nb and Ti. In addition, the precipitates were mainly distributed in interdendritic regions and were composed of NbC, Laves,γ′, and δ phases. The homogenization process suggested that the interdendritic detrimental precipitated Laves phase can be eliminated or redissolved after homogenization at 1150°C for 20 h, suggesting it was the most suitable homogenization treatment. Thermal compression test results showed that the GH4169D alloys after homogenization treatment had no cracks and dynamic recrystallization occurred, with recrystallization volume fraction increasing with temperature, indicating a good working plasticity at temperatures from 1050 to 1200°C.

关键词： GH4169D superalloy as-cast microstructure segregation homogenization thermal deformation

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Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

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International Journal of Minerals,Metallurgy and Materials 2010年第3期17卷 312-317页

作者： Zhong-nan Bi jian-xin dong Mai-cang Zhang Lei Zheng Xi-shan Xie School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677℃ were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with 6 phase are （010）d/（1- 10）*** and [100]d/If 11 ]α-Cr- A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.

关键词： Inconel 718 precipitation mechanism crystallography thermodynamics kinetics

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Effect of boron addition on the microstructure and stress-rupture properties of directionally solidified superalloys

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International Journal of Minerals,Metallurgy and Materials 2014年第11期21卷 1120-1126页

作者： Bao-ping Wu Lin-han Li jian-tao Wu Zhen Wang Yan-bin Wang xing-fu Chen jian-xin dong Jun-tao Li School of Materials Science and Engineering University of Science and Technology Beijing Central Iron & Steel Material Research Institute

This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. With increasing boron content in the as-cast alloys, there is an increase in the fraction of the γ′/γ eutectic and block borides precipitate around the γ′/γ eutectic. At a high boron content of 0.03wt%, there is precipitation of lamellar borides. Upon heat treatment, fine block borides tend to precipitate at grain boundaries with increasing boron content. Overall, the rupture life of the directionally solidified superalloy is significantly improved with the addition of nominal content of boron. However, the rupture life decreases when the boron content exceeds 0.03wt%.

关键词： superalloys directional solidification microstructure boron stress-rupture properties

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