Microstructure Evolution During Continuous Cooling in Niobium Microalloyed High Carbon Steels

Zhaodong Li,Qilong Yong,Zhengyan Zhang,Xinjun Sun,Jianchun Cao,Haiquan Qi,Zhi Liao 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.5

Effects of microalloyed niobium (Nb) on the austenite decomposition behaviors and microstructure evolutionduring continuous cooling in the near eutectoid steels were investigated. Compared to the Nb freesteel, the Nb microalloyed steel was refined with regard to polygonal ferrite grain, pearlite block and colonysizes. This was because its austenite grain size was smaller. The volume fraction of polygonal ferrite transformedwas more in the Nb microalloyed steels, which indicated the eutectoid carbon content exceededthat of pure carbon steel. The spheroidization of pearlite during continuous cooling was enhanced by Nbmicroalloying, mainly due to a higher critical transformation temperature and the finer pearlite structurewith smaller colony size and narrower interlamellar spacing. Hot deformation right above the equilibriumeutectoid temperature accelerated the spheroidization kinetics of pearlite, especially in the Nb microalloyedsteel.

Bismuth stannate nanoparticles for enhancing fire safety of flexible polyvinyl chloride: Preparation, evaluation, and mechanism

Zhaodong Yuan,Xiaowei Zhao,Shuaiqiang Nie,Xiaohong Li,Zhijun Zhang,Zhiwei Li 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.122 No.-

To replace traditional toxic Sb2O3 flame retardants, Bi2Sn2O7 (BSO) nanoparticles were prepared by a coprecipitationmethod and used as flame retardants of flexible polyvinyl chloride (PVC) for the first time. Structural characterization revealed that as-prepared BSO nanoparticles had a cubic phase with an averagediameter of 20 nm. Under 3 wt% loading, the PVC/BSO composite gained a limiting oxygen index of29%, very close to 29.5% of PVC/Sb2O3. In particular, the PVC/BSO composites passed the UL-94V-0 rating,while PVC/Sb2O3 failed. The PVC/BSO composite also showed better heat and smoke suppression performancethan Sb2O3, with a 27.4% decrease in peak heat release rate and a 39.9% decrease in total smokeproduction, compared with the PVC matrix. The excellent performance is attributed to following two reasons:In the gas phase, similar to Sb, Bi can form BiCl3, which dilutes the combustion gas and captureshydroxyl radicals; In the condensed phase, Sn in BSO helps form more protective char residue with theleast pores and the highest degree graphitization. In addition, the tensile strength and elongation at breakof PVC/BSO were also slightly superior to those of PVC/Sb2O3. In conclusion, BSO nanoparticles will be apromising substitute for toxic Sb2O3 flame retardants.

Effect of Cr Doping on Oxidation Resistance and Oxidation Mechanism of TiC Reinforced Steel Matrix Composites: Experiments and First-Principles Calculations

Chengru Li,Xiaolin Li,Yanmei Li,Xiangtao Deng,Zhaodong Wang 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.11

Oxidation is an inevitable problem and accelerates the wear of materials under high temperature wear conditions. To enhancethe oxidation resistance of TiC particle–reinforced steel matrix composites (TiC-SMCs), the role of Cr on the oxidationmechanism of TiC-SMCs at 600 °C was investigated through experimentation and first-principles calculations in this work. The results indicated that the addition of 3 wt% Cr could induce a transformation from internal oxidation to external oxidationbecause the diffusion energy barrier of O atoms was increased from 0.66 to 0.91 eV. Furthermore, The adsorption ofthe Fe and O atoms was reduced via Cr addition. Consequently, the oxidation resistance of TiC-SMCs was improved andinternal oxidation was inhibited with increasing Cr content, where the oxidation rate coefficients of TiC-SMCs with 3 wt%and 0.3 wt% Cr content were 3.79 × 10−4 and 4.84 × 10−1 mg2cm−4 h−1, respectively. The present study would not onlyprovide the basic understanding for the role of Cr on oxidation behavior, but also contribute to the design of TiC reinforcedsteel matrix composites with excellent oxidation resistance.

ZmFKBP20-1 improves the drought and salt tolerance of transformed Arabidopsis

Yanli Yu,Yanjiao Li,Fengjuan Jia,Meng Zhao,Wencai Li,Qi Sun,Nana Li,Wenlan Li,Zhaodong Meng 한국식물학회 2017 Journal of Plant Biology Vol.60 No.6

FK506-binding proteins (FKBPs), which belongto the peptidyl-prolyl cis/trans isomerase superfamily, areinvolved in plant response to abiotic stresses. A number ofFKBP family genes have been isolated in plants, but littlehas been reported of FKBP genes in maize. In this study, adrought-induced FKBP gene, ZmFKBP20-1, was isolated frommaize and was characterized for its role in stress responsesusing gene expression, protein subcellular localization,transformation in Arabidopsis, expression patterns of thestress-responsive genes, and physiological parameter analysis. During drought and salt stresses, ZmFKBP20-1 transgenicArabidopsis plants exhibited enhanced tolerance, which wasconcomitant with the altered expression of stress/ABAresponsivegenes, such as COR15a, COR47, ERD10, RD22,KIN1, ABI1, and ABI2. The resistance characteristics ofZmFKBP20-1 overexpression were associated with a significantincrease in survival rate. These results suggested thatZmFKBP20-1 plays a positive role in drought and salt stressresponses in Arabidopsis and provided new insights into themechanisms of FKBP in response to abiotic stresses inplants.

Effects of Electromagnetic Fields on Interfacial Bonding Strength of Ti/Al Clad Sheet Processed by Horizontal Twin-Roll Casting

Jiujian Xu,Guangming Xu,Yong Li,Zhaodong Wang 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.10

In this study, a Ti/Al clad sheet was fabricated using horizontal twin-roll casting (HTRC) with the application of pulsedelectric field (PEF) and electromagnetic oscillation field (EOF), and the effects of different external fields on interfacialbonding strength were investigated in detail. The external electromagnetic fields have little influence on the stability of HTRCprocess. With the application of PEF and EOF, the width of diffusion layer at the Ti/Al interface increases obviously, andthe interfacial bonding strength increases from 20.1 to 21.4 N/mm and 24.5 N/mm, respectively. When the EOF is applied,the electromagnetic volumetric force is generated in the liquid cavity of cast-rolling zone, which is much larger than theelectromagnetic force caused by single PEF. Under the action of the electromagnetic volume force, aluminum melt in theliquid cavity oscillates repeatedly, which scours the surface of the titanium strip and makes the newly formed crystal nucleifall off the surface of strip. In addition, the oscillation effect reduces the temperature gradient at the contact area betweenstrip and melt and slows down the solidification process, thus prolonging the contact time between aluminum and titanium. All of these effects make the melt spread more sufficient on the surface of titanium strip and promote the interdiffusionbetween atoms. As a result, more metallurgical bonding regions are formed and enhanced, which leads to the improvementof bonding strength of the clad sheet.

Optimization of image reconstruction method for dual-particle time-encode imager through adaptive response correction

Zhao Dong,Jia Wenbao,Hei Daqian,Cheng Can,Cheng Wei,Liang Xuwen,Li Ji 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.5

Time-encoded imagers (TEI) are important class of instruments to search for potential radioactive sources to prevent illicit transportation and trafficking of nuclear materials and other radioactive sources. The energy of the radiation cannot be known in advance due to the type and shielding of source is unknown in practice. However, the response function of the time-encoded imagers is related to the energy of neutrons or gamma-rays. An improved image reconstruction method based on MLEM was proposed to correct for the energy induced response difference. In this method, the count vector versus time was first smoothed. Then, the preset response function was adaptively corrected according to the measured counts. Finally, the smoothed count vector and corrected response were used in MLEM to reconstruct the source distribution. A one-dimensional dual-particle time-encode imager was developed and used to verify the improved method through imaging an AmeBe neutron source. The improvement of this method was demonstrated by the image reconstruction results. For gamma-ray and neutron images, the angular resolution improved by 17.2% and 7.0%; the contrast-to-noise ratio improved by 58.7% and 14.9%; the signal-to-noise ratio improved by 36.3% and 11.7%, respectively.