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Zhou D.Q.,University of Science and Technology Beijing | Zhao W.X.,University of Science and Technology Beijing | Mao H.H.,KTH Royal Institute of Technology | Hu Y.X.,University of Science and Technology Beijing | And 3 more authors.
Materials Science and Engineering A | Year: 2015

In this paper, the dynamic evolution of precipitates and its influence on the high-temperature mechanical properties of newly developed AFA steels were systematically investigated. At 1023K or above, three main types of precipitates, i.e., the B2-NiAl, Laves-Fe2Nb, and δ/σ phases, were formed in the base steel, and the major strengthening medium is Laves-Fe2Nb, which coarsened quickly, leading to undesirable creep properties. Phase competition between the most effective strengthening NbC nanosized precipitates and the Laves-Fe2Nb phase was analyzed, and it was found that adjusting the Nb/C ratio in the steels could enable the precipitation of highly stable, fine NbC particles. In addition, the formation of detrimental σ phases could be suppressed by lowering the Mo and Si content in the alloy. Eventually, a new type of AFA steel consisting of a high density of nanosized NbC particles homogeneously dispersed in the austenitic matrix was successfully developed, and significant enhancement in the creep resistance was achieved due to the effective strengthening resulting from the tiny secondary NbC particles. © 2014 Elsevier B.V.

Li X.-H.,Shandong Xiangguang Copper Co. | Wan S.,Shandong Xiangguang Copper Co. | Liu Z.-J.,Shandong Liaocheng Entry Exit Inspection and Quarantine Bureau | Guo F.-F.,NCS Testing Technology Co.
Yejin Fenxi/Metallurgical Analysis | Year: 2016

The content range of calibration curve was broadened using certified reference material of copper concentrate and adding spectral-purity substance or standard solution of single element. The sample was prepared by fusion method. The content of copper, lead, chromium, arsenic, silver, antimony, bismuth, nickel, iron and aluminum in copper concentrate was determined by wavelength dispersive X-ray fluorescence spectrometry(XRF). The fusion conditions were obtained by experiments and listed as follows: the lithium tetraborate-lithium metaborate mixed flux (m:m=33:67) was used; the dilution ratio was 1:20; the pre-oxidization time was 5 min; the pre-oxidization temperature was 700℃; the fusion time was 10 min; the fusion temperature was 1 000-1 050℃ ; the silicon dioxide was used as glassing reagent; 3-4 drops of 500 g/L lithium bromide solution was used as releasing reagent. The interference of coexisting elements and spectral overlapping could be corrected by theoretical influence coefficient method. The detection limits were between 12 μg/g and 156 μg/g. The precision test was conducted using one copper concentrate sample. The relative standard deviations (RSD, n=11) of determination results of testing elements were between 0.19% and 11.3%. The found results of three actual copper concentrate samples were consistent with those obtained by standard analysis method. The proposed method could meet the requirements of rapid analysis of copper concentrate samples. © 2016, CISRI Boyuan Publishing Co., Ltd. All right reserved.

Chen J.Y.,Beijing Institute of Technology | Li Q.,Beijing Institute of Technology | Li J.,NCS Testing Technology Co. | Tang X.,Beijing Institute of Technology | Xiao C.B.,Beijing Institute of Technology
Materials Science Forum | Year: 2016

The effects of Co additions on the evolution of γ’ precipitates and topologically close-packed (TCP) phases during thermal exposure at 950 °C were investigated for two Ni-based single crystal superalloys with 7.9 wt.% Co and 9.1 wt.% Co. The results indicated that the γ′ morphology was not affected by Co content, whereas γ′ volume fraction decreased and precipitate size increased due to lower Co addition after standard heat treatment. The coarsening of γ′ precipitates in both alloys was controlled by diffusion. The γ′ coarsening rate increased, while the stability of γ′ volume fraction decreased due to lower level of Co addition during 950 °C thermal exposure because more Co addition suppressed the diffusion process. High Co addition promoted the formation of μ phase after thermal exposure at 950 °C for 1000 h due to higher γ′ volume fraction, more stable γ′ volume fraction and higher electron vacancy number. The experimental results of μ phase precipitation showed good agreement with thermodynamic calculation by JMatPro. © 2016 Trans Tech Publications, Switzerland.

Wan S.,Shandong Xiangguang Copper Co. | Guo F.-F.,NCS Testing Technology Co. | Li X.-H.,Shandong Xiangguang Copper Co. | Liu Z.-J.,Shandong Liaocheng Entry Exit Inspection and Quarantine Bureau
Yejin Fenxi/Metallurgical Analysis | Year: 2016

0.040 0 g of sample was transferred into crucible (which had been burned before) containing 0.3 g of vanadium pentoxide flux. Then, 0.2 g of tin particles was added followed by covering with 0.15 g of vanadium pentoxide flux and 1.4 g of tungsten particles. The calibration curves were prepared with potassium sulfate. Thus, a determination method of sulpfur with mass fraction of 5.00%-40.00% in copper concentrate was established by high frequency combustion infrared absorption method. The results showed that the calibration curves could be prepared with integral area as horizontal ordinate and absolute sulfur content as vertical coordinate. The linear equation of calibration curve was Y=37.02X-1.52 with linear correlation coefficient of R=0.999 8. The detection limit of method was 0.017%. The proposed method was applied to the determination of sulfur content in copper concentrate actual sample. The results were consistent with those obtained by gravimetric method or combustion-titration method. The certified reference material of copper concentrate was determined according to the experimental method, and the results were consistent with the certified values. The actual samples and certified reference material of copper concentrate were determined for six times. The relative standard deviations (RSD, n=6) were between 0.41% and 0.72%. © 2016, CISRI Boyuan Publishing Co., Ltd. All right reserved.

Liang Y.,Control Iron and Steel Research Institute, China | Shen X.,Control Iron and Steel Research Institute, China | Shen X.,NCS Testing Technology Co. | Qu H.,NCS Testing Technology Co. | Zhou W.,NCS Testing Technology Co.
Zhongguo Xitu Xuebao/Journal of the Chinese Rare Earth Society | Year: 2015

A new rapid quantitative analysis method was developed for the determination of yttrium oxide in ionic adsorption mines by Port-X300 portable X-ray fluorescence spectroscopy. By the systematic optimization of voltage, electricity, testing time and according to the mathematical correction model, the precision, accuracy and stability of the results were improved. The relative standard deviations(RSD) of determination results were less than 2%, and the results were fundamentally the same with inductively coupled plasma atomic emission spectrometry. The detection limit of yttrium oxide was 9.93 mg·kg-1 which could satisfy the actual need of Southern rare earth prospecting completely. The method not only has the advantages of simple operation, fast detection, non-destructive analysis, but also meets the identification and quantitative accurately. This work would be significant for the prospection of rare earth resources. ©, 2015, Chinese Rare Earth Society. All right reserved.

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