Papers by Author: Xin Fang Cui

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Authors: Xin Fang Cui, Shuang Quan Fang, Ying Jie Qiao, Qi Jia
Abstract: Ti5Si3 matrix composites reinforced by carbon nanotubes were fabricated by vacuum hot pressing sintering. X-ray diffraction and scanning electron microcopy were carried out to analyze the phase and microstructure of the composites. The effects of carbon nanotubes on mechanical properties were investigated. Experimental results showed that the nanotubes partly reacted with Ti and Si powders to obtain Ti5Si3 and Ti3SiC2, TiSi2 when the sintering temperature is about 1380oC. The mechanical properties of composites can be affected by carbon nanotubes. Meanwhile, the maximal increments of Vickers hardness, bending strength and fracture toughness of the composites, compared with the Ti5Si3 matrix, were 62.9%, 160.9% and 159.3%, respectively. Both of transgranular and intergranular fracture in the composites were the main fracture mode. The fracture manners of composites mainly include “bridging” of CNTs, “deflection” of minor phases and the evolution of grain.
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Authors: Li Li, Qing Fen Li, Er Jun Guo, Er Bao Liu, Xin Fang Cui, Xiao Xue Xu
Abstract: According to the non-equilibrium grain-boundary segregation (NGS) kinetics curve of phosphorus, a series of Charpy impact tests was performed in an industrial steel 12Cr1MoV, at solution temperature 1050oC, with isothermal holding temperature 540oC, on specimens of different holding time (at the segregation process, the critical time, and the desegregation process respectively). The DBTT values were measured and a temper embrittlement kinetics curve was given. The reverse temper embrittlement NGS mechanism for steel 12Cr1MoV was proposed.
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Authors: Qing Fen Li, Xin Fang Cui, Hui Min Zhou, Ming Liu
Abstract: Temper embrittlement and fracture control method based on both non-equilibrium grain-boundary segregation (NGS) theory and grain refinement technique are studied in this paper. Grain refinement technique by deformation induced phase transformation in low-alloy steels, 12Gr1MoV and 2.25Gr1MoNb, is investigated. A single-pass hot rolling process by using a Gleeble-1500 system is performed. Experimental results show that steel strength and toughness may be controlled and improved by grain refinement, and that the grain sizes were affected by the deforming temperature, strain reduction, and strain rate. According to the NGS theory, a control method of brittle fracture along grain-boundary is proposed so that some catastrophically brittle fracture failure may be averted. Grain refinement may decrease both the concentration of phosphorus at grain boundaries and the critical time. With the grain refinement technique, the temper embrittlement of steel may be improved, and the critical time may be shortened. The cost of heat treatment for fracture control will therefore be reduced.
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