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Yang W.,Nanchang Hangkong University | Zhang Y.,Nanchang Hangkong University | Yu H.,Nanchang Hangkong University | Yan Q.,Nanchang Hangkong University | And 2 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

Non-equilibrium solidification of AZ91 magnesium alloy containing RE elements was performed by a copper mould casting method, and the effects of category of RE (RE=Ce, Er) and its content (0.25, 0.5, 0.75, 1 wt%) on the primary grain size, solute concentration and phase structures were researched. Results show that less solute content exists in α-Mg grain for Ce addition, accompanied by the serious solute enrichment ahead of solid/liquid interface and the formation of Al11Ce3 phase with high melting point. Consequently, the refinement effect of Ce is more significant than that of Er. With increasing the amount of Ce, both the primary grain size and the ratio of β-Mg17Al12 phase decrease continuously, with the dispersive distribution of eutectic phase in the matrix. In contrast, grain coarsening appears when the Ce content is larger than 0.75 wt%. On this basis, the refinement mechanism was explained according to nucleation and growth processes, which was further verified by the differential thermal analysis experiment. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.

Yang W.,Nanchang Hangkong University | Yang W.,Collaborative Innovation Center for Aviation Manufacturing Industry of Jiangxi | Xia W.,Nanchang Hangkong University | Xu Z.,Nanchang Hangkong University | And 2 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2016

Adopting differential scanning calorimetry and copper-mould spray-casting methods, the near-equilibrium and sub-rapid solidification of K424 superalloy were investigated within a wide range of cooling rate between 0.17 K/s and 100 K/s. Using OM, SEM and EDS, the evolutions of primary γ phase, precipitated γ' phase, MC carbides and eutectic microstructure were described as a function of cooling rate. It is shown that γ phase is refined with the increasing of cooling rate, and the secondary dendrite spacing decreases from 84 μm at 0.17 K/s to 5 μm at 100 K/s. Moreover, the average size of precipitated γ' phase decreases because of the shortened time for transformation. Precipitation occurs once again as for heating the formed supersaturated solid solution during sub-rapid solidification. Both the refinement of γ phase and solute trapping decrease the extent of solute segregation, which leads to the reduction of the sizes of γ+γ' eutectic and carbides. © 2016, Science Press. All right reserved.

Li L.-H.,Northwestern Polytechnical University | Mo R.,Northwestern Polytechnical University | Chang Z.-Y.,Northwestern Polytechnical University | Zhang H.-M.,Avic South Aviation Industry Ltd Corporation
Jisuanji Jicheng Zhizao Xitong/Computer Integrated Manufacturing Systems, CIMS | Year: 2015

To solve the problems of poor effect and difficulty of multi-factors coordination in man-made qualitative evaluation method for aero-engine assembly task priority, an evaluation method based on balanced weight and improved Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) was proposed. A synthetical and hierarchical evaluation model was built according to the relationship of task attribution, and the quantitative representation of indicators was given. The subjective and objective weights were separately determined by trapezoidal fuzzy scale-rough AHP and coefficient variation method, and the weight contribution balanced model was established to integrate subjective and objective weights. An improved TOPSIS replacing of Euclidean distance by Kullback-Leibler divergence was used to sort the weighted indicator values of evaluation objects. An enterprise application example was given to illustrate the correctness and feasibility of the proposed method. ©, 2015, CIMS. All right reserved.

Hu S.,Northwestern Polytechnical University | Yang H.,Northwestern Polytechnical University | Zhang Z.,Avic South Aviation Industry Ltd Corporation | Zhao J.,Northwestern Polytechnical University | Chang Z.,Northwestern Polytechnical University
Jisuanji Fuzhu Sheji Yu Tuxingxue Xuebao/Journal of Computer-Aided Design and Computer Graphics | Year: 2014

A similarity measure method based on the geometry evolution sequence of three-dimensional process model is presented against the criterion that “similar parts structure have similar process” which would result in disadvantages such as big process knowledge granularity. First, we use a group of physical feature vectors which are affine-invariant, called shape descriptors, to express the feature value of the three-dimensional process model's geometry; Then, the changed voxels in the process model sequence will be obtained through comparing the difference of the shape descriptors; Next, we build the attribute adjacency graphs of two adjacent process models' geometry evolution by using the changed voxels and use the sequence of the attribute adjacency graph to express the geometry evolution process of the process model; Finally, a novel similarity measure method of machining process is achieved by comparing the sequence's similarity of the attribute adjacency graph. The case results proved the validity of the method.

Zeng Q.,Control Iron and Steel Research Institute, China | Yan P.,Control Iron and Steel Research Institute, China | Zhao J.C.,Control Iron and Steel Research Institute, China | Zhang L.F.,Control Iron and Steel Research Institute, China | Li L.,Avic South Aviation Industry Ltd Corporation
Materials Science Forum | Year: 2014

A long term aging treatment at 900°C for 3000h was carried out on a conventional cast nickel base superalloy with standard solution and aging treatment. The microstructural evolution including the phases within grains and at grain boundaries (GBs) during thermal exposure in the alloy was observed using OM and SEM. It was shown that the major phases in the alloy after standard heat treatment were γ' precipitates and coarse blocky MC carbides, both of which were distributed not only within grains but also at GBs. During aging, the size of MC carbides and γ' precipitates both within grains and at GBs increased with increasing aging time. It was found that two characteristics of MC carbide and γ' precipitates evolved with aging time: the one is that the coarsening ratio of carbides and γ' precipitates at GBs were significantly higher than that of carbide and γ' precipitates inside the grains; the other is that the coarsening ratio of carbides was markedly higher than that of γ' precipitates. M6C carbide and h phase initially formed in the edge of MC carbide at the expense of MC carbides and γ' precipitates in the vicinity of MC during the early stage of aging. After 3000h, MC carbides inside the grains were covered by h phase films, while those distributed at GBs were completely decomposed into h phase and M6C particles. © (2014) Trans Tech Publications, Switzerland.

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