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排序方式: 共有5134条查询结果,搜索用时 15 毫秒
91.
Xu Qingyan Zhang Hang Liu Baicheng 《中国铸造》2014,(4):268-276
As the key parts of an aero-engine,single crystal(SX)superalloy turbine blades have been the focus of much attention.However,casting defects often occur during the manufacturing process of the SX turbine blades.Modeling and simulation technology can help to optimize the manufacturing process of SX blades.Multiscale coupled models were proposed and used to simulate the physical phenomena occurring during the directional solidification(DS)process.Coupled with heat transfer(macroscale)and grain growth(meso-scale),3D dendritic grain growth was calculated to show the competitive grain growth at micro-scale.SX grain selection behavior was studied by the simulation and experiments.The results show that the geometrical structure and technical parameters had strong influences on the grain selection effectiveness.Based on the coupled models,heat transfer,grain growth and microstructure evolution of a complex hollow SX blade were simulated.Both the simulated and experimental results show that the stray grain occurred at the platform of the SX blade when a constant withdrawal rate was used in manufacturing process.In order to avoid the formation of the stray crystal,the multi-scale coupled models and the withdrawal rate optimized technique were applied to the same SX turbine blade.The modeling results indicated that the optimized variable withdrawal rate can achieve SX blade castings with no stray grains,which was also proved by the experiments. 相似文献
92.
《Intermetallics》2014
Porous bulk metallic glasses (BMGs) are promising biomedical materials to be used for surgical implants. Here we report on successful formation of porous Ni-free Ti-based BMGs with a diameter exceeding 15 mm by spark plasma sintering the mixture of the gas-atomized Ti-based (Ti45Zr10Cu31Pd10Sn4) glassy alloy powder and solid salt powder, followed by leaching treatment into water to eliminate the salt phase. Corrosion behaviour of the produced porous Ti-based BMGs was investigated in Hanks' solution. The potentiodynamic polarization curves showed that the anodic current density in the porous Ti-based BMGs slowly increased during anodic polarization, suggesting the crevice corrosion. 相似文献
93.
Bao-ping Wu Lin-han Li Jian-tao Wu Zhen Wang Yan-bin Wang Xing-fu Chen Jian-xin Dong Jun-tao Li 《北京科技大学学报(英文版)》2014,(11):1120-1126
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%. 相似文献
94.
J. C. Álvarez Hostos A. D. Bencomo E. S. Puchi Cabrera I. M. Figueroa Poleo 《International Journal of Cast Metals Research》2018,31(1):47-55
The present work has been conducted in order to develop a novel solution for the heat transfer problem during the continuous casting of steel billets and blooms, by using the element-free Galerkin method under a pseudo-transient moving cross-section slice approach. The transport laws, non-linear aspects and boundary conditions of the initial value problem have been specified. A detailed explanation concerning the characteristics inherent to the application of the element-free Galerkin method to this problem has also been provided. The feasibility and suitability of this novel approach has been verified by comparison with the numerical techniques proposed and the results reported by other researchers as well as an analytical solution of a simple 1-D alloy solidification problem. The results have revealed that this technique could be used successfully in the pseudo transient moving cross-section solution of the heat transfer problem involved in the continuous casting of blooms and square billets. 相似文献
95.
96.
The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn (mass fraction) alloy. The morphology was investigated by optical metallograph and electron back-scattered diffraction technique. Results showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas, which were separated by coherent and incoherent twin boundaries. Both the primary trunk and all lateral arms of twinned dendrites grew along 〈110〉 directions, unlike regular 〈100〉 α(Al) dendrites. The facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection, and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned dendrites. The formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically. 相似文献
97.
Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate (VL) and the cooling rate (TR). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for TR>5.0 K/s. Cellular (lc) and primary dendrite arm spacings (l1) are determined along the length of the directionally-solidified casting. Experimental growth laws relating lc and l1 to VL and TR are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed. 相似文献
98.
Dendritic coarsening in Al-2mol%Si alloy during isothermal solidification at 880K was investigated by phase field modeling. Three coarsening mechanisms operate in the alloy: (a) melting of small dendrite arms; (b) coalescence of dendrites near the tips leading to the entrapment of liquid droplets; (c) smoothing of dendrites. Dendrite melting is found to be dominant in the stage of dendritic growth, whereas coalescence of dendrites and smoothing of dendrites are dominant during isothermal holding. The simulated results provide a better understanding of dendrite coarsening during isothermal solidification. 相似文献
99.
采用华铸CAE软件对铝合金定子铸件的砂型铸造过程进行数值模拟,通过对铸造工艺方案的数值模拟和实验,优选出了最佳的铸造工艺用于生产,成功地消除了定子铸件生产过程的缩孔缩松缺陷.模拟结果与实际生产中的情况吻合较好.结果表明CAE技术能为工艺方案的评价和改进提供科学的依据,能缩短新产品的开发周期,为企业带来了显著的经济效益. 相似文献
100.