赵九洲
,
李海丽
,
何杰
,
张显飞
金属学报
利用气体雾化方法研究了Cu--20%Co (质量分数) 合金的快速凝固行为, 获得了富Co相以微细球形粒子形式分布于基体的合金粉末. 建立了Cu--Co雾化液滴快速凝固过程模型,模拟分析了雾化液滴凝固的动力学细节. 结果表明:所建模型能很好地描述Cu--Co合金雾化液滴冷却凝固过程;液--液相变过程中组织演变是弥散相液滴形核、长大、碰撞凝并和空间迁移共同作用的结果; 雾化液滴尺寸越大,冷却越慢, 富Co相液滴的形核速率越低, 凝固后富Co相的弥散度越差.
关键词:
Cu-Co合金
,
Rapid solidification
,
Atomization
,
Modeling
D.R. Liu
,
E.J. Guo
,
L.P. Wang
金属学报(英文版)
Numerical investigations of the `banding' microstructure formation during solidification of Ti-6Al-4V alloy in the centrifugal casting are conducted using a multi-scale model, which combines the finite difference method (FDM) at the macroscale with a cellular automaton (CA) model at the microscale. The macro model is used to simulate the fluid flow and heat transfer throughout the casting. The micro model is used to predict the nucleation and growth of microstructures. With the proposed model, numerical simulations are performed to study the influences of the nucleation density, mould rotation speed, and casting size upon the banding' microstructure formation. It is noted that changing the nucleation density has a minor effect on the microstructure formation. The rotation speed promotes the formation of `banding' microstructure, which is more noticeable for larger size castings.The major mechanism responsible for this `banding' phenomenon is thespatial variation in cooling rates created by centrifugal force.
关键词:
Modeling
,
null
,
null
J.W. Zhao
,
H. Ding
,
W.J.Zhao
,
F.R. Cao
,
H.L. Hou
,
Z.Q. Li
金属学报(英文版)
A cellular automaton (CA) model is established to
simulate dynamic recrystallization (DRX) in the $\beta$ single-phase
field of Ti6Al4V alloy, and the kinetics during DRX processing has
been analyzed. The model employed considers the influences of
dynamic recovery, nucleation rate, strain rate and dislocation
density on DRX, and practical deformation parameters, such as
temperature, strain and strain rate on DRX have been considered in
the simulation. The simulated DRX grain size and DRX grain shape
agree well with the experimental results, which shows the
availability and feasibility of the cellular automaton method for
the simulation of DRX. The result of kinetics analysis of DRX
reveals that the Avrami exponent is variable ranging from 2.4 to
2.9, which increases with the increase of strain rate.
关键词:
Ti6Al4V alloy
,
null
,
null
,
null
,
null
,
null
Lugui CHEN
,
Yong LING
,
Xiuhong KANG
,
Lijun XIA
,
Dianzhong LI
材料科学技术（英文）
A large-scale, thin wall duplex stainless steel impeller with complex geometry was deformed severely and unpredictably during casting and heat treatment processes resulted in dimensional failure for the final part. In this paper, the distortion of the impeller during casting and heat treatment was calculated. A commercial software, Experto-ViewCast, was used to simulate the transient heat transfer, solidification and mechanical behaviors during the casting and the heat treatment process. The coupled set of governing differential equations for mass, energy and mechanical balance were solved by finite control volume and finite element method. A thermoelastic-visco-plastic rheological model was used to compute the constrained shrinkage of the casting. At each time increment, a coupling of the heat transfer and mechanics was performed. Comparison of the experimental measurements with the model predictions showed good agreement. From the calculated displacements of key points of the blade, the proper inverse displacements were determined to provide an optimum casting pattern and to achieve a uniform and reasonable machining allowance for both faces of the blade.
关键词:
Numerical simulation
,
null
,
null
,
null
,
null
Jiuzhou ZHAO
,
L.Ratke
,
Jun JIA
,
Qingchun LI
材料科学技术（英文）
The microstructure development during a cooling period of alloys being immiscible in the liquid state such as Al-Pb or Al-Bi has gained renewed scientific and technical interest during the last decades. Experiments have been performed to investigate the phase transformation kinetics in the liquid miscibility gap and numerical models have been developed to simulate and analyze the solidification process. The recently developed computational modeling techniques can, to some extent, be applied to describe the decomposition, the spatial phase separation and the microstructure evolution during a cooling period of an immiscible alloy through the miscibility gap. This article overviews the researches in this field.
关键词:
Immiscible alloy
,
null
,
null
,
null
Xiaochun SHA
,
Chunli MO
,
Dianzhong LI
,
Yiyi LI
材料科学技术（英文）
Based on hot rolling production line of strip steel, the off-line in-house software, termed as ROLLAN (Rolling Analysis), is developed. The code is mainly used to predict the evolution of temperature, rolling force, fraction and grain size of recrystallization, fraction and grain size of phase transformation and final mechanical properties. Almost all the processing parameters affecting microstructure and mechanical properties in the schedule from reheating to the coiling process are considered in detail. Self-learning coefficient is adopted to adjust the deviation between predicted and measured temperatures, such as roughing exit temperature (RT2), finishing exit temperature (FT7) and coiling temperature (CT). Due to the application of low-speed-threading, increasing-speed-rolling and decreasing-speed-delivery process during finishing rolling and different cooling condition, after coiling the thermal-mechanical history of different position, along strip longitudinal direction is different resulting in inhomogeneous mechanical properties. So the segments are divided along longitudinal direction to identify the variation of microstructure and mechanical properties. An example of plain carbon strip steel Q235 with various thickness is used to compare the calculated mechanical properties with measured ones. For the specific grade of Q235 , the maximum deviation of tensile strength is less than 10.3 MPa, the yield strength is less than 13.2 MPa, and elongation is less than 1.99%. Further work will focus on the on-line application and consider the effect of macrosegregation and sulfur content of cast slab.
关键词:
Microstructural evolution
,
null
,
null
,
null
Jiuzhou ZHAO
,
Dongming LIU
,
Hengqiang YE
材料科学技术（英文）
In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for Al-4.5~wt~pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.
关键词:
Rapid solidification
,
null
,
null
,
null
Weitao LIU
,
Changchuan XIE
,
Michel Bellet
,
Herve
金属学报(英文版)
doi:10.1016/S1006-7191(08)60094-0
In order to improve the prediction accuracy of macrosegregation channel, an algorithm for dynamic remeshing is proposed. The basic idea is to generate fine elements near the liquidus isotherm. The norm of the gradient of solid fraction is used for piloting the remeshing in the mushy zone; whereas, the objective mesh size in the liquid is considered as a function of the distance to the liquidus isotherm. The efficiency of mesh adaptation is demonstrated by prediction of macrosegregation channel in a case of unidirectional solidification.
关键词:
Freckle
,
null
,
null
,
null
Jiuzhou ZHAO
材料科学技术（英文）
Modeling and simulation have been carried out for Al-Pb alloys to investigate the Brownian coagulation effect on the microstructure development in a gas-atomized drop during the liquid-liquid decomposition. The results indicate that Brownian coagulation has a weak effect on the nucleation and a relatively strong effect on coarsening the minority phase droplets. The influence of Brownian coagulation on the liquid-liquid decomposition decreases with the increase in the diameter (or the decrease in the cooling rate) of the atomized drop.
关键词:
Immiscible alloy
,
null
,
null
,
null
,
null
孙天鸣
,
董利民
,
王晨
,
郭文利
,
王莉
,
梁彤祥
新型炭材料
doi:10.1016/S1872-5805(13)60087-6
依据经典流体力学理论,建立了真实密度和孔隙率对炭素材料电阻率影响规律的模型.模型计算结果表明,真实密度对炭素材料的电阻率影响较小,偏差小于3％;开孔气孔率对电阻的影响大于闭孔气孔率,开孔气孔率增加40％时电阻率增加了250％,而相同幅度闭孔气孔率的增加引起电阻率的增加值只有25％.模型计算结果与实测值偏差小于2％,表明模型具有较好的精度.
关键词:
模型
,
炭材料
,
电阻
,
气孔率
