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991.
综述了喷射沉积材料的半固态成形的研究进展,展望喷射沉积材料的半固态成形的发展趋势,分析了喷射沉积材料的半固态成形工艺、半固态变形特征和半固态成形的加热和保温过程中组织演变规律,提出高固相分数的触变成形是喷射沉积材料半固态成形的发展方向. 相似文献
992.
油气田生产中都会产生大量的各种含油污泥,其会对环境造成污染。采用固化的方法对磨72井回注站产生的含油含硫污泥治理进行了研究,实验研究表明采用适宜的固化剂配方能够对含油含硫污泥进行固化作业,且其固化物的浸出物浓度和抗压强度均能满足安全填埋要求。 相似文献
993.
本文采用耦合凝固和熔化效应的二维元胞自动机(cellular automaton, CA)模型,对温度梯度区域熔化(temperature gradient zone melting, TGZM)效应引起的熔池在固液两相区中的迁移现象进行模拟研究.模拟分析了抽拉速度、熔池初始位置、温度梯度和合金成分等因素对TGZM动力学的影响,并将模拟结果与解析模型的预测结果进行比较验证.通过模拟发现,在温度梯度作用下,熔池总是向着高温方向迁移;当抽拉速度低于或高于临界抽拉速度时,熔池朝向移动的液相线或固相线迁移;对于给定的抽拉速度,位于糊状区内临界位置以上的熔池会迁移进入液相,而位于临界位置以下的熔池会逐步靠近固相线.此外,温度梯度越高,合金成分越低,熔池的迁移速度越快. 相似文献
994.
The Green’s function method is applied for the transient temperature of an annular fin when a phase change material (PCM) solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases. 相似文献
995.
Esad Tombarević & Igor Vu&scaron anović 《advances in applied mathematics and mechanics.》2011,3(3):354-369
Phase change in ice-water systems in the geometry of horizontal
cylindrical annulus with constant inner wall temperature and adiabatic
outer wall is modeled with an enthalpy-based mixture model. Solidification
and melting phenomena under different temperature conditions are
analyzed through a sequence of numerical calculations. In the case of freezing
of water, the importance of convection and conduction as well as the influence
of cold pipe temperature on time for the complete solidification is examined.
As for the case of melting of ice, the influence of the inner pipe wall
temperature on the shape of the ice-water interface, the flow and temperature
fields in the liquid, the heat transfer coefficients and the rate of melting
are analyzed. The results of numerical calculations point to good qualitative
agreement with the available experimental and other numerical results. 相似文献
996.
Crystallographic Texture and Domain Structure of Nd3:8Dy0:7Pr3:5Fe86Nb1B5 Nanocomposite Prepared by Direct Rapid Solidification 下载免费PDF全文
"Strong crystallographic texture and high performance of Nd3:8Dy0:7Pr3:5Fe86Nb1B5 (containing 30% ff-Fe) nanocomposite permanent magnetic material was prepared by direct rapid solidification. X-ray diffraction analysis and magnetic measurement indicated that the ribbons had preferential orientation. The easy magnetization direction switched from perpendicular to the ribbon plane to parallel to the ribbon plane direction as the wheel speed increased from 10 m/s to 30 m/s. The multigrain domains were observed by scan probe microscope (SPM) in the ribbons prepared at wheel speed of 10-30 m/s. The Henkel plots were employed to investigate the interactions of the grains in the samples. A very fine and uniform microstructure with the average grain size about 16 nm was obtained in the sample prepared at wheel speed of 30 m/s. The sample consisted of highly oriented hard magnetic phase (Nd,Dy,Pr)2(Fe,Nb)14B and soft magnetic phase ff-Fe. High performance of Br=1.29 T, Mr/Ms= 0.76 and (BH)max=158.4 kJ/m3 was achieved due to the strong crystallographic texture, fine and homogeneous microstructure and enhancement of the exchange coupling between the soft and hard magnetic phases in this sample. The mechanism of the formation of the crystallographic texture and the multigrain domains was also discussed." 相似文献
997.
We have performed molecular dynamics simulations of structural changes due
to quenching the melting interface at a Cu $\Sigma $5(310)/[001]
symmetrical tilt grain boundary. The simulation results suggest that the
grain boundary structures due to quenching are different from those due to
heating up to the same temperature. The calculated atom density profiles
show that the grain boundary structures can be significantly changed as they
are quenched to quite low temperatures. 相似文献
998.
Absolute stability of the solidification interface in a laser resolidified Zn--2wt.%Cu hypoperitectic alloy 下载免费PDF全文
This paper reports on laser surface remelting experiments performed on a
Zn--2wt.%}Cu hypoperitectic alloy by employing a 5kW CW CO2 laser at
scanning velocities between 6 and 1207mm/s. The growth velocities of the
microstructures in the laser molten pool were accurately measured. The planar
interface structure caused by the high velocity absolute stability
was achieved at a growth velocity of 210~mm/s. An implicit expression
of the critical solidification velocity for the cellular--planar transition was
carried out by nonlinear stability analyses of the planar interface. The results
showed a better agreement with the measured critical velocity than that predicted by
M--S theory. Cell-free structures were observed throughout the whole molten pool at
a scanning velocity of 652~mm/s and the calculated minimum temperature gradient in
this molten pool was very close to the critical temperature gradient for high
gradient absolute stability (HGAS) of the \eta phase. This indicates that HGAS
was successfully achieved in the present experiments. 相似文献
999.
Metastable phase separation and rapid solidification of undercooled Co-Cu alloy under different conditions 下载免费PDF全文
The metastable liquid phase separation and rapid solidification behaviours
of Co61.8Cu38.2 alloy were investigated by using differential
thermal analysis (DTA) in combination with glass fluxing, electromagnetic
levitation (EML) and drop tube techniques. It is found that the liquid
phase separation process and the solidification microstructures intensively
depend on the experimental processing parameters, such as undercooling
level, cooling rate, gravity level, liquid surface tension and the wetting
state of crucible. Large undercooling and surface tension difference of the
two liquids tend to facilitate further separation and cause severe
macrosegregation. On the other hand, rapid cooling and low gravity
effectively suppress the coalescence of the minority phase. Severe
macrosegregation patterns are formed in the bulk samples processed by both
DTA and EML. In contrast, disperse structures with fine spherical Cu-rich
spheres homogeneously distributed in the matrix of Co-rich phase have been
obtained in drop tube. 相似文献
1000.
Under the conventional solidification condition, a liquid aluminium alloy can be hardly undercooled because of oxidation.
In this work, rapid solidification of an undercooled liquid Al80.4Cu13.6Si6 ternary eutectic alloy was realized by the glass fluxing method combined with recycled superheating. The relationship between
superheating and undercooling was investigated at a certain cooling rate of the alloy melt. The maximum undercooling is 147
K (0.18T
E). The undercooled ternary eutectic is composed of α(Al) solid solution, (Si) semiconductor and θ(CuAl2) intermetallic compound. In the (Al+Si+θ) ternary eutectic, (Si) faceted phase grows independently, while (Al) and θ non-faceted
phases grow cooperatively in the lamellar mode. When undercooling is small, only (Al) solid solution forms as the leading
phase. Once undercooling exceeds 73 K, (Si) phase nucleates firstly and grows as the primary phase. The alloy microstructure
consists of primary (Al) dendrite, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic at small undercooling, while
at large undercooling primary (Si) block, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic coexist. As undercooling
increases, the volume fraction of primary (Al) dendrite decreases and that of primary (Si) block increases.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101, 50395105) and the Doctorate Foundation
of Northwestern Polytechnical University (Grant No. CX200419) 相似文献